New mammal faunal data from Cerdas, Bolivia, a low latitude Neotropical site that chronicles the end of the middle Miocene climatic optimum in South America.

CROFT, D.; ANAYA, F.; BRANDONI, D.; CARLINI A. A.; CATENA, A.; CIANCIO MR; ENGELMAN, R.K.

Dallas

Congreso; 75th Annual Meeting of Society of Vertebrate Paleontology: Dallas; 2015

SVP

Many groups of South American mammals apparently underwent northward rangecontractions following the Middle Miocene Climatic Optimum (MMCO) includingprimates, porcupines (Erethizontidae), palaeothentid marsupials (Paucituberculata), andastrapotheres (a native ungulate group). Determining the precise timing of these shifts hasbeen hampered by a scarcity of (1) early middle Miocene (Langhian) sites from tropicallatitudes, and (2) late middle Miocene (Serravallian) sites from the Southern Cone.Cerdas, Bolivia (ca. 21° S) is one of only three sites of Langhian age that documents􀀱􀁈􀁒􀁗􀁕􀁒􀁓􀁌􀁆􀁄􀁏􀀃 􀁐􀁄􀁐􀁐􀁄􀁏􀀃 􀁇􀁌􀁖􀁗􀁕􀁌􀁅􀁘􀁗􀁌􀁒􀁑􀁖􀀃 􀁑􀁈􀁄􀁕􀀃 􀁗􀁋􀁈􀀃 􀁈􀁑􀁇􀀃 􀁒􀁉􀀃 􀁗􀁋􀁈􀀃 􀀰􀀰􀀦􀀲􀀑􀀃 􀀲􀁘􀁕􀀃 􀁗􀁈􀁄􀁐􀂶􀁖􀀃 􀁕􀁈􀁆􀁈􀁑􀁗􀀃fieldwork at the site recovered specimens from low in section that represent three groupspreviously undocumented at the site: a meat-eating metatherian (Sparassodonta), aproboscis-bearing ungulate (Astrapotheria), and a megatheriid sloth. Paleosols from thisportion of the section are weakly to moderately developed, have compound andcomposite profiles, and preserve several types of ichnofossils including lined and unlinedburrows, rhizohaloes, and rhizotubules. The sparassodont remains include thebasicranium and most of the mandible of a species comparable in size to the hathliacynidCladosictis patagonica from the late early Miocene of Santa Cruz, Argentina. However,several features suggest borhyaenoid rather than hathliacynid affinities including ajugular fossa, a non-pneumatized squamosal, and the lack of a hypoconulid on m4. Theastrapothere remains consist of many tooth fragments with an unusual combination offeatures not typical of late early Miocene Astrapotherium magnum nor late middleMiocene members of the Uruguaytheriinae; these include relatively smooth premolarectolophs and very large upper molar cingulae. A partial megatheriid sloth dentarypreserving the last molariform likely pertains to a Megatheriinae, which suggests that thissubfamily could have originated in lower latitudes and later spread into Patagonia. Anewly discovered specimen of a horned armadillo (Peltephilidae) from Cerdas includes apartial articulated carapace that supports its identification as a new species. Theosteoderms of this specimen are characterized by a surface texture of small tubercles andpits, a central longitudinal elevation (acute in cross section) surrounded by a deep, widegroove extending over most of the osteoderm, and depressions along the border arrangedin a unique, radial pattern. Ongoing studies at Cerdas aim to place these mammals in arefined paleoenvironmental context.