Denning behavior in the Giant Short-faced Bear

One of the most exciting things in paleontology to me is when we can begin to tease apart how extinct animals, animals that humans often never set eyes upon, lived their everyday lives. I am often amazed at how my colleagues can drill deep into questions that at first seem unanswerable; using creative ways to get answers from all the evidence that has survived, the bones, teeth, and sometimes trace fossils.

There are many examples of using the clues provided in the fossil record to come to better understand beasts from the past. In an earlier story, we looked at a disease process in Tyrannosaurus, and glimpsed how the mighty tyrant king could be brought down by a lowly protozoan. Here, we will explore some evidence for denning in the Giant Short-faced Bear (GSFB).

In a paper from several years ago Schubert and Kaufmann (2003) discussed the discovery of a GSFB in an Ozark cave. While incomplete, it is still one of the most complete specimens of the bear ever found. In addition to bones in partial articulation, they also found a thin layer of clay and minerals underneath the skeleton that preserves the remains of hair. Unfortunately, the hair is too deteriorated to tell us what color it was or exactly what its texture might have been, but its discovery is tantalizing.

This Ozark specimen is small compared to others of its species. There is a lot of evidence that there was a significant difference in size between male and female GSFBs. For example, at Rancho La Brea in southern California, both smaller and larger individuals have been found in contemporaneous deposits. It is easy to tell if the individuals are adult, so seeing large and small forms suggests two options: either there are two species, or there is one species with large and small individuals. It later is most likely. This is not surprising as all modern bears are sexually dimorphic.

Schubert and Kaufmann noted that over 1/3 of the known specimens of the GSFB come from caves, and that those specimens are smaller in general than the specimens found in open environments. (See the story about the type specimen, also found in a cave in northern California). It is logical to reason that the smaller individuals using the caves are predominately female.

Modern female bears are much more prone than males to den during periods of unfavorable conditions. And male bears are more likely to remain active throughout the year. It seems as if the GSFB followed a similar pattern—the females were using caves as denning sites, and were denning when they perished. In Cope’s original paper (1879), he called this new animal the cave bear of California—seems he was right.

From the accumulation of small bits of information we continuously piece together the lives of prehistoric beasts, slowly bringing them into sharper focus. That is the thrill of paleontology.

Cope, E. D. 1879. The cave bear of California. American Naturalist 13:791.
Schubert, B. W., and J. E. Kaufmann. 2003. A partial short-faced bear skeleton from an Ozark cave with comments on the paleobiology of the species. Journal of Cave and Karst Studies 65(2):101-110.

There are many other interesting facts here at Boneblogger. Just look around and enjoy.

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