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DIETARY CONSISTENCY AND SUTURAL MORPHOLOGY: THE COMPLEXITY
OF THE MID-PALATAL SUTURE IN Procolobus badius AND Colobus polykomos
JENNIFER LANE HOTZMAN
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ARTS
UNIVERSITY OF FLORIDA
Jennifer Lane Hotzman
I would like to take this opportunity to thank Dr. Scott McGraw for allowing me to
use his collection of specimens housed at Ohio State University. I also would like to
thank Dr. David Daegling (University of Florida) for all of his guidance and advice
throughout this project. My fellow colleagues Ron Wright and Joe Hefner also offered
assistance throughout a difficult period and helped me to problem shoot certain aspects of
this project. Lastly I would like to thank my parents, Malcolm Hotzman and Linda Petty,
as well as Benjamin Ripy for their continued support and encouragement. This project
would not have been possible without the help and support I received from all of these
TABLE OF CONTENTS
A C K N O W L E D G M E N T S ................................................................................................. iii
LIST OF TABLES ..................................... .. .......... .................................... vi
LIST OF FIGURES ......................................... .................................... vii
ABSTRACT ................................................... ................. viii
1 M ECHAN ICS IN BONE GROW TH .....................................................................1...
W o lff s L a w .................................................................................................................. 1
C oncepts of Stress and Strain ........................................ ....................... ...............4...
Prim ary and Secondary C artilages........................................................... ............... 5
B one M odeling and R em odeling ............................................................. ...............6...
Effect of Dietary Consistency on Bone Growth.................................... ............... 11
2 GR O W TH OF TH E PALA TE ...................................... ...................... ................ 16
Embryological Growth and Developm ent............................................. ............... 16
Postnatal G row th and D evelopm ent...................................................... ............... 18
3 S U T U R E S ................................................................................................................. .. 2 2
Functions of Sutures ............................ .......... ........................ 22
Sutural Biology and M orphology ....................... ............................................... 24
Sutures and Loads ..... .. ................... ........... .....................................27
4 ECOLOGY AND DIET OF COLOBUS MONKEYS.........................................30
B ackgrou n d Inform action .............................................................................................30
S tu d y S am p le .............................................................................................................. 3 1
5 FR A C TA L A N A L Y SIS .............................................. ......................................... 33
Box Dimension and Information Dimension Methods.........................................34
R u ler D im en sio n ......................................................................................................... 3 5
6 M A TERIAL S AN D M ETH OD S ............................................................ ................ 36
7 R E S U L T S ........................................................................................... .................... 3 9
8 D ISCU SSION ............................................................................... . .. ...............52
9 CON CLU SION ...........................................................................................................58
LIST O F R EFEREN CE S .................................................................................................60
BIO GR APH ICAL SK ETCH ................ .. ........................ ..................... ................ 67
LIST OF TABLES
1 D efinitions of m easurem ents collected ............................................... ................ 36
2 Basic statistics for variables associated with Colobuspolykomos ........................ 40
3 Basic statistics for variables associated with Procolobus badius .........................41
4 Bootstrapped versus parametric means for ruler fractal dimension......................43
5 Boostrapped versus parametric means for information fractal dimension ............43
6 Significant regressions ............. ................ ................................................ 43
7 Fractal dim tensions of Colobuspolykomos.......................................... ................ 44
8 Fractal dim tensions of Procolobus badius ........................................... ............... 45
9 Box dim tensions for Procolobus badius .............................................. ................ 56
10 Box dim tensions for Colobuspolykomos............................................. ................ 57
LIST OF FIGURES
1 "V principle of bone rem odeling ...................................................... ................ 19
2 B ox plot for ruler fractal dim ension ................................................... ................ 42
3 Box plot for information fractal dimension.........................................................42
4 Mid-palatal suture of Procolobus badius 2107. .................................................46
5 Mid-palatal suture of Procolobus badius 9433. .................................................47
6 Regression of ruler versus information dimension. ............................................48
7 Mid-palatal suture of Procolobus badius 227 ................................................... 49
8 Mid-palatal suture of Procolobus badius 942 ....................................................50
9 Mid-palatal suture of Colobus polykomos 2103..................................................51
10 Regression of ruler versus box dimension ..........................................................57
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Arts
DIETARY CONSISTENCY AND SUTURAL MORPHOLOGY: THE COMPLEXITY
OF THE MID-PALATAL SUTURE IN Procolobus badius AND Colobus polykomos
Jennifer Lane Hotzman
Chair: David Daegling
Major Department: Anthropology
The mechanical environment is one of many influential factors affecting
craniofacial growth and development. Although the mechanism is unclear, consensus
exists that loads elicit a morphogenetic response from bone in general, including the
maxillary bone in the craniofacial region. Mastication is one of the major sources of
loading for the facial and cranial regions. The morphology of cranial and facial sutures is
thought to be affected by the loading environment to which it is exposed. If this is true,
then dietary consistency, which requires changes in the mechanics of mastication, should
also affect the morphology of sutures.
The hypothesis under construction is that the higher the loads the suture is
exposed to, the more complexity the suture should exhibit. In order to test this
hypothesis, the mid-palatal suture of two sympatric species of colobus monkeys was
examined. One species (Colobuspolykomos) has a particularly hard seed present in its
diet that Procolobus badius does not have. If the above hypothesis is true, then Colobus
polykomos would be expected to have a more complex mid-palatal suture due to its
requirement of producing larger masticatory forces than Procolobus badius. Fractal
analysis was used to measure the complexity of the sutures. Once the fractal dimensions
were obtained, a 2-way ANOVA was performed, separating the species as well as the
sexes. There were no significant differences in the complexities of the mid-palatal
sutures of the two species. The data collected do not support the hypothesis that
masticatory changes associated with diet directly influence sutural complexity.
MECHANICS IN BONE GROWTH
Craniofacial growth and development is influenced by many different factors,
including the mechanical environment (Herring 1993). The maxillary bone, in particular
the palate, is more than likely exposed to different types of loads throughout the earliest
stages of growth. For example, human infants suckle and as they grow older, are weaned
and then engage in mastication. These different activities likely result in different types
and magnitudes of stress, which elicit a morphogenetic response from the bone (Herring
1993, Martin et al. 1998). When mastication begins, the consistency of the diet has been
shown experimentally to affect craniofacial growth and development (Beecher et al.
1983, Kiliaridis et al. 1985, Yamamoto 1996, Ciochon et al. 1997).
In addition to affecting overall bone growth and development, masticatory loads
may also influence the morphology of cranial sutures. Several researchers have
postulated that sutural morphology can reflect the load history of the structure in question
(Herring 1972, Herring and Teng 2000, Wagemans et al. 1988). Provided this is the case,
then the morphology of the sutures located in the palate should reflect its load history. If
development is mechanically mediated, sutural morphology could provide insight into
possible etiologies for abnormal craniofacial developments such as cleft lip and palate, a
common birth defect requiring surgical intervention.
The idea that bone adapts to its mechanical environment is not new. Julius Wolff
has been credited with formulating this idea in the late 1800s, but the idea has been traced
as far back as Galileo in the 1600s (Martin et al. 1998). Wolff's law states that the
architecture of living bone continuously adapts to changes in the mechanical environment
to which bone is subjected. Although Wolff's law is generally accepted as true, the
biological aspects of the law that he formulated have proven to be false (Dibbets 1992).
Three main biases exist in his arguments: his theory on interstitial bone growth, the role
of heredity in bone growth, and his concept of function (Dibbets 1992).
Wolff was convinced that bone growth underwent the same mechanisms as soft
tissue growth, which is to say that bone growth consisted solely of cell division and the
accumulation of intracellular material. He adamantly denied the process of remodeling
because he did not believe that bone actually resorbed. Dibbets (1992) points out that the
reason Wolff held so firmly to this concept of interstitial bone growth was because, in his
view, the trabecular architecture preexisted in the compact (cortical bone) and was not
the result of a dynamic process.
The idea that trabecular bone architecture was inherited was based on the fact that
Wolff had observed the distinct trabecular patterns in fetuses, which could not have been
exposed to loads yet (Dibbets 1992). However, the fetus is exposed to mechanical forces
in utero. Forces are intermittently imposed on the fetus by skeletal tissue stresses that are
caused by muscular contractions from the increasingly strong and active developing
muscular system (Carter and Beaupre 2001).
Wolff s concept of function is the third bias because the definition he provided
differs greatly from how function is usually defined today. If researchers were asked to
define the term function today, they would probably define it as changing structure, i.e. a
dynamic process requiring action (Wainwright 1988). Wolff defined function as a static
requirement that needed to be met (Dibbets 1992). Unfortunately, the term function is
often not explicitly defined by researchers, which causes ambiguity as to exactly which
definition of function is being applied.
If Wolff defined function completely differently than it is defined by most today,
where did the modem day definition develop? The answer is from one of Wolff s
contemporaries, Wilhelm Roux. Roux saw function as a dynamic interaction as opposed
to a static constraint and recognized that information for the developing bone was
partially provided by loading and unloading (Dibbets 1992). He referred to the
physicochemical processes that aid development as "Entwicklungsmechanik" or
"developmental mechanics" (Carter et al. 1998).
The forces that affect skeletogenesis can be studied at different scales of analysis,
including the molecular, cellular, tissue, and organ levels (Carter and Beaupre 2001). In
the time period in which Wolff and Roux worked, the analyses generally took place on
the tissue level due to lack of technology. As technological advances are made, more
studies are conducted at the molecular and cellular levels (Carter et al. 1998). Molecular
level studies have begun to study the role of integrins, which are cell surface receptors
involved in cell adhesion to other cells and the extracellular matrix, and the cytoskeleton,
while cellular studies have shown that hydrostatic pressure and shear loading of cells
have a direct influence on gene expression and cell biosynthesis (Carter et al. 1998). The
tissue level, however, is still the scale at which most analyses occur, including the one
conducted here. One reason for this is because the technology needed to conduct tissue
level analyses is generally more accessible than the technology needed for cellular and
molecular studies. Analyses can also be conducted at the organ level, but they provide
little insight into the underlying mechanisms of how bone responds to different
mechanical conditions (Carter and Beaupre 2001). Only when the organs are broken
down into smaller units, e.g., tissues, can we begin to evaluate and understand the
physical conditions of connective tissue cells (Carter and Beaupre 2001).
Concepts of Stress and Strain
Two very important concepts that are useful when studying mechanical forces at
the tissue level are stress and strain. When discussing stress and strain in biological
materials, it is important to keep in mind that they are defined as if the tissue under study,
in this case bone, was a homogenous material (Carter et al. 1998). In this "continuum
model" representation, the fact that bone consists of molecules, discrete atoms, and
crystals interacting with one another is ignored (Carter and Beaupre 2001). This means
that the material properties represent average properties over some volume that is large in
comparison to the microstructural features of the tissue (Carter and Beaupre 2001).
Stress is a measure of normalized intensity of a force and is the load per unit area,
while strain is a measure of normalized load deformation. Strain, in simplest terms, is
defined as the fractional change in dimension of a loaded body (Martin et al. 1998). Both
stress and strain are tensor quantities, so they have a magnitude and direction. The stress
state can also be represented with scalar quantities referred to as invariants. Scalar
quantities have a magnitude, but no direction. The two most common stress invariants
are referred to as hydrostatic stress and octahedral shear stress. Hydrostatic stress can
either be positive (hydrostatic tension) or negative (hydrostatic compression or pressure)
and is calculated as the average value of the three principal stresses. On the other hand,
octahedral stress can only be a positive number and will only change the shape and not
the volume of the material in question (Carter and Beaupre 2001). These two stress
invariants affect cartilage growth and ossification differently. Octahedral shear stress
causes an acceleration of cartilage growth and ossification, while hydrostatic compressive
stress slows it down (Carter and Beaupre 2001).
Primary and Secondary Cartilages
Primary and secondary cartilages are both important to skull growth. These two
cartilages are distinguished based on the timing of their formation. Primary cartilage
precedes the development of the replacement bones that form the primary skeleton.
Secondary cartilage is different because it does not form on dermal bones until after
intramembranous ossification has begun (Hall 1984). Unlike most of the bones in the
human skeleton, dermal bones are not preformed in cartilage, but arise directly from
connective tissue membranes. When studying the influence of mechanics on craniofacial
growth, the secondary cartilage is important because it does not develop in the absence of
mechanical stimulation (Herring 1993). Secondary cartilage only differentiates from
progenitor cells in response to mechanical stimulation (Hall 1984). This cartilage is
found in association with many cranial bones, sutures, and the upper and lower alveolar
processes in mammals. These locations are sites of either articulations or muscle
attachments, which provides support for the idea that mechanical stimulation is necessary
for the differentiation of secondary cartilages (Herring 1993).
The mandibular condyle is the only major growth site of secondary cartilage
anywhere in the mammalian skeleton (Herring 1993); therefore most of the studies on
jaws have been on the condyle (Simon 1977, Copray 1985, Throckmorton and Dechow
1994). However, the condyle is not the only secondary cartilage that is sensitive to
mechanical changes in the environment. Hinton (1988) studied the response of the
cartilage that is present in the mid-palatal suture to changes in masticatory function. He
divided rats into separate groups based on dietary consistency and/or incisor amputation,
then performed biochemical and histological analyses. Dietary consistency and/or incisor
amputation did alter the morphology and the metabolism of the mid-palatal suture to
varying degrees. The group of rats that were fed a soft diet and had their incisors
amputated were affected the most, with their sutures becoming largely fibrous. The
effect of dietary consistency on bone growth will be discussed in more detail later.
Bone Modeling and Remodeling
There is consensus that the mechanical environment affects bone growth, but how
is another story. Several factors are involved when discussing the mechanical
environment, such as the frequency of the loading and the types of loads applied. Bone
growth and modeling are not the only processes that the loading conditions affect. Bone
remodeling is also heavily influenced by mechanical conditions. Bone modeling and
remodeling both refer to the actions of osteoblasts and osteoclasts in reshaping and
replacing portions of the skeleton (Martin et al. 1998). However, these two processes are
different from one another in several ways.
Martin et al. (1998) provide a list of differences that exist between the processes
of modeling and remodeling. Although both modeling and remodeling involve
osteoblasts and osteoclasts, in modeling these two cell types work independently while in
remodeling their actions are coupled, i.e. sequential. Another difference between these
two processes is that modeling affects the size and/or shape of the bone, while
remodeling typically does not affect either size or shape. Modeling and remodeling are
both most active before skeletal maturity is reached; however, the rate of modeling versus
remodeling is much more reduced after skeletal maturity is reached. Unlike modeling,
remodeling occurs throughout life. Finally when modeling occurs at a particular site the
process is continuous and prolonged while remodeling is episodic and has a definite
beginning and ending.
Although both modeling and remodeling are affected by mechanical conditions,
most of the experimental studies have only involved the process of remodeling (Lanyon
et al. 1982, O'Connor et al. 1982, Carter 1984, Lanyon 1984, Lanyon and Rubin 1984,
Meade et al. 1984, Burr et al. 1985, Rubin and Lanyon 1985). The reason for this is that
mature experimental animals are used to try to eliminate as many unknown variables as
possible. So many factors influence bone growth that controlling all these variables,
some of which are still unknown, is difficult, if not impossible. For this reason, most of
the experimental research focuses on the process of remodeling since modeling is
practically nonexistent once the skeleton has reached full maturity.
Three important variables that are known to influence remodeling include strain
magnitude, strain rate, and strain distribution (Lanyon 1984). Lanyon et al. (1982)
conducted an experiment using mature sheep that involved excising a portion of a sheep's
ulna and then exposing the sheep to peak principle walking strains. They found that the
bone adapted to produce strains that were lower than before the osteotomy, which is not
consistent with the view that bone reacts to control strain magnitude. Instead, they
concluded that adaptive remodeling of periosteal bone is influenced by alterations in
strain distribution rather than peak strains alone. Rubin and Lanyon (1985) conducted a
similar study using turkeys and came to a comparable conclusion that bone remodeling is
sensitive to both strain distribution as well as strain magnitude.
Strain rate is also an influential variable in bone remodeling. In order to evaluate
how strain rate affects remodeling, O'Connor et al. (1982) chronically inserted implants
into the radius and ulna of mature sheep. These implants were subjected to both bending
and compressive loads while varying the peak strains and strain rates. Their conclusion
was that in order for remodeling to occur there needs to be sufficiently high strains and
appropriate strain rates. This leads to the question of whether or not the frequency of the
loads, i.e. static and dynamic loads, affect bone remodeling.
Lanyon and Rubin (1984) conducted experiments on avian ulna in order to
address the question of whether or not both static and dynamic loads affect bone
remodeling. Remodeling activity was assessed under three different conditions, disuse
alone, disuse with a superimposed continuous compressive load, and disuse interrupted
by a short daily period of intermittent loading. From this experiment, Lanyon and Rubin
(1984) concluded that remodeling occurs under both dynamic and static loads when the
bone is exposed to strains within the functional strain range, but the remodeling is more
effective under dynamic loading conditions. Meade et al. (1984) conducted a similar
experiment by exposing the femora of adult dogs to continuously applied loads and noted
that there was an outward movement of the periosteal surface in response to the
continuously applied loads, but little or no effect was seen on the endosteal surface of the
In addition to the changes in strain distribution, strain magnitude, and strain rate,
bone also initiates remodeling as a response to fatigue microdamage (Burr et al. 1985).
Burr et al. (1985) tested the validity of the theory that osteonal remodeling is triggered by
microdamage by conducting several different experiments on adult dogs. The data that
was collected support the idea that fatigue microdamage is a significant factor in the
initiation of remodeling.
No doubt exists that the mechanical environment is influential to bone remodeling.
Factors other than mechanical environment, however, can also affect bone remodeling.
For example, bioelectrical currents generated by blood flow and cell membranes may
also affect bone remodeling, so the situation is not straightforward (Rubinacci and
According to Herring (1993), characterization of the real loading regime of
skeletal elements is needed in order to determine the functional influences of bone
growth. Although computer models and strain gage technology have been helpful in
trying to determine stress distributions, both have limitations. The major limitation of the
computer models is that all local effects must be ignored or modeled precisely, which is
currently impractical. Strain gages help overcome this problem, but they are limited to a
very restricted area of the structure being studied. Even though there are technological
difficulties when trying to determine the loading regime of skeletal elements, successful
experiments have been conducted that yielded useful information.
Lanyon (1973, 1974) performed experiments on the calcaneus of sheep using
rosette strain gages and was able to demonstrate that the trabecular orientation
corresponded with the principal compressive and tensile strain directions. This
experiment was able to confirm what Wolff had postulated earlier about principal stress
directions coinciding with trabecular orientation (Martin et al. 1998). Once this was
confirmed, attention turned to the question of what type of load is responsible for
apposition and resorption. Herring (1993) argues that resorption corresponds to the
orientation of compressive strain, while periosteal bone growth corresponds generally
with the orientation of tensile strain. Of course, as mentioned earlier, it is not only the
type of force applied, but also the frequency and magnitude that determines whether or
not bone is deposited or resorbed.
The skull may experience loading from several sources including forces from the
inertia and weight of the skull itself, joint reaction forces, forces from the muscles, and
trauma (Russell and Thomason 1993). If these forces act directly on the structure, then
shearing stresses will result. Other types of forces that the skull may experience include
bending and torsion. Preuschoft (1989) stated that the bite forces inside the upper jaw
evoke shearing forces, torsional moments, and bending moments; unfortunately he does
not specify the sources or nature of these different loading conditions. Different regions
of the facial skeleton seem to experience variable amounts of stress during biting and
mastication, so every facial bone may not be specifically designed for countering
mechanical loads from mastication (Hylander et al. 1991, Hylander and Johnson 1997).
The mandible is one area of the face where extensive research has been conducted
to determine the forces experienced during mastication (Hylander 1975, Hylander 1979).
Hylander (1975) explored the issue of whether or not the mandible functions like a lever
during mastication and concluded that the mandible does function like a lever and
behaves more or less like a curved beam. Hylander (1979) also explored the functional
significance of the primate mandibular form and concluded that the symphseal region
does appear to be an adaptive response to masticatory loads, particularly unilateral molar
bite force. Unfortunately the upper and lower jaws do not function in the same manner.
Due to the structural nature of the maxilla, modeling the lower jaw experimentally has
been difficult, if not impossible, to date. Although the conclusion can be made that the
maxilla does experience bending and twisting like the mandible due to the presence of the
hard palate, there is no experimental evidence present that does state what type of stresses
the maxilla experiences during mastication (Daegling and Hylander 1997). Nevertheless,
the forces generated by mastication are still of particular interest when examining the
Effect of Dietary Consistency on Bone Growth
Several studies have been conducted over the years that support the idea that
dietary consistency affects craniofacial bone growth and development. Many of these
studies were initiated in an attempt to determine why Western societies had such high
rates of malocclusion compared to non-industrial societies (Beecher et al. 1983, Ciochon
et al. 1997). The theory that forceful chewing was necessary for proper growth became
one avenue of exploration. Beecher et al. (1983) examined this hypothesis by raising two
groups of squirrel monkeys; one group was given a naturally tough diet while the other
was given a diet of artificially softened foods. Significant differences were noted
between the two groups and they concluded that there is a minimum threshold of stress
needed for proper craniofacial development to occur.
The animals given the soft diet in the study of Beecher et al. (1983) exhibited
maxillary arch narrowing and increased palatal height. These two characteristics
occurring simultaneously suggests that maxillary arch collapse maxillaryy arch
narrowing), the most common occlusal problem in American youths, probably occurs
because of differences in the growth of the mid-palatal suture and the fact that teeth from
the maxillary alveolar process are not correctly aligned with the mandibular teeth. Other
cranial sutures were also affected by dietary consistency. Distinct differences in
calcification were seen in the lambdoid and sagittal sutures through the use of
radiographs. The soft diet animals had a much broader radiolucent area at the sutures
than the hard diet animals, which means that the sutures in the soft diet area are more
patently opened and less calcified.
Squirrel monkeys are not the only experimental animals that have supported the
idea that craniofacial growth and development is affected by the consistency of diet.
Experiments have also been conducted using rats (Beecher and Corruccini 1981, Bouvier
and Hylander 1984, Kiliaridis et al. 1985, Yamamoto 1996) and minipigs (Ciochon et al.
1997). Differences were found in the mandibles of Yucatan minipigs that were raised on
diets of varying consistencies (Ciochon et al. 1997). In addition to examining the bones,
Ciochon et al. (1997) also examined the weight of the muscles involved in mastication.
They found that the weights for the superficial masseter, deep masseter, and temporalis
muscles were all significantly higher in the hard diet group. The frontal profiles of the
cranium also differed between the two groups; the hard diet group displayed a steep
profile while the soft diet group displayed an overall more horizontally oriented profile.
Morphological differences in the shape of the mandible between the two groups were
also noted. Unfortunately, the maxilla was not the main focus of this study so very little
information concerning this structure was presented. However, Ciochon et al. (1997) did
note that the palate was relatively longer in the soft diet group. They also took
measurements of the maxillary arch breadth and unlike the results reported by Beecher et
al. (1983) in the squirrel monkeys, there was no difference found between the groups of
the Yucatan minipigs.
Rats have served as another common experimental animal for pursuing the effects
of dietary consistency on craniofacial growth and development. Beecher and Corruccini
(1981) conducted a study using rats that consisted of two groups, a soft diet group and a
hard diet group. They reported that the rats fed a soft diet had a significantly narrower
maxillary arch breadth compared to the hard diet group. The animals in the soft diet
group weighed approximately 13% less than the animals in the hard diet group at the end
of the experiment; however, the weight difference was not found to be significant.
Bouvier and Hylander (1984) disagree with Beecher and Corruccini (1981) about the
weight differences not being significant. Bouvier and Hylander (1984) conducted a
similar experiment and found that the maxillary arch length was significantly different
between the animals raised on different diets, but once corrections were made for the
weight differences, the maxillary arch differences became nonsignificant.
Kiliaridis et al. (1985) used cephalometric longitudinal analysis for growing rats
using a normal diet group and a group fed a soft diet. Differences were noted in the
growth patterns of both the neurocranium and the viscerocranium between the two
groups. The viscerocranium of the soft diet group showed a more orthocranial position,
which refers to the skull being of medium height relative to length, with the most
noticeable changes occurring in the nasal area. Changes were also noted in the incisors
of the upper jaw as well as the mandible. The incisors of the upper jaw showed a greater
proclination in relation to occlusal and palatal planes in the soft diet group, while the
gonial angle of the mandible showed a decreased appositional rate.
As can be seen by comparing the studies of Beecher and Corruccini (1981) and
Bouvier and Hylander (1984), no consensus exists on the effect dietary consistency has
on the growth of the palate. Yamamoto (1996) examined how food consistency effects
the growth of the palatal region of the maxillary complex through the use of bone
histomorphometry to try to aid in the resolution of this issue. Specifically, the goal was
to investigate how the consistency of the diet affected the pattern of bone apposition at
the growth site of the palatal region. As with the previous studies, the rats were divided
into two groups; one was fed a hard (solid) diet while the other was fed a soft (liquid)
diet. There were significant differences found between the two groups.
Yamamoto's (1996) results agreed with those of Kiliaridis et al. (1985) in that the
vertical growth of the palate differed between the two groups and there was a more
anteriorly directed growth rotation of the palate in the soft diet group. Other studies that
examine the underlying mechanism for this difference have noted a marked decrease in
the bone appositional rate in the areas of muscle insertion in the anterior part of the
viscerocranium (Engstrom et al. 1986); however, the area under consideration in
Yamamoto's (1996) study is not an area of muscle insertion. This implies that the
changes in the palatal region of the maxilla cannot be caused directly by activities such as
muscle action; however, muscle action can have large effects due to mechanical activities
such as bending and twisting. Yamamoto (1996) proposes that although the mechanical
forces generated by mastication probably have an indirect affect on the growth, another
factor to consider is that the growth of other structures such as the neurocranium also
affects the growth of the viscerocranium under different occlusal loading conditions.
As mentioned previously with the study of Ciochon et al. (1997), the growth of
the mandible has also been explored in relation to dietary consistency. One line of
reasoning is if an animal has a diet that consists of hard items then their mandible would
be more massive in terms of bone than a similar sized animal with a softer diet. Just like
the differences reported in the maxillary arch breadth between the different studies cited
above, differences exist on this issue concerning the mandible. A study conducted by
Daegling and McGraw (2001) does not support the line of reasoning expressed above.
They examined the mandibles from two different species of colobus monkeys that are
similar in size and sympatric, but one of the species (Colobuspolykomos) has a diet
containing food items of harder consistency. One would expect that Colobuspolykomos
would have a more robust mandible than the other species (Procolobus badius), but this
is not the case. In fact, mandibular morphology does not reflect the differences in diet.
The studies mentioned so far have been concerned with mastication, but this is not
the only process that mammals use for oral food intake. Infant mammals engage in a
unique form of feeding referred to as suckling. Although the mechanism of suckling has
been explored (German et al. 1992) as well as the transition from suckling to drinking at
weaning (Thexton et al. 1998), there have been no studies conducted on the types of
loads this mechanism produces and whether or not these loads also affect craniofacial
growth and development.
GROWTH OF THE PALATE
Embryological Growth and Development
Facial development begins around the third week of gestation with the development
of five facial swellings, or primordia, in the frontonasal and visceral arch regions. These
five primordia consist of the frontonasal prominence, which forms the forehead and nose,
two maxillary prominences, which form the lateral stomodeum, or primitive mouth, and
two mandibular prominences, which form the caudal stomodeum (Bender 2000, Scheuer
and Black 2000). Within each of these prominences, neural crest cells differentiate into
fibrous connective tissue, all the dental tissues except enamel, skeletal and connective
tissue of the face, cartilage, and bone. By the end of the fourth week, the lower aspect of
the frontonasal prominences develop bilateral oval thickenings of the surface ectoderm
known as nasal placodes, which will produce the medial and lateral nasal prominences
(Kirschner and LaRossa 2000, Moore and Persaud 2003). The intermaxillary segment of
the maxilla forms when the medial nasal prominences merge. This segment gives rise to
the philtrum of the upper lip, the premaxillary part of the maxilla, and the primary palate
(Moore and Persaud 2003). The maxillary prominences enlarge during the fifth week and
connect with the lateral nasal prominences to establish continuity between the nose and
the cheek while the maxillary prominences fuse with the medial nasal prominences to
complete the lip.
Palatogenesis begins at the end of the fifth week and continues until the twelfth
week. The median palatine process develops from the intermaxillary segment during the
sixth week (Moore and Persaud 2003). This process forms the primary palate, which
gives rise to the premaxillary part of the maxilla. In the adult hard palate, the premaxilla
represents only a small portion of the hard palate anterior to the incisive foramen forming
the part of the maxillary alveolus that bears the incisors.
During the sixth week, the secondary palate develops from the paired lateral
palatine processes also known as the palatal shelves. The lateral palatine processes are
two mesenchymal projections that extend from the internal aspects of the maxillary
prominences (Moore and Persaud 2003). Initially both palatal shelves are oriented
vertically on either side of the developing tongue. As the tongue descends, the palatal
shelves gradually move to a horizontal position where they will meet and fuse at the
midline. An intrinsic shelf elevating force is believed to be responsible for the movement
of the palatal shelves. This force is generated by the hydration of hyaluronic acid in the
mesenchymal cells within the palatal processes (Moore and Persaud 2003). Hyaluronic
acid acts as a water barrier and provides "tissue turgor" that moves the palatal shelves
(Brinkley and Morris-Wiman 1984). The movement of the palatal shelves begins in the
seventh week, but fusion is not completed until the twelfth week. Fusion of the palatal
shelves results in the formation of the uvula, soft palate, and hard palate posterior to the
incisive foramen (Kirschner and LaRossa 2000).
For nonhuman primates such as baboons and macaques, palatogenesis occurs
approximately at the same stage as humans (Hendrickx and Peterson 1997). The
underlying mechanisms for palatal closure are also thought to be the same between these
primate species and humans (Bollert and Hendrickx 1971, King and Schneiderman
1993). Since the timing and the underlying mechanisms of palatal closure are similar in
baboons, macaques, and humans, then catarrhine primates may be appropriate animals to
use in order to explore orofacial teratogenesis in humans (Bollert and Hendrickx 1971).
Postnatal Growth and Development
Growth refers to a structure, in this case bone, changing in magnitude (Enlow and
Hans 1996). Contrary to prior belief, there are no centralized and self-contained growth
centers; instead all portions of the bone play a role in the growth of the structure (Enlow
and Hans 1996). As opposed to growth centers, the functional matrix is the determinant
of the skeletal growth processes. The functional matrix is all the tissues and spaces that
work together to fulfill a particular function (Moss 1969). This concept provides an
explanation of what happens during craniofacial growth, but not how the cellular and
molecular mechanisms underlying growth work.
Remodeling and displacement are two basic kinds of growth movements involved
in facial growth. Remodeling serves five main functions that are outlined by Enlow and
Hans (1996): 1) progressively changes the size of the whole bone, 2) sequentially
relocates the component regions of the whole bone to allow for overall enlargement, 3)
shapes the bone for its functions, 4) fine-tunes the outline of separate bones to each other
and their surrounding soft tissues, and 5) carries out structural adaptations to the intrinsic
and extrinsic changes in conditions. This remodeling is not synonymous with the type of
remodeling discussed earlier. Unlike Martin et al. (1998), Enlow and Hans (1996) do not
make a distinction between the processes of modeling and remodeling. Instead, Enlow
and Hans (1996) make a distinction between remodeling (as defined above) and
displacement. Displacement is the process of the physical movement of the whole bone
and occurs when remodeling is simultaneously resorbing and depositing bone.
Palatal remodeling occurs through a process known as the "V" principle. This
concept is based on the fact that many cranial and facial bones, including the palate, have
a V-shaped configuration (Enlow and Hans 1996). Bone deposition takes place on the
inner side of the V while resorption takes place on the outer side of the V (Figure 1,
adapted from Enlow and Hans (1996)). In the case of the maxillae, the external side of
the anterior part of the maxillary arch is resorbed while bone is deposited on the inside of
the arch. This process increases the width of the arch causing the palate to become wider
(Enlow and Hans 1996). Growth along the mid-palatal suture also adds to the
progressive widening of the palate and maxillary (alveolar) arch (Friede 1998).
Widening of the palate continues into adulthood (Scheuer and Black 2000).
Figure 1. "V" principle of facial growth. As the V moves from position A to position B,
the structure increases in overall dimensions. The + marks indicate bone
deposition on the inner side of the V, while the marks indicate bone
resorption on the outside surface.
Lengthening of the hard palate occurs partly in the transverse suture and partly by
the apposition of bone to the posterior margin (Melsen 1975). The growth in the
transverse suture continues until puberty, but the appositional activity continues until
approximately 18 years of age. Disagreement exists concerning the appositional activity
on the posterior margin of the palate. According to Sejrsen et al. (1996), little growth
occurs at the posterior border of the hard palate. They reached this conclusion by
studying archaeological samples that show a constant distance between the greater
palatine foramen and the posterior margin of the palatine bone at various dental stages.
Sejrsen et al. (1996) attribute lengthening of the hard palate almost solely to growth in the
transverse suture. Although the amount of apposition that occurs on the posterior margin
is controversial, consensus exists on the fact that little to no apposition occurs on the
anterior margin. The transverse palatine suture remains in the posterior part of the bony
palate from birth to adulthood regardless of the minute amount of activity on the anterior
margin, which suggests that highly differentiated growth must occur postnatally in the
transverse palatine suture (Silau et al. 1994).
The palatal growth rates of several nonhuman primates, specifically Macaca
nemestrina and Papio cynocephalus, were investigated to see if there were any
differences between the two genera (Swindler and Sirianni 1973). Although the absolute
size of these primates is different, the growth of the palate occurred at similar rates with
both gradually decelerating with age. The deceleration of the growth rate is also
characteristic of humans. Another significant finding from this study is that no sexual
dimorphism exists in the rate of growth of the palate within either species (Swindler and
As previously noted, both the mid-palatal and transverse palatine sutures play a
role in the growth of the palate. In the embryonic stage, the incisive suture separates the
premaxilla and the maxilla, but this suture fuses before birth; although a slight visible
suture line may appear on the lingual surface of the palate and persist into adulthood
(Mann et al. 1987). The mid-palatal and transverse palatine sutures fuse erratically, but
they remain open well into adulthood. The morphology of these two sutures changes
throughout the different stages of palatal growth. The transverse suture begins broad and
slightly sinuous at birth and later develops into a typical squamous suture (Melsen 1975).
The mid-palatal suture progresses through three stages; in the first stage the suture is
short, broad, and Y-shaped, with the vomerine bone in the groove of the Y between the
two maxilla halves; in the second stage the suture is more sinuous; and in the third stage
the suture is heavily interdigitated (Melsen 1975). The change in sutural morphology
may be attributed to changes in the mechanical environment. Sutural biology, function,
and morphology will be explored further as well as how sutures are affected by loads.
Functions of Sutures
Sutures are any articulation between dermal bones of the skull (Herring 2000).
These articulations are usually fibrous but sometimes contain cartilage or fibrocartilage.
Evolutionarily, the earliest sutures developed in the armored jawless fish and consisted
simply of the skin that remained between the dermal plates. The properties that are
typically associated with sutures, mobility, growth, and the potential for synostosis
(closure), were already present in these armored jawless fish (Herring 2000). Mammals
show no evolutionary progression of sutures; in fact, they have lost some of the sutural
diversity. All taxonomic groups that have sutures show a complete range of sutural
morphology, from loose connective tissue to elaborate interdigitations joined by a well-
defined ligament (Herring 2000).
Three main biological functions are associated with sutures: to unite bones while
still allowing slight movement, to act as growth areas, and to absorb mechanical stress
(Persson 1995, Cohen Jr. 2000). Two types of movements typically take place at the
sutures. At birth is when the first type of movement occurs, which entails the
displacement of the calvaria bones as the human head is compressed through the birth
canal (Persson 1995). This causes a molding of the head that resolves during the first
week of life through cranial re-expansion and widening of the sutural areas (Cohen Jr.
2000). The other type of movement at the sutures is caused by the displacement of bones
relative to one another as the skull grows (Persson 1995).
As previously mentioned, the amount of growth that occurs at the sutures is
debated, but there is no doubt that sutures do play a role in craniofacial growth. Sarnat
(2003) conducted experiments on macaque monkeys that involved surgically producing
clefts of the palate on one side only. The severity in the clefts varied from a narrow slit
to almost the entire half of the palate excised. No significant differences were noted in
the growth and development of the hard palate or maxillary arch between the operated
and unoperated sides or between the experimental (operated) and control (not operated)
macaques. Sarnat (2003) postulated two possible conclusions; either the transverse
palatine and mid-palatal sutures do not make a primary contribution to growth or other
areas of growth compensated for the altered condition. From this particular experiment
there is no way to decide which conclusion is correct, but other researchers have
postulated that the palatal sutures only secondarily contribute to growth (Melsen 1975).
Not only does the same suture grow differentially at various times, but the rate and the
amount of growth varies for different sutures at different times (Persson 1970, Sarnat
2003). The problem with intervention studies is that they create a situation that will
never be found in nature, so the results cannot be applied to animals in nature.
Persson (1970) conducted a study on the postnatal growth of facial sutures in the
rat that revealed different growth patterns in individual sutures as well as in the bony
margins of the same suture. Four different growth patterns were observed. The first
pattern was appositional growth against both sutural margins, which was observed in the
premaxillary part of the mid-palatal suture. Another type of pattern observed was
appositional growth against only one sutural margin while the other remained inactive.
This pattern was found in the main part of the naso-premaxillary suture. The palato-
maxillary suture showed appositional growth against one sutural margin, while the other
margin showed resorption. This contradicts Sarnat (2003) who states that sutural growth
is only through apposition with no resorption involved. The final growth pattern
observed by Persson (1970) is perichondral growth in the maxillary part of the mid-
palatal suture. This suture is an example of cartilage being present in the articulation as
opposed to just collagenous fibers (Herring 2000).
Mechanical environment also affects sutural growth and development. Mao
(2002) concluded that sutural growth is accelerated when exposed to tension and
compression. Another potential stimulus for sutural growth is the oscillatory component
of cyclic force. Kopher and Mao (2003) demonstrated that small doses of oscillatory
mechanical stimuli can affect sutural growth by either accelerating osteogenesis of the
suture or initiating net sutural bone resorption. This information can potentially affect
therapeutic goals in craniofacial disorders.
The third biological function of sutures is that they act either as a shock absorber
for mechanical stress or to transmit force across the sutures (Herring 1972, Persson
1995). The majority of mechanical stress in the suture areas is associated with
mastication (Persson 1995). Sutural morphology has been postulated to reflect the
loading environment under which the suture is subjected (Herring 1972, Wagemans et al.
1988, Herring and Teng 2000). Whether or not this is true will be explored in the
Sutural Biology and Morphology
Pritchard et al. (1956) outlined the development of cranial and facial sutures based
on six different species: humans, sheep, pigs, cats, rabbits and rats. At all stages of
development, sutures exhibit five intervening layers as well as two uniting layers between
the adjoining bones. The five intervening layers consist of a pair of cambial layers, a pair
of periosteal fibrous capsular layers, and a middle looser layer of cellular mesenchymal
tissue. The cambial layers are the sites of active osteogenesis producing woven bone, but
the capsular layers must also expand in order to keep pace with the growing bone. The
two uniting layers occur when the fibrous capsules are joined by means of two fibrous
laminae, an external and an internal. The extremities of the fibrous capsules retain their
separate identities due to the intervening layer of loose mesenchymal tissue.
The facial and cranial sutures have the same structure, but they arise somewhat
differently. Before the sutures are formed in the face, the cambial and capsular layers are
already present with the middle and uniting layers being derived from the mesenchyme
between the approaching bone territories. The bones in the cranial vault approach each
other within an already differentiated fibrous membrane referred to as the ectomeninx.
The capsular layers do not form in the cranium until the cambial layers have almost met
and the middle and uniting layers are derived from the delamination of the ectomeninx
between the bones (Pritchard et al. 1956).
The histological structure of sutures, however, is not agreed upon. Pirelli et al.
(1999) conducted a study using biopsy samples of the mid-palatal suture obtained from
patients ranging in age from 10 years old to 30 years old. They reported that the capsular
and cambial layers reported by Pritchard et al. (1956) were not detected in any of their
samples nor were the cells typically associated with these layers, osteoblasts and
osteoclasts. The absence of osteoblasts and osteoclasts suggest that the bone was in a
resting period at the time of the sample. Unlike the woven bone detected by Pritchard et
al. (1956), Pirelli et al. (1999) stated that all the sutures were formed by lamellar and
bundle bone. Bundle bone is the term used to describe bone in the suture that closely
resembles the alveolar bone lining the periodontal ligament with a high turnover rate
(Pirelli et al. 1999). Although the functional significance of the lamellar bone in the
sutures is unclear, Pirelli et al. (1999) stated that the lamellar bone may possibly
progressively replace the bundle bone when the suture is no longer active in growth and
remodeling. If this is the case, the lamellar bone may represent the structural basis of the
physiological process of synostosis (Pirelli et al. 1999). The discrepancies in the sutural
structures between Pritchard et al. (1956) and Pirelli et al. (1999) may be attributed to the
differences in the ages of the samples examined.
The functional significance of the presence of cartilage in some of the postnatal
sutures is heavily debated. The cartilage is only present for a limited time and usually
only appears in the midline sutures, i.e. the sagittal and mid-palatal sutures. The function
of this cartilage seems to be linked to changes in the mechanical environment
(Wagemans et al. 1988). Sutures are normally under tension, but during growth the
sutures may be exposed to particularly strong pressure and shearing stresses (Pritchard et
al. 1956). The secondary cartilage that is present in these sutures is mainly found in
rapidly growing areas (Perssons 1995). Pritchard et al. (1956) recommends that the
effect of masticatory forces should be considered in relation to the development of
The morphology of sutures is not only different between sutures, but the
morphology of a single suture can vary throughout its life. Melsen (1975) identified
three morphological stages in the development of the mid-palatal suture: Y-shaped,
slightly sinuous at birth, and interdigitated at puberty. Del Santo Jr. et al. (1998)
conducted a study of the morphological aspects of the mid-palatal suture in the human
fetus that partially confirmed the changes in morphology described by Melsen (1975).
The first group of fetuses (16-23 weeks) in this study showed a mid-palatal suture that
was rectilinear in nature with a wide zone of intense cellular proliferation. The second
(24-31 weeks) and third groups (32-39 weeks) displayed a sinuous form with a narrower
cellular proliferation zone.
The complex morphology of sutures is thought to reflect their functional
environment (Rafferty and Herring 1999). Oudhof (1982) found that although sutural
tissue has hereditary characteristics that determine the specific differentiation, certain
environmental influences are necessary for the manifestation and development of
qualities associated with sutures. For example, in the transplantation experiments
conducted by Oudhof (1982), when a portion of a suture was relocated to an area of little
or unspecified growth, the suture gradually lost its specific structure. On the other hand,
when a suture was transplanted to an area of active growth, the suture adapts to its
surroundings. This was witnessed when a portion of the sagittal suture of a rat was
transplanted into a coronal suture. The sagittal suture adapted by developing a more
intensive formation of fibers and more and longer lingulae (Oudhof 1982). The influence
of the mechanical environment on sutures will be the next topic covered.
Sutures and Loads
Suture morphology is extremely complex and several researchers have postulated
that the mechanical environment is one factor that influences their morphology (Linge
1970, Herring 1972, Oudhof 1982, Wagemans et al. 1988, Herring and Teng 2000, Mao
2002). Herring (1972) examined sutural morphology in suoids to explore the use of
cranial sutures as indicators for the amount and direction of stress in the skull. She
assessed sutural morphology in two ways: first she examined disarticulated sutural
surfaces for six specimens, second she examined dried articulated suoid skulls and
subjectively categorized them as straight, slightly interdigitated, interdigitated, and very
interdigitated. Another way to classify sutures is as either beveled or butt-ended.
One tentative conclusion that Herring (1972) drew from this research was that the
beveling of sutures may allow adjustive movements or stress reductions during forceful
operations, like rooting in pigs. Another conclusion was that interdigitations are
instrumental in the transmission of force from one bone to another and to resist shear
loads. Generally speaking, the interdigitations of the sutures will be either perpendicular
or parallel to the main force applied and these interdigitations serve to increase the
surface area for collagen fibers to attach (Herring 1972, Jaslow 1990, Rafferty and
Herring 1999). Jaslow (1990) examined the mechanical properties of sutures and
concluded that increased interdigitations do improve the bending strength when sutures
are loaded slowly when compared to cranial bone alone.
Jaslow (1990) was also able to provide support for the hypothesis that sutures act
as shock absorbers in the skull. This is based on the discovery that cranial bone with a
suture present was able to absorb more energy, regardless of the sutural morphology, than
the pure cranial bone. The sutural morphology also influences the amount of energy
absorbed. Energy absorption increased as the complexity of sutural interdigitation
increased. Interdigitation also seems to be correlated with the degree of compressive
strain. The more compressive strain a suture is exposed to, the higher the degree of
interdigitation (Rafferty and Herring 1999). Adjacent sutures also seem to experience
large magnitude strains of opposite polarity during normal mastication, at least in pigs
(Rafferty and Herring 1999). This result is intuitive because when one side of a structure
is experiencing tension, the other side is experiencing compression.
The cranium is a difficult bone to model because of its unusual morphology. The
palate in general provides special difficulties because the structure is curved which makes
techniques such as strain gages difficult to use. Since the loading environment influences
craniofacial growth and development, determining the loading environment of bones
such as the maxilla is important.
ECOLOGY AND DIET OF COLOBUS MONKEYS
Historically, researchers have classified colobus monkeys as specialists, based on
the amount of leaves in their diets. The origin of this belief seems to stem from an early
paper by Booth (1956) that refers to colobus monkeys as 'purely leaf-eating.' Casual
observations and the study of the contents of the stomach formed the basis of this
assumption. Anatomical features such as the large complex stomach and high-crowned
molars and premolars also support the notion that colobus monkeys are largely leaf-eaters
(Campbell and Loy 2000). Recent evidence, however, suggests that this initial view of
colobines is not accurate, at least not for all species and/or groups (Maisels et al. 1994).
Leaves do make up a large portion of most, if not all, colobus monkey diets, but seeds,
fruits, and flowers also contribute significantly to their diets. The original belief that
colobines were specialists was based on studies conducted on groups of colobines in east
Africa (Dasilva 1994). Research at sites such as Tiwai Island in western Africa has
shown that seasonal variability exists in their diets, including seeds, fruits, and both
young and mature leaves (Dasilva 1994, Davies et al. 1999).
Feeding techniques do not vary much between different species of colobines. The
type of food eaten affects the technique used, but regardless of the food type, there is very
little manual manipulation involved (Clutton-Brock 1975). Colobus monkeys have
reduced thumbs, which may explain the little amount of manipulation. This appendage
does not provide them with the grip of other primates who have larger thumbs that allow
more precise gripping. Clutton-Brock (1975) did observe some manipulation, though,
such as stripping the pinnules off of the leaf stem by gripping the stem in their teeth and
dragging the stem through their clenched fists. He states that he never saw them use their
hands to strip or break open fruit; if the covering was removed from a fruit they opted to
use their teeth instead (Clutton-Brock 1975).
One difference between red colobus (Procolobus badius) and king colobus
(Colobuspolykomos) is their preference for location of feeding. The former usually
acquires a large portion of their food from some of the largest trees in the upper canopy
of their habitat, while the latter choose to forage lower in the canopy (Oates 1994). In
areas where both of these colobine groups co-occur, the red colobus monkeys choose a
more diverse diet than the king colobus. Another difference is the amount of seeds that
are consumed. All colobus species ingest seeds, but only in the black and white forms do
seeds sometimes dominate the diet (Oates 1994). Some researchers argue that African
colobines eat a large portion of seeds whenever the quality of the tree foliage is poor via
poor soils (Maisels et al. 1994). Evidence supports this statement for some areas such as
Zaire (Maisels et al. 1994), but this explanation does not explain the difference in seed
exploitation between sympatric species of colobus monkeys.
The colobus monkeys used in this study are Procolobus badius (n=39) and Colobus
polykomos (n=13) from the Tai Forest of Cote d'Ivoire. They are sympatric throughout
most of their range and are similar in body size and diets except the king colobus exploits
a particularly hard seed from the African oil bean (Pentaclethra macrophylla,
Mimosaceae) at a much larger frequency than the red colobus monkeys.
This African oil bean tree is usually 21 m in height with a girth of about 60 cm.
The pods are 40-50 cm long and usually 5-10 cm wide. Inside the pods are 6-10 flat
glossy brown seeds that are up to 7 cm long. Colobuspolykomos focuses on seeds from
this plant and others like it whereas Procolobus badius focuses on leaf eating (Davies et
al 1999). The reason for this difference probably stems from their individual preference
in foraging, i.e. upper versus lower canopy.
When the king colobus preys on these hard seeds, they expend a great amount of
effort gnawing them until they break through the encasing (Davies et al. 1999). As
mentioned earlier, Daegling and McGraw (2001) predicted that the species exploiting the
hard seeds should have a more robust mandibular corpus than the species that does not
exploit this food item. This prediction is based on the reasoning that the king colobus
would have to apply larger loads, therefore stressing the mandible more, to gnaw through
the tough encasements. The results of the study, however, showed that the variation in
mandibular morphology in these two sympatric colobines does not correspond to the
predictions based on the dietary differences (Daegling and McGraw 2001).
The underlying reasoning behind the current project is that the palates of these two
species of colobus monkeys are exposed to different loading environments. The
extensive gnawing of Colobuspolykomos on the hard seeds may cause a significantly
larger amount of force on the palate. If this is the case, the complexity of the palatal
sutures of these two species may reflect this difference in loading environment. In order
to test this hypothesis, fractal analysis was completed on the mid-palatal sutures of
Colobus polykomos and Procolobus badius.
One of the most difficult tasks facing morphologists is that of quantifying and
measuring size and shape. Traditionally, parameters such as length and volume were
used to try to quantitatively describe and compare morphological characteristics. In
Euclidean geometry linear measures are considered one dimension, smooth surfaces are
two dimensions, and volumes and weights are three dimensions. Objects that occur in
nature, however, seldom have edges that are straight or surfaces that are smooth (Long
1985). Some objects in nature possess certain qualities that can be described by a non-
Euclidean fractional dimension, which lies between the values of one and two
(Mandelbrot 1977). These objects are known as fractals. Fractals are geometric objects
that are self-similar in nature. Self-similarity means that the fractal object is composed of
smaller units that possess the same shape as the whole object. Fractals have complex
edges or surfaces that increase linearly as the resolution of the units used to measure them
increase (Hartwig 1991). Fractal analysis is a technique used to interpret the geometric
complexities of fractals.
Several researchers believe some cranial sutures are fractal objects (Long 1985,
Hartwig 1991, Long and Long 1992, Gibert and Palmqvist 1995, Montiero and Lessa
2000, Yu et al. 2003). Long (1985) explored the idea of whether or not complex sutures
exhibit fractal properties such as self-similarity and a dimension between one and two.
To address this question, Long (1985) examined the sutures on the shells of extinct
ammonites and cranial sutures of white-tailed deer. The sutures in both of these
organisms are incredibly complex and did exhibit fractal properties. Other cranial sutures
that have been examined using fractal analysis are the sagittal suture in humans (Hartwig
1991, Yu et al. 2003), the sagittal and lambdoidal sutures in humans (Long and Long
1992, Gibert and Palmqvist 1995), and cranial sutures in the genus Caiman (Montiero
and Lessa 2000). In each of these studies, the structures under examination exhibited the
characteristics of fractals.
In this study, fractal analysis was conducted with the use of a software program
known as Benoit 1.3 (St. Petersburg, FL). This program allows the user to choose from
several different methods on how the fractal analysis is conducted. The different
methods provided in this program are tailored to accommodate different types of data
sets. Based on this data set, three methods seemed equally applicable. Each of these is
discussed in further detail.
Box Dimension and Information Dimension Methods
The box dimension method of fractal analysis is one of the most widely used
methods due to the relatively simple mathematics involved (Falconer 1990). In Benoit
1.3, the box dimension is defined as the exponent Db in the relationship:
where N(d) is the number of boxes of linear size d necessary to cover a data set of points
distributed in a two-dimensional plane. A number of boxes are used to cover the data set
points that are evenly distributed on a plane. This may indicate that point density may
influence the results, i.e. the number of data points collected will affect the outcome of
the fractal dimension. This method is often referred to as the grid dimension because the
boxes used are usually part of a grid system.
To accomplish this method, a series of different box sizes d are laid over the
object and the program works by tallying the number of boxes filled during each box size
overlay. One of the problems with this method is that the boxes are weighted the same
whether the entire box is full or just a tiny portion. The information dimension method
addresses this problem by assigning weights to the boxes so boxes containing more
points are counted more than the boxes with fewer points (Benoit 1.3). Unfortunately
this makes the mathematics involved much more complicated.
Mandelbrot (1977) examined the coastline of Britain and determined that this
object was fractal. How was the fractal dimension of this jagged, self-similar line
calculated? The method he used is now referred to as the ruler, or yardstick, method.
The ruler method Dr is defined as:
N(d) & d Dr
where N(d) represents the number of steps taken to walk a divider (or ruler) that is length
d. According to Benoit 1.3, the formal equivalence between this method and the box
dimension can be shown mathematically. Algebraically, this claim is logical, since the
box dimension is simply the reciprocal of the ruler dimension.
MATERIALS AND METHODS
The skulls of 39 Procolobus badius and 13 Colobuspolykomos were examined
from a collection housed at Ohio State University. Eight measurements were also taken
from each skull: palate height, internal palate breadth, external palate breadth, palate
length, palate depth, upper facial height, facial width, and skull length. With the
exception of palate depth and palate height, the measurements are defined in Bass (1995).
Table 1 provides a brief definition of the six measurements taken from Bass (1995).
Palate depth was measured using an instrument colloquially referred to as a carpenter's
tool or a contouring tool. The contour was traced from the edge of the alveolar ridge of
the second molar to the level of the mid-palatal suture. The height of the contoured
tracings was then measured resulting in the depth of the palate. Palate height was
measured with sliding calipers by placing one edge of the caliper on the mid-palatal
suture and one edge on the alveolar ridge at the level of the second molar.
Table 1. Definitions of measurements collected.
Measurement Definition (Craniometric Points*)
Facial width zygion to zygion
External palate breadth ectomolare to ectomolare
Internal palate breadth endomolare to endomolare
Palate length prosthion to alveolon
Skull length alveolare to opisthocranion
Upper facial height nasion to alveolare
*Craniometric points defined in Bass (1995)
In addition to the measurements taken, the palate of each specimen was
photographed using a Minolta 35mm camera with a macro lens attached. Each specimen
was oriented with the palate parallel to the lens of the camera. The film was developed
and the negatives were made into 35 mm slides. These slides were then scanned into the
computer and saved as bitmap images. Each image was imported into SigmaScan where
the mid-palatal suture of each specimen was digitized. The x-y coordinates were
imported into SigmaPlot and subsequently graphed using a single spline curve. The
spline curve option was chosen over the single straight line option because this
represented a more accurate depiction of the sutures. The reason this has to be done is to
override the automated scaling function of SigmaPlot. The scale of the graphs were
changed so equal units were represented on the x and y axes. The image was then
inverted from black on white to white on black. This was done because Benoit 1.3
software recognizes white points as data points and the black points as the background.
The images were converted to bitmap files and imported into Benoit 1.3 for the
fractal analysis. After exploring the different methods available through the software, the
two methods chosen were the information dimension and ruler dimension. The
information dimension was chosen over the box dimension because the boxes are
weighted and therefore provide a more accurate fractal dimension than the box
dimension. There was not, however, an obvious advantage of either the information
dimension or ruler dimension over the other, so both were used to calculate the fractal
dimensions of the colobine mid-palatal sutures. Other researchers have chosen one of the
methods over the other but the reasoning behind their choice is often not made clear,
although the researchers who chose the ruler dimension often state that they use this
method because Mandelbrot (1977) used this method when examining the coastline of
Once the fractal dimensions were obtained, several statistical procedures were
conducted. A 2-way ANOVA was run separating the sexes and species which resulted in
four groups. Regressions were also conducted between the fractal dimensions and each
size/shape variable to try to determine if there was a predictable relationship between any
of these variables. The regressions were conducted with only the species separated not
the sexes. Both of these procedures were evaluated for significance based on a P-
value<0.05. The fractal dimension data for the four groups was also bootstrapped to
obtain a more reliable mean since the sample sizes were small. Bootstrapping makes no
assumptions about the distributional properties of the data.
Including both fractal dimensions, ten variables were examined. Basic statistics
were computed for each variable independently (Tables 2 and 3). The parametric
medians for each group are graphically represented for both fractal dimensions in Figures
2 and 3. Since the samples sizes for these groups are small, the data was bootstrapped for
1000 iterations to try to obtain more reliable means and standard errors, since no
assumption is made regarding the distribution of the data. As shown in Tables 4 and 5,
there was little difference between the parametric mean and the bootstrapped mean.
The ruler and information fractal dimensions for each species were regressed
against each of the measured size/shape variables. Out of the 32 regressions performed,
only three resulted in significant P-values, i.e. P-values less than .05. However, the
coefficient of determination (r-squared) was very weak for these three regressions,
ranging from 12.1% to 37.2% (Table 6).
Tables 7 and 8 report the ruler and information fractal dimensions calculated for
both species. One interesting (and seemingly impossible) aspect of two of these fractal
dimensions is that they are below 1.0. Note in Table 3, Procolobus badius specimen
number 2107 (Figure 4) has a ruler fractal dimension of 0.99209 and P. badius specimen
number 9433 (Figure 5) has a ruler fractal dimension of 0.98466. However, their
information fractal dimensions are both above
Table 2. Basic statistics for variables associated with Colobus polykomos
Variable N Mean Median StDev SE Mean Minimum Maximum Q1 Q3
Ruler Fractal 13 1.1880 1.1903 0.0599 0.0166 1.0795 1.2836 1.1416 1.2341
Information 13 1.0994 1.1018 0.0404 0.0112 1.0268 1.1659 1.0781 1.1247
Palate Height 13 12.550 12.500 1.268 0.352 10.400 14.800 11.495 13.680
Internal Palate 13 18.472 19.400 2.513 0.697 12.100 20.700 17.120 20.045
External Palate 13 36.278 36.800 1.906 0.529 32.200 38.800 35.310 37.450
Palate Length 13 44.138 44.600 2.992 0.830 36.600 48.200 42.800 45.990
Palate Depth 13 6.808 7.000 1.032 0.286 5.000 8.000 6.000 8.000
Upper Facial 13 40.124 40.200 3.350 0.929 34.200 46.410 38.700 42.000
Facial Width 13 75.91 74.00 5.53 1.53 67.90 83.60 71.75 81.25
Skull Length 13 108.96 108.00 4.01 1.11 103.00 115.70 106.05 112.65
Table 3. Basic statistics for variables associated with Procolobus badius
Variable N Mean Median StDev SE Mean Minimum Maximum Q1 Q3
Ruler Fractal 39 1.1355 1.1093 0.0983 0.0157 0.9847 1.3455 1.0615 1.2121
Information 39 1.1085 1.1058 0.0276 0.0044 1.0643 1.1676 1.0883 1.1310
Palate Height 39 10.086 9.970 1.181 0.189 6.830 12.130 9.470 10.870
Internal Palate 39 16.347 16.460 1.554 0.249 12.180 18.740 15.380 17.370
External Palate 39 32.081 32.030 1.441 0.231 29.280 35.040 30.910 33.000
Palate Length 38 39.170 39.085 2.035 0.330 35.340 43.570 37.615 41.030
Palate Depth 39 6.122 6.000 1.305 0.209 3.000 8.500 5.000 7.000
Upper Facial 39 40.784 41.150 2.743 0.439 34.010 44.990 38.900 42.910
Facial Width 37 77.686 78.510 5.002 0.822 68.110 86.750 73.725 81.975
Skull Length 36 101.46 101.90 3.56 0.59 93.54 109.27 99.69 103.71
P. badius females
P. badius males
C. polykomos females
C. polykomos males
1.0 1.1 1.2 1.3
Ruler Fractal Dimension
Figure 2. Box plot of median values for the ruler fractal dimensions.
P. badius females -
P. badius males -
C polykomos females -
C polykomos males -
1.00 1.05 1.10 1.15 1
Information Fractal Dimension
Figure 3. Box plot of median values for the information fractal dimensions.
Table 4. Bootstrapped versus parametric means for ruler fractal dimension
Species Sex N Bootstrap Bootstrap Parametric Parametric
Mean for Standard Error Mean Standard
1000 samples Error
Colobus Male 4 1.1365 0.0200 1.1500 0.0244
Colobus Female 9 1.1953 0.0172 1.2049 0.0195
Procolobus Male 23 1.1295 0.0178 1.1380 0.0194
Procolobus Female 16 1.1230 0.0230 1.1362 0.0274
Table 5. Boostrapped versus parametric means for information fractal dimension
Species Sex N Bootstrap Bootstrap Parametric Parametric
Mean for Standard Error Mean Standard
1000 Samples Error
Colobus Male 4 1.0748 0.0145 1.0817 0.0163
Colobus Female 9 1.1000 0.0118 1.1072 0.0143
Procolobus Male 23 1.1078 0.0056 1.1107 0.0062
Procolobus Female 16 1.1030 0.0061 1.1070 0.0071
Table 6. Significant regressions
Species Variables N Slope Y- r r-squared
Regressed intercept (%)
Procolobus Ruler vs Palate 39 0.0289 0.844 .35 12.1
Procolobus Ruler vs Palate 39 0.0289 0.959 .38 14.7
badius Depth ________
Colobus Information vs 13 0.3100 0.624 .61 37.2
Polykomos Facial Width
According to Benoit 1.3 software, the ruler and information fractal dimensions are
equivalent. If this is true, then a simple regression of these two dimensions should show
a linear relationship. As Figure 6 shows, this is not the case. In fact, there is no
discernible pattern whatsoever in this graph and the r-squared value is 0.0402. Another
indication that these methods for determining fractal dimensions are not equivalent is that
Table 7. Fractal dimensions of Colobus polykomos
Specimen Sex Ruler Fractal Information Fractal
Designation Dimension Dimension
2100 Male 1.07953 1.03320
2216 Male 1.19034 1.09408
2311 Male 1.15727 1.10373
9418 Male 1.17273 1.09593
2102 Female 1.28359 1.08546
2103 Female 1.24256 1.02679
2119 Female 1.22849 1.10182
2123 Female 1.23009 1.13283
2124 Female 1.11034 1.11666
2238 Female 1.14829 1.15345
2245 Female 1.13496 1.16592
2314 Female 1.22786 1.07076
9426 Female 1.23806 1.11099
the specimens exhibiting the highest and lowest fractal dimension values differ between
these two methods. The highest ruler fractal dimension is 1.34546 (Procolobus badius
227, Figure 7) while the highest information fractal dimension is 1.16761 (Procolobus
badius 942, Figure 8). The lowest ruler fractal dimension is 0.98466 (Procolobus badius
9433, Figure 5) while the lowest information fractal dimension is 1.02679 (Colobus
polykomos 2103, Figure 9).
Regardless of which fractal dimension is used, a pure model II 2-way ANOVA
showed that no significant differences exist in the fractal dimensions between species or
sexes. There is also no interaction effect between species and sex. A pure model II was
chosen because there were no fixed treatment effects but rather only random effects
(Sokal and Rohlf 1981).
Table 8. Fractal dimensions of Procolobus badius
Specimen Sex Ruler Fractal Information Fractal
Designation Dimension Dimension
2027 Male 1.04962 1.08833
2028 Male 1.29563 1.10579
2118 Male 1.06146 1.14878
2125 Male 1.12647 1.11583
2126 Male 1.30574 1.11583
2013 Male 1.15642 1.11931
2022 Male 1.07645 1.08920
2104 Male 1.13798 1.09966
2105 Male 1.07308 1.09533
2110 Male 1.24166 1.11158
2113 Male 1.23780 1.15081
222 Male 1.13614 1.14766
2231 Male 1.00705 1.10777
224 Male 1.11669 1.11242
2243 Male 1.22389 1.06426
2255 Male 1.07371 1.08930
232 Male 1.10572 1.08667
233 Male 1.06071 1.08017
235 Male 1.07599 1.09189
239 Male 1.14051 1.12176
9413 Male 1.05565 1.11252
942 Male 1.02873 1.16761
945 Male 1.31662 1.06753
2005 Female 1.05978 1.09521
2032 Female 1.09483 1.10217
223 Female 1.30888 1.13372
227 Female 1.34546 1.07348
2014 Female 1.11507 1.16151
2107 Female 0.99209 1.13472
2112 Female 1.09099 1.09856
2215 Female 1.10713 1.11771
2219 Female 1.14706 1.14561
2220 Female 1.10925 1.11490
2240 Female 1.29973 1.07179
2313 Female 1.20520 1.07042
236 Female 1.21207 1.08017
9422 Female 1.07231 1.13104
9433 Female 0.98466 1.08724
972 Female 1.03491 1.09268
Figure 4. Mid-palatal suture of Procolobus badius specimen 2107 with a ruler fractal
dimension of 0.99209 and information fractal dimension of 1.13472. The
suture is oriented with the anterior portion at the top of the page.
Figure 5. Mid-palatal suture ofProcolobus badius 9433 with a ruler fractal dimension
0.98466 and information fractal dimension of 1.08724. The suture is oriented
with the anterior portion at the top of the page.
1.3 -* .
0.9 -...... .
1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14 1.16 1.18
Information Fractal Dimension
Figure 6. Regression of ruler fractal dimension vs information fractal dimension.
Figure 7. Mid-palatal suture ofProcolobus badius specimen 227 with a ruler fractal
dimension of 1.34546 and information fractal dimension of 1.07348. The
suture is oriented with the anterior portion at the top of the page.
Figure 8. Mid-palatal suture of Procolobus badius specimen 942 with a ruler fractal
dimension of 1.02873 and information fractal dimension of 1.16761. The
suture is oriented with the anterior portion at the top of the page.
Figure 9. Mid-palatal suture of Colobus polykomos specimen 2103 with a ruler fractal
dimension of 1.24256 and information fractal dimension of 1.02679. The
suture is oriented with the anterior portion at the top of the page.
The results of the 2-way ANOVA indicate that the hypothesis proposed for this
study, i.e. these two species would differ in mid-palatal suture complexity, is not
supported. The colobine monkeys used in this study only have one major difference in
their diets. Colobuspolykomos must gnaw through a tough pod in order to gain access to
a particular type of seed they eat. One possible explanation for why no significant
differences were found is that the seeds do not make up a large enough portion of their
diets to have an effect on the sutural complexity. In other words, seed-eating is dominant
in both of these colobine monkeys, but the actual proportion of Pentaclethra macrophylla
seeds to the Colobuspolykomos diets has never been identified (Davies et al. 1999). The
difference in masticatory loads between these two species may not be large enough to
elicit a morphological response from the mid-palatal suture.
The distribution of stress throughout the palate during mastication may also be a
contributing factor to the non-significant results reported here. Although numerous
studies exist that explore the loading environment during mastication in certain parts of
the face and cranium, few studies mention any stress the palate may receive during this
activity. Due to the morphological structure of the palate, mechanical modeling is
difficult. Although the palate probably experiences different types of stress such as
shearing forces, torsional moments, and bending moments (Preuschoft 1989), it is
possible that the stress level is not significant enough to elicit a response from the bone.
In order to figure out what the strains are, the maxilla needs to be explored
experimentally. As mentioned earlier, the issue becomes how to model the maxilla. One
possible reason the maxilla may experience small loads is the presence of the hard palate.
Unlike the mandible, the maxilla has the hard palate which may serve to eliminate or
greatly reduce twisting and bending (Daegling and Hylander 1997).
Measurements of different size/shape variables were also taken from each
specimen in order to determine whether or not a relationship exists between these
particular measurements and the fractal dimensions of the mid-palatal sutures. Only
three regressions showed significance, but the correlation values were very weak (Table
6). When these measurements were regressed against the ruler fractal dimension, palate
height and palate depth in Procolobus badius showed significance. Interestingly there
were no significant regressions in Colobuspolykomos for the ruler fractal dimension.
However, the opposite is true for the information fractal dimension. No significant
results were found for Procolobus badius, but the regression of information fractal
dimension versus facial width in Colobuspolykomos showed significance. The fact that
the so-called equivalent fractal dimensions yield different significance is further
evidence that these are not equivalent measures. More than likely the significant P-
values for these three regressions reflect a type I error instead of real significance,
although there is no way to truly know if a type I error was committed. The results of the
regressions suggest that there is no predictable pattern between either of the fractal
dimensions and any of the size/shape variables.
One problem limiting interpretation was small sample sizes. When dealing with
biological samples, obtaining sufficiently large sample sizes can be a problem. An
attempt to deal with this problem was made by bootstrapping the data. However, as
previously mentioned, the bootstrapped means were very similar to the parametric means
calculated from the raw data, which suggests that the variation captured in this study is
probably a fairly accurate representation of the populations in question.
Another issue arising in this study may stem from the methodology used. Fractal
analysis has become a popular method for quantifying the complexity of intricate cranial
sutures. Long (1985) published one of the earliest works on fractals in biology when he
examined the sutures present on the shells of ammonites and the cranial sutures of
antlered deer. This study was also the first to describe how fractal elaboration is
important in the evolutionary process. Long and Long (1992), however, criticize the use
of fractal analysis on human cranial sutures because they feel that these particular sutures
are not self-similar and therefore are not fractals even though they yield a dimension
between 1 and 2. They state that some waveform curves may yield a dimension up to
1.2, but this is not sufficient to classify them as fractals. Using this reasoning, Long and
Long would probably say the sutures presented in this paper are not fractals. If this is
true, then this could be an explanation for why the two fractal analysis methods used here
do not show equivalence.
The problem with the above supposition is that these sutures do fit the definition of
a fractal, i.e. they are self-similar and have a dimension between 1 and 2. The main
critique of Long and Long (1992) is that the waveforms that possess a dimension above 1
are not self-similar. Studies conducted on human cranial sutures using the box dimension
have shown that human cranial sutures are self-similar through the use of logarithmic
plots. These graphs show the relationship of the logarithms of the number of squares
with length r occupied by the suture against the logarithm of 1/r. Benoit 1.3 provided the
logarithmic graphs for each suture analyzed in both of the methods and all of them
clearly showed a linear relationship. This suggests that these sutures are self-similar and
therefore, by definition, are fractal.
Unfortunately this still leaves the problem of trying to provide an explanation for
why the ruler and information fractal dimensions are not demonstrating equivalence like
they should. One possibility is that due to the complicated mathematics that are
introduced into the information dimension in order to weight the boxes, the equivalence
that exists between the box and ruler dimension is lost. To test this theory, fractal
analysis was conducted again on the same sutures using the box dimension (Tables 9 and
10). A simple regression was conducted and as Figure 9 demonstrates there is still no
linear relationship (r-squared 0.0804). This does not support the idea that the more in
depth mathematical calculations affected the equivalence. The reason for this may be
that the number of points collected could affect the outcome of the fractal dimension.
This implies that these different methods of fractal analysis are not measuring
complexity in the same fashion. Uncertainty exists as to which method is more
appropriate for analyzing human cranial and facial sutures, but one insight gained is that
these methods are not equivalent. This means more testing (e.g.) needs to be completed
in order to try to determine which method is more accurate. Besides the type of dataset
utilized, another factor that may affect which method is better is how the data is
collected. In other words, it may be that both methods are appropriate for analyzing
human sutures, but depending on the method used to extract the suture from the specimen
and manipulate it so it can be imported into this software, one method may prevail over
the other. Regardless of which method was used, no significant results were discovered
from this data.
Table 9. Box dimensions for Procolobus badius
Specimen Designation Sex Box Dimension
2027 Male 1.15339
2028 Male 1.11262
2118 Male 1.18019
2125 Male 1.14647
2126 Male 1.12777
2013 Male 1.12626
2022 Male 1.14486
2104 Male 1.11175
2105 Male 1.12366
2110 Male 1.09819
2113 Male 1.14137
222 Male 1.16990
2231 Male 1.12637
224 Male 1.12912
2243 Male 1.11433
2255 Male 1.12925
232 Male 1.12130
233 Male 1.11166
235 Male 1.12101
239 Male 1.15034
9413 Male 1.12463
942 Male 1.17601
945 Male 1.10132
2005 Female 1.11475
2032 Female 1.14087
223 Female 1.12508
227 Female 1.11091
2014 Female 1.17835
2107 Female 1.12846
2112 Female 1.11445
2215 Female 1.13767
2219 Female 1.14574
2220 Female 1.13643
2240 Female 1.11797
2313 Female 1.12303
236 Female 1.13915
9422 Female 1.12672
9433 Female 1.12309
972 Female 1.11693
Table 10. Box dimensions for Colobus polykomos
Specimen Designation Sex Box Dimension
2100 Male 1.12953
2216 Male 1.11993
2311 Male 1.10920
9418 Male 1.10893
2102 Female 1.10568
2103 Female 1.10836
2119 Female 1.13348
2123 Female 1.17746
2124 Female 1.12773
2238 Female 1.15679
2245 Female 1.17051
2314 Female 1.10595
9426 Female 1.13959
Box Fractal Dimension
Figure 10. Regression of ruler fractal dimension vs box fractal dimension.
** -** -
One of the proposed functions of cranial sutures is that they play a role in the
transmission and absorption of mechanical loads (Herring 1972). If this is true, it stands
to reason that the morphology of the sutures may reflect the loading environment to
which it is subjected (Rafferty and Herring 1999). Using this reasoning, the hypothesis
was made that the more complexity a suture exhibits, the higher amounts of stress it
experiences. One problem is how one quantitatively measures sutural complexity. One
method that has been applied to this problem over the past two decades is fractal analysis.
The fractal analysis conducted on the mid-palatal sutures of these two species of
colobus monkeys did not show a significant difference. Sex also did not have a
significant effect on the complexity of the mid-palatal sutures. Although this study does
not support the hypothesis that mechanical loading is at least partially responsible for the
morphological complexity of sutures, it by no means discredits this idea. The most
probable reason behind the lack of support is that the differences in the diet are not great
enough to cause significantly more stress in the palate of Colobuspolykomos. Another
aspect that should be examined in the future is the overall structure of the maxilla of these
two species. There may possibly be a larger concentration of bone between the point of
impact (the teeth) and the mid-palatal suture. If so, this bone may absorb the stress
before it reaches the suture. Unfortunately, at this point in time, this is pure speculation.
The suggestion has also been made that most cranial sutures are not intricate
enough to be fractals (Long and Long 1992), but as the term is currently defined human
cranial sutures are fractal objects. This leads to the question of which fractal analysis
technique is most appropriate for examining human cranial sutures. One conclusion that
must be drawn from this study is that the box (information) dimension and the ruler
dimension methods are not equivalent. So, which one provides a more accurate depiction
of the dimension of these structures? Unfortunately, more intensive investigation is
required in order to provide an answer for this question.
The complexity of these particular sutures did not differ significantly between these
species, but this does not mean that the loading environment has no effect on sutural
growth and morphology. Enough evidence exists to merit further exploration of this
topic. Mechanical environments do elicit morphological responses from bone throughout
all stages of life whether in modeling or remodeling. An important point to consider is
that sutural complexity may not only be influenced by mechanical factors. The sutures
serve other functions besides absorption and transmission of loads. These other
functions, such as growth, may also affect the complexity of the sutures. Although this is
possible, mechanical loading seems to be the most likely factor contributing to the
complex morphology of the suture. Many factors play a role in palate growth and
development; however, exploring the role of mechanical forces is essential to a
comprehensive understanding of this process.
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Jennifer Hotzman is one of four children and was born in Meridian, Mississippi.
She received her Bachelor of Arts degree in anthropology from the University of
Southern Mississippi in 2000. After graduation she continued her education at the
University of Florida. While completing her graduate studies, Ms. Hotzman also worked
full-time for Regeneration Technologies, a company that manufactures allografts for
surgical procedures. After obtaining her Master of Arts degree, she plans on continuing
her graduate studies at the University of Florida.