LATE PLEISTOCENE AIRPORT LANE FOSSIL SITE, LA GRANDE, NE OREGON.

Short-faced Bear (Arctodus simus simus)

Abstract

Measurements of the proximal end of the left femur of a short-faced bear from the Airport Lane site suggest that the femur is from a male or very large giant short-faced bear (Arctodus simus simus) similar to those of the Potter Creek Cave fauna in California, the site where this species was first identified in 1879.  The Airport Lane short-faced bear weighed 300-400 kg.

Introduction

The proximal end of the left femur of a short-faced bear was discovered along with mammoth, giant bison, ground squirrel and other fossils at the late Pleistocene Airport Lane fossil site in January 2010 (Figure 1).  According to Kurtén (1967) Arctodus simus was the largest carnivore in the Pleistocene fauna of North America.  It may have preyed on bison, deer, horses, and ground sloths and also eaten shellfish.  This view has been questioned by researchers who postulate that Arctodus was predominantly a scavenger (Matheus, 1995; Sorkin, 2006; Figueirido and others, 2010).  Large individuals may have weighed as much as 700 kg, and some may have reached more than a metric ton (Christiansen, 1999).

Figure 1. Proximal end of left femur of a short-faced bear (Arctodus simus simus) found at the Airport Lane Site.  A. Proximal view.  B. Anterior view.  C. Superior view.

                  The first short-faced bear fossil discovered in North America was the lesser short-faced bear Arctodus pristinus.  It was a relatively lightly-built form with small teeth, slender limb bones, and a comparatively long face described by Leidy (1854) from the Ashley River Beds of North Carolina.  Cope (1879) described a larger, more powerful animal with a shorter face, greater crowding of the anterior premolars, cheek teeth that are much larger in relation to the jaws, and a deeper and heavier mandible from the Potter Creek Cave fauna of Shasta County, California and introduced the name Arcotherium for North American short-faced bears.  Kurtén (1967) argued that the name Arctodus took precedence and renamed the greater short-faced bear Arctodus simus (Cope 1879).  Richards and Turnbull (1995) recognized two subspecies of giant short-faced bears:  Arctodus simus simus (Cope 1879) and the larger Arctodus simus yukonensis (Lambe 1911).

                  Giant short-faced bears ranged from the middle Irvingtonian through the Rancholabrean North American Land Mammal Ages and became extinct near the end of the Pleistocene (Kurtén, 1967; Richards and others, 1996).  The oldest acceptable radiocarbon date for a giant short-faced bear in the lower 48 states is 34,080 ± 480 RCYBP from Island Ford Cave, Virginia, and the youngest is a 9630 ± 60 RCYBP date from Bonner Springs, Kansas, although an additional date of 10,921 ± 50 BP on the same specimen indicates a possible precision problem with this age (Schubert, 2010).  Fiedel (2010) suggested that  Arctodus  went extinct between 11,610 ± 90 to 10,870 ± 75 RCYBP.

                  Arctodus simus yukonensis occurred in western North America during the Irvingtonian and by Rancholabrean times had differentiated into measurably smaller individuals (Arctodus simus simus) south of the region covered by Wisconsinan ice, but a population of larger individuals (Arctodus simus yukonensis) persisted in northern latitudes and individuals of some southern populations may have retained the large size of their ancestors.  Both subspecies eventually moved east of the Mississippi river, but did not range into the extreme southeast, which had been occupied by Arctodus pristinus since the Irvingtonian.

                  The Airport Lane site is the third Oregon locality to yield short-faced bear fossils.  The first Arctodus fossils discovered in Oregon were a right cuneiform, a worn metapodial, and a proximal phalanx from the late Pleistocene Fossil Lake fauna.  Based on the close similarity of the cuneiform to one of from Potter Creek Cave, California, and the similarity of its shape to an Arctotherium cuneiform from Rock Creek, Texas.  Elftman (1931) assigned the Fossil Lake bear to Arctotherium sp.  Kurtén (1967) reassigned the Fossil Lake bear to Arctodus simus and Richards and others (196) list its age as Rancholabrean.  The second Oregon short-faced bear fossil s to be discovered were the tracks of a short-faced bear found at the late Pleistocene Drews Gap locale in Lake County , Oregon.  Packard and Allison (1980) made casts of the tracks and concluded that they were made by giant bears with feet similar to those from the La Brea tar pits in Los Angeles, Calfornia.

The Airport Lane Arctodus

The proximal end of the left femur of the short-faced bear found at the Airport Lane site is slender like most bear femurs.  It has an overall shape that is very similar to the short-faced bear femur illustrated by Richards and Turnbull (1995; Figure 14 A,B,C).

Figure 2. Terminology used to describe the Airport Lane short-faced bear femur.  Bp: Greatest breadth of the proximal end of the femur.  SD: Smallest breadth of the diaphysis (least transverse width).  HD: Maximum head (caput) diameter.

                  Measurements of the short-faced bear femur from the Airport Lane site were made using the guidelines of von den Driesch (1976) with the exception that the maximum diameter of the caput was measured because the caput is partially missing, making it impossible to measure the greatest depth of the caput femoris in an anteroposterior direction (Figure 2).  The overall length of the Airport Lane femur is 147.8 mm from the proximal end of the caput to the broken distal end of the diaphysis and the greatest breadth of the posterior end is 128.9 mm.  The maximum caput diameter is 66.5 mm.  The capitular epiphysis is present.  The greater trochanter is mostly intact and the trochanter epiphysis is fused with the diaphysis.  The smallest breadth of the diaphysis on the broken distal end of the femur is 56.8 mm

                  The presence of the capitular epiphysis and the fused trochanter epiphysis suggest that the Airport Lane Arctodus was a mature individual.  The length of the proximal end of the femur and the maximum caput diameter of the femur both fall in the range of the femurs of Arctodus simus simus found at the Rancholabrean Potter Creek Cave site in California.  The Airport Lane Arctodus femur is slightly larger than the giant short-faced bears from Rancho La Brea and much smaller than those of the larger giant short-faced bear Arctodus simus yukonensis (Table 1).  These measurements suggest that the Airport Lane short-faced bear can be classified as:

                                                      Class                          Mammalia

                                                      Order                        Carnivora

                                                      Family                      Ursidae

                                                      Genus                       Arctodus Leidy 1854

                                                      Species                                    Arctodus simus (Cope 1879)

                                                      Subspecies           Arctodus simus simus (Cope 1879)

Table 1.  Measurements of Arctodus Femurs

                  The Airport Lane femur measurements fall in the upper part of the range of the short-faced bear femurs from the Potter Creek Cave fauna.  This may indicate that the Airport Lane short-faced bear is a male.  Since the Potter Creek Cave short-faced bears are predominantly females (Kurtén, 1967), it is possible that the Airport Lane short-faced bear femur is from a large female.

                  Kurtén (1967) noted that the body weight of bears is proportional to the cross-sectional area of the femoral diaphysis and used this to estimate that male Arctodus simus simus bears weighed ~375-400 kg and the weights of females of this subspecies ranged from ~250-300 kg.  This suggests that the weight of the Airport Lane Arctodus was in the range of 300-400 kg.

 Conclusions

 The femur found at the Airport Lane site comes from a mature short-faced bear that was similar to the largest of the short-faced bears of the subspecies Arctodus simus simus from the Potter Creek Cave site in California and smaller than the giant short-faced bear Arctodus simus yukonensis.  The Airport Lane short-faced bear was either a male or a very large female that weighed 300-400 kg.

Acknowledgments

 We are grateful to Greg McDonald for identifying the bear femur.  Blaine Schubert also helped us identify the fossils.

References Cited

Agenbroad, L.D., and Mead, J.I., 1986, large carnivores from the Hot Springs mammoth site, South Dakota: National Geographic Research, v. 2, p. 508-516.

Cope, E.D., 1879, The cave bear of California: American Naturalist, v. 13, p. 791.

Elftman, H.O., 1931, Pleistocene mammals of Fossil Lake, Oregon: American Museum Novitates no. 481, 21 p.

Fiedel, S., 2009, Sudden deaths: The chronology of terminal Pleistocene megafaunal extinction, in Haynes, G., ed., American megafaunal extinction at the end of the Pleistocene: New York, Springer, p. 21-37.

Figueirido, B., Perez-Claros, J.A., Torregrosa. V., Martin-Serra, A., and Palmqvist, P., 2010, Demythologizing Arctodus simus, the 'short-faced' long-legged and predaceous bear that never was: Journal of Vertebrate Paleontology, v. 30, no. 1, p. 262-275.

Harris, A.H., 1987, Reconstruction of mid-Wisconsin environments in southern New Mexico: National Geographic Research, v. 3, p. 142-145.

Kurtén, B., 1967, Pleistocene bears of North America. 2. Genus Arctodus, short-faced bears: Acta Zoologica Fennica 117, 60 p.

Lambe, L.M., 1911, On Arctotherium from the Pleistocene of Yukon: Ottawa naturalist, v. 25, p. 21-26.

Leidy, J., 1854, (Remarks on Sus americanus or Harlanus americanus, and on other extant mammal): Proceedings of the Philadelphia Academy of Sciences, v. 7, p. 89-90.

Matheus, P.E., 1995, Diet and co-ecology of Pleistocene short-faced bears and brown bears in Eastern Beringia: Quaternary Research, v. 44, p. 447-453.

Merriam, J.C., and Stock, C., 1925, Relationships and structure of the short-faced bear, Arctotherium, from the Pleistocene of California: California Institute of Washington Publication 347, p. 1-35.

Packard, E.L., and Allison, I.S., 1980, Fossil bear tracks in Lake County, Oregon:  Oregon Geology, v. 42, no. 4, p. 71-72.

Richards, R.L., and Turnbull, W.D., 1995, Giant short-faced bear (Arctodus simus yukonensis) remains from Fulton County, northern Indiana: Fieldiana, Geology, new series, no. 30, p. 1-34.

Richards, R.L., Churcher, C.S., and Turnbull, W.D., 1996, Distribution and size variation in North American short-faced bears, Arctodus simus: in Stewart, K.M., and Seymour, K.L., eds., Palaeoecology and palaeoenvironment of Late Cenozoic mammals, Tribute to the career of C.S. (Rufus) Churcher: Toronto, University of Toronto Press, p. 191-246.

Schubert, B.W., 2010, Late Quaternary chronology and extinction of North American giant short-faced bears (Arctodus simum): Quaternary International, v. 217, Issues 1-2, p. 188-194.

Sorkin, b., 2006, Ecomorphology of the giant short-faced bears Agriotherium and Arctodus: Historical biology, v. 18, no. 1, p. 1-20.

von den Driesch, A., 1976, A guide to the measurement of animal bones from archaeological sites: Peabody Museum Bulletin 1, 137 p.