A Funetional Analysis of Molar Morphometrics in Living and Fossit Hominoids Using 2-D Digitized ...

301 Pages·2000·17.09 MB·English

A Funetional Analysis of Molar Morphometrics in Living and
Fossit Hominoids Using 2-D Digitized Images
Emma Smith
A thesis submitted in conformity with the requirements
for the degree of Doctor of Philosophy
Graduate Department of Anthropology
University of Toronto
@ Copyright by Emma Smith (1999)
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A Functional Analysis of Molar Morphometics in Living and Fossil
Hominoids Using 2-D Digitized Images
hy Emma Smith
Doctor of Philosophy, 1999
Department of Anthropology, University of Toronto
Abstract
Diet is an important factor in the overali biology of animals. It is part of a number
of cornplex phenornena involved in the anatomy, physiology and behaviour of the
individual. Thus when fossil taxa are represented by dentitions, either pnncipally or
completely, a large arnount of information regarding the biology of the taxon can be
revealed by determining the diet as accurately as possible.
This thesis examines the functional aspects of molar occlusal morphology among
hominoids. The prirnary goal is to discover new or more detailed aspects of the diets of
Miocene horninoids. The fossil remains of the dentitions of these animals are often badly
preserved or extremely worn such that traditional analyses (e-g. simple observational
techniques, microwear analysis, shearing quotient caiculations or enarnel thickness
estimates) are not possible. At best they may include ody a small percentage of the entire
sample available. The technique of digitized morphometrics employed here c m obtain
fünctionally important information from the cusp areas of molars, including relatively worn
teeth. This involves a new approach and a larger sample size in the ongoing investigation
into the fiinction of hominoid teeth.
Extant hominoids are used as an analogy for the fossil taxa. The diets of living
hominoids have been extensively studied and are relatively well understood. A mode1 of
rnolar functional morphology based on known diets is developed here and applied to the
fossil horninoids.
It is more difficult to predict dietary strategies of fossil hominoids ffom the early
Miocene, based on living taxa. This is either due to their remarkably different diets or due
to the possibility that adaptation toward modem ape molar morphologies had not yet
developed. Later Miocene hominoids are much easier to
Acknowledgments
1 would Iike to thank the members of my dissertation cornmittee, Drs. D.R. Begun, M.
Gagnon and L. Sawchuck for their guidance and support throughout this study. 1a m especially
indebted to Dr. David Begun for his knowledge, interest and encouragement. He allowed
uniimited access to his coIlections and resources and time. 1 could not ask for a better thesis
advisor.
1 would also like to thank the government of Kenya for permission to conduct research in
their country. Particular acknowledgment goes to Emma Mbua and William Anonge for their
help with the collections in their care. Thanks also go to Dr. Peter Andrews for permission to
study original fossil material under his care at the British Museum of Natural History and for
insightful comments both in the museum and in the field at Rudabanya. David Pilbeam was also
rnost gracious for allowing me to collect data fiom his cast collection at the Peabody Museum.
Harvard. Erksin Gulec also provided access to the Ankarnpzthenrs specimens at the MTA for
which 1a m most gratefbl.
Special thanks go to Richard Thorington and Linda Gordon at the Smithsonian Institution,
Vim VanNeer at the Koninklijk Museum. Bryn Mader at the American Museum of Natural
History, Maria Rutzmeyer at the MCZ, Harvard and Dr. and Mrs. Howlett at the Powell-Cotton
Museum for providing access to the extant hominoid collections in their care.
Very special thanks to Myriam Zylstra, my colleague, sounding-board, source of sanity,
traveling cornpanion and best of ail, my fiiend. Without her this thesis may never have corne to
fruition.
1a m grateful to the University of Toronto, School of Graduate Studies at the University
of Toronto, govemment of Ontario, Amencan Museum of Natural History, NSERC and David
Begun for providing fiinds necessary for completion of this study.
Finally a special thank-you to al1 my friends and family who supported me 100%. In
particular rny mother and sister who listened, advised and ignored me just enough to get me
through. 1 am most especially thankful for the support of Liviu Amstei, my best fiend, who
showed the greatest patience, understanding and encouragement.
Table of Contents
Absmcr Ï
-.-
A cknowledgments I I I
Table of Contents v
LÏst of Tables viii
List of Figr~res xii
List of Appendices
Chapter 1
Introduction
B ackgound
A. Behaviourai evidence of diet in living hominoids
A. 1 SoR-fruit fiugivores
A.2 Hard-object fiugivores
A.3 Folivores
B. Dental evidence for diet
B. 1 Overall dental morphology
B.2 Dentai microwear
B.3 Enamel thickness
B.4 S hearing quotients
B.5 Digitizing and dental morphometrics
Chapter 2
A. Materials
A. 1 The sarnple
A.2 The equipment
B. Method
B. 1 Museum work
8 . 2 Digitizing and measurements
B.3 Analysis
Chapter 3
Extant Horninoids
A. The data sample
A. 1 Descriptive statistics
A.2 Ailornetry
A.3 Sexual dimorphism
Table of Contents (Continued)
B. Dental morphometrics 60
B. 1 Traditional methods involving molar shape and relative
molar size order 60
B .2 Frugivores 67
B .3 Folivores 71
B -4 Frugivores and folivores 75
B.5 Goodness of fit of the extant hominoid mode1 83
B .6 Surnmary and interpretation 85
Chapter 4
Early Miocene Fossil Hominoids 89
a) Procomtl 89
b ) Afropithenrs turkmensis, Tirrkmpithectrs kalakolensis and
Heliopithecus Zeakeyi 10 6
c) Rangwapilhears gordoni and Nyamapithecirs 111
d) Summary of early Miocene horninoid diets 120
Chapter 5
Middle Miocene Fossi! Horninoids
a) Kenyapithems
b) Griphopithecus
c ) Summary of rniddle Mïocene hominoid diets
Chapter 6
Late Miocene Fossils Hominoids
a) Dryopithecrrs
b) Ozrranopithenrs
c) L zrfengpitheais
d) Oreopithears
e) Ankmapi fhecus
f ) Sivapithecm
g ) Summary of late Miocene hominoid diets
Chapter 7
Miocene Hominoids Considered Together 175
a) Summary of Miocene hominoid diets 175
b) The significance of thick enamel 177
c) The significance of molar cingula 179
d) Dietary and evolutionary trends throughout the Miocene 181
vii
Table of Contents (Continued)
Chapter 8
Surnmary and Conclusions
a) The extant hominoid mode1
b) Functional implications
c ) Similatities and dflerences with previous work
d) Questions for future research
References cited
List of Tables
1.1 Dietary proportions of Pm
1.2 Dietary proportions of Gibbons
1.3 Dietary proportions of Pongo
1.4 Dietary proportions of Gorilla
1.5 Dietary proportions of Hyiobates syndactylzis
2.1 Number of individuals of extant horninoids employed in the study
2.2 Number of molars per taxon employed in the study
2.3 Number of fossils hominoid molars emptoyed in the study
3.1 Differences in C.V. of M 2 relative metaconid area between folivores
and frugivores
3.2 Slopes of regressions of log (cusp area) on log (crown area)
3.3 Regression slopes of each dietary group for cusp to crown area
3.4 Mean Mi relative cusp areas of male and female Gorilla gori(ln
gorilla
3.5 Results of MCA for lower MI
3.6 Ratios of mean molar length to breadth
3.7 Results of one way ANOVAs testing for differences in mean molar
length ratios among dietary groups
3.8 List of included and discarded cusp areas fiom PCA
3.9 Counts and percentages of classifications of individual molars to
dietary groups
3.10 Summary of molar occlusal morphologies associated with dietary
specidization
Coefficients of variation for relative cusp areas of Proconslil species
Mean length to breadth ratios of Proconsd molars
Percentage of correct classifications to site
Predicted dietary group membership of Proconstil species
Predicted dietary group membership of Proconszci species with
afïects of cingula removed
Predicted dietary group membership of Afropilhecus specimens
Mean length to breadth ratios of Nyanzapithe~-zcasn d Rangwupithencs 1 1 5
Predicted dietary group memberships for Nyanrapithecus and
Rangwapilhents 117
New predictions of dietary groups of Ranpvapithems based on
removai of aEects of cingula 119
Mean length to breadth ratios of Kenyapitherus molars
Predicted dietary group membership of Kenynpifhenls