University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1981 Morphological variation of grizzly bear skulls from Yellowstone National Park Harrie W. Sherwood The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Sherwood, Harrie W., "Morphological variation of grizzly bear skulls from Yellowstone National Park" (1981). Graduate Student Theses, Dissertations, & Professional Papers. 7381. https://scholarworks.umt.edu/etd/7381 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. COPYRIGHT ACT OF 1976 Th is is ah unpublished m a n u s c r ip t in w h ic h c o p y r ig h t s u b ­ s i s t s . Any fu r th er r e p r in t in g of it s co ntents must be a ppr o ved BY th e a u t h o r . Ma n s f ie l d L ib r a r y Un iv e r s it y of Ho n tan a D A T E i _ l M l _ MORPHOLOGICAL VARIATION OF GRIZZLY BEAR SKULLS FROM YELLOWSTONE NATIONAL PARK By M arrie W. Sherwood B.A., University of Colorado, 1974 Presented in partial fulfillm ent of the requirements for the degree of Master of Science UNIVERSITY OF MONTANA 1981 Approved Chairman,^BoaN oNExamfners D ^ n , Graduate School I s. - a 5-^ I Date UMI Number: EP38182 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMT Oi«Mrtation PVMiaNng UMI EP38182 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code uesf ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 -1346 ABSTRACT Sherwood, Harrie W., M.S., Fall 1981 Wildlife Biology Morphological Variation of Grizzly Bear Skulls from Yellowstone National Park / O / / ’ I Director: Philip L. Wright (j .A Cranial characters of tooth eruption of the permanent dentition tooth wear, cra n ia l sutures, and 24 cran ia l measurements were examined on 68 (44 males, 24 females) grizzly bear (Ursus arctos h o rrib ilis) skulls from Yellowstone National Park to investigate the cranial variations of grizzlies with respect to age, sexual, and individual variation and to examine the u tility of using cranial characters of indicators of age and sex. Twenty four of the bear skulls were of known age whose ages ranged from cubs to 11 years old. The eruption of the grizzly bear dentition began sometime before the f i f t h month o f l i f e and was completed by the seventeenth month, except for the canines and M 3 which were erupted by the third year of life . Tooth wear increased with age but was poorly correlated with age due to considerable variation between in d ivid u a l bears o f the same age class. The sequence o f cranial suture closure occurred at approximately the same age for all grizzlies. For taxonomic and statistical purposes of skull size, bear skulls were classified into six age classes on the basis of tooth eruption and wear, bone fu sio n , changes in cra n ia l s tru c tu re , and chronological age. Female grizzly skulls attained adult size earlier and were significantly smaller than adult male grizzly s k u lls . Maximum female cra n ia l size was reached between the ages o f 6 to 11 years. Male g riz z lie s did not grow appreciably in length beyond 12 years o f age, but continued to grow in breadth and height beyond 12 years o f age. Age estim ation by m u ltip le regression, discriminant analysis, and cranial sutures gave reliable results. As age increased there was an increased difference in cranial size between male and female g riz z lie s . S kulls o f a d u lt male grizzlies averaged 13 percent larger than adult female skulls. Sex-related differences in size of the sagittal crest, mastoid breadth, zygomatic breadth, as well as discriminant analysis were useful in determining the sex of unknown adult grizzly skulls. Young bears of the same age-sex class were more variable in skull size than adult bears of the same age-sex class. Individual differences in the presence or absence of the anterior premolars was of little taxonomic consequence. ACKNOWLEDGEMENTS Financial support for the study was provided by the Montana Cooperative W ild life Research U nit (Montana Department o f Fish, W ild life and Parks, University of Montana, United States Fish and W ildlife Service, and the W ildlife Management Institute, cooperating). I express my thanks and indebtedness to my committee members. Dr. Philip Wright, my major advisor, and Drs. Charles Jonkel and Bart O'Gara who selflessly gave their guidance in preparation and critical review of the manuscript. I thank Dr. John Craighead, who generously loaned the use o f his bear skulls with data for purposes of study. I thank Jay Sumner for collating the data on the Craighead bear skulls and for the age estimates he provided on some of those specimens. I express my g ra titu d e to Ken Greer (Montana Dept. Fish, W ildlife and Parks) for use of state-owned bear skulls and his helpful suggestions and cooperation. I appreciate the comments and suggestions of my fellow graduate students, especially Steve Albert for his statistical and computer assistance. Bob H ollister, Ph.D. candidate in Mathematics, provided assistance in statistical treatments. I express my deepest appreciation to my wife, Kathy, for her sharing and p a tie n t support. TABLE OF CONTENTS Page ABSTRACT....................................................................................................................... i i ACKNOWLEDGEMENTS....................................................................................................... i i i LIST OF TABLES........................................................................................................... v1 LIST OF FIGURES......................................................................................................... v ii LIST OF PLATES........................................................................................................... v i i i CHAPTER I. INTRODUCTION.................................................................................................. 1 I I . MATERIALS AND METHODS................................................................................ 5 Age Variation ............................................................................................ 5 Secondary Sexual V a ria tio n .................................................................. 12 Individual Variation .............................................................................. 13 I I I . RESULTS............................................................................................................. 14 Age Variation ............................................................................................ 14 Permanent D e n titio n ............................................................................ 14 Tooth Wear............................................................................................... 16 Cranial Sutures .................................................................................... 21 Cranial Measurements .......................................... 23 Characteristics of Growth................................................................ 26 Estim ation o f Age................................................................................. 34 Secondary Sexual V a ria tio n .................................................................. 49 Cranial Measurements .......................................................................... 49 Sexual Dimorphism ................................................................................ 49 Individual Variation .............................................................................. 54 Permanent D e n titio n ............................................................................. 54 Cranial Measurement ............................................................................. 54 IV. DISCUSSION....................................................................................................... 57 Age Variation ............................................................................................. 57 Permanent D e n titio n ............................................................................. 58 Tooth Wear............................................................................................... 58 Cranial Sutures ..................................................................................... 59 Cranial Measurements ........................................................................... 60 Estimation of Age................................................................................. 61 i V Page Secondary Sexual V a ria tio n .................................................................. 66 Sexual Dimorphism ...............................................................................