Paleoecology and ecomorphology of the giant short-faced bear in Eastern Beringia Item Type Thesis Authors Matheus, Paul Edward Download date 30/09/2021 10:40:05 Link to Item http://hdl.handle.net/11122/9491 \ t INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be * from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. 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PALEOECOLOGY AND ECOMORPHOLOGY OF THE GIANT SHORT-FACED BEAR rN EASTERN BERINGIA A THESIS Presented to the Faculty o f the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Paul Edward Matheus, B.A. Fairbanks, Alaska December 1997 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 9816411 UMI Microform 9816411 Copyright 1998, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALEOECOLOGY AND ECOMORPHOLOGY OF THE GIANT SHORT-FACED BEAR IN EASTERN BERINGIA By Paul Edward Matheus RECOMMENDED: Department Head, Biology and Wildlife APPROVED: Dean, College of Science, Engineering and Mathematics Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT The short-faced bear {Arctodus simus) was a widespread Tremarctine bear indigenous to North America until its extinction around 11.500 BP. Arctodus inhabited Pleistocene ice-free refugia in Eastern Beringia (the northwestern limit of its range) until at least 20.000 BP. Because of its gracile. long-legged build and extremely large size, most paleontologists believe this bear was a high-speed pursuit predator which had preyed on the largest herbivores of Pleistocene North America. Alternatively, energetic arguments have been used to suggest that Arctodus was too large to be carnivorous and evolved its large size within an herbivorous or omnivorous niche. To test these competing hypotheses. I reconstructed aspects of Arctodus' trophic position and paleodiet by analyzing stable isotope ratios (5 nC and 6 15N) in bone collagen extracted from east Beringian fossils. Other bears and carnivores from Beringia were analyzed to help interpret the results. Isotopes reveal that Arctodus was highly carnivorous, it fed on herbivores w hich consumed C3 vegetation, and it did not eat salmon. The herbivore/omnivore hypothesis is thus rejected. Predatory hypotheses predict that we should find certain morphological features in a predatory bear which would enhance one or more of the following skills: top running speed, acceleration, or maneuverability’ at high speeds. 1 re-analyzed the postcranial morphology of Arctodus and used data on running speed and bone strength in other large mammals to show that a bear the size of Arctodus with long, gracile limbs would not have been able to endure the extreme dy namic forces incurred during predatory activities. Instead. Arctodus' morphology and body size indicate it had evolved to maximize locomotor efficiency using a pacing gait. I suggest that Arctodus evolved as a specialized scavenger adapted to cover an extremely large home range in order to seek out. procure, and defend large-mammal carcasses from other carnivores. By modeling herbivore populations and their mortality. I show that enough carcass biomass was being produced in Pleistocene Beringia to make this scavenging niche energetically feasible. The model helps show thatArctodus' extinction probably is best tied to a reduction of year-round carcasses on the landscape, a condition which arose in the Holocenc when the herbivore fauna became less diverse and began to experience more seasonal mortality. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IV EXTENDED ABSTRACT The giant short-faced bear {Arctodus simus) was a widespread Tremarctine (New World) bear indigenous to North America until its extinction around 11,500 BP. Arctodus inhabited Pleistocene ice- free refugia in Eastern Beringia (the northwestern limit of its range) until at least 20.000 BP. Arctodus was the largest bear and perhaps the largest species of Carnivora that ever lived, yet it was characterized by a gracile post-cranial morphology and it was relatively long-legged. Most ecological models reconstruct this bear as a high-speed cursorial pursuit predator w hich preyed on a the largest herbivores of Pleistocene North America. However, it also has been argued on energetic grounds that this bear was too large to be carnivorous and evolved its large size within an herbivorous/omnivorous niche. Within both models, the immigration of brown bears into North America during the late Pleistocene has been invoked as a possible cause for the extinction of Arctodus. I extracted fossil bone collagen from east Beringian short-faced bears, brown bears, and other carnivores for stable isotope analysis (5 13C and 6 I5N) in order to test competing dietary models and the competition hypothesis. Results reveal that Arctodus was highly carnivorous, that its diet was completely terrestrial (i.e.. no salmon), and that it fed on herbivores which consumed C3 vegetation. The herbivore/omnivore foraging model is thus rejected. Stable isotope data from Pleistocene and modem brown bears reveal that Pleistocene brown bears from non-coastal regions of east Beringia w ere omnivores that relied on terrestrial C3 vegetation, limited amounts of terrestrial meat, and varying amounts of anadromous salmon running up the Yukon River drainage system (except for bears from the Yukon Territory, which show no signs of salmon eating). Isotopically. this Pleistocene population of inland brown bears most closely resembles modem populations from coastal Alaska that feed on salmon to varying degrees. In contrast, modem inland bears show no isotopic indication of salmon use. Because of the disparate resource base of Pleistocene brown bears and short-faced bears, and the clear physical dominance of Arctodus. the competition hypothesis is rejected and it is unlikely that brown bears played any role in Arctodus' extinction. Given the knowledge that Arctodus was carnivorous. I re-examined its postcranial morphology and locomotor abilities in order to test predictions of the predatory model. Within this model there are two sub-hypotheses that can be constructed based on the types of prey which w ere available to Arctodus: 1) Arctodus preyed on the largest and slowest megafaunal species, or 2) Arctodus preyed on faster, moderate­ sized megafaunal species. The first hypothesis predicts a large body and strong, robust build in Arctodus and must be rejected because of Arctodus' gracile postcranial morphology The second hypothesis predicts that we should find certain morphological features in Arctodus which would enhance one or more of the following skills: top running speed, ability to accelerate, or ability to maneuver at high speeds Data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V collected on running speed and bone strength in other large mammals show that a bear the size of Arctodus with long gracile limbs would not have been able to endure the extreme dynamic forces incurred at high speeds, during rapid acceleration, or during sharp turns, making it unsuitable as a predator. Therefore, while the first predatory sub-hypothesis accurately predicts Arctodus' large size, it does not predict Arctodus' gracile build. The second predatory sub-hypothesis is consistent with Arctodus' gracile build but cannot explain its large size. On the other hand, numerous aspects of Arctodus' morphology and body size indicate that it was an incipient cursor that had not evolved for speed, but rather for increased locomotor efficiency during prolonged travel. It swung its legs in a more parasagital plane