Bears of the Pleistocene

[brotherbear]

http://www.bearbiology.com/fileadmin/tpl/Downloads/URSUS/Vol_11/Stiner_Vol_11.pdf 

CAVE BEAR ECOLOGY AND INTERACTIONS WITH PLEISTOCENE HUMANS 
 
( I will copy and pasted a portion )... 


SEXUAL SIZE DIMORPHISM IN CAVE
BEARS
Moder bears exhibit comparatively high levels of size
dimorphism between the sexes. Grossly analogous differences
in adult stature and weight have been inferred
for Pleistocene Ursus species of the northern hemisphere
based on the dimensions of canine teeth and weight-bearing
limb bones (e.g. Koby 1949; Kurten 1958, 1976).
The results on the Yarimburgaz cave bears (Stiner et al.
1998) are based on measurements of carpal or wrist bones
(pisiform and scapholunate; Stiner et al. 1998), using
Josephson et al.'s (1996) method-of-moments (MoM)
technique. This technique assumes that the total distribution
of a metric trait is composed of 2 underlying normal
distributions, one for males and one for females.
Three moments around the mean of the combined-sex
distribution are used to estimate the means and the common
standard deviation of the 2 underlying distributions.
The scale of measurement most easily controlled in paleontological
studies is a simple linear one and, to some
extent, areal measurements computed therefrom. If the
Yarimburgaz size data are extrapolated to yet a third scale
of measurement, analogous to body volume or mass, adult
male cave bears would have been roughly twice the lean 
body weight of adult females. This level of sexual size
dimorphism is relatively extreme among terrestrial mammals,
but not unusual among large-bodied populations
of modem brown bears. We infer from this that their
mating system was similar to that of extant Ursus species. 
 
HOW DID COEXTANT CAVE AND

BROWN BEARS DIFFER?

Osteometric techniques demonstrate the presence of 2

Middle Pleistocene bear species in the Middle Pleistocene

deposits of Yarimburgaz Cave-Ursus (Spelearctos)

deningeri, a large cave bear, and U. arctos or brown

bear-the former abundant and the latter rare. Acknowledging

potential time-averaging effects on fossil assemblages,

it nonetheless seems that cave and brown bears

coexisted in many areas of Eurasia. Cave bears may have

been more prevalent in some regions and periods, possibly

at the expense of brown bears, and vice versa.

Brown bear teeth from Yarimburgaz Cave are easily

distinguished from cave bear teeth on the basis of size.

The only brown bear tooth in the M2 sample, for example

(Fig. 5), falls well below the maximum (mean) proportional

size difference that can be expected between the

sexes in any terrestrial mammal (roughly males/females

= 1.45-1.50 by a linear standard), even in highly size

dimorphic lineages such as bears or the great apes

(Pongidae). The other 64 data points form a single cluster

(Fig. 5), representing a continuous distribution of male

and female cave bear tooth measurements. In addition,

an informal comparison of the fifth metacarpals of a

mature cave bear and a mature brown bear from

Yarimburgaz Cave (Fig. 6) exemplifies dramatic structural

differences between the 2 species. The brown bear

metacarpal is only somewhat shorter than that of the cave

bear, but the difference in robusticity is great.

The limb allometry of cave and brown bears also differed.
Cave bears possess relatively shorter distal limb 
elements and longer upper elements than is typical in

brown bears (Kurten 1976, Mattson 1998). The cave

bear build is interpreted to have emphasized strength over

agility or a quick gate, whereas brown bears are relatively

fast runners over short distances. Tooth morphology

testifies further to differences among brown and cave

bears, not least of which were the extraordinary milling 

capabilities evidenced in the latter. The hyper-developed

dental architecture of the cave bear is arguably among

the most telling feature in its ecology, as it is expressed

by highly conservative elements in the evolution of mammalian

skeletons-molar and premolar teeth.

The evolutionary effects of limiting similarity are expressed

in the bone and dental structures of cave and

brown bears. It is interesting in light of this that we

cannot distinguish the diets of coextant cave and brown

bears in the Yarimburgaz sample on the basis of carbon

and oxygen isotope analyses. The isotope data do yield

some insights on the diets of cave bears, but these approaches

may lack much of the resolution required to

differentiate between coextant cave and brown bear diets;

perhaps many of the dietary differences exist within

the food categories compared by isotope studies (e.g.,

among C3 plants). In addition to anatomical differences,

cave bear hibernation sites tend to be concentrated at

relatively high altitudes, thus accounting for their high

density in the moder countries of Switzerland and Austria

(Rabeder and Nadel In Press). Cave bears were not

confined to highlands-their remains also occur in caves

at sea level in low frequencies (e.g. Stiner 1994)-but

brown bear remains seem to be more common at lower

altitudes, as are human archaeological sites dating to
before the Upper Paleolithic period. Reply