I'aleoHios, Volume 14, Number 1, Pages 9-12, April 24, 1992 A Scimitar Cat (Homotherium serum) From the Late Pleistocene Merrell Locality, Southwestern Montana Robert G. Dundas Museum of Paleontology University of California Berkeley, CA 94720 INTRODUCTION For years local residents have reported finding fossil bones throughout the Centennial Valley of southwestern Montana. Yet, these fossil sites have been accorded little attention by professional paleontologists. The Merrell locality is one of the first late Pleistocene fossil assemblages to be studied in the region. The discovery of the scimitar cat, Homotherium serum, at the Merrell locality represents the first documented occurrence of the species in Montana. The Merrell site, located approximately 21km (13mi) east of Lima, Beaverhead County, Montana on the southwest shore of Lima Reservoir, lies at an elevation of 2012m (6600ft) (Fig. 1). The locality is on land administered by the Butte District, Bureau of Land Management (BLM). The site's map coordinates are NW1/4, NE1/4, NW1/4, Sec.5, T14S, R6W, Lima Dam Quadrangle (USGS 7.5' series topographic). HISTORY OF INVESTIGATIONS In the Fall of 1988 local residents discovered bone fragments on the shore of Lima Reservoir and large in situ limb bones in the adjacent cutbank exposure. One of the residents, Mr. Donald Merrell, after whom the site is named, reported the find to the BLM. The locality was subsequently examined by Mr. Gerald Clark, then Butte District, BLM archaeologist. With the aid of Mr. Merrell and other local residents, Mr. Clark combed the beach collecting bones and bone fragments as well as removing an in situ right mammoth tibia from the cutbank exposure. It was during this occasion that two specimens of Homotherium serum were recovered from the reservoir shore. A more thorough investigation of the locality followed during the summer of 1989 when Dr. Thomas Foor, of the University of Montana Department of Anthropology, accompanied by an archaeological field crew and various volunteers, surveyed the site and collected all exposed fossil material. Neither major excavation nor screening for micromaterial was attempted. All fossil material collected _Lima Dam Figure 1. Generalized map noting the location of the Merrell locality east of Lima, MT. from the Merrell locality is conserved in the University of Montana Museum of Paleontology vertebrate collections (UMV). LOCALITY DESCRIPTION The locality consists of "terrace sediments exposed in a cutbank 4m high by 180m wide along the reservoir shore. The sediments consist mainly of massive units of sandy-silts, silts and clays with a minor pebble-gravel component, although a thin gravel bed is traceable throughout the exposure. Disarticulated fossils occur within a zone .4m-2.5m below the terrace surface. A pure quartz sand lens and a gravel-boulder channel lag deposit occur on the west end of the terrace. Fossils are distributed throughout the channel lag deposit" (Dundas, 1990). Page 10 Homotherium serum I) u rid as SYSTEMATIC PALEONTOLOGY Class Mammalia Linnaeus, 1758 Order Carnivora Bowdich, 1821 Family Felidae Gray, 1821 Genus Homotherium Fabrini, 1890 Homotherium serum Cope, 1893 Figures 2, 3 Referred specimens: UMV10001, proximal left ulna; UMV10002, left metacarpal IV. Description: UMV10001, a proximal left ulna, possesses extensive damage to the olecranon process and is broken 2-3cm below the radial notch. Viewed from either the radial or medial sides, the trochlear notch is fairly open in outline (Fig. 2A, C). The anconeal process is not strongly developed (Fig. 2B). On the radial side of the trochlear notch, the proximal anterior border below the anconeal process is straight (Fig. 2B). There are two distinct facets on the radial notch for articulation with the radius (Fig. 2A). The distal portion of the medial side of the articulating surface of the trochlear notch, although widest posteriorly, is narrow and nearly the same width throughout its length (Fig. 2B). The coronoid process is not expressly prominent. UMVI0002, a left metacarpal IV, is complete with the exception of missing the distal epiphysis due to breakage. Examination of the proximal end (Fig. 3A) denotes the following features with respect to shape and outline. The lateral border of the surface articulating with the unciform curves into the posterior border. The posterior border is straight but angles anteriorly toward the medial border. The medial border is deeply notched near the middle. The anterior border possesses a slight indentation near the middle between the articulating surfaces for the unciform and metacarpal III. Viewed from the anterior side (Fig. 3B), the plane of the surface for the unciform and the plane of the surface for the metacarpal III are comparable; little deflection in the angle of the two planes is noted. The shaft is straight and sub-triangular in cross- section (Fig. 3B, C, D). Discussion: The characteristics cited above distinguish UMV10001 and UMV10002 from both Smilodon and Panthera leo atrox (Merriam and Stock, 1932). The following comparison is made with respect to the ulna. In Homotherium serum, as with Panthera leo atrox, the trochlear notch is more open in outline than in Smilodon. The anconeal process in both Panthera leo atrox and Smilodon are well developed in contrast to Homotherium serum. The proximal anterior border below the anconeal process on the radial side of the trochlear notch is curved in both Panthera leo atrox and Smilodon in difference to the straight border exhibited by Homotherium serum. The articular surface for the head of the radius forms one large facet in Panthera leo atrox and Smilodon whereas in Homotherium serum there are two smaller distinct articular facets. In contrast to Homotherium serum the distal portion of the medial side of the articulating surface of the trochlear notch, in both Panthera leo atrox and Smilodon, is widest medially and not the same width throughout its length. In Homotherium serum the coronoid process is significantly less prominent than in either Panthera leo atrox or Smilodon. The following comparison is made with respect to the metacarpal IV. In Homotherium serum, as with Smilodon, the lateral border of the surface articulating with the unciform curves into the posterior border. In Panthera leo atrox the lateral border is straight. In Homotherium serum the posterior border is straight, as in Smilodon, but it also angles anteriorly toward the medial border. In Panthera leo atrox the posterior border is notched near the middle. The medial border in Homotherium serum, as with Panthera leo atrox, is deeply notched near the middle in contrast to the unnotched medial border in Smilodon. The anterior border in Homotherium serum is more distinctly notched than in Smilodon but not as deeply notched as in Panthera leo atrox. In contrast to Smilodon, the planes of the surfaces for the unciform and metacarpal III are comparable in both Panthera leo atrox and Homotherium serum when viewed anteriorly. In Smilodon these two planes form distinct angles with one another. The shaft in both Panthera leo atrox and Smilodon is curved and round in cross-section in contrast to the straight shaft of sub-triangular cross-section in Homotherium serum. Both UMV10001 and UMV10002 were compared to Homotherium serum material from Friesenhahn Cave, Texas and found to be within the range of variation exhibited by those specimens. Based on comparisons with the Friesenhahn Cave specimens the partial ulna and metacarpal IV are inferred to represent an average-sized adult, possibly the same individual. Dundas Homotherium serum Page 11 B Figure 2. Homotherium serum, proximal left ulna, UMVlOOOl. A) radial view; B) anterior view; C) medial view. Illustration X .75 original size. Bar scale = 2 cm. B I'-' I D ¦iiii; !."•. i Figure 3. Homotherium serum, left metacarpal IV, UMV10002. A) proximal view; B) anterior view; C) medial view; D) lateral view. Illustration X .8 original size. Bar scale = 2 cm. Page 12 Homotherium serum 1) Hildas ASSOCIATED FAUNA In addition to the specimens of Homotherium serum, eight other mammal species and one bird comprise the Merrcll fauna. These include the following taxa: Ursus americanus (black bear), Castor canadensis (beaver), Ondatra zibcthicus (muskrat), Equus sp. (horse), Camelops cf. hesternus (Yesterday's camel), Antilocapridae (pronghorn antelope), Bison sp. (bison), Mamtnuthus cf. columbi (Columbian mammoth), and Anseriformes (waterfowl). AGE The presence of Bison and Ondatra zibethicus indicate a Rancholabrean age for the fauna (Kurten and Anderson, 1980). However, it is uncertain whether the terrace sediments, and thus the fossil material, were deposited contemporaneously, even though the appearance and preservation of the fossil specimens is similar throughout the locality. As noted above, specimens were recovered from a 2.1m zone within the main section of the terrace and also from a channel fill deposit on the west end of the terrace. Two bone samples, one from each of these areas, were submitted for radiocarbon dating analysis to Beta Analytic Inc., Coral Gables, Florida. "The bones were first physically cleaned and extraneous material removed. They were then crushed and put into dilute, cold acid. The acid was periodically renewed over the next days as the mineral portion of the bones dissolved. After that, the collagen fractions remaining were washed in deionized water. Good collagen was obtained. This was combusted in an enclosed system. The following benzene syntheses and countings went normally" (Tamers, personal communication, 1990). Beta-26205, a mammoth metatarsal collected from the channel fill deposit, yielded a date of 25,030 +/- 510 BP. Beta-36206, a mammoth fibula recovered from the main section of the terrace, "showed an activity that was statistically indistinguishable from the background" (Tamers, personal communication, 1990). Therefore Beta-36206 could only be assigned a minimum age of greater than 33,990 BP. Based on this evidence the channel fill may be younger than the remainder of the terrace. However, further analysis is necessary to resolve the question of contemporaneity. SUMMARY This discovery of Homotherium serum specimens represents the first record of the rare Pleistocene felid in Montana. Furthermore, the cat and associated fauna provide valuable biogeographic information regarding the late Pleistocene biota of Montana, about which little is known (Kurten and Anderson, 1980; Graham, Wilson and Graham, 1987; Harris, 1985). Owing to the significance of the Mcrrell site and its potential to yield additional specimens and new taxa, the locality warrants further investigation, involving major excavation in a multidisciplinary format. The results of such a study could greatly enhance our knowledge of this region during the late Pleistocene. ACKNOWLEDGEMENTS Tom Foor brought this fauna to my attention. David Polly and Elaine Anderson aided in identification of specimens. Both Elaine Anderson and Tom Foor provided valuable suggestions in their reviews of the manuscript. Melissa Winans of the Texas Memorial Museum kindly provided a loan of comparative specimens. The personal communications of Murry Tamers (co-director Beta Analytic, Inc.) cited above are excerpts from the radiocarbon dating report to the BLM. I thank Jennifer Hogler for providing editorial comments. Finally I express my great appreciation to Laura Cunningham for providing the specimen illustrations. REFERENCES Dundas, R.G. 1990. The Mcrrell Locality: A Late Pleistocene Fauna From Southwestern Montana. Geological Society of America Abstracts with Programs, 22(6):8-9. Graham, M.A., M.C. Wilson, and R.W. Graham. 1987. Paleoenvironments and Mammalian Faunas of Montana, Southern Alberta, and Southern Saskatchewan, p.410-459. in Late Quaternary Mammalian Biogeography and Environments of the Great Plains and Prairies (R. W. Craham, H. A. Scmken, Jr. and M. A. Graham, eds.) Illinois State Museum Scientific Papers, v.22, 491p. Harris, A.H. 1985. Late Pleistocene Vertebrate Palcoecology of the West. University of Texas Press, Austin. 293p. Kurten B. and E. Anderson. 1980. Pleistocene Mammals of North America. Columbia University Press, 442p. Merriam, J.C. and C. Stock. 1932. The Felidae of Rancho La Brca. Carnegie Institution of Washington Publication 422, 232p.