Preliminary Report on the Fossil Bears of El Capitan Cave, Prince of Wales Island, Alaska

Timothy H. Heaton
Department of Earth Sciences and Physics, University of South Dakota, Vermillion, SD 57069

Frederick Grady
Department of Paleobiology, Smithsonian Institution, Washington, D.C. 20560

For the last five years officials of Tongass National Forest and cavers of the National Speleological Society have joined forces to find and survey caves in the extensive limestone exposures of Prince of Wales Island, one of the largest islands of the Alexander Archipelago. During the 1990 field season an important and unexpected paleontological site was discovered by expedition leader Kevin Allred. In a remote high passageway of El Capitan Cave, Alaska's largest known cave, Allred found the complete skeleton of a black bear (Ursus americanus) in nearly perfect condition, parts of at least two other black bears, and fragments of a second species of bear that is much larger. Together with these were piles of small ground fish bones that appear to be remnants of the bears' excreta.

It is virtually impossible that bears could have entered this passage by the treacherous route the cavers used. Allred discovered, however, that the bone deposit was close to the surface, and after some digging in a high rubble pile at the end of the passage he was able to see daylight through a now sealed entrance. Thus the passage containing the bones was presumably used as a den by bears before this entrance became choked with rocks and soil.

Together with Allred we conducted a preliminary survey of the site in 1991. The passage containing the bear remains ranges from 1 to 3 m in width and height and extends 20 m between a pool and the choked entrance. This part of the cave is very wet and stays at a temperature near 40 F. The complete black bear skeleton lies near the lake on flat bedrock, clean rock rubble, and shallow clay. The bone is clean and in excellent condition, and it has taken on a deep reddish color. Bones of the other black bears are in good to fair condition but are more widely scattered. Some are buried in shallow clay; others are under water when the pool is high. Bones of the large bear are highly fragmented and are mixed with soil and rock rubble that has come in through the sealed entrance. Also found was the complete skull and jaws of an ermine (Mustela erminea) and bones of several bats. Sediments may be too thin near the pool and too disturbed near the sealed entrance to provide a stratigraphic relationship between the skeletons.

The two black bears represented by skulls are young adults with fully-erupted teeth, but some bone epiphyses are not fully fused. Five humeri measured (probably from three individuals) have lengths ranging from 28 to 33 cm, which spans the upper size range for modern black bears.

The identification of the large bear remains unresolved. Parts found thus far include a partial right maxilla with P4, an upper left canine, the distal end of a left humerus, the distal end of a left femur, the shaft of a left tibia, and a partial pelvis, all presumably from the same individual. The P4 measures 20.5 mm in length compared to 13.6 and 13.7 mm for the black bears. In size the large species closely matches the extinct giant short-faced bear (Arctodus simus) as reported by Merriam and Stock (1925), Kurten (1967), and Emslie and Czaplewski (1985). However, the distal humerus, though somewhat eroded, appears to lack the entepicondylar foramen diagnostic of Arctodus, suggesting that the large bear is some species of Ursus. The diastema is too short and P4 too wide for polar bear (Ursus maritimus), so what we may have is an exceptionally large grizzly bear (Ursus arctos). Since only black bears now inhabit Prince of Wales Island, the large bear is significant regardless of its identification.

Samples of the complete black bear and the large bear were removed for radiocarbon dating by accelerator mass spectrometry (AMS) to obtain an approximate minimum and maximum age for the deposit, respectively. Unexpectedly the black bear turned out to be older at 10,745+/-75 yr B.P. (AA-7793). We suspect that the other black bears will yield even older dates. The large bear dated at 9,760+/-75 yr B.P. (AA-7794). Thus the age of the deposit falls near the end of the Wisconsin glacial, and the two species of bears must have been early post-glacial inhabitants of Prince of Wales Island. Since El Capitan Cave is located in a deeply-eroded glacial valley, the bears provide a terminal date for substantial deglaciation.

During the 1991 field season we surveyed the location of the bear entrance and established voice contact between the cave and the surface. During the 1992 field season we plan to remove the large log and rocks that block this entrance and reopen it in order to make a complete excavation more practical. We believe that more material of the large species can be recovered from the deep fill that has fallen in from the surface, and we hope this additional material will allow us to make a full analysis of this enigmatic bear.

We thank Kevin Allred for taking us to the site, Julie Heaton for helping locate the bear entrance on the surface, Jim Baichtal and Cat Woods of Tongass National Forest for providing housing and food during our stay and for funding the radiocarbon dates, and to the University of South Dakota for providing partial travel funds.

References Cited

Emslie, S. D., and N. J. Czaplewski 1985 A New Record of Giant Short-faced Bear, Arctodus simus, from Western North America with a Re-evaluation of its Paleobiology. Natural History Museum of Los Angeles County, Contributions in Science 371:1-12.

Kurten, B. 1967 Pleistocene Bears of North America. 2. Genus Arctodus, Short-faced Bears. Acta Zoologica Fennica 117:1-60.

Merriam, J. C., and C. Stock 1925 Relationships and Structure of the Short-faced Bear, Arctotherium, from the Pleistocene of California. Carnegie Institution of Washington, Contributions to Paleontology 347:1-35.

Timothy H. Heaton: E-mail, Home page, Phone (605) 677-6122, FAX (605) 677-6121