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Protypotherium Locomotion:

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Material and Methods
Appendicular Morphology
Multivariate Analyses


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For most of the Tertiary, South America was geographically and biotically isolated from other major land masses – a period of "splendid isolation" for the mammals of that continent (Simpson 1980). A diversity of endemic clades flourished during this interval and representatives of many of these still characterize South American faunas today (e.g., armadillos, sloths, opossums, marmosets, capybaras, chinchillas; Patterson and Pascual 1968; Flynn and Wyss 1998). Some of these clades left no living representatives, most notably the various groups of hoofed plant eaters that likely filled niches presently occupied in South America by deer, camels, tapirs, peccaries, and other groups (Bond 1986; Bond et al. 1995; Croft 1999). Among these extinct ungulate clades, the notoungulates ('southern ungulates') were the most speciose and morphologically diverse; the group reached its zenith in the Oligo-Miocene and was still represented by several lineages in the Pleistocene (Cifelli 1985; Marshall and Cifelli 1990; Croft 1999).

One of the most successful notoungulate clades in terms of temporal range, geographic range, and abundance was the Interatheriidae (suborder Typotheria). Although this group did not persist past the Pliocene, interatheriids are the longest ranging notoungulate family and are common constituents of most late Eocene to middle Miocene faunas (e.g., Simpson 1967; Tauber 1996; Reguero et al. 2003; Hitz et al. 2006; Croft 2007; see Croft et al. 2004 and Croft and Anaya 2006 for exceptions to this pattern). Like most typotheres, interatheriids were small to medium in size (body mass < 15 kg) and all Miocene species were characterized by ever-growing/rootless (hypselodont) molars. Like nearly all notoungulates, they lacked any form of cranial appendages. They have traditionally been regarded as cursorial (i.e., adapted for running and/or moving efficiently over long distances) and as grazers (i.e., consuming mostly grass and/or other low, open habitat vegetation) (Sinclair 1909; Scott 1932; Bond 1986; Tauber 1996). The idea that interatheriids were grazers has recently been called into question based on new data from enamel microwear (Townsend and Croft 2005, in press). The locomotor adaptations of the group have yet to be rigorously investigated; several studies have included descriptions of interatheriid postcranial elements (e.g., Sinclair 1909; Stirton 1953; Tauber 1996; Shockey and Anaya, in press; Hitz et al., in press), or included interatheriids in investigations of other notoungulates (Elissamburu 2004), but none of these has investigated potential locomotor habits relative to extant mammals.

This study focuses on the postcranial morphology of a common interatheriid, Protypotherium (Figure 1). The genus occurs in various Miocene faunas in Argentina (Bordas 1939; Bondesio et al. 1980a, b; Barrio et al. 1989; Kramarz et al. 2005), Chile (Flynn et al. 2002, in press; Wyss et al. 2003), and possibly Venezuela (Linares 2004) but is best known from the coastal deposits of the Santa Cruz Formation of Patagonia, Argentina (approx. 50-51.5° S, Santa Cruz Province). These exceptionally rich deposits are late early Miocene in age (ca. 16-17.5 Ma; Flynn and Swisher 1995) and have produced the largest and best-preserved sample of Tertiary mammals in South America, including many specimens of Protypotherium (Simpson 1940; Marshall 1976; Marshall et al. 1986; Tauber 1997). Charles Darwin was among the first to comment on Santa Cruz mammals (based on fossils found by Captain B.J. Sulivan; Brinkman 2003), and important collections of Santa Cruz fossils were later made by Carlos Ameghino, John Bell Hatcher, and Elmer Riggs (Marshall 1976; Simpson 1984). Fossils collected by Hatcher (now curated at Yale Peabody Museum of Natural History) were described by W.B. Scott (e.g., Scott 1903a, 1903b) and J.W. Sinclair (e.g., Sinclair 1909) in the spectacularly illustrated Reports of the Princeton University Expedition to Patagonia, 1896-1899. Many of the mammals from the Santa Cruz Formation are represented by skulls and/or partial skeletons (Scott 1932), and many of these are the most completely known representatives of extinct families and/or subfamilies. Owing to these exceptional fossils, Santa Cruz Formation mammals are highly amenable to paleoecological investigations of diet and locomotion, such as those undertaken here (e.g., Tauber 1991; Vizcaíno 1994; Vizcaíno and Fariña 1997; Argot 2003; Vizcaíno et al. 2006).


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Protypotherium Locomotion
Plain-Language & Multilingual  Abstracts | Abstract | Introduction | Materials and Methods
Appendicular Morphology | Multivariate Analyses | Discussion | Conclusions
Acknowledgements | References | Appendix

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