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1981
Morphological variation of grizzly bear skulls from Yellowstone National Park
Harrie W. Sherwood The University of Montana
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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
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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
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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 ...... 66 Individual Variation ...... 67 Permanent D e n titio n ...... 67 Cranial Measurement ...... 68 Taxonomy ...... 70
LITERATURE CITED...... 74
APPENDICES
A. Description of tooth wear in a series of known and assigned-age bears ...... 77
B. Description of suture closure in a series of known and assigned- age bears...... 79
C. Age variation of cranial measurements of grizzly bears from Yellowstone National Park ...... 81
D. Age group mean values of cranial measurement for substitution into discriminant or regression equations ...... 91
E. Record o f g riz z ly bears used in the study ...... 93 LIST OF TABLES
Page
Table
1. Age distribution of the known age and assigned age bear sample ...... 6
2. The six age classes used in the study with delineation by morphological characteristics and chronological age ...... 25
3. Maximum growth c la s s ific a tio n of cranial measurement by age class and sex ...... 27
4. Age variation in 5 cranial characters of grizzly bears from Yellowstone National Park ...... 29,30,3
5. Standardized discriminant function coefficients of male and female age groups...... 38
6. Unstandardized discriminant function coefficients and their group means fo r males and female age groups ...... 39
6A. Discriminant functions evaluated at group means (group c e n tro id s ) ...... 39
7. Comparison of age estimates on seven unknown age g riz z ly bears from Yellowstone National Park, ...... 43
8. Secondary sexual v a ria tio n in 24 cranial measurements in adult (age class V and VI) grizzly bears from Yellowstone National Park ...... 50
9. Standardized and unstandardized discriminant function coef ficients of sex on adult grizzlies ...... 53
9A. Discriminant functions evaluated at group means ...... 53
VI LIST OF FIGURES
Page
Figure
1. Measurements of g riz z ly bear s k u lls ...... 11
2. F irs t and second year eruption sequence of the permanent d e n titio n ...... 15
3. Sequence of tooth wear in grizzly bears from Yellowstone Park...... 18
4. Sequence of suture closure in grizzly bears from Yellowstone Park...... 22
5. Representative growth curves by age class of 5 cranial characters of grizzly bears from Yellowstone National Park...... 32
6. Discrim inant p lo t of male age groups ...... 41
7. Discriminant plot of female age groups ...... 42
8. Sexual dimorphism of g riz z ly bear measurements ...... 52
v n LIST OF PLATES
Page
Plates
1. Progressive tooth wear details of the upper and lower jaws of 2 year, 5 year, 7 year, 10 year, 15 year, and 18 year old grizzly bears ...... 20
2. Comparative cranial size and suture closure of a 2 year, 5 year, 9 year, and 18 year old male grizzly bear ...... 46
3. Comparative cranial size and suture closure of a 2 year, 5 year, 9 year, and 18 year old female grizzly bear ...... 48
4. Individual variations in 4 old adult male grizzly skulls ...... 58
V I I I CHAPTER L
INTRODUCTION
As a preliminary to the taxonomic study of a species, under standing the morphological variation within that species clearly is important. "Morphological variation within an intrabreeding population of brown bears (Ursus arctos L.) is of three major types: differences between sexes, changes w ith age and in divid u a l v a ria tio n . . . . Much o f the past confusion obscuring the taxonomic status of this species has resulted from attempts to compare specimens w ithout adequate considera tion for these variables." (Rausch 1963:33).
The great proclivity of brown bears to vary in size was recognized early by von Middendorf (1851). He concluded that the shape of the skull profile (vaulting of the profile) was a mixture of age and individual variation. He understood that the variability in cranial characteristics demonstrated that the Palaearctic and Nearctic forms of brown bears were conspecific.
The publica tion s o f Merriam (1896, 1914, 1918) and his "new species" clearly indicate his lack of understanding and consideration for variability when he concluded that 86 species of brown bears existed in North America alone. Most species were id e n tifie d on the basis o f few, sometimes a single, specimen. His conclusions, unfortunately, seriously hampered and influenced the work of contemporary taxonomists. Rausch (1953, 1963) has g re a tly improved the understanding
of the systematics of the brown and grizzly bears of North America.
He demonstrated the significance of individual variation in cranial
characteristics of bear skulls from the Alaska region and disclosed
the erroneous assumptions upon which Merriam derived his species
classification (Rausch 1953). He concluded that all North American
grizzlies and brown bears belong in one highly variable species, Ursus
arctos and recognized five North American subspecies (lU.^. horribil is
Ord; IJ.a^. middendorffi Merriam; JJ.^. gyas Merriam; jJ.ja. richardsonii
Swainson; and ]J.a^. californicus Merriam).
Rausch (1963) later studied a long series of local samples
with regard to condylobasal length. He demonstrated that geographic
variation was essentially clinal, decreasing in size north, east and
south from a maximum on the Alaska Peninsula and Kodiak and Afognak
Islands. As a result, he differentiated the North American brown and
grizzly bears to two forms, the very large coastal and island form in
Alaska and British Columbia (U.^. middendorffi Merriam) and the smaller
form occupying the remainder of the geographic range of North America
(]J.£. horribil is Ord).
Kurtéh (1973) demonstrated that, with regard to width/length allometry, there are two groups of bears possessing different growth patterns; the re lict, broad-skulled growth form that occupied the
Pacific coast of Beringia that now persists on Kodiak and Afognak Islands; and the narrow-skulled growth pattern of the form that inhabited inner and northern Beringia. He concluded that it was possible to distinguish between only three subspecies o f brow n-grizzly bears now liv in g in the Nearctic region. The three subspecies he designated were:
1) Ursus arctos middendorffi Merriam 1896. — Kodiak and Afognak Islands, larger than the grizzly, on an average broader-skulled than mainland brown bears;
2) Ursus arctos d a lli Merriam 1896. — south coast o f Alaska, west coast of British Columbia, larger than grizzly, on an average more narrow-skulled than U.^. middendorffi; and
3) Ursus arctos h o r r ib ilis Ord 1815. - - a ll of Nearctic range except areas mentioned above, smaller than U.a^. middendorffi and U.a d a lli.
The problem of North American grizzly bear taxonomy is further complicated by Hall (1981). In his latest edition of The Mammals of
North America, he disregards the taxonomic conclusions of Rausch (1953,
1963), Kurtén (1973), Erdbrink (1953) and others by listing 90 or so species-subspecies names of brown-grizzly bears; mostly those described by Merriam (1914, 1918). Thus disagreement among experts persists regarding the specific-subspecific status of the brown-grizzly bear complex o f North America.
Contemporary taxonomy is characterized by a synthesis of morphological definition combined with biological definition, which takes ecological, geographical, genetic and other factors into consideration (Mayr, 1953). "The population, represented by an adequate sample, the series of the museum worker, has become the basic taxonomic unit- (Mayr 1953:13). With statistics and computers, q u a n tita tiv e analyses o f v a ria tio n can be measured and compared in a standardized, precise, and meaningful way. Unfortunately, this type of treatment on the systematics of grizzly bears has been lacking and thereby in h ib ite d the advancement o f g riz z ly bear taxonomy. Manning's
(1971) work on the geographic variation of polar bears (Ursus maritimus
Phipps) provides an e xce llen t example o f how these techniques can be used to their greatest benefit for taxonomic purposes.
Grizzly bear studies in Yellowstone National Park by Drs.
John and Frank Craighead from 1959 to 1967 (Craighead et al. 1974) assembled inform ation on the biology, ecology and population dynamics
of the Yellowstone grizzly. As a part of their studies, a unique series
of grizzly bear skulls was collected with complete data on sex, age, and other biological information.
Such a valuable series afforded an excellent opportunity to examine the morphological v a ria tio n o f g riz z ly bear sku lls w ith in a
local, intrabreeding bear population. Additional grizzly skulls from
Yellowstone were loaned by Ken Greer of the Bozeman W ildlife Laboratory
(Montana Department o f Fish, W ild life , and Parks).
The goal of my research was to determine the morphological characteristics of the central Rocky Mountain grizzlies, and to thereby provide baseline data on bears of this area, in order that other studies could follow, and so that future comparisons could be made with other more northern grizzly populations.
My specific objectives were to:
1) examine the cran ia l v a ria tio n o f g riz z ly bear sku lls with respect
to age, sex, and in d ivid u a l v a ria tio n ;
2) describe the morphometric characteristics of the Yellowstone bear
population; and
3) examine the u tility of using cranial characters as indicators of age
and sex. CHAPTER LI
MATERIALS AND METHODS
Sixty eight grizzly skulls (44 males, 24 females) were
measured. A ll o f the s k u lls were obtained as part o f an extensive
population study of grizzly bears in Yellowstone Park from 1959 to 1971
(Craighead et al. 1974). Ken Greer, Montana Department Fish, W ildlife,
and Parks, loaned seven s k u lls (4 males, 3 females) th a t were used to
estimate age and sex.
Age Variation
Age Determination
Twenty six s k u lls (14 males, 12 females) were o f known age
from bears that had been ear tagged as cubs or yearlings (whose marked mother had been identified with cubs the previous year) (Table 1). The
remaining 42 skulls (30 males, 12 females) were assigned ages by cementum annuli of the canine (Rausch 1969), fourth premolar (Craighead et al. 1970) or other teeth available (Table 1). Age estimates by tooth cementum layers were determined by John Craighead and Jay Sumner (J. J.
Craighead, in prep.). An arbitrary birthdate of 1 Feb. was assumed for all calculations. Information about age and sex of individual bears used in the study is provided in Appendix E. Table 1 . Age d is trib u tio n o f the known age and assigned age bear sample
AGE RANGE IN YEARS
0.2 3-5 6-11 12-23
KNOWN AGE 12 9 5 0
ASSIGNED AGE 7 6 10 19
TOTAL 19 15 15 19
Permanent D e ntitio n
The eruption sequence o f the permanent d e n titio n was examined by placing cubs, yearlings, and 2 -yr. olds in a series ranging from youngest to oldest. The eruption of each tooth was examined in relation to its placement within the aveolar margin. The sequence of tooth eruption was classified into three stages: 1) crown of the tooth had not erupted above the aveolar margin, but was visible through the aveolar opening; 2 ) crown o f tooth had erupted above aveolar margin, but eruption was s till occurring; and 3) the dentino-enamel junction of the tooth had emerged beyond the aveolar margin and tooth eruption was complete. Root closure o f the teeth was not examined to evaluate tooth development.
Tooth Wear
The degree of tooth wear was categorized into five levels.
Each tooth o f each specimen was assigned a value equal to the amount of wear. The categories o f tooth wear were defined as: 0 = no wear;
1 = slight wear (crown tip worn fla t, but no dentine was exposed);
2 - moderate wear (wear o f tooth cusps or crown showed in terrupted
exposure o f the enamel by the dentine); 3 = heavy wear (tooth worn to
the level of the dentino-enamel junction of the incisors, canines and
premolars or tooth worn to the level of the cingulum of the molars);
and 4= severe wear (tooth worn to the aveolus o f the to o th ).
Cranial Sutures
The coalescence o f cranial sutures was examined by placing
aged specimens in a series ranging from youngest to olde st. Each suture was examined separately for degree of fusion and assigned a numerical
value. The stages of suture closure were numerically classified as:
1 = suture open; 2 = suture partially closed (suture firm ly closed, but
s till visible); 3 = suture in final stages of obliteration; and 4 =
suture obliterated.
Cranial Measurements
Twenty fou r cran ia l measurements were taken w ith d ia l calipers to the nearest 0.10mm (Fig. 1). Measurements were taken on the le ft side of the skull unless that side was damaged. Measurements followed by an asterick (*) indicate measurements to be the same or very similar to those described by Manning (1971) for polar bears. The measurements taken were as fo llo w s.
CBL.* Condylobasal length: from the anterior extremity of the premaxilla (not teeth) to the posterior extremity of the condyle. MPI.* Molar-premaxilla length: one jaw of the calipers was placed
across the posterior border of both M 2 's either at the widest point of
the cingtila or the a ve o li, whichever gave the greater measurement. The
other jaw was placed across the anterior extremity of the premaxi 11ae,
thus giving the distance along the central line of the skull. If the
c a lip e r jaws were not long enough, a piece o f s tra ig h t edged metal was
placed across the back o f the teeth and the measurement taken from th is .
MB.* Mastoid breadth: greatest breadth across the mastoid processes.
SB.* Supraorbital breadth: maximum breadth across the supraorbital
processes.
ZB.* Zygomatic breadth: greatest breadth across the zygoma. Where the
squamosal and jugal had parted, the squamosal was assumed to give the
correct breadth.
CL.* Cranial length: from the inion to the midpoint between the
supraorbital processes. A line can be drawn on the skull joining the
extremities of the processes. The inion is here defined as the most
posterior point on the skull at or near the junction of the lambdoidal
and sagittal crests.
FL.* Facial length: from the midpoint between the supraorbital
processes to the extremity of the premaxillae.
MSH.* Maxilla-supraorbital height: distance between the highest part of the lower border of the le ft maxilla posterior to Mg and a point on the dorsal surface of the frontal immediately above this. This point is approximately at the intersection of a line joining the extremities of the supraorbital processes and a line tangent to the inner border of the o r b it. LCB.* Least cranial breadth: the least width of the cranium posterior
to the supraorbital processes.
IB.* Interorbital breadth: minimum width between the orbits measured
across the frontal s.
BC.* Breadth of canines: greatest breadth of the rostrum at or above
the canines. This is normally 5 to 10mm. above the alveoli of the
canines, but in young g riz z lie s w ith permanent canines only p a r tia lly
erupted it is distinctly higher up.
PB.* Palatal breadth: distance between the outer borders of the alveoli
of the posterior root of
LP4M2.* Length P4 to M2: distance between anterior extremity of the
cingulum of P4 and the posterior border of the cingulum of M2.
LM2.* Crown length of M2: from the posterior border of the cingulum
near the midline to the anterior border in line with the two outer
cusps.
LMl.* Crown length of Ml: from the posterior border of the cingulum
near the midline to the anterior border in line with the two outer
cusps.
CH.* Coronoid height: with the bar of the calipers at right angles to
the long axis of the mandibles, one caliper jaw was placed on the top
of the coronoid process, the other at the bottom of the angle.
CPL.* Condylopalatal length: from the le ft condyle to the posterior border of the palate. The palatal notch that occurs in some skulls was not included.
CRH. Cranial height: greatest distance between the lowest extremity of the pterygoid process to the highest point immediately above the pterygoid on the dorsal surface of the cranium. This point is
approximately located where the paired frontals and parietals all fuse
together.
BB. Breadth of braincase: greatest breadth recorded between the
parietal-squamosal sutures. In older grizzlies, where the parietal-
squamosal suture has fused, a distinctly visible line or ridge usually
persists at the suture.
HSC. Height of the sagittal crest; distance between the lowest
extremities of the occipital condyles to the highest point on the dorsal
surface of the sagittal crest in adults or to the highest point of the
inion in young g riz z lie s w ith undeveloped s a g itta l crests.
LSC. Length of the sagittal crest: from the posterior extremity of the
sagittal crest to the anterior-most extremity of the sagittal crest.
This point is usually located at the bifurcation of the temporal ridges.
In young grizzlies with undeveloped sagittal crests, a rudimentary form
o f the cre st was measured.
BOC. Breadth of the occipital crest: greatest width across the
exoccipital processes.
GLS. Greatest length of skull: greatest distance from the anterior-
most extremity of the skull (including the teeth) to the posterior-most
extremity of the sagittal crest.
CC. Cranial capacity: a volume index of the cranial cavity was measured
by f i l l i n g the c a v ity w ith #2 lead birdshot and then depositing the lead
shot from the skull in a 1000 ml graduated cylinder. Large foramina where lead might leak out were plugged.
10 CL
LSC
LCB FL FL CL CRH SB BOC BB MSH GL^
HSC
CBL
LM2 MPL CPL BC PB MB ZB CH
Figure 1. Measurements of grizzly bear skulls. u.. r, _ "" Characteristics of Growth. Bear skulls were grouped into six age classes on the basis of cranial structure and chronological age.
A one-way analysis o f variance combined w ith Duncan's m u ltip le range mean te s t was used to te s t fo r s ig n ific a n t differences between age classes. Treatments were separate fo r males and females.
Estimation of Age. A multiple regression analysis was used
to predict age using the cranial measurements as the predictor
variables. Sexes were treated separately. A multiple discriminant
function analysis was used to predict the group membership of an
individual bear into one of four age classes. Analyses were separate
fo r sexes.
Secondary Sexual V ariations
Cranial Measurements
Two types of t-test were used to test for significant differences between mean size of ad ult cranial measurements.
Sexual Dimorphism
A discriminant function analysis was performed to determine if bear skulls could be segregated by sex on the basis of their cranial measurements.
12 Individual Variation
Permanent D e ntitio n
The frequency of the different premolar combinations was
recorded and summarized. Where the number of premolars differed between le ft and right side, the side with more premolars was recorded as the
premolar combination of that individual.
Cranial Measurements
C o e fficie n ts o f v a ria tio n were computed fo r each sex and age class.
13 CHAPTER I I I
RESULTS
Age Variation
Permanent D entition
The eruption o f g riz z ly bear permanent d e n titio n began sometime
before the fifth month of life , by which time the eruption of P^,
M^, and was complete and the P^, 1^, I^ , and were in place and
eruption was occurring. By the seventh month of life the Ip I 2 » and 2 4 I had erupted and the P , P^, and Mg were in place and erupting. No
data were ava ilab le from sku lls between the eighth and sixteenth month.
By July o f the follow ing year (17th month) a ll o f the permanent
teeth had erupted, except the canines and M^, which were erupting.
Eruption of M^ was nearly complete, but the posterior heel of the tooth did not completely erupt until the third summer of life . The eruption sequence o f the permanent teeth during the f i r s t and second summers is shown in Fig. 2.
Eruption of the canine teeth occurred over an extended period o f several years. By the second summer o f l i f e (17th - 18th month) the canines had begun to erupt. Bears killed as 3-yr. olds had the dentino-enamel junction of the canine crowns erupted beyond the aveolar margin. A complete treatment of canine tooth development of brown bears from arctic Alaska was presented by Rausch (1969).
14 FIGURE 2 FIRST AND SECOND YEAR ERUPTION SEQUENCE OF THE PERMANENT DENTITION
c p ’ • q: ÜJ CL a. D
q: LU ■4 M.H
M; M.
4 ------1------JULY AUGUST SEPTEMBER JULY AUGUST
FIRST YEAR SECOND YEAR
Crown of tooth has not erupted above alveolar margin Crown of tooth has erupted above aveolar margin; eruption is incomplete Tooth eruption is c o m p le te
15 Tooth Wear
The amount of wear exhibited by the teeth of bears increased
with age, but there was substantial individual variation within and
between any age groups. L it t le wear was evident before the th ird year
of l i f e . The f i r s t teeth to show wear were those th a t had been erupted
the longest; namely the and By the th ird year o f l i f e the
tip s o f the in ciso rs may be worn f la t in some in d iv id u a ls , but no wear
was evident in other bears. The lingual cusps of and the buccal
cusps o f may be worn f la t .
In the fifth year of life , tooth wear had progressed in some
in d ivid u a ls to the extent th a t the dentine was becoming exposed. The
dentine was i n it ia lly and co n siste n tly exposed on and Mg,
although dentine exposure may be observed on any tooth of some
individuals. The dentine usually appeared as a dark brown spot in the
center of the cusp surrounded by gray-white enamel.
By the seventh year most individuals had dentine exposure on
the incisors or molars. The firs t and second incisors (uppers and
lowers) were worn more than the third incisors, and the upper incisors
were worn more than the lower incisors. The dentine appeared as a small
circle or spot in the center of the incisors. Small dentinal grooves
developed on the protocones and hypocones o f the upper molars where
they occluded with the protoconids and hypoconids of the lower molars, which also had dentinal grooves. The protocone and tetracone of the
were worn fla t and dentine was visible in some individuals. The
smaller premolars and canines showed little abrasive tooth wear, but many premolars were chipped and canines cracked.
.16 Ten year old bears regularly exhibited exposed dentine in
the molars, in c is o rs , and With increased age, tooth wear continued
to be most severe on the incisors and molars. Incisors of ten year old bears frequently had half or more of the tooth removed by wear. A longitudinal groove obliterating the protocone and hypocone of the was sometimes present along the crown o f the tooth. The area o f tooth wear had expanded on the hypoconid and protoconid o f the M^. The amount of wear on M , Mg, and Mg varied considerably, but was generally less
than that of the firs t molars.
The f i r s t in ciso rs o f 14 year old bears were often worn down
to the dentino-enamel junction with no enamel le ft around the tooth.
The second and th ird in ciso rs sometimes displayed a narrow band o f enamel around the tooth. Heavy wear was observed on the lingual half 1 2 on the M and M , but little or no wear was present on the buccal cusps.
Extensive wear on the p o ste rio r cusps o f the upper molars had worn these teeth down to the level of the cingulum. The buccal cusps of the lower molars were worn down to the gumline. The wear of the Mg had ra p id ly advanced and h a lf o f the rough surface o f the tooth had been worn smooth.
Bears 18 years old or older had teeth badly worn or broken.
Periodontal disease and dental decay were commonly observed. Broken canines had been worn down even w ith the gumlines and decay was prevalent. Progressive tooth wear and decay sometimes extended in to the pulp c a v itie s . Sometimes, only smoothly worn roots were a ll th a t remained. Tooth wear in grizzlies is similar to that described for black bears by Rausch (1961). Figure 3 summarizes the extent and
17 FIGURE 3. SEQUENCE OF TOOTHWEAR IN GRIZZLY BEARS FROM YELLOWSTONE PARK
r
I p- hi
M'
<1
<2 SUI
>3 ]
£ J i m
p hi >1 = T
2 P.
M,
M.
M. £ 8 10 12 14 16 IT 20 22 21 AGE IN YEARS
LITTLE WEAR C _ U MODERATE WEAR HEAVY WEAR i H SEVERE WEAR
18 Upper toothrow of a Upper toothrow of a Upper toothrow of a
2-year old grizzly. 5-year old grizzly. 7-year old grizzly.
A B C
Lower jaw of a Lower jaw of a Lower jaw of a
2-year old grizzly. 5-year old grizzly. 7-year old grizzly.
0 E F
Upper toothrow of a Upper toothrow of a Upper toothrow of an
10-year old grizzly. 15-year old grizzly. 18 -year old grizzly.
G H 1
Lower jaw of a Lower jaw of a Lower jaw of an
10-year old grizzly. 15-year old grizzly. 18 -year old grizzly.
J K L
Pîate 1. Upper and lower toothrows of Yellowstone grizzlies showing progressive tooth wear from ages of 2-year through 18 years (see text for descriptions) (O.AO actual size).
19 y
m
I sequence of tooth wear for grizzlies. Plate 1 illustrates the comparative tooth wear of young and old grizzlies. Appendix A gives the description of tooth wear for individual bears.
Cranial Sutures
Fifteen cranial sutures and the mandibular symphysis were selected as being indicative of age. The general sequence of suture closure was as follows: occipital components^ lanibdoidal, interparietal, inter frontal, frontoparietal, basioccipital-basisphenoid, premaxillae- maxillae, squamosoparietal, nasofrontal, nasopremaxillae, intemasal, raaxofrental, mandibular symphysis, and interpremaxillae (see Fig. 4).
The occipital components (scpraoccipital-exoccipital, exoccipital -basioccipital) were fused during the second year of most individuals, but may be fused in some first year bears as well. The lanibdoidal and interparietal were becoming obliterated by the develop ment of the occipital and sagittal crests. These sutures were closed in all 5 year old bears and in most 3 and 4 year olds.
The interfrontal began coalescing at 5 years of age, the basioccipital-basisphenoid at age 6 and the frontoparietal at age 7.
By the age of 10 these sutures were no longer visible. The basioccipital- basisphenoid tended to fuse earlier in females than males and the lateral ends of the suture may not become completely obliterated until several years later. The premaxillae-maxillae, nasofrontal and squamoso parietal were obscured in most bears 10 to 12 years old, but were obliterated in grizzlies 13 years old or older. The interpremaxillae and nasopremaxillae were nearly obliterated in most bears 13 to 18 years
21 FIGURE4. SEQUENCE OF SUTURE CLOSURE IN GRIZZLY BEARS FROM YELLOWSTONE PARK
EXOCCIPITAL- BASIOCCIPITAL SUPRAOCCIPITAL- EXOCCIPPITAL LAMBDOIDAL
INTERPARIETAL
FRONTOPARIETAL
INTERFRONTAL
BASIOCCIPITAL- BASISPHENOID PREMAXI LLAE- MAXILLAE SOUAMOSO-PAR I ETAL CN
NASO- FRONTA L
INTERNASAL
NASOPREMAX I LLAE
MAXOFRONTAL
MANDIBULAR SYMPHYSiS INTERPREMAXI LLARY
s q u a m o s a l - ju g a l
<1 8 9 10 11 12 13 14 15 16 17 18 19 20 2 0 -*’ AGE IN YEARS
SUTURE WAS OPEN □ SUTURE WAS PARTIALLY CLOSED. BUT STILL VISIBLE m SUTURE WAS PARTIALLY OBLITERATED OR OBLITERATED IN MOST INDIVIDUALS OF AN AGE CLASS SUTURE WAS OBLITERATED IN ALL INDIVIDUALS OF AN AGE CLASS old and completely obliterated in all bears 18 years old or older.
The maxofrontal was o b lite ra te d in most 12 to 16 year old bears and
in all bears 18 or older.
By the 18th year all sutures, except the squamoso-jugal
(zygomatic) suture, were closed. The breadth of the zygoma continues
to grow in grizzlies until death. The mandibular symphysis is solidly
fused and hyperostosis may be evident in bears 18 years old or older.
In some older adult grizzlies the articular process of the mandible
was "locked" in articulation with the glenoid fossa of the squamosal
bone. The mandibles could move only in an up and down direction and
could not be detached from the skull without breaking the squamosal
bone. This phenomena was observed and described by Long (1965) in old
adult badgers (Taxidea taxus). Appendix B provides the description of
sutural stages for individual bears.
Cranial Measurements
For taxonomic purposes, physiological age as revealed by
phenomena such as tooth eruption and wear, bone fusio n, and changes in cranial structure is more important than chronological age. However
knowing the average chronological age at which such phenomena take place is desirable.
I therefore classified bear skulls into six age classes on the basis of ( 1) tooth eruption, ( 2 ) tooth wear, (3) bone fusion,
(4) changes in cranial stru ctu re , and (5) chronological age.
Insufficient sample sizes of bear skulls segregated by chronological age and sex required the grouping of bears into homomorphic subsets to
23 permit meaningful statistical treatments. Table 2 gives the information
used to derive the six age classes. The d is trib u tio n of specimens
assigned to an age class follows: age class I, 4 males and 1 female;
age class II» 5 males and 2 females; age class I I I , 2 males and 4
females; age class IV, 10 males and 5 females; age class V, 9 males
and 6 females; age class V I, 13 males and 6 females.
A one way analysis o f variance combined w ith Duncan's
multiple range mean test was used to test for significant differences
between age classes. Because male g riz z lie s are la rg e r than females,
treatments were separate fo r males arvd females.
In general, measurements fo r younger age classes were
significantly smaller than older age classes. Age class I males were
s ig n ific a n tly the sm allest in 14 out o f 24 measurements. (Table 4,
Appendix C). In supraorbital breadth, interorbital breadth, palatal
breadth, and breadth of braincase age classes I and II were not
significantly different from each other, but were different from age
classes III, IV, V, VI. Least cranial breadth, length of the sagittal
crest and cranial capacity were not significantly different in male age
classes I, II, and III, but were different from age classes IV, V, and
VI. No significant differences were noted among male age classes of
the tooth measurements length P4 to M2 and length of M2, although small
insignificant decreases in tooth measurement occurred due to wear of the teeth. Length of Ml did show significant differences between some age classes, but that was a result of small sample size and individual v a ria tio n .
24 Table 2. The six age classes used in this study with delineation by morphological characteristics and chronological age. Characteristics apply to both male and female grizzlies.
Age Cl ass/Agé in Years Cranial and Dental _Characteristics ______
1/0-1 Replacement o f the deciduous d e n titio n by the permanent d e n titio n is occurring; eruption of ll. Ml, Pi, and M% is complete. All other teeth are in process of eruption. No wear is v is ib le on the permanent d e n titio n . A ll cranial sutures are open and growth is rapidly occurring.
I I / 1 .0 -1 .9 Eruption of the permanent d e n titio n is complete, except for M3 and the canines. Sutures surround ing the parietals (fronto-parietal, interparietal, squamoso-parietal and lambdoidal) and the occipi ta l components (s u p ra o c c ip ita l-e x o c c ip ita l, exoc cipital -basioccipi tal ) are closed but s till visi ble. Slight wear is visible on the incisors.
II1/2.0-2.9 Canine teeth are still erupting. The occipital components are fused and o b lite ra te d . The in te r parietal suture is tightly closed, but s till visible, and the temporal ridges are developing in a V -shaped conformation.
IV/3.0-5.9 Canine teeth have erupted. ThelT" -shaped temporal ridges converge to form the developing sagittal crest. The interparietal suture is o b lite ra te d by the s a g itta l c re s t. Moderate wear of the incisors and molars is beginning to appear in some individuals.
V/6.0-11.9 The basioccipital-basisphenoid, fronto-parietal, interfrontal, premaxillae-maxillae sutures are becoming o b lite ra te d . Tooth wear o f the in ciso rs and molars show interrupted exposure of the enamel by the dentine.
W12+ The internasal, nasofrontal, maxofrontal inter- premaxillary, and nasopremaxillae sutures are becoming o b lite ra te d . The zygomatic (squamoso- jugal) suture remains open and width of the zygoma is s till increasing. The temporal ridges and s a g itta l creast are pronounced and f u lly developed. The incisors and molars are badly worn and broken in the older individuals. The mandibular symphysis is becoming fused and evidence of hyperostosis is present in some individual s.
25 Two measurements, fa c ia l length and condylobasal length,
completely separated age class I females from all other age classes.
Age class I and II females could not be differentiated statistically
by 12 measurements, but they were s ig n ific a n tly sm aller in size than
age classes III, IV, V, and VI (Table 4, Appendix C). Palatal breadth,
cranial height, length of sagittal crest and cranial capacity of females
showed no significant differences between age classes I, II, and III,
but these classes were significantly different from age classes IV, V,
and VI. Breadth of canines showed no significant differences between
female age classes I, II, III, IV. Four measurements (least cranial
breadth, length of P4 to M2, length of M2 and breadth of braincase)
showed no significant differences among age classes of females. Length
of Ml showed significant differences among age classes because of
small sample size and individual variation. Details of age variation
between age classes by Duncan's analysis fo r the 24 measurements are found in Table 4 and Appendix C.
Characteristics of Growth. Using Duncan's multiple range mean te s t, maximum size or growth o f each measurement was c la s s ifie d at an age class beyond which it no longer continued to significantly
increase in size (i.e . if non-significant differences in measurement size occurred between an age class and a ll older age classes, as shown by Duncan's analysis, then maximum growth was considered to have been attained by that age class). Table 3 shows the cranial measurements classified for maximum size by age class and sex.
26 Table 3. Maximum growth classification of cranial measurements of grizzly bears from Yellowstone National Park. Maximum growth for each measurement was determined by the results of Duncan's analysis (Table 4 and Appendix C).
AGE CLASS II III IV VI Males
LP4M2 LCB MPL CBL MB LM2 BB CL SB BOG MSH ZB CC CPL FL GLS IB BC PB CRH CM HSC LSC
Females
LCB LP4M2 MPL CBL SB BB LM2 MB ZB BOC CL IB FL MSH BC PB CRH CH CPL HSC LSC GLS CC
27 The five measurements in Table 4 and Figure 5 illustrate the
c h a ra c te ris tic growth patterns by which the measurements were c la s s ifie d
by age class and sex.
The general pattern of growth was for skull size to increase
with age, but this was not always the case. Measurements for which maximum size had been attained at age class I were: least cranial breadth,
and breadth of braincase for females; no measurement had attained maxi
mum size at age class I for males. An example, least cranial breadth
(LCB), is given in Table 4 and Figure 5.
Tooth measurements, length P4 to M2 and length o f M2 reached maximum size at age class II for both males and females. Breadth of
occipital crest reached maximum size by age class II for females (Table
4, Figure 5).
Least cranial breadth, breadth of braincase, breadth of occipital crest, and cranial capacity reach maximum size by age class
III for males. Examples given in Table 4 and Figure 5 are breadth of occipital crest and least cranial breadth for males. Only molar- premaxilla length attained maximum size by age class III in females
(Table 4, Figure 5).
Only one measurement, m olar-prem axilla length, attained maximum size by age class IV in males (Table 4, Figure 5), whereas most o f measurements (14) a tta in maximum size by age class IV fo r females.
These include: condylobasal length, mastoid breadth, cranial length, facial length, maxilla-supraorbital height, breadth of canines, palatal breadth, cranial height, coronoid height, condylopalatal length, height of sagittal crest, length of sagittal crest, greatest length of skull,
28 Table 4. Age variation results in 5 cranial characters of grizzly bears from Yellowstone National Park showing some typ ic a l Duncan results used to classify growth patterns by age class. The vertical lines of Duncan's analyses connect the means of maximum non-significant subsets at the .05 level. The growth curves of these measurements are illustrated in Figure 5.
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN.
LEAST CRANIAL BREADTH
MALE 7.582* I 4 64.47± 4.76 61.20-66.80 3.69 1 I I 5 67.14+ 11,13 62.70-76.00 8.29 1 III 2 70.00± 1.70 69.40-70.60 1.21 11 IV 9 72.62+ 7.00 66.50-77.90 4.82 1 V 8 73.11+ 5.66 67.00-76.60 3.87 1 VI 11 74.25± 5.02 69.90-77.00 3.38 1
FEMALE 1.043 I 1 60.90 - — — - 1 II 2 63.85± 14.57 58.70-69.00 11.41 1 III 4 67.35+ 6.20 64.60-71.80 4.60 1 IV 5 67.42± 7.71 61.30-72.00 5.72 1 V 6 68. 88+ 10.52 63.20-77.70 7.64 1 VI 6 69.13+ 6.72 64.00-72.80 4.86 1
BREADTH OF OCCIPITAL CREST
MALE 25.059* I 4 54.10± 2.31 52.50-55.00 2.14 1 I I 5 67.38+ 13.31 59.90-77.60 9.87 1 III 2 78.90+ 11.60 74.80-83.00 7.35 1 IV 8 83.06+ 16.26 67.00-90.90 9.87 1 V 7 88.14+ 12.42 79.40-98.70 7.05 1 VI 9 88.87+ 9.62 79.90-96.50 5.41 1
ILE 3.946* I 1 53.00 - - - - 1 II 1 63.00 - — — - 11 III 4 71.07+ 19.87 59.00-79.90 13.98 1 IV 5 75.98+ 12.89 69.10-84.00 8.48 1 V 5 78.66+ 7.37 74.90-84.20 4.68 1 VI 6 76.15± 7.87 68.90-80.40 5.16 1
* P < .05
29 Table 4. (continued). Age variation results in 5 cranial characters of g riz z ly bears from Yellowstone National Park showing some typical Duncan results used to classify growth patterns by age class. The vertical lines of Duncan's analyses connect the means of maximum non-significant subsets at the .05 level. The growth curves of these measurements are illustrated in Figure 5.
ÂGÉ ~ SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN
MOLAR-PREMAXILLA LENGTH
MALE 45.803* I 4 97.25± 13.00 87.80-102.40 6.68 1 II 5 126.02± 11.33 116.60-132.00 4.50 1 III 2 136.05+ 17.11 130.00-142.10 6.29 11 IV 10 144.27+ 14.47 128.80-151.60 5.01 11 V 8 144.80± 12.58 133.50-155.00 4.34 11 VI 12 149.17+ 11.95 137.70-155.80 4.00 1
FEMALE 6.724* r 1 101.90 1 II 2 116.40+ 13.01 111.80-121.00 5.59 n I I I 4 127.37+ 21.28 118.30-142.50 8.35 11 IV 5 131.92± 13.46 122.20-140.00 5.10 1 V 6 132.68+ 11.27 125.00-141.00 4.25 1 VI 6 134.73+ 3.52 132.20-136.70 1.30 1
CONDYLOBASAL LENGTH
MALE 75.656* I 4 192.12+ 6.66 188.10-195.50 1.73 1 II 4 250.00± 32.36 230.70-270.30 6.47 1 III 2 293.00+ 42.99 278.60-309100 7.34 1 IV 7 318.18± 41.32 282.30-344100 6.49 11 V 7 334.57± 18.61 322.00-347.00 2.78 11 VI 11 348.09± 32.29 325.00-371.00 4.64 1
FEMALE 15.665* I 1 198.30 1 II 1 237.50 - — “ — 11 III 4 264.55+ 54.27 237.90-300.40 10.26 1 IV 5 293.92± 27.78 275.60-306.00 4.73 1 V 6 300.38± 13.61 294.00-309.50 2.27 1 VI 6 303.33+ 8.72 295.60-309.00 1.44 1
* P < .05
30 Table 4. (continued). Age variation results in 5 cranial characters of g riz z ly bears from Yellowstone National Park showing some typical Duncan results used to classify growth patterns by age class. The vertical lines of Duncan's analyses connect the means of maximum non-significant subsets at the .05 level. The growth curves of these measurements are illustrated in Figure 5,
ÂGË SEX CLASS N MEAN± 2 S.D. RANGE C.V. F. DUNCAN
ZYGOMATIC BREADTH
MALE 110.714* I 4 11I.90± 8.78 108.30-117.70 3.92 1 I I 5 131.84± 18.61 120.00-144.60 7.06 1 III 2 167.25± 34.93 154.90-179.60 10.44 1 IV 9 186.07+ 26.39 163.00-202.80 7,09 1 V 7 207.03+ 24.17 191.80-228.80 5.84 1 VI 12 229.14+ 16.59 217.00-248.20 3.62 1
FEMALE 2 3 .9 8 1 * I 1 115.30 1 II 2 134.95+ 17.96 128.60-141.30 6.65 11 III 4 145.72+ 26.62 130.60-160.80 9.13 1 IV 5 168.92+ 20.70 156.90-179.00 6.13 1 V 6 184.27+ 19.75 169.90-196.00 5.36 1 VI 6 187.90± 9.32 181.90-194.90 2.48 1
* P < .05
31 -3 5 0 -340 C BL 1-330 -320
-310 -300 -2 9 0 -280
-2 7 0 -2 6 0
-250 - 240 cr> -230 ÛC. -2 2 0 -2 1 0 -2 0 0 -1 9 0 -180
-170 -160 -150 MPL '-MO -130 -120 -1 10 '1 0 0 - 90 BOC - 80 — 70
— 60
- 50
80 70 LCB 60
I I I I 11 III IV V VI
AGE CLASS Figure 5. Representative growth curves by age class of 5 cranial characters of grizzly bears from Yellowstone National Park. Lines connect age class mean values given in Table 4. In each case the upper curve is that for males, the lower for females.
32 and crantai capacity. Maximum size by age class IV for females is exemplified by cordylobasal length (CBL) (Table 4, Figure 5).
Condylobasal length, cranial length, maxilla-supraorbital height, condylopalatal length, and greatest length of skull reach maximum size at age class V in males while supraorbital breadth,
zygomatic breadth, and interorbital breadth reach maximum size in
females. Examples given in Table 4 and Figure 5 are condylobasal length (CBL) fo r males and zygomatic breadth (ZB) fo r females.
Males continue to grow in size in to age class VI, w hile
females have achieved maximum size in a ll measurements by age class V.
Males achieve maximum measurement by age class VI in the fo llo w in g : mastoid breadth, supraorbital breadth, zygomatic breadth, interorbital breadth, facial length, breadth of canines, palatal breadth, cranial height, coronoid height, height of sagittal crest, and length of
sagittal crest. An example, zygomatic breadth (ZB), is shown in Table 4 and Figure 5.
The above revealed a gradual increase in length, breadth and height of the skull, in most instances, as age increased. Interest
ingly, the skull, a unified whole, showed differential growth patterns; some proportions grew quickly and early in life while other proportions grew more slowly and continuously. Plates 2 and 3 illustrate the cranial changes associated with growth of grizzly bears from Yellowstone
National Park. Those parameters best showing the various size increases
(length, width, height) should be useful in future population analyses and those parameters that vary little with age should be even more valuable in evaluating geographic variability. Measurements not shown in Table 4 can be referred to in Appendix C.
33 Dorsal view of a 2-yr. old male Lateral view of a 2-yr. old male grizzly. The interparietal g riz z ly . suture is becoming obliterated by the developing sagittal crest All other visible sutures are open.
B
Dorsal view of a 5-yr. old male Lateral view of a 5-yr. old male grizzly. Sagittal crest is grizzly. The sagittal crest is developing into adult form. beginning to develop. The fronto Interparietal suture is fused; parietal and squamoso-parietal other sutures are s t i l l open. sutures are open.
D
Dorsal view of a 9-yr. old male Lateral view of a 9-yr. old male grizzly. The interfrontal and grizzly. The frontoparietal and premaxillae-maxillae sutures squamoso-parietal sutures are are nearly obliterated. The becoming closed. naso-frontal, maxo-frontal, internasal, and naso premaxil lae sutures are s t i l l open.
Dorsal view of an 18-yr. old Lateral view of an 18-year old male male grizzly. All sutures are grizzly. All sutures are fused, fused, except the anterior end except the squamoso-jugal (zygomatic) of the internasal suture. The suture. Note the periodontal dis- , prominent temporal ridges merge ease and tooth decay of the rig h t C . to form the pronounced s a g itta l crest.
Plate 2: Dorsal and lateral views of male grizzly bear skulls from Yello stone showing comparative size and suture closure of 2 -yr., 5-yr., 9-yr., and 18-yr. old bears. (Size = 0.13 actual size)
34 unhmcum Cl H n Ml n tv
%
C IM ftM lim *
I Nil M( n#\ Dorsal view of a 2 -yr. old fe Lateral view of a 2-yr. old female male grizzly. All sutures, in g riz z ly . cluding the interparietal, are open.
A B
Dorsal view of a 5-yr. old fe Lateral view of a 5 -yr. old female male grizzly. The interparie grizzly. The sagittal crest is tal suture is closed and the beginning to develop. The fronto interfrontal sutures is nearly parietal and squamosoparietal su closed. The sagittal crest tures are open. is beginning to develop.
C D
Dorsal view of a 9-yr. old fe Lateral view of a 9-yr. old female male g riz z ly . The in te r fr o n ta l, grizzly. The frontoparietal and frontoparietal, maxofrontal, squamosoparietal sutures are now nasofrontal, internasal, pre fused. m axillae-m axillae, nasopremax illae sutures are all fused and total growth has nearly been attained.
E F
T Dorsal view of an 18-yr. old Lateral view of an 18-yr. old fe female grizzly. All sutures male g riz z ly . A ll sutures are are fused. Pronounced features closed, except the squamosojugal of the temporal ridges and suture. sagittal crest are evident.
G H
Plate 3: Dorsal and lateral views of female grizzly bear skulls from Yellowstone showing comparative size and suture closure o f 2 - y r ., 5-yr., 9-yr., and 18-yr. old bears. (Size = 0.12 actual size)
36 (.1
V
ce N lIW illl»
» 14 J ^ V -O C» NIIMItfll» Estimation of Age. Univariate analyses were attempted to p re d ict age o f in d ivid u a l bears. However, the complexity and variability of growth required multivariate statistical treatment.
The 24 cra n ia l measurements from 25 knov/n-age and 30 assigned-age bears were used to construct a model from which the ages o f in d ividu al bears could be estimated. An F-test revealed non-significant differences
(P - .05) between the known-age and assigned-age bear groups fo r any measurement, thus the two populations were pooled together fo r analyses.
A multiple regression analysis was used to produce the least biased model to predict age. Age was the dependent variable to develop the prediction equation based upon the cranial measurements as predictor variables. Since the growth rates of male and female grizzlies differ, analyses were separate fo r sex.
Because the growth rates of young male bears is greater than th a t o f olde r bears, two analyses were generated; one fo r bears less than
12 years old and another one grouping all males of all ages. There was an insufficient number of male grizzlies older than 12 to allow a separate analysis of these individuals, but since males grow throughout their entire lives, an analysis was performed on the entire sample of male grizzlies of all ages to allow age prediction of older grizzlies.
Because female bears do not grow s ig n ific a n tly beyond 12 years o f age, only one analysis was performed on female grizzlies less than 12 years o ld .
For males, the two equations produced to predict age were:
1 . bears less than 12 years old;
Y = 0.12 (MB) - 0.16 (PB) + 0.98
38 = 0.85, 3 .E . = 1.05
2 . bears of all ages;
Y = 0.20 (SB) -0.6 (MSH) - 0.24 (BB) + 0.5 (IB) + 0.23
(HSC) - 1.45
= 0.93, S.E. = 1.97
For females the equation produced to predict age was:
1. females less than 12 years old.
Y = 0.14 (ZB) - 0.23 (MPL) + 0.091 (FL) - 2.93
R^ = 0.98, S.E. = 0.33
Regression calculatio ns were computed on the known-age bear
sample to check the c a p a b ility o f the three models to pre d ict age.
Thirteen male bears were o f known age. For the equation o f male bears
less than 12 years old, calculations of age could not be computed for
3 o f the 13 bears because o f missing values from skull damages. Ages were correctly predicted to within a one-year margin for 8 of the
remaining 10 male bears.
For the equation of all male bears of all ages, calculations o f age could not be computed fo r 4 o f the 13 bears, but ages were correctly predicted to within a one-year margin for 5 of the remaining
9 bears. Because the male known-age bear sample only includes bears from 0.5 to 7.5 years o f age, calculatio ns o f age were also computed on 9 assigned-age bears older than 7.5 years o f age. Two bears were deleted because o f skull damage and 4 o f the remaining 7 were c o rre c tly aged to within a one-year margin.
Ages were calculated fo r 12 known-age female bears by the regression equation for females less than 12 years of age. Ages were
39 correctly predicted to within a one-year margin for 10 o f the 12 female bears. These checks o f the regression models should not be confused as being a test of the accuracy of the technique; it is merely a check of technique re lia b ility, A valid test of accuracy would have to be performed on a d iffe re n t sample o f known-age bears than the sample used to develop the technique. However, no other known-age bear samples were a va ila b le to te s t the technique.
Multiple discriminant function analysis is another multi va ria te procedure th a t can be used to p re d ict group membership o f an
individual on the basis of a set of predictor variables. For this purpose, the ages o f the bears were categorized in to 4 age groups as f o l1ows:
1. juveniles = cubs, yearlings, and 2 -year olds;
2. subadults = bears 3-5 years old;
3. adult I = bears 6-11 years old; and
4. adult II = bears older than 12 years.
Analyses were separate for sex.
The results of the discriminant analysis for males is given in Tables 5 and 6. Three discriminant functions were produced from the analysis for male grizzlies. The firs t function was highly correlated with age (canon, corr. = 0.99) and accounted for 96% of the total discriminative power. The second and third functions only contributed
4% toward group classification. For this reason, I used only the firs t function for prediction of age group membership. The age groups of the firs t function were significantly different; Wilks lambda = 0.0826
(P = 0.022).
40 The discriminant equation of the firs t function from which the age group membership o f male bears can be predicted was:
= 0.181 (MB) + 0.282 (ZB) - 0.711 (PB) + 0.073 (CH) - 0.130 (CPL)
+ 0.213 (HSC) - 0.225 (BDC) - 10.474
The group centroids (Table 6) were the mean discrim inant scores fo r the
4 age groups. That group centroid which a computed score was closest to in value gave the probable group membership of that score.
To check the capability of the discriminant function to predict age group membership, the discriminant scores of 26 male bears were calculated. The c la s s ific a tio n re s u lts by age group and percent that correctly predicted the proper group membership for individuals were: juveniles (89%); subadults (100%); adult I (100%); adult II (100%), for a total of 96% male bears correctly classified. The error that occurred in classifying the male bears was a large 2 -year old bear
(no. 205), which by its large size and shape for its age was incorrectly classified as a subadult bear, instead of as a juvenile. Figure 6 illustrates the excellent ability of the 3 discriminant functions to segregate the male age groups.
Tables 5 and 6 show the results of the discriminant analysis for females. Three discriminant functions were produced. The firs t function was highly correlated with the age groups (canon, corr. - .99) and accounted for 99.7% of the discriminative power, while the second and third functions only added 0.3% discriminating capability. Because of the minor discriminating power of the second and third functions, I
41 Table 5. Standardized Discriminant Function Coefficients of Male and Female Age Groups
MALES Function 1 Function 2 Function 3
Character MB 1.82253 1.43829 2.00093 ZB 3.37480 -1.54370 -0.92670 PB -3.74896 -1.49037 -0.03574 CH 0.54112 1.48119 -0.55267 CPL -1.35556 0.47489 -2.27703 HSC 1.10930 -0.60077 0.18462 BOC -1.54496 0.34835 2.01800
FEMALES Function 1 Function 2 Function 3
Character MB -25.30368 0.84760 -5.03617 ZB -1.93852 -1.53725 5.16634 BB 14.58130 -2.94508 1.31608 BOC 19.56506 1.44434 1.21235 CC -6.47598 2.20465 -2.51894
42 Table 6. Unstandardized Discriminant Function Coeffiecients for Male and Female Age Groups
MALES Function 1 Function 2 Function 3
Character MB 0.181 0.143 0.198 ZB 0.282 -0.129 -0.077 PB -0.711 -0.283 -0.007 CH 0.073 0.200 -0.075 CPL -0.130 0.046 -0.219 HSC 0.213 -0.115 0.035 BOC -0.225 0.051 0.294 Constant -10.474 9.070 -1.065
FEMALES Function 1 Function 2 Function 3
Character MB -2.605 0.087 -0.518 ZB -0.149 -0.118 0.399 BB 2.810 -0.567 0.254 BOC 2.193 0.162 0.136 CC -0.183 0.062 0.071 Constant -31.623 33.774 -15.333
Table 6A. D iscrim inant Functions Evaluated a t Group Means (Group Centroids)
Function 1 Function 2 Function 3
Age Group Male Female Male Female Male Female Juveniles -17.739 51.773 -1.518 -0.497 0.115 -0.077 Subadults -1.435 -11.419 1.745 2.886 -1.118 -0.815 A d ult I 0.918 -18.647 1.559 0.281 3.000 2.003 A d ult I I 9.760 -31.729 -1.215 -1.614 -0.126 -0.715
43 used only the f i r s t function to p re d ict age group membership. The age
groups of the firs t function were not significantly different; Wilks
lambda - 0.068 (P = 0.1466). The discriminant equation of the firs t
function for female age groups was:
= -2.605 (MB) - 0.149 (ZB) + 2.810 (BB) + 2.193 (BOC) - 0.183
(CC) - 31.623.
Classification results of 22 female bears by age group and
percents correctly classified individual bears were: juveniles ( 100%);
subadult (80%); adult I (60%); adult II (67%), resulting in a total of
77% correctly classified female bears. Most of the errors in classify
ing female bears occurred between adult I and adult II age groups.
Because most of the total growth and size of the female is attained in early adulthood, the discrimination of young and old female bears is of
limited value by discriminant analysis. Figure 7 shows the poor ability of the discriminant function to segregate the subadult, adult I and adult II age groups of female bears.
To determine the age group membership o f an in dividu al bear by discriminant analysis, the score produced from the above discriminant equations w ill approximate the value of one of the age group means
(group centroids) given in Table 6 for an age group of that sex. That group mean which the score came closest to was the probable age group membership o f th a t in d ivid u a l bear.
To summarize and compare the methods o f estim ating the age of individual bears, I have estimated the ages of 7 (4 male, 3 female)
44 104
0 -
-1 0 "
-10
ir\ •it
o
Figure 6 . D iscrim inant p lo t o f male age groups. Group centroids represent 1) juveniles, 2) subadults, 3) adult I, 4) adult II age groups. 55-
2 5 -
0 -
- 1 5 -
- 1 5 5 5 - 3 5
-20
Hgure 7. Discriminant plot of female age group. Group centroids represent 1) juveniles, 2) subadults, 3) adult i, 4) adult II age groups. unknown-age bears from Yellowstone on the basis o f: 1) suture closure;
2) tooth wear; 3) multiple regression; 4) discriminant analysis; and
5) tooth section (Table 7). Ken Greer, Montana Department Fish,
W ildlife and Parks, provided the age estimates of the bears by tooth
section.
Estimating the age of a bear by suture closure was possible
by comparing those sutures which were fused versus those sutures which
were not. For example, a bear must be at le a st 5 years old i f its
o c c ip ita l components and in te rp a rie ta l sutures were fused (Figure 3),
but if its interfrontal, frontoparietal, and basioccipital-basisphenoid
sutures were not fused, the bear was probably less than 7 and must be
less than 10 years old. Thus the estimate was 5 to 7 years old.
The same method o f deduction was used to estimate age by
wear o f in d ivid u a l teeth (Figure 2 ).
Having estimated age by suture closure and tooth wear,
calculations of the regression and discriminant equations were computed,
In some instances, skull damages may have prevented measurement o f a
p a rtic u la r cran ia l character. However, a mean value (Appendix D)
provided fo r each measurement broken down by age class and sex was
substituted into a regression or discriminant equation if necessary;
however, the error of the estimate was increased by doing this. The
re su lts o f the age estimates fo r the 7 unknown-age bears are given in
Table 7.
47 Table 7. Comparison o f age estimates on seven unknown age g riz z ly bears from Yellowstone National Park.
______AGE ESTIMATE______BEAR DATE TOOTH MULTIPLE MULTIPLE . DISCRIM- TOOTH NO. SEX KILLED SUTUREHEAR REGRESSION^ REGRESSION^ INANT SECTION I I Aug 177548 Male 1977 10 10 7 8.5 6-11 10
9 Sep 177561 Male 1977 10 10 6 7 6-11 11
19 Oct 178174 Male 1979 7-10 7-10 6 13 12+ 7
10 Aug 178382 Male 1980 2-5 2-5 4 5 3-5 4
22 Sep 177383 Female 1976 10-12 12 6 - 6-11 11
7 Jul 177718 Female 1978 5-7 5-10 5 - 6-11* 5
30 Aug 178158 Female 1979 7-10 7-10 6 - 3-5 8
?: regression model for bears less than 12 yrs . old : regression model for all bears *: mean value substitute for CC
48 Secondary Sexual V ariation
Cranial Measurements
The skulls of adult male grizzly bears averaged larger than those of adult females (Table 8). From Table 8 the average mean percent diffe ren ce between the sexes was males 13% la rg e r than females, ranging from a low of 6% difference in least cranial breadth to a high of 32% difference in length of sagittal crest.
Two types of t-test were utilized to test for significance between mean size o f a d u lt bear cran ia l measurement. A t- te s t cannot be legitim ately computed for differences in sample means of populations of unequal variances. Instead, an approximation of t may be computed on the basis of separate variances estimates. An F-test was computed to determine if the variances were significantly different. For those
F values that were not significantly different, t was computed and for those that were significantly different an approximation for t was computed (Table 8). In a ll measurements o f ad ult g riz z lie s the computed t (true or approximate) was significantly different (P £ .05) for all
24 cran ia l measurements.
Sexual Dimorphism
It was not possible to distinguish the sex of a grizzly skull from any single measurement because o f the considerable overlap in skull size between the sexes. Size o f the s a g itta l c re s t has often been employed to discriminate the sex of adult grizzly bear skulls. Length of the sagittal crest or height of the sagittal crest when used
kS Table 8. Secondary sexual variation in 24 cranial measurements in adult (age class V and VI) grizzly bears from Yellowstone National Park.
MALES FEMALES mean #
CHARACTER N J ± S.O. N J ± S .0. difference F t
CBL 18 342.831 15.16 12 301.86+ 5.66 12% 7.17* 10.43*
MPL 20 147.421 6.33 12 133.71+ 4.12 9% 2.36* 7.42*
MB 16 166.001 7.89 12 137.681 2.84 17% 7.71* 13.25*
SB 19 119.011 8.87 12 102.971 8.03 13% 1.22 5.08*
ZB 19 220.991 14.52 12 186.081 7.60 16% 3.65* 8.75*
CL 18 204.221 11.04 11 174.26+ 7.52 15% 2.16* 7.92*
FL 20 188.271 11.43 12 164.38+ 6.65 13% 2.96 6.58*
MSH 20 99.201 6.37 12 86.32+ 3.18 13% 4.01* 7.59*
LCB 19 73.771 2.64 12 69.011 4.21 6% 2.55 3.89*
IB 19 78.011 5.73 12 68.691 4.14 12% 1.92 4.87*
BC 13 81.451 5.35 6 70.181 2,11 14% 6.47 4.92*
PB 20 89.801 4.30 12 81.45+ 3.19 9% 1.82 5.82*
LP4M2 20 77.161 4.58 12 71.48+ 2.78 7% 2.72 3.88*
LM2 20 38.011 2.41 12 36.041 1.45 5% 2.78 2.56*
LMl 20 22.931 0.81 12 21.331 1.12 7% 1.93 4.67*
CRH 20 130.841 7.45 11 112.631 4.84 14% 2.37 7.28*
BB 16 106.521 2.89 11 99.731 2.84 6% 1.03 6.04*
CH 19 108.071 6.47 12 90.90+ 5.05 16% 1.64 7.80*
CPL 18 164.961 7.95 11 142.05+ 3.33 14% 5.68* 10.78*
HSC 15 113.581 5.44 11 94.361 4.35 17% 1.56 9.65*
LSC 18 135.111 20.98 11 92.951 23.43 32% 1.25 5.11* 6.03* BOC 16 88.551 5.28 11 77.291 3.86 13% 1.87 9.20* GLS 19 364.841 18.56 11 318.631 8.84 13% 4.41* 3.92* CC 15 315.201 37.78 11 325.55+ 21.19 13% 3.18
* P <_.05 \ it Mean Percent Difference =
50 in d iv id u a lly to segregate sex o f bear s k u lls were o f modest value.
When they were used together in a scatter diagram or added together,
they w ill separate the sexes in to two d is tin c t groups (F ig. 8). I f the
sum of the 2 measurements was greater than 215mm, then the skull was a
male; if less than 215mm, then it was a female. One hundred percent of
the male and the female grizzlies were correctly segregated by this
criteria (N = 26). Also, the bivariate distribution of zygomatic
breadth versus mastoid breadth was useful in distinguishing the sex of
grizzly skulls (Fig. 8). I f the sum o f the 2 measurements was greater
than 352mm, then the skull was a male; if less than 352mm, then it was
a female.
A discriminant analysis was performed to see if the sex of
bear skulls could be segregated. One function was produced. The
differences between ad ult males and females were s ig n ific a n t; W ilk's
lambda = 0.0004 (P = 0.0000). One hundred percent of the total
discriminative power was explained by the function.
Table 9 shows the standardized and unstandardized discriminant
function coefficients. From the standardized coefficients, least cranial
breadth contributed the largest percentage (23%) to the variability of
the function; followed in descending order of percent variability by breadth o f o c c ip ita l cre st (19%), supraorbital breadth (15%), breadth of canines ( 11%), breadth of braincase ( 10%) and other minor contribu
tions were made by mastoid breadth, palatal breadth and length of Ml.
Classification results of 14 adult grizzlies by sex and percent c o rre c tly c la s s ifie d were: males ( 100%) and females ( 100%).
Thus, all individuals were correctly classified to sex by the discriminant
51 187 -
1 7 3 - A = VAIES (N=l ')
0 = FEMALES [H-U] 159-
m H 5. O
^ 131
O> 117-
m O O «/* 89 O O
75-
61- O o 4 7 - ' T i'" i " T " I ■ 8 7 91 95 103 107 111 115 11? 123 127
HEIGHT OF SAGITTAL CREST
17a-
173-
168
163 -
153- g> -4 153-1
148-
143-
138- O O O
■33-f I 1% I a . 169 177 19Î 193 201 209 217 225 233 2 4# 249
ZYGOMATIC BREADTH
Figure 8. Sexual dimorphism of grizzly bear cranial measurements. Jhe lines are drawn midway between the means of the male and female measurements.
52 Table 9. Discriminant Function of Sex by Cranial Measurements.
Function 1 Standardized Percent Unstandardized Character Coefficient Variability Coefficients MPL 9.87774 10% 1.9465210 MB 1.45506 1% 0.2732958 SB 14.85838 15% 2.6584810 LCB -22.27721 23% -6.2174760 BC -10,77591 11% -3.2785630 PB 7.03986 7% 2.1031280 LMI -3.19226 3% -4.5659810 BB 9.52571 10% 3.5221000 BOC 18.87527 19% 3.2900800 Constant -648.9342000
Table 9A. Discriminant Functions Evaluated at Group Means .
Function 1 Sex Group Mean Male 35.00062 Female -56.00100
53 function. The equation used to classify the sex of a grizzly s k u ll was:
- 1.95 (MPL) + 0.27 (MB) + 2.66 (SB) - 6.22 (LCB) - 3.28 (BC)
+ 2.10 (PB) - 4.56 (LMl) + 3.52 (BB) + 3.29 (BOC) - 648.93
The resultant sum, compared with the group mean (Table 9A), w ill identify the sex of the skull.
Individual Variation
Permanent D e ntitio n
The permanent d e n titio n o f the brown bear is represented by the formula The first three premolars, above and below, are small and variable in size and position. They have little value in mastication, but probably aid in protection of the gums.
Seven different combinations of premolar frequency were recorded. Eighty three percent o f the specimens were represented by a
premolar combination. The P^ occurred in only 6 percent of the sample, represented by a premolar combination. The five other premolar combinations and their percent occurrences were: (4.3%);
(2.8% (1.4%^, (1.4% (1.4%).
Cranial Measurements
The s ta tis tic a l measure, c o e ffic ie n t o f v a ria tio n is o f value in the comparison of range of variation among various parameters of
54 differing size ranges. Coefficient of variation was computed for each
sex and age class for all 24 cranial measurements (Table 4, Appendix C).
The average CV fo r 24 measurements was 6.70 and CV's of
females 6.58 averaged s lig h tly less than males 6.83. However CV was not computed for all age class I female subsets and some age class II female subsets due to small sample size and this no doubt would affect
the re s u lta n t average CV fo r females. Average CV's fo r males o f the age classes were: I, 5.82; II, 7.28; III, 9.37; IV, 8.25; V, 5.28;
VI, 5.21; for females, the values were: I, none recorded; II, 6.37;
III, 9.40; IV, 7.66; V, 5.84; VI, 4.38. Thus younger bears (age classes
I, I I , I I I , IV) were move variable than older bears (age class V, V I).
Age class VI gave the lowest CV fo r both males and females.
The measurements w ith the lowest CV's fo r males were: palatal breadth (3.69), breadth of braincase (3.74), least cranial breadth (4.21), length P4 to M2 (4.42), length o f Ml (4.8 7). For females, the measure ments with the lowest CV's were: length of M2 (4.05), breadth of brain case (4.08), length P4 to M2 (4.56), condylobasal length (4.67), and molar-premaxilla length (4.92).
The most variable (highest CV's) measurements fo r males were: length of sagittal crest (29.69), cranial capacity (11.05), mastoid breadth (7.28), interorbital breadth (6.98), coronoid height
(6.8 5), cra n ia l length (6 .7 1 ); fo r females, the most variable measure ments were; length of sagittal crest (26.52), cranial capacity (8.23), breadth of occipital crest (8.07), coronoid height (7.68), supraorbital breadth (7.41), and interorbital breadth (7.03).
55 Most o f the v a r ia b ility in the measurements was due to differences in age and sex, however not all variability is explained by these factors. Individual differences in food habits, reproductive status, social status and genetic variability are just a few of the differences that are probably influencing variability as well.
56 Plate 4: Dorsal and la te ra l views of 4 old adult male g riz z ly skulls showing individual variations in skull size and shape; especially in supraorbital breadth, zygomatic breadth, cranial height and condylo basal length. (Size = 0.11 actual size) N £ m
«««!•>* UNI»
■
# CHAPTER IV
DISCUSSION
Age Variation
Permanent D e ntitio n
Because the ages o f g riz z lie s were calculated from an assumed
b irth date o f 1 Feb., va ria tio n s in the eruption of the permanent
dentition resulted from absolute differences in the ages of individual
bears, births having occurred over a period of several weeks.
The sequence o f tooth eruption was based upon the s ku lls o f
5 cubs (4 male, 1 female) and 6 yearlings (5 male, 1 female).
Because of individual differences of date of birth and a
disproportionate number of males and females, no observable differences
in tooth eruption were found between male and female g riz z lie s .
Craighead (1970) reported that the permanent fourth premolars norm ally erupt between the 5th and 6th month of a grizzly's life . My
results show that P^ was erupting during the 5th and 6th month and th a t eruption was complete sometime between the 7th to 17th month o f the bear's life .
No measurements were taken on crown length o f the canine teeth because most skulls had either a canine extracted or damaged.
Thus absolute differences in the rate of canine tooth eruption was not determined. The rate of canine tooth eruption was based upon the
59 relative position of the dentino-enamel junction to the aveolar margin of the tooth. Rausch (1969) found that tooth eruption occurred at a low rate throughout the life of the individual bear. He also stated
that "In old animals, the rate of eruption appeared to be related to
the rate of abrasion of the so that the total erupted length of
these teeth tended to remain constant" (Rausch 1969:171). While I did
not measure canine tooth eruption, my observations of young versus old canine teeth supported this conclusion.
Tooth Wear
Tooth wear increased with age but was poorly correlated with age. Individual variation within any age group was so great as to
preclude the definition of age groups by this criteria. The rate at which tooth wear occurred varied in d iv id u a lly , but the sequence remained
relatively constant.
Tooth wear is highly dependent upon several factors not directly related to age: individual habits (food selection, degree of mastication), substrate, and differences in the alternating annual
periods of activity versus torpidity in bears. Food selection, substrate, and annual periods of activity vary widely from region to region in bears. Regional differences in tooth hardness may even occur, depending upon the availability of calcium, fluorine, and other compounds vital to the processes of calcification in food and drinking water. Thus tooth wear in isolation should be regarded only as a very rough and f a llib le guide to re la tiv e age.
60 Cranial Sutures
The cranial sutures of grizzlies tended to coalesce at
approximately the same age in all bears. Most sutures were open for
several years, followed by an intervening period when some individuals
may or may not have their sutures obliterated. Beyond a certain age
all individuals had their sutures closed, except for the squamosal-jugal
(zygomatic) suture which remained open throughout the life of the bear.
In g riz z lie s from the Yukon, Pearson (1975) found th a t male
g riz z lie s were less than 8 years old if the basioccipital-basisphenoid
suture was open and more than 11 years old if it was closed. For females,
he found that a bear was less than 7 years old if the suture was open
and more than 10 if it was obliterated. My results were similar and
showed that a grizzly was less than 7 years old if the basioccipital-
basisphenoid suture was open and older than 10 years old if it was
o b lite ra te d , although some in d ivid u a ls between the ages o f 7 and 10
years had this suture closed (Appendix B). Also, if the lateral ends
of the suture were not completely fused, I classified the suture as
partially closed.
Female grizzlies tended to close sutures earlier than males,
although too few female skulls were available to determine if differences
in suture closure were sexual or individual. Differences between sexes were so slight that I lumped all bears of the same age together and
evaluated suture closure on bears only on an age basis.
The interparietal suture tended to coalesce earlier in 2
and 3 year old male bears than females due to the precocious growth of
the s a g itta l crest in males (Appendix B). By 5 years o f age, both sexes
61 had their interparietal suture obliterated and immature sagittal crests present.
Cranial Measurements
The greatest variation in cranial size was age variation and
involved proportions as well as general size. Analysis of age variation
in male g riz z lie s showed th a t they do not grow appreciably in length beyond age class V, but the breadth and height of the skull may continue to grow into age class VI. The coronoid height (CH), supraorbital breadth
(SB), zygomatic breadth (ZB), interorbital breadth (IB), cranial height
(CRH), mastoid breadth (MB), and the pronounced features o f the s a g itta l crest and tempera1 ridges continued to develop into age class VI due to the continued stresses provided by the temporal, masseter, pterygoid, and mastoid muscles and associated tendons.
Female skulls attain adult size earlier than males. No statistically significant differences in skull size were noted between age class V and VI female grizzlies, thus maximum cranial size was reached between the ages o f 6 to 11 years.
The female age of physical maturity corresponds to the age of sexual maturity reported by Glenn et al. (1976) for brown bears at
McNeil R iver, Alaska. Pearson (1975) reported th a t observed known-age female brown bears of the Yukon Territory^ Canada, were not sexually mature under age 6.5 years. Craighead (1969) reported that the age of sexual maturity for female grizzlies of Yellowstone National Park varied w idely, but averaged between 4 and 5 years o f age. Thus, sexual m aturity usually occurred before complete maturity of cranial size.
62 Two female grizzlies (J. C. nos. 6 and 29) were k ille d as
6 year old bears and both had successfully bred at age 5 1/2 years
(Craighead 1969). Cranial size of those two individuals showed them to be within the female adult size range. The basioccipital-basis phenoid sutures of these bears were nearly obliterated, thus the skull was verging upon total length and adult size. Female no. 163 was killed as a 5 1/2 year old bear with cubs (Craighead 1969), so she was sexually mature at 4 1/2 years. Her skull status at 5 1/2 years based on size and suture closure was that of a subadult with most sutures partially closed and comparatively small skull size. Consequently, physical maturity in skull size is not correlated with sexual maturity of female grizzly bears of Yellowstone National Park.
Estimation of Age
Because the grizzly is characterized by a relatively late sexual maturity, a slow rate of growth, and a long life span, as compared with most mammals, the detection of changes in cranial structure is measurable over the course of the animal's life .
A major problem in estimating the ages of bears resulted in the character of individual variation, especially in old bears where age changes were so small th a t they were obscured by the magnitude o f v a ria tio n between in d iv id u a ls . Individual v a ria tio n was an inherent fa c to r which caused d if f ic u lt y and e rro r in estim ating age by growth rates of cranial characters. Looking at humans, it is obvious that some people age and develop faster than others, that some adults are smaller than others, and that females generally develop earlier than
63 males. The same has been demonstrated to be true of grizzly skull growth. Therefore^, age estimates based upon growth rates of cranial characters must accept a certain margin of error as inevitable and the results should be treated with appropriate caution. The best way to compensate for the effects of individual variation lies in analysis of large sample sizes. However, w ith g riz z lie s , obtaining a large enough series to make the desired analysis is exceedingly d ifficu lt, if not impossible.
It is not known what the effects of feeding at garbage dumps might have been on the growth and size of bear skulls. Rausch (1969) showed that the proportions and conformation of a captive brown bear skull resembled that of a bear at least one year older than a wild brown bear of the same age. Rausch's captive bear, however, did not overwinter in a torpid state and growth was continuous. Grizzlies from Yellowstone
National Park exhibited normal denning behaviors and a c tiv itie s
(Craighead and Craighead 1972), and annual growth was discontinuous
(Craighead et al. 1970). Therefore, I assumed that the effects of garbage dump feeding on skull size were no greater than any other factors of individual variation.
Fundamentally, age estimation by regression analysis of the cranial characters was a valid and useful procedure for estimating age.
This was shown by the high correlation statistics of the regression equations. Statistically, R (coefficient of determination) represented the proportion (percentage) of variability in age that was explained by 2 the cranial measurements of the regression equations. The R values of the regression equations ranged from .85 to .98, therefore, close to
64 90% of the variation in age was explained by the cranial measurements of the regression equations. The values must not be misunderstood as being an equivalent of percentage accuracy of the technique, but rather as an expression of the high correlation between age and cranial size. The standard error (S.E.) of the regression equation can be interpreted as a measure of predictive accuracy. The standard error expressed the distribution of the data points about the regression line.
The standard errors of the regression equations ranged from .33 to 1.97 which indicated a narrow distribution about the regression line; thus the age estimates by multiple regression should be reasonably accurate.
When considering which age estimation technique to use in a study, one must consider the parts of the animal available, the effects of the technique on those parts, as well as the purposes for which the age estimate is to be used. For example, the skulls of hunted grizzly bears in the state of Montana are retained for a period of time by the
Department o f Fish, W ild life and Parks (Bozeman Research Laboratory) for age determination. Some sportsmen may be concerned about possible damages that may occur by tooth extraction and sectioning. Possible damages from tooth extraction may also be unacceptable to the taxonomist who wishes to retain an intact skull for comparative purposes. I was unable to assess the value of the canine teeth for age and sex correla tions in this study because many of the skulls had their canines extract ed. The field biologist may have similar limitations placed upon him.
Age estimation by tooth wear is of value to the field biologist or sportsman who wishes to make a judgment as to relative age of the bear. The accuracy in predicting age by tooth wear is
65 lim ited, but it is useful in determining relative age between young,
subadult, adult, and old-aged bears. Perhaps together with evaluations
of body size, condition, gum condition, scars, etc., reasonable estimates
can be made by experienced biologists. Age estimation by tooth eruption
sequence is valuable fo r estim ating the age o f 1 and 2 year old bears
when estimates by tooth section, suture, toothwear, and cranial
measurement are not meaningful.
Age estimation by cranial sutures has important value to the
taxonomist who must segregate unknown aged skulls into relative age
groups. It is of value to resource management agencies who have
responsibilities to the sportsman, as explained earlier. It is also
useful to sportsmen’s groups who wish to know the age of record-sized
animals, but who do not have the sophisticated equipment or the financial
means to obtain age estimates by cementum layers.
Age classification by cranial size is important to the
taxonomist. It has been shown that with discriminant analysis, age and
sex variations can be differentiated into homomorphic subsets.
Age estimation by regression analyses can be used to estimate
ages of individuals to produce life table analyses of grizzly populations,
Regression analysis must be done on dead animals, whereas age estimation by tooth cementum layers can be performed on either live or dead speci mens (Craighead et al. 1970).
Age estimation by skull size is useful to sportsmen’s groups such as the Boone and Crockett Club which keeps a Record L is t o f big bears killed in North America by sportsmen. Eleven of the 20 adult bears I examined were o f Record size (CBL + ZB ^ 23 in .) and th e ir ages
66 ranged from 9 to 23 years old. Thus size of big bears is not necessarily age-dependent beyond a minimum age o f perhaps 9 years.
Age estimation by the cementum layer technique, (Craighead et al. 1970), (Mundy and Fuller 1969), (Rausch 1969) and others, is the most prevalent method for determining age of grizzlies now used.
The discontinuous growth of the tooth cementum reflects the regular annual periods of summer growth and winter inactivity of bears. Annual layers of the cementum can be counted to give an accurate estimate of
bear age. The main d if f ic u lt y w ith the technique lie s in the in te rp re
tation of the tooth sections; multiple growth lines can occur between the more distinct annual lines. In older animals, the total cementum
layer may not be very thick; growth lines are therefore packed closely together making them d iffic u lt to count and interpret correctly.
Individual variations are evident in the growth patterns of the annual layering. The process of tooth sectioning involves considerable time and effort and tooth removal may lessen the taxonomic value of the skull.
Age estimation by cementum layers requires experience and practice to guard against misinterpretation, more than any other technique
I have described. However, when properly and con fid e n tly executed, i t gives the most accurate estimates of age.
While no single method of estimating age is useful for all purposes of age determination, the assortment of techniques assessed above should provide something to meet almost any need. Also, the comparison of age estimates from several different techniques should enhance the accuracy and confidence o f the estim ate.
67 Secondary Sexual V ariation
Difference in cranial size between the sexes increased as age increased. The s k u lls o f ad ult male g riz z lie s were s ig n ific a n tly larger, longer, and more sharply ridged than those of adult females.
Skull sizes were s im ila r between the sexes o f bears less than 1 year old, but female sk u lls were generally smaller than those o f males a fte r th a t age. This corresponds w ith re su lts reported by Glenn (1980) fo r brown bears of the central Alaska Peninsula. No statistically signifi cant differences in male and female skull size were computed fo r age classes I , I I , I I I , and IV because female sample sizes were too sm all.
Sexual Dimorphism
Larsen (1971) found that the length of the maxillary and mandibular row of polar bears from the Svalbard region exhibited sex related differences, with a 5% overlap in size. Because the length of the molar rows are not correlated with age, this provides an excellent method of differentiating the sex of polar bears older than
8 months. Mean percent difference of length P4 to M2 (LP4M2) was 1% larger in adult male grizzlies than females and the difference between the means of males and females was statistically significant, but the range of overlap in size was too great to show sexual dimorphism,
Rausch (1961) found that the transverse diameter of the right upper canine was useful in determining the sex of black bears from Alaska. The transverse diameter was measured just proximal to and parallel with the dentino-enamel junction. Using the coefficient
68 difference (tfeyr et al. 1953), a 3% joint overlap in size between the sexes was calculated. I was interested in measuring the breadth of canines but didn't want to cause any further damages to the canines or skulls, thus I did not assess the sexually dimorphic character of the canine teeth.
I found no age independent variables that were useful in determining the sex of a grizzly skull. The ability to determine sex by cranial measurement vms age dependent and useful only in determining the sex of adult grizzly skulls at least 6 years old. Because the sagittal crest did not develop until bears were at least 6 years old, the separation of male and female grizzlies based upon sagittal crest vms only useful for adult (age class V and VI) grizzlies.
Individual Variation
Permanent Dentition
The grizzly shows a reduction in the number of premolars.
This reduction in premolar numbers has been proposed by many authors as being phylogenetic in origin (Erdbrink 1953). Erdbrink (1953:377) suranarizes the controversy of the irregular occurrence of premolars by stating "In any case the presence or absence of one or more of the anterior three upper and lower premolars does not constitute a stable characteristic for determination of the species as has been and still is, thought."
Hall (1928) collected data on the occurrence of the number of premolars in brown bears from Alaska. His results show that the
69 most frequently encountered premolar combination is that In which the upper dentition had three premolars. The same results were also reported by Degerbjôl (1933), fo r Norwegion brown bears, by von
Middendorf (1851) for brown bears from the Baltic region, Siberia, and
Alaska, and by myself for grizzly bears from the Yellowstone National
Park area. Thus, it seems unlikely that presence or absence of premolars has any value specifically or subspecifically for brown bears.
Cranial Measurement
With respect to individual variation in cranial size, younger bears were more variable than older bears. Because chronological ages of bears were grouped into age classes, individual differences in absolute age would inflate the coefficient of variation during these formative years of growth. Also, individual differences in food habits, reproductive status, and genetic variability would effect the coefficients of variation. The higher coefficients of variation in younger age classes supports the statement o f Simpson e t a l. (1960) th a t only ad ult specimens can be used fo r obtaining a true perspective o f how a given measurement varies within a population.
The measurements showing a large c o e ffic ie n t o f va ria tio n win probably be consistent throughout the species. If this is true, d ire c t comparisons between populations based on such measurements would be relatively meaningless as intrapopulational variability due to individual variation could be greater than interpopulational variation. Those measurements with low coefficients of variation would be most useful in determining geographic variability because
70 differences probably would not be obscured by intrapopulational v a ria tio n .
Most o f the v a r ia b ility in the various measurements was obviously associated with differences in age and sex. Some of the unexplained variations may result from individual differences in food habits, dominant individuals, reproductive status, or genetic vari ability. These, and probably other influencing factors, are virtually impossible to determine from museum specimens. A complete analysis of populational variability could be determined by an integrated ecological, behavioral, and physiological study of bears before they become museum specimens.
The possibility of sampling error cannot be ignored as a fa c to r in measurement v a r ia b ility . The high c o e ffic ie n t o f v a ria tio n values of length of sagittal crest and cranial capacity were in part a result of the d ifficu lty to measure these characters in a completely precise, standardized method. Length of sagittal crest was d ifficu lt to measure in young bears (age classes I , I I , I I I , IV) because the crest was in a developing stage of growth. Variations in measurement of cranial capacity occurred because the lead birdshot did not always displace the cranial c a v ity in a uniform manner. Thus, these 2 measure ments did not provide completely reliable results of cranial size and should be disregarded for future analyses of age variations in skull size of grizzly bears.
71 Taxonomy
"The specific status of North American grizzly bears is one o f the most complex problems o f mammalian taxonomy. The d iff ic u lt y stems directly from the work of Merriam (1918), who concluded that there are 86 forms of grizzlies (and brown bears) in North America."
(Rausch 1953:96).
In assigning s p e c ific names to the various specimens he obtained, Merriam overlooked, or did not understand, the effects of age on the size and shape of adult male grizzly skulls. In his review,
Merriam (1918) presented a series of bear skull photos to illustrate some of his "species types". Most photos compare old adult male
"species types", but several photos were o f young ad ult male g riz z lie s , as revealed by several open sutures on their skulls.
It seems Merriam attempted to identify grizzly species based on specimens of dissim ilar age and cranial development, thus giving a false impression of size differences between "species".
Further, Merriam's classification of bears was based on descriptions and comparisons of cranial characters, many of which I have shown to vary s ig n ific a n tly w ith age in adult male g riz z lie s .
Merriam frequently compared differences in the size and shape of the postorbital processes, zygomatic arches, sagittal crest, mastoid processes, and "coronofd blade", as well as other characters to describe and compare differences in his "species types". My results
(Table 2) show that most cranial characters, including those of
Merriam's, differ significantly in size between young and old adult male g riz z lie s .
72 Also, the coefficient of variation (C.V.) values computed for adult male cranial characters show that considerable variation in size occurred between individual bears of similar age from Yellowstone
National Park. Rausch (1953) concluded that a single, highly variable species of grizzly bear extended across arctic Alaska because it was not possible to distinguish specific differences from individual differences o f bears. Therefore, because Merriam fa ile d to adequately assess the range of variability in grizzly skull size and shape associated with differences in age and between individuals, his concept of bear spécia tion must be considered invalid. His classification of grizzlies should be gradually repudiated and replaced as more specimens become available and future studies continue to sort out the complexities of bear taxonomy.
Merriam (1918) recognized 5 species of grizzly bears within and surrounding the region of Yellowstone National Park. The species with their ("type locality") were:
1. Ursus horribilis imperator Merriam (Lake Hotel, Yellowstone
National Park);
2. Ursus idahoensis (North Fork, Teton River, eastern Idaho);
3. Ursus mirus (Slough Creek, Yellowstone National Park);
4. Ursus rogersi rogersi (Upper Greybul1 River, Absaroka Mountains,
Wyoming); and
5- Ursus washake Merriam (North Fork Shoshone River, Absaroka
Mountains, western Wyoming).
Plotting the locations of these "type specimens" on a map shows that a ll species occur within a 50-mile range of Yellowstone
73 National Park. Radio tracking studies in Yellowstone National Park of grizzly bear ranges and movements (Craighead 1976) showed that the home ranges o f male a d u lt g riz z lie s may be hundreds of km^ and th a t seasonal movements may range far beyond park borders; the greatest linear distance was reported as 96 km. over extremely rugged terrain. Thus, we must conclude that there is considerable species overlap among Merriam's bear "species".
Merriam (1918) based his bear classification on the erroneous assumption that "species" of bears occurring in the same region preserve their identity by segregated breeding. In reference to this, Merriam
(1918:8) stated: "Some writers have advanced the view that the various species of bears freely interbreed. Let those so minded ask themselves the question, i f promiscuous interbreeding were to take place, what would become of the species?" Observations of breeding behavior of
Yellowstone grizzlies (Craighead et al. 1969) show that mating is polygamous and copulation occurs on a chance basis according to oppor tunity. Thus, we can be certain that segregated breeding among Yellow stone grizzly bears does not exist and that the 5 species of bear Merriam
(1918) recognized in the region are part of a single intrabreeding population of grizzlies. In fact, a 5 million acre area including
Yellowstone National Park, parts of Grand Teton National Park, and parts of 5 national forests surrounding Yellowstone Park has been designated as the Yellowstone grizzly bear ecosystem (Craighead et al. 1974) as determined from the long-term population studies of grizzlies in the region. Grizzlies within the ecosystem are considered to be a single
74 intrabreeding population of bears. Thus, I conclude that the 5 "species" of grizzly bear Merriam classified for the Yellowstone region represent only onoj but highly variable, species of grizzly bear.
I did not have the opportunity to measure the skulls of
Merriam's 5 "species", housed in the United States National Museum.
However, there is apparently so much v a ria tio n in adult male g riz z ly skulls, that it would be meaningless to compare separate skulls in detail. Thus, in my opinion, there is no justification for considering
Yellowstone grizzlies as subspecifically distinct from Ursus arctos horribilis Ord, as other investigations (Rausch 1953, 1963), (Kurtén
1973) have concluded.
75 LITERATURE CITED
Craighead, F. C., Jr., and J. J. Craighead. 1972. Grizzly bear prehibernation and denning activities as determined by radio tracking. W ildlife Mono. 32. 35 pp.
1976. Grizzly bear ranges and movements as determined by radiotracking. Pages 97-109 in M. R. Pel ton, J. W. Lentfer, and G. E. Folk, Jr., eds. Bears--their biology and management. I.U.C.N. Publ., new series 40.
Craighead, J. J., M. G. Hornacker, and F. C. Craighead. 1969. Reproductive biology of young female g riz z ly bears. J. Reprod. Fert. Suppl. 6:447-475.
______., Craighead, F. C ., and McCutchen, H. E. 1970. Age determina tion of grizzly bears from fourth premolar tooth sections. J. W ildl. Mgmt. 34(2):353-363.
______., Varney, J. R ., and Craighead, F. C. 1974. A population analysis of the Yellowstone grizzly bears. Montana Forest and Conservation Expt. Station Bull. 40. University of Montana, Missoula. 20 pp.
______. (in prep.). Growth and development of grizzly bears as related to sex and age.
Degerb/61, M. 1933. v Danmarks Pattedyr i Fortiden i somnenl igning med recente former I. Meddelelser fra Dansk Naturhistorik Forening, Bd 69, Festskrift II, Ursidae:467-529 (original not seen, referred to by Erdbrink (1953)).
Erdbrink, D. P. 1953. A review of fossil and recent bears of the Old World, Jan de Lange, Deventer, 597 pp., 2 vols.
Glenn, L. P., J. W. Lentfer, J. B. Faro, and L. H. Miller. 1976. Reproductive biology o f female brown bears (Ursus arctos), McNeil River, Alaska. Pages 381-390 in M. R. Pel ton, J. W. Lentfor, and G. E. Folk, Jr., eds. Bears--their biology and management. I.U.C.N. Publ. new series 40.
. 1980. Morphometric characteristics of brown bears on the central Alaska Peninsula. Pages 313-319 in C. J. Martinka and K. L. McArthur, eds. Bears--their biology and management. U. S. G o v't. P rin tin g O ffic e , Wash. D.C.
76 H a ll, E. R. 1928. Records o f supernumerary teeth in bears. Univ. California Publ. Zool. 30(11):243-250.
. 1981. The mammals o f North America. John Wiley and Sons. New York. 2:951-958.
Kurtén, B. 1973. Transberingian relatio nsh ips o f Ursus arctos Linne (brown and grizzly bears). Commentât. Biol. 65, 10 pp.
Larsen, T. 1971. Sexual dimorphism in the molar rows of the polar bear. J. Wildl. Mgmt. 35(2):374-377.
Long, Charles A. 1965. Functional aspects of the jaw articulation in North American Badger, with comments on adaptiveness and tooth wear. Trans. Kans. Acad, o f Science. Vol. 68, No. 1.
Manning, T. H. 1971. Geographic v a ria tio n in the polar bear Ursus maritimus Phipps. Canadian W ildlife Service Report Series. Number 13.
Mayr, E ., E. G. Lensley, and R. Z. Usinger. 1953. Methods and p rin cip le s of systematic zoology. McGraw-Hill, New York, 336 pp.
Merriam, C. H. 1896. Preliminary synopsis of the American bears. Proc. B io l. Soc. Wash. 10:65-83.
. 1914. Description of thirty apparently new grizzly and brown bears from North America. Proc. Biol. Soc. Wash. 27:173-196.
______. 1981. Review o f the g riz z ly and big brown bears o f North America. North Am, Fauna, No. 41. U. S. Gov't. Printing Office, Washington, D.C.
von M iddendorff, A, T. 1851. Reise in den aussersten Norden und Osten Sibiriens. 2. Saugethiere, Vogel und Amphibien. Petersburg. (Original not seen, referred to by Erdbrink (1953)).
Mundy, K. R., and W. A. Fuller. 1964. Age determination in the grizzly bear. J. Wildl. Mgmt. 28(4):863-866.
Pearson, A. M. 1975. The northern interior grizzly bear Ursus arctos L. Canadian W ildlife Reprt. Series, Number 34.
Rausch, R. L. 1953. On the status o f some a rc tic mammals. A rc tic 6:91-148.
1961. Notes on the black bear, Ursus americanus Pallas in Alaska, with particular reference to dentition and growth. Z. Saugetierk 26:77-107.
77 . 1963. Geographic variation in size in North American brown bears, Ursus arctos L., as indicated by condylobasal length. Canadian J. Zool. 41:33-45.
1969. Morphogenesis and age related structure of canine teeth in the brown bear. Ursus arctos L ., in a rc tic Alaska. Z. Morph. T iere , 66:167-188.
Simpson, G. G., A. Roe, and R. C. Lewontin. 1960. Quantitative Zoology. Harcourt, Brace and Co., New York, 440 pp.
78 APPENDIX A
Description of tooth wear in a series of known-(*) and assigned-age grizzly bears. 0=no wear, l=s1ight wear (enamel smooth, but no dentine exposed), 2=moderate wear (interrupted exposure of the enamel by the d e n tin e ), 3 =heavy wear (tooth worn to the level of the dentino-enamel junction of the incisors, canines and premolars, or tooth worn to the cingulum of the upper molars), 4=severe wear (tooth worn to the aveolus).
CRAIGHEAD MT. F.W. p l p i AGE SEX l ‘ c ' P^ I3 M2 FIELD NO. & P. NO. I I ^2 Cl " l P4 «1 «3
1.5 M 0 0 0 0 0 0 0 0 0 0 1 1 0 0 176493
1. 5* M 1 1 1 0 1 0 1 0 0 1 1 1 0 1 1 0 0 53 176379
1. 5* M 1 1 1 0 1 1 1 0 0 1 1 1 1 1 1 1 0 0 114 176380
1 .5 M 1 1 1 0 1 1 0 0 0 1 1 1 1 0 1 0 0 176517
1.5 M 1 I 0 0 0 1 1 1 1 1 0 0 176507
1. 5* F 1 1 0 0 0 1 0 0 1 1 0 0 1 0 0 225 176492
2 . 5* M 1 1 1 1 1 1 1 0 0 1 1 1 0 1 1 0 0 205
2 .5 M 1 1 1 1 1 1 1 0 1 1 1 1 1 0 I 0 0 M.S.U.Z. No. 12920
2 .5 F 1 1 1 1 1 1 0 0 0 1 1 1 0 1 1 1 0 0 79 176410
2 . 5* F 1 1 2 1 1 1 0 0 0 1 1 1 1 1 1 1 0 196
2 .5 F 1 1 1 1 1 1 0 0 0 1 1 1 0 1 0 1 1 0 176374
2 .5 F 1 1 1 1 1 0 0 0 1 1 1 0 1 0 118 176381
3 . 5* M 1 1 1 1 1 1 1 1 1 1 1 1 I 0 1 1 0 145 202 176505 3 . 5* H 1 1 1 1 0 1 1 1 1 1 1 1 1 0 4 3 .5 M 1 1 1 1 1 1 1 1 1 1 1 1 1 0
91 176411 3 .5 F 1 1 1 1 1 0 I 1 1 1 1 0 1 1 0 198 4 .0* M 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 98 176540 4 . 0* M 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 1 1 185 176504 4 . 5* M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M.S.U.Z. No. 10912 4 .5 M 1 1 1 1 1 1 1 1 1 1 1 1 I 1 1 167 176490 4 . 5* F 1 1 1 1 1 I 1 1 1 1 1 1 I 1 2 2 1 183 176514 5 . 5* M 1 1 1 1 1 l 1 1 1 1 1 1 1 1 1 2 2 176478 5 .5 M 2 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 2 2 1 176520 5 .5 M 2 1 1 1 1 1 1 I 1 1 1 1 1 1 1 2 2 1 163 176502 5 . 5* F 2 1 1 1 1 1 2 2 1 1 1 l 2 2 1 131 176412 5 .5 F 2 1 1 1 1 1 1 2 1 1 1 1 2 2 2 2 2 2 2 2 l 31 5 .5 F 2 2 2 2 2 2 2 2 1 2 1 1 1 1 1 176424 6.0 M 2 2 1 1 1 1 1 1 1 1 I 2 1 1 215 176506 6 .5 M 2 1 1 1 1 2 1 2 1 1 1 2 2 1 29 176539 6 . 5* F 2 1 1 1 1 1 2 1 1 1 2 2 1 6 176538 6 . 5* F 2 1 1 1 2 2 1 1 2 1 2 2 1 1 l 2 2 1 51 7. 5* M 2 2 1 1 176489 1 1 2 2 2 2 2 1 1 2 2 2 7 .5 M 2 2 1 176526 1 1 2 3 2 2 2 2 2 3 2 141 7. 5* F 2 2 2 1 2 1 2 2 2 1 1 2 2 1 176423 8.0 M 2 2 2 2 1 2 2 2 1 176335 I 1 2 2 2 2 3 2 9 .5 M 3
79 APPENDIX A (continued)
Description of tooth wear in a series of known-{*) and assigned-age grizzly bears. 0=no wear, l= slight wear (enamel smooth, but no dentine exposed), 2=moderate wear (interrupted exposure of the enamel by the d e n tin e ), 3 =heavy wear (tooth worn to the level of the dentino-enamel junction of the incisors, canines and premolars, or tooth worn to the cingulum of the upper molars), 4=severe wear (tooth worn to the aveolus).
craighe Sî) MT. F.W. AGE SEX i l l2 c l p l p3 p4 m1 m2 FIELD NO. & P. NO. 11 l2 I3 Cl Pl P4 " l «2 M3
9 .5 M 2 2 2 1 1 1 2 2 2 2 2 2 1 1 1 2 2 1 176804
9 .5 M 2 2 1 2 2 2 2 2 2 2 2 2 2 2
9 .5 F 2 2 2 2 2 2 2 3 3 2 2 2 2 2 2 2 3 3 176510
10.5 M 2 2 1 2 2 2 2 2 2 2 1 2 2 1 176509
10.5 F 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 23
11. 5* F 2 2 2 2 1 1 2 2 2 2 2 2 2 2 2 2 2 40 176547
12.5 M 2 2 2 3 2 3 2 3 3 2 2 2 2 2 2 217 176487
12.5 M 2 2 2 2 2 1 3 3 2 2 2 2 2 2 2 2 3 176796
13.5 M 2 2 2 2 2 2 2 2 3 2 2 2 176486
13.5 M 2 2 2 2 2 2 2 3 3 2 2 2 2 2 2 2 2 3 176458
13.5 M 2 2 2 3 3 2 3 2 2 2 2 2 2 3 M.S.U.Z. No. 10905
13.5 F 2 2 2 2 3 3 2 2 2 2 2 3 3 176
14.5 M 2 2 2 3 2 3 3 2 3 2 2 2 3 176512
14.5 M 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 M.S.U.Z. No. 6249
14.5 F 3 2 2 2 2 2 2 2 2 2 2 3 2 2 2 3 180 176503
15.5 F 3 3 2 2 2 2 3 3 3 3 2 2 2 2 3 3 3 176809
16.5 F 3 2 2 3 2 2 3 2 2 2 3 2 2 3 177042
18.5 M 3 3 2 3 2 2 2 3 3 2 2 3 2 2 2 3 176795
18.5 M 2 2 2 2 3 3 2 2 2 3 155
30 176488 18.5 M 3 2 2 2 2 2 2 3 3 2 2 2 2 1 2 2 2 2
75 18.5 F 3 3 3 2 2 3 3 3 3 2 3 3 3
3 3 3 148 18.5 F 3 3 3 3 3 3 3 3 2 2 2 2 3 176508 2 0.5 M 3 2 2 3 2 3 3 3 2 2 2
3 2 2 2 2 3 179 2 1.5 M 4 4 2 3 2 2 2 2 3 3 2 2 2 2 3 13 2 3.5 M 4 4 3 2 2 2 2 3 3
80 APPENDIX B
Description of sutural stages in a series of known-(*) and estimated-age grizzly bears. l=suture open, 2=suture partially closed (suture closed, but s till visible), 3=suture partially obliterated, 4=suture obliterated, R=suture ridged.
i i _i tK.ce. ^ 5 0£ O ii ëi ëS 2 si ill II
0 . 5* M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 24
0 , 5* M 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 243 176494
0 . 5* M 2 1 1 1 1 1 1 1 2 1 2 2 2 1 1 134 176413
0 .5 M 1 1 1 1 1 1 1 1 2 1 2 1 1 1 1 248 176495
0 . 5* F 2 1 1 2 1 1 1 1 2 1 1 2 1 1 1 71 176356
1 . 5* M 1 1 1 2 2 2 2 2 2 2 2 2 2 IR 1 53 176379
1 . 5* M 2 1 1 2 2 2 2 2 2 2 1 3 3 R IR 1 114 176380
1 .5 M 2 1 1 1 1 1 1 2 1 2 2 2 2 IR 1 176493
1 .5 M 1 1 1 1 1 1 1 2 2 2 1 2 176517
1 .5 M 1 1 1 1 1 1 1 2 1 2 2 3 3 IR 1 176507
1 . 5* F 1 1 1 1 1 1 2 2 2 2 2 2 1 IR 1 225 176492
2 .0 M 2 2 2 2 2 2 2 2 2 3 2 4 4 IR 2 176330
2 . 5*M 2 2 2 2 2 2 2 2 3 4 2 4 3 IR 2 205
12920 2 .5 M 2 2 2 2 2 2 2 2 3 R 3 2 4 4 IR 2
2 , 5* F 2 1 1 1 2 2 1 2 2 2 2 3 3 1 2 79 176410
2 . 5*F 2 2 2 2 2 2 2 2 2 3 2 4 4 IR 2 196
176374 2 .5 F 2 2 2 2 2 1 2 2 2 3 2 4 3 IR 1
176381 2 .5 F 2 2 2 2 2 2 2 2 2 3 2 4 4 IR 2 lis
145 3 . 5* M 2 2 1 2 1 1 2 2 3 R 4 2 R 4 4 IR 2
2 202 176505 3 . 5* M 2 2 1
4 2 4 3 .5 M 1 1 2 1 2 1 1 2 3 R 4 2 R 4
IR 2 91 176411 3 . 5* F 2 2 2 2 2 1 2 2 2 R 3 2 R 4 3
4 4 IR 2 198 4 . 0* M 2 1 1 1 1 1 1 2 3 R 3 2 R 2 98 176540 4 . 0* M 2 2 2 2 2 2 2 2 3 R 2 R
4 4 IR 2 185 176504 4 . 5* M 2 1 1 1 2 2 1 2 4R 4 2 R
4 2 R 4 4 2 R 2 10912 4 .5 M 2 2 2 2 2 2 2 2 3 R
4 2 R 4 4 2 R 2 167 176490 4 . 5* F 1 1 1 1 1 1 1 2 4R
4 3 2 R 4 4 IR 2 183 176514 5 . 5* M 2 2 2 2 2 2 2 2 R
4R 4 2 4 4 IR 1 176520 5 .5 M 2 2 1 2 2 2 2 2
2 4 R 4 2 R 4 4 IR 2 176478 5 .5 M 2 2 2 2 2 2 2
2 4R 4 2 R 4 4 2 R 2 163 176502 5 . 5* F 2 2 2 2 2 2 2
3 2 4R 4 2 R 4 4 2 R 2 131 176412 5 .5 F 2 2 2 2 2 2
2 2 4 4 2 4 4 2 2 31 6992 5 .5 F 2 2 2 2 2 2
4R 4 2 R 4 4 . 2 R 1 176424 6 .0 M 2 2 2 2 2 2 2 2
8l APPENDIX B (continued)
Description of sutural stages in a series of known-(*) and estimated-age grizzly bears. l=suture open, 2 =suture partially closed (suture closed, but s till visible), 3 = s u tu re partially obliterated, 4=suture obliterated, R=suture ridged.
S 1 5 E 3 w J i 3 i i _i Z i 1 II i 3 i g § oc d I I < W 1 il cû 1 1 1 g ii O co i I i i 0 i l d R 1— o œ m 2 I 1 z 1 s i î i I 1 I ! 2 m 1 #
6,5 M 2 2 1122 124R42R14 4 2R 1 215 176506
6.5* F 2 2 2 1 2 2 1 2 4R 4 2R 2 3 4 3 2 29 176539
6.5* F 1 2 2 1 2 2 2 4R 4 2R 2 4 3 3 1 6 176538
7.5* M 3 3 3 2 2 2 3 2 4R 2R 2 2 51
7.5 M 2 4 3 3 2 2 4 4 4R 4 2R 2 4 4 3 3 176489
7.5* F 2 3 2 2 2 2 3 3 4R 4 2R 2 4 4 4 2 141 176526
8.0 M 2 3 2 2 2 2 3 2 4R 4 2R 2 2 176423
9.5 M 3 4 2 2 2 2 4 3 4R 4 2R 2 4 4 4 2 176335
9.5 M 2 3 2 2 2 2 4 2 4R 4 2R 2 4 4 3 2 176804
9.5 M 2 3 3 2 2 2 3 2 4R 4 2R 2 4 4 4 2 2
9.5 F 4 4 4 3 4 4 4 4 4 4 4 2 4 4 4 2 176510
10.5 M 2 4 2 3 3 2 4 4 4R 4 4 2 4 4 4 2 176509
10.5 F 2 4 3 3 4 4 4 4 4 4 4 2 4 4 4 2 23
11.5* F 2 4 2 3 2 2 4 4 3 2 4 2 40 176547
12.5 M 3 4 3 4 4 4 4 4 4R 4 3 4 4 4 3 217 176487
12.5 M 2 4 2 3 2 2 4 4 4R 4 4 2 4 4 4 2 176796 176486 13.5 M 3 4 4 4 4 4 4 4 4R 4 4 2 4 4 4 4 176458 13.5 M 2 4 3 3 4 4 4 4 4 4 4 2 4 4 4 2 3 10905 13.5 M 4 4 3 4 4 4 4 4 4R 4 4R 3 4 4 4 2 176 13.5 F 4 4 2 3 4 4 4 4 4 4 4 2 4 4 4 4 3 176512 14.5 M 3 4 3 4 4 4 4 4 4R 4 4 3 4 4 2 6249 14.5 M 3 4 3 4 4 2 4 2 4 4 3 180 176503 14.5 F 3 4 3 3 4 3 4 4 4R 4 4 3 4 4 4 3 176809 15.5 F 4 4 3 3 3 4 4 4 4 4 4 2 4 3 4 4 4 3 177042 16.5 F 2 4 3 3 4 3 4 4 4R 4 4 4 2 4 4 2 30 176488 18.5 M 2 4 2 3 2 2 4 4 4 4 4 4 2 4 4 4 4 176795 18.5 M 4 4 4 4 4 4 4 4 4 4 4 2 4 4 4 4 155 18.5 M 4 4 4 3 4 4 4 4 4 4R 4 4 2 4 4 4 4 75 18.5 F 4 4 4 4 4 4 4 4 4 4R 4 4 2 4 4 4 4 148 18.5 F 4 4 4 4 4 4 4 4 4 4 4 2 4 4 4 4 176508 20.5 M 4 4 4 4 4 4 4 4 4R 4 4 2 4 4 4 4 179 21.5 M 4 4 4 4 4 4 4 4 4 4R 4 4 2 4 4 4 4 13 23.5 M 4 4 4 4 4 4
82 APPENDIX C
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. DUNCAN
MASTOID BREADTH
MALE 86.819* I 4 85.00± 9.02 80.00- 90.90 5.31 1 II 5 101.08i 19.44 91.30-116.90 9.61 1 III 2 126.35+ 34.36 114.20-138.50 13.60 1 IV 7 145.43+ 23.34 122.50-159.00 8.02 1 V 6 159.13+ 11.89 151.60-166.20 3.73 1
IE 16.233* I 1 88.40 - - - - 1 II 1 96.00 - — — - n III 4 109.67+ 25.96 95.40-124.00 11.84 1 IV 5 130.28+ 21.67 118.50-144.50 8.32 1 V 6 137.37+ 4.92 134.50-140.10 1.79 1 VI 6 138.00+ 6.77 133.70-142.00 2.45 1
SUPRAORBITAL BREADTH
MALE 79.693* I 4 66.80± 5.67 63.40- 70.20 4.24 1 II 5 74.68+ 9.17 68.70- 81.20 6.14 1 III 2 89.90± 19.23 83.10- 96.70 10.70 1 IV 10 101.68+ 17.81 84.40-113.70 8.76 1 V 7 109.47+ 9.41 101.80-116.30 4.30 1 VI 12 124.58+ 9.98 116.30-132.60 4.00 1
FEMALE 13.827* - 1 I 1 63.60 - — — II 2 72.05+ 11.17 68.10- 76.00 7.75 11 III 4 82.72+ 11.10 77.00- 89.20 6.71 11 IV 5 91.42+ 14.13 83.20-100.00 7.73 11 V 6 99.77+ 15.72 88.50-109.10 7.88 11 VI 6 106.17+ 14.88 100.50-116.70 7.00 1
* P < .05
83 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN
CRANIAL LENGTH
MALE 71.063* I 4 108.37+ 6.43 105.60-113.00 2.97 1 II 5 132.94+ 23.75 116.10-149.60 8,93 1 III 2 157.25± 34.93 144.90-169.60 11.11 1 IV 8 181.91+ 27.26 152.50-196.10 7.49 1 V 7 197.68+ 19.72 181.30-208.80 4.97 1 VI 11 208.37+ 19.99 192.50-226.00 4.80 1
FEMALE 14.330* I 1 102.50 1 I I 1 129.20 - - - - n I I I 4 146.17+ 35.29 127.10-166.00 12.07 1 IV 5 165.92± 14.98 158.50-176.50 4.51 1 V 5 171.56+ 16.87 163.30-185.50 4.91 1 VI 6 176.52± 13.06 166.90-183.70 3.70 1
FACIAL LENGTH
MALE 55.049* I 4 112.50+ 4.70 109.30-114.80 2.09 1 II 5 140.00+ 10.31 134.70-147,90 3.68 1 III 2 163.60+ 31.11 152.60-174.60 9.51 1 IV 10 179.66+ 20.30 154.30-188.50 5.65 1 V 8 182.19+ 16.94 171.40-195.60 4.65 1 VI 12 192.33+ 23.24 176.10-218.30 6.04 1
FEMALE 8.937* I 1 110.00 1 II 2 137.40+ 22.06 129.60-145.20 8.03 1 III 4 143.40+ 30.76 130.60-165.70 10.73 11 IV 5 156.48+ 20.89 139.40-166.00 6.68 11 V 6 162.78+ 13.28 155.30-170.90 4.08 1 VI 6 165.98+ 13.72 158.80-175.70 4.13 1
* P < .05
84 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan’s analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN
MAXILLA-SUPRAORBITAL HEIGHT
MALE 52.575* I 4 57.00± 5.79 54.10- 60.30 5.08 1 II 5 67.88± 12.20 60.50- 77.50 8.98 1 III 2 81.65± 8.91 78.50- 84.80 5.45 1 IV 10 91.20+ 11.90 78.20- 98.60 6.52 1 V 8 96.09+ 9.57 90.00-103.80 4.98 11 VI 12 101.27+ 13.25 86.60-112.50 6.54 1
FEMALE 11.818* I 1 55.00 1 II 2 68.10+ 9.05 64.90- 71.30 6.64 11 III 4 73.85± 18.87 60,00- 81.20 12.78 11 IV 5 80.96+ 8.87 75.50- 85.70 5.48 11 V 6 85.60+ 8.77 79.30- 90.90 5.12 1 VI 6 87.05± 2.68 84.70- 88.40 1.54 1
INTERORBITAL BREADTH
MALE 51.336* I 4 46.12+ 4.03 43.50- 47.90 4.37 1 II 5 51.92+ 8.83 46.70- 58.60 8.51 1 III 2 62.50+ 13.58 57.70- 67.30 10.86 1 IV 10 67.47+ 11.86 58.70- 76.50 8.79 1 V 7 72.66+ 5.38 68.20- 77.00 3.70 1 VI 12 81.13+ 9.16 73.20- 89.90 5.65 1
FEMALE 10.066* I 1 43.00 - - - - 1 II 2 50.70+ 3.11 49.60- 51.80 3.07 11 III 3 59.53+ 15.10 52.00- 67.10 12.68 11 IV 5 62.56± 9.63 58.00- 68.80 7.69 11 V 6 67.63+ 10.45 59.60- 73.70 7.73 11 1 VI 6 69.75+ 5.53 65.60- 74.10 3.96
* P < .05
85 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN+ 2 S.D. RANGE C.V. F DUNCAN
BREADTH OF CANINES
MALE 38.524* I 4 49.67± 3.92 47.60-51.40 3.95 1 II 3 60.83± 4.50 58.90-63.30 3.69 1 III 1 67.40 - — — - n IV 6 71.73+ 10.94 61.40-75.80 7.62 1 V 5 77.68+ 8.30 71.90-83.30 5.34 1 VI 8 83.81+ 9.55 74.50-91.90 5.70 1
FEMALE 5.803* I 1 51.20 1 II 2 57.85± 4.95 56.10-59.60 4.28 1 III 2 59.25+ 12.30 54.90-63.60 10.38 1 IV 2 63.05± 15.41 57.60-68.50 12.22 n V 3 69.80+ 6.35 66.30-72.50 4.55 1 VI 3 70.57± 1.47 70.00-71.40 1.05 1
PALATAL BREADTH
MALE 26.153* I 4 69.17+ 3.69 67.30-71.00 2.67 1 II 5 75.02+ 6.66 71.10-78.50 4.44 1 III 2 82.95± 0.71 82.70-83.20 0.43 1 IV 10 83.83± 10.53 71.50-90.40 6,28 1 V 8 87.00± 7.55 80.50-90.90 4.34 1 VI 12 91.67± 7.32 87.30-98.80 3.99 1
FEMALE 5.184* I 1 68.80 1 II 2 71.25+ 10.60 67.50-75.00 7.44 1 III 4 74.55+ 6.55 71.20-78.30 4.39 n IV 5 78.92+ 9.31 71.40-83.00 5.90 11 V 6 81.00± 8.28 76.90-88.40 5.11 1 VI 6 81.90+ 4.33 79.80-85.30 4.33 1
* P < .05
86 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN
LENGTH P4 TO M2
MALE .335* I - tooth eruption incomplete II 5 79.12+ 3.41 76.50-80.80 2.15 1 I I I 2 77.75± 6.36 75.50-80.00 4.09 1 IV 10 76.75± 5.89 71.20-81.00 3.83 1 V 8 77.35+ 8.77 70.70-84.40 5.67 1 VI 12 77.03+ 9.77 71.60-88.40 6.34 1
FEMALE 1.093* I - tooth eruption incomplete II 2 70.10+ 5.94 68.00-72.20 4.24 1 I I I 4 74.77+ 9.68 71.00-81.50 6.47 1 IV 5 71.28+ 6.03 67.20-75.10 4.23 1 V 6 70.90+ 6.43 68.00-76.60 4.54 1 VI 6 72.07+ 4.81 70.60-76.90 3.33 1
LENGTH M2
MALE 1.345* I - tooth eruption incomplete I I 5 38.80+ 3.31 36.00-40.20 4.27 1 III 2 34.85± 6.65 32.50-37.20 9.54 1 IV 10 37.96+ 3.18 35.80-40.60 4.19 1 V 8 38.46+ 5.44 35.00-43.10 7.07 1 VI 12 37.71+ 4.51 34.50-41.00 5.98 1
MALE 0.621* I tooth eruption incomplete II 2 34.65+ 0.42 34.50-34.80 0.61 III 4 36.70+ 5.08 34.70-40.00 6.92 IV 5 36.60+ 3.21 34.70-38.50 4.39 V 6 35.87+ 2.72 34.00-38.00 3.80 VI 6 36.22+ 3.27 34.20-38.70 4.51
* P < .05
87 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN
LENGTH Ml
MALE 3.647* I 4 25.07± 0.87 24.70- 25.70 1.73 1 i r 5 23.60± 1.94 22.00- 24.50 4.12 1 I I I 2 23.80+ 5.66 21.80- 25.80 11.88 n IV 10 23.08± 1.95 21.20- 24.30 4.23 1 V 8 23.10± 1.94 22.00- 24.60 4.20 1 VI 12 22.82+ 1.40 21.60- 24.00 3.07 1
FEMALE 2.228* I 1 23.30 11 II 2 23.60+ 3.39 22.40- 24.80 7.19 1 III 4 22.55+ 2.66 21.50- 24.50 5.91 11 IV 5 21.54± 3.13 19.40- 23.10 7.27 11 V 6 20.78+ 2.53 18,70- 22.30 6.08 1 VI 6 21.88± 1.35 21.10- 23.00 3.08 11
CRANIAL HEIGHT
MALE 61.825* I 4 81.37± 11.27 73.80- 87.10 6.92 1 II 5 94.70+ 5.43 91.80- 97.70 2.87 1 III 2 111.50+ 14.14 106.50-116.50 6.34 1 IV 9 115.60+ 14.28 103.80-126.60 6.17 1 V 8 125.81+ 11.60 119.60-138.90 4.61 1 VI 12 134.19± 13.22 124.40-150.50 4.93 1 4.854* FEMALE _ I 1 86.00 1 II 1 88.60 - — - - 11 III 4 100.15+ 23.70 86.70-115.50 11.83 m IV 5 106.04+ 15.62 95.80-115.00 7.36 in V 5 111.18+ 10.92 101.80-115.70 4.91 11 VI 6 113.83+ 8.75 109.40-119.30 3.84 1
.05
88 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN
BRAIN CASE BREADTH
MALE 10.982* I 4 90.85± 6.61 87.90- 95.50 3.64 1 II 5 95.42± 8.38 91.20-102.40 4.39 11 III 2 101.35± 4.95 99.60-103.10 2.44 11 IV 8 104.20+ 14.37 93.50-116.70 6.89 1 V 7 107.71+ 4.89 104.70-112.00 2.27 1 VI 8 105.60± 5.99 100.50-110.00 2.84 1
FEMALE 1.464* I 1 91.90 - — — - 1 I I 1 91.50 - - - - 1 III 4 97.87+ 10.44 92.70-102.90 5.33 1 IV 5 97.56± 11.11 88.20-102.00 5.69 1 V 5 98.56± 9.25 96.30-101.60 2.15 1 VI 6 100.70+ 6.35 95.30-104.80 3.15 1
CORONOID HEIGHT
MALE 66.249* I 3 52.50± 3.14 51.40- 54.30 2.99 II 5 68.98+ 10.84 61.20- 76.30 7.86 III 2 86.20+ 21.78 78.50- 93.90 12.63 IV 10 95.99± 15.91 84.40-112.70 8.29 V 7 102.73+ 9.60 97.00-109.50 4.67 VI 12 111.18+ 10.42 101.70-120.00 4.68
FEMALE 9.501* I 1 55.60+ - - - - 1 IL 2 69.05± 8.91 65.90- 72.20 6.45 n 1 III 4 77.10+ 21.61 63.80- 89.60 14.01 IV 5 88.42+ 12.99 80.00- 95.70 7.34 V 6 89.68+ 13.00 82.50-101.40 7.36 VI 6 92.12+ 5.99 86.70- 94.80 3.25
* P < .05
89 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect aae class means o f non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2: S.D. RANGE c.v. F DUNCAN
CONDYLOPALATAL LENGTH
MALE 65.798* I 4 91.27+ 2.26 90.20- 92.30 1.24 1 I I 4 117.35+ 14,68 109.00-126.90 6.25 1 III 2 140.45+ 25.59 131.40-149.50 9.11 1 IV 7 153.17+ 20.38 135.00-167.30 6.65 1 V 7 162.44+ 13.30 153.60-172.50 4.09 1 VI 11 166.55± 17.15 154.30-181.90 5.15 1
FEMALE 12.257* I 1 93.20 1 I I 1 117.50 - — — — 1 III 4 124.72+ 27.19 108.70-140.90 10.90 1 IV 5 139.54+ 12.81 132.30-145.60 4.59 1 V 5 140.94+ 7.77 136.30-146.50 2.76 1 VI 6 142.97+ 5.63 140.30-146.60 1.97 1
HEIGHT OF SAGITTAL CREST
MALE 84.274* I 4 61.85+ 5.38 58.90- 65.00 4.35 1 II 4 80.02+ 11.62 75.30- 88.30 7.26 1 III 2 85.75+ 14.00 80.80- 90.70 8.16 1 IV 7 96.77+ 11.70 85.00-102.50 6.04 1 V 5 109.30+ 7.34 103.80-113.00 3.36 1 VI 10 115.72+ 9.95 107.20-122.90 4.30 1 10.455* FEMALE _ I 1 64.00 1 II 1 74.50 - — — - 11 III 4 78.90± 13.71 72.20- 85.30 8.69 1 IV 5 90.18+ 12.34 80.70- 95.20 6.84 1 V 5 93.62+ 9.31 87.70- 99.60 4.97 1 VI 6 94.98+ 8.85 88.40-101.30 4.66 1
* P < .05
90 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park- Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. DUNCAN
LENGTH OF SAGITTAL CREST
MALE 40.065* I 4 15.95+ 14.33 9.50- 22.50 44.94 1 II 5 28.26+ 14.50 18.60- 38.90 25.65 1 III 2 45.65± 41.44 31.00- 60.30 45.38 1 IV 8 90.77± 60.06 51,50-137.50 33.08 1 V 7 122.71± 16.47 101.20-150.30 16.47 1 VI 11 143.00± 36.18 117.40-182.60 12.65 1
FEMALE 6.208* I 1 11.50 - — —■ - 1 II 1 29.50 - — — - 11 I I I 4 37.32± 15.66 28.20- 46.70 20.99 11 IV 5 73.60± 47.44 44.00-104.20 32.23 11 V 5 87.60+ 48.33 47.50-110.60 27.58 1 VI 6 96.12+ 48.63 56.40-120.70 25.29 1
GREATEST LENGTH OF SKULL
MALE 66.759* I 4 201.75+ 4.43 199.00-204.00 1.10 1 II 5 254.60+ 31.13 233.00-277.00 6.11 1 III 2 302.50± 57.98 282.00-323.00 9.58 1 IV 8 337.87± 52.97 290.00-360.00 7.84 1 V 8 354.50+ 29.08 330.00-376.00 4.10 11 VI 11 372.36± 36.00 346.00-402.00 4.83 1
LE 14.164* L 1 204.00 - — — - 1 II 1 244.00 - - - - 11 III 4 272.50+ 60.23 245.00-314.00 11.05 1 IV 5 307.60+ 31.16 287.00-325.00 5.06 1 V 5 316.04+ 19.91 307.20-330.00 3.15 1 VI 6 320.78+ 16.07 310.00-332.00 2.50 1
* P < .05
91 APPENDIX C (continued)
Age variation of cranial measurements of grizzly bears from Yellowstone Park. Vertical lines of Duncan's analyses connect age class means of non-significant subsets at the P = .05 level
AGE SEX CLASS N MEAN± 2 S.D. RANGE C.V. F DUNCAN
CRANIAL CAPACITY
MALE 8.182* I 4 246.75+ 61.00 208.00-277.00 12.36 1 I I 4 272.50± 74.93 240.00-326.00 13.75 1 I I I 2 325.00+ 14.14 320.00-330.00 2.17 11 IV 7 336.57+124.04 204.00-384.00 18.43 1 V 6 358.00+ 74.66 312.00-406.00 10.43 1 VI 9 386.67+ 70.91 336.00-432.00 9.17 1
FEMALE 4.643* I 1 234.00 1 I I 1 250.00 — — - 11 III 4 285.00+ 52.81 256.00-316.00 9.26 111 IV 5 300.40+ 61.08 266.00-348.00 10.17 111 V 5 320.60± 47.48 300.00-355.00 7.41 11 VI 6 329.67+ 40.11 302.00-352.00 6.08 1
* P < .05
92 APPENDIX D
Age group mean values of cranial measurement for substitution into discriminate or regression equations
CRANIAL MEASUREMENT CBL MPL MB
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 252.83 235.00 124.60 113.43 100.90 100.33 SUBADULTS 317.06 290.80 141.48 131.10 144.12 125.60 ADULT I 336,00 301.75 146.95 135.15 163.35 137.25 ADULT I I 346.17 301.20 147.92 134.70 170.00 138.80 TOTAL 318.30 279.30 141.41 127.69 148.12 124.31
CRANIAL MEASUREMENT SB ZB CL
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 74.80 72.33 134.57 131.93 131.60 128.97 SUBADULTS 101.54 91.60 185.88 169.05 179.58 168.15 ADULT I 110.85 104.80 203.40 189.05 196.05 176.25 ADULT I I 123.12 101.73 228.02 185.27 206.22 176.17 TOTAL 105.78 91.50 194.25 166.78 182.63 160.42
CRANIAL MEASUREMENT FL MSH LCB
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 143.04 126.53 68.67 65.77 65.73 62.00 SUBADULTS 177.34 152.70 90.24 80.60 71.28 66.65 ADULT I 187.40 163.10 99.65 88.75 74.55 72.20 ADULT I I 189.67 164.77 98.58 87.47 73.93 68.07 TOTAL 176.79 150.55 90.50 79.84 71.64 66.79
CRANIAL MEASUREMENT IB BC PB
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 52.40 53.23 62.20 56.97 75.87 70.83 SUBADULTS 66.96 63.40 71.28 63.05 82.90 76.10 ADULT I 72.70 69.90 76.95 71.55 88.65 83.90 ADULT I.L 78.82 68.37 82.15 70.57 92.13 82.13 TOTAL 69.39 63.14 74.36 65.18 85.76 77.89
93 APPENDIX D (continued)
Age group mean values of cranial measurement for substitution into discriminate or regression equations
CRANIAL MEASUREMENT LP4M2 LM2 LMl
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 78.93 69.50 37.80 34.60 24.37 23.15 SUBADULT 74.74 69.50 36.86 36.60 22.78 21.10 ADULT I 79.10 74.05 40.15 37.35 22.75 21.45 ADULT I I 75.78 70.80 37.73 35.07 22.83 21.67 TOTAL 76.46 70.94 37.77 35.81 23.09 21.82
CRANIAL MEASUREMENT CRH SB CM
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 99.13 91.67 94.80 95.43 69.30 69.40 SUBADULTS 116.46 105.40 102.92 93.60 97.68 86.65 ADULT I 125.25 114.70 107.35 99.70 102.80 95.40 ADULT I I 133.83 114.47 105.17 109.97 109.85 90.93 TOTAL 120.82 105.86 102.79 97.88 97.56 84.51
CRANIAL MEASUREMENT CPL HSC LSC
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 119.03 113.20 78.60 74.60 25.40 26.87 SUBADULTS 153.34 139.25 96.84 87.95 97.06 62.00 ADULT I 165.40 144.00 108.70 96.05 120.05 97.95 ADULT I I 166.23 141.57 114.48 94.10 136.78 99.60 TOTAL 153.25 133.08 101.52 87.41 101.39 69.93
CRANIAL MEASUREMENT BOC GLS CC
AGE GROUP MALE FEMALE MALE FEMALE MALE FEMALE
JUVENILES 69.90 65.60 256.67 240.67 279.33 260.00 SUBADULTS 80.76 75.60 333.20 306.00 319.20 307.00 ADULT I 95.40 81.40 359.00 318.60 391.00 327.50 ADULT I I 88.53 74.10 368.17 318.67 384.33 327.33 TOTAL 83.47 73.31 335.19 292.72 345.12 303.10
94 CRAIGHEAD FIELD NUMBER
MT. F.W. & P. COLL. NO.
M.S.U.Z. NO.
SEX
DATE MARKED
DESIGNATED AGE 5 5. g WHEN MARKED
DATE KILLED VO v n
zzzzzzzzzzzzzzzzzzzzzzzzzzzzz LOCATION KILLED
KNOWN OR ESTAS. AGE WHEN k i l l e d IN YEARS(MONTHS)
ASSIGNED AGE BY TOOTH SECTION
COMMENT CRAIGHEAD FIELD NUMBER
MT. F.W. & P. COLL. NO.
M .S .U .Z . NO.
SEX
DATE MARKED
DESIGNATED AGE WHEN MARKED
LO (JN DATE KILLED
0 0 CD CO OD
LOCATION KILLED
KNOWN OR ESTAB. AGE WHEN KILLED IN Y EARS(MONTHS)
ASSIGNED AGE BY TOOTH SECTION
COMMENT