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A New Occurrence of Paramylodon harlani from Power County, Idaho R. Jeff Castro 1, 2 and Kevin C. Bell 1, 3 Idaho Museum of Natural History, ISU Stop 8096, Pocatello, Idaho 83209 Idaho State University, Department of Anthropology, ISU Stop 8005, Pocatello, Idaho 83209 BYU Idaho, Department of Mechanical Engineering, 525 S. Center Austin Building, Rexburg, ID 83460 This work was supported by NSF Award 1156879 ABSTRACT The Idaho Museum of Natural History (IMNH) is entrusted with the conservation and storage of Idaho’s collection of fossilized faunal material. The vertebrate paleontology collections located within the IMNH contain the fossils of four extinct ground sloth species located within the boundaries of Idaho. Two species, harlani and chapadmalensis, belong to the genus Paramylodon; and two species, jeffersoni and leptostomus, belong to the genus Megalonyx. The recent accumulation of faunal material from excursions in Power County over the past year has been compared to the faunal material housed at the IMNH. Specimens of both giant ground sloths have been found from numerous sites in southeastern Idaho. Six fossilized faunal bones have been determined to be the remnants of Paramylodon harlani, and at least one of these fossils is that of a young sloth. Figure 1: Right humeri of giant ground sloth, A. M. jeffersoni (IMNH 71001/23034) B. Juvenile sloth (IMNH 2561/49966) C. P. harlani (IMNH 50001/2645). The most diagnostic specimen (IMNH 2561/49966) is a humerus from a juvenile sloth (Figure 1). This specimen was compared to the adult humeri of the two Pleistocene ground sloths in Idaho, Paramylodon and Megalonyx. The humerus of M. jeffersoni possesses a distinct feature on the medial portion called the entepicondylar bar. Even though our specimen is a juvenile this region is displayed and there is no entepicondylar bar so we have assigned it to Paramylodon harlani. Figure 2: Fifth metatarsal of giant ground sloth, A. Paramylodon harlani (IMNH 71003/26685) B. Minidoka Bison Site sloth (IMNH 2561/49967). Another distinct bone is the fifth metatarsal. Upon comparison, IMNH 2561/49967 can also be assigned to Paramylodon harlani (Figure 2). This element is designed specially to support the greater weight of P. harlani. This ground sloth walks on the lateral side of its foot whereas Megalonyx tends to be flat-footed. Other elements that have been collected from this site are the radius, cuboid, intermediate phalanx (Figure 3), and ungual phalanx (Figure 4). With these elements, size and articulation surfaces are the keys for identification. Comparison with material from the IMNH collection with both giant ground sloths suggests they are P. harlani. Figure 3: Intermediate phalanx of giant ground sloth, A. Paramylodon harlani (IMNH 50001/32609) B. Minidoka Bison Site sloth (IMNH 2561/49968). Figure 4: Ungual phalanx of giant ground sloth, A. Paramylodon harlani (IMNH 387/39488) B. Minidoka Bison Site sloth (IMNH 2561/49969). INTRODUCTION Unlike many species that came into North America across the Bering Land Bridge, giant ground sloths came from South America. The earliest dispersal was approximately 4.9 million years ago. Two genera of giant ground sloth made their way northward into the Pliocene and Pleistocene faunas of Idaho: Paramylodon and Megalonyx. In February of 2014, specimens were collected from a new site (Minidoka Bison Site IMNH 2561) in southeastern Idaho. This yielded six specimens that we have attributed to Paramylodon harlani. This ground sloth lived in an open grassland habitat with a diet of mainly grasses. It is larger than Megalonyx jeffersoni, the other giant ground sloth that is found in Idaho Pleistocene faunas. REFERENCES McDonald, H. Gregory. 1977. Osteology of Megalonyx, M.S. Thesis, University of Florida, 328 pp. ACKNOWLEDGEMENTS The authors would like to thank John Braastad and the U.S. Fish and Wildlife for providing access to this material. We would also like to thank Greg McDonald and Mary Thompson for their assistance in identification of this material.
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Page 1: REU Sloth Poster

A New Occurrence of Paramylodon harlani from Power County, Idaho R. Jeff Castro 1, 2 and Kevin C. Bell 1, 3

Idaho Museum of Natural History, ISU Stop 8096, Pocatello, Idaho 83209Idaho State University, Department of Anthropology, ISU Stop 8005, Pocatello, Idaho 83209

BYU Idaho, Department of Mechanical Engineering, 525 S. Center Austin Building, Rexburg, ID 83460

This work was supported by NSF Award 1156879

ABSTRACTThe Idaho Museum of Natural History (IMNH) is entrusted with the conservation and storage of Idaho’s collection of fossilized faunal material. The vertebrate paleontology collections located within the IMNH contain the fossils of four extinct ground sloth species located within the boundaries of Idaho. Two species, harlani and chapadmalensis, belong to the genus Paramylodon; and two species, jeffersoni and leptostomus, belong to the genus Megalonyx. The recent accumulation of faunal material from excursions in Power County over the past year has been compared to the faunal material housed at the IMNH. Specimens of both giant ground sloths have been found from numerous sites in southeastern Idaho. Six fossilized faunal bones have been determined to be the remnants of Paramylodon harlani, and at least one of these fossils is that of a young sloth.

Figure 1: Right humeri of giant ground sloth, A. M. jeffersoni (IMNH 71001/23034) B. Juvenile sloth (IMNH 2561/49966) C. P. harlani (IMNH 50001/2645).

The most diagnostic specimen (IMNH 2561/49966) is a humerus from a juvenile sloth (Figure 1). This specimen was compared to the adult humeri of the two Pleistocene ground sloths in Idaho, Paramylodon and Megalonyx. The humerus of M. jeffersoni possesses a distinct feature on the medial portion called the entepicondylar bar. Even though our specimen is a juvenile this region is displayed and there is no entepicondylar bar so we have assigned it to Paramylodon harlani.

Figure 2: Fifth metatarsal of giant ground sloth, A. Paramylodon harlani (IMNH 71003/26685) B. Minidoka Bison Site sloth (IMNH 2561/49967).

Another distinct bone is the fifth metatarsal. Upon comparison, IMNH 2561/49967 can also be assigned to Paramylodon harlani (Figure 2). This element is designed specially to support the greater weight of P. harlani. This ground sloth walks on the lateral side of its foot whereas Megalonyx tends to be flat-footed.

Other elements that have been collected from this site are the radius, cuboid, intermediate phalanx (Figure 3), and ungual phalanx (Figure 4). With these elements, size and articulation surfaces are the keys for identification. Comparison with material from the IMNH collection with both giant ground sloths suggests they are P. harlani.

Figure 3: Intermediate phalanx of giant ground sloth, A. Paramylodon harlani (IMNH 50001/32609) B. Minidoka Bison Site sloth (IMNH 2561/49968).

Figure 4: Ungual phalanx of giant ground sloth, A. Paramylodon harlani (IMNH 387/39488) B. Minidoka Bison Site sloth (IMNH 2561/49969).

INTRODUCTIONUnlike many species that came into North America across the Bering Land Bridge, giant ground sloths came from South America. The earliest dispersal was approximately 4.9 million years ago. Two genera of giant ground sloth made their way northward into the Pliocene and Pleistocene faunas of Idaho: Paramylodon and Megalonyx. In February of 2014, specimens were collected from a new site (Minidoka Bison Site IMNH 2561) in southeastern Idaho. This yielded six specimens that we have attributed to Paramylodon harlani. This ground sloth lived in an open grassland habitat with a diet of mainly grasses. It is larger than Megalonyx jeffersoni, the other giant ground sloth that is found in Idaho Pleistocene faunas.

REFERENCESMcDonald, H. Gregory. 1977. Osteology of Megalonyx, M.S. Thesis, University of Florida, 328 pp.

ACKNOWLEDGEMENTSThe authors would like to thank John Braastad and the U.S. Fish and Wildlife for providing access to this material. We would also like to thank Greg McDonald and Mary Thompson for their assistance in identification of this material.