New specimens of the Late Cretaceous mammal Coloniatherium cilinskii (Mammalia, Meridolestida): dental anatomy, reconstruction of the dental series, and relationships of South American meridolestids

GUILLERMO ROUGIER; AGUSTIN MARTINELLI; M. SCHÖNING

Los Angeles

Congreso; 73th Meeting of the Society of Vertebrate Paleontology; 2013

Coloniatherium cilinskii, from the Late Cretaceous La Colonia Formation, Chubut province, Patagonia, Argentina is known by a collection of more than a hundred specimens. Most of the fossils come from the ?El Uruguayo? locality, but a few other specimens are known from other localities of the same unit. The bulk of the specimens are isolated teeth, but a few jaws, petrosals and postcranial elements can be referred to this taxon. Comparing the jaws in the collection and isolated dental elements of Coloniatherium, with the closely related meridiolestids Mesungulatum and Peligrotherium we have reconstructed the whole postcanine dental dental series. The dental formula is interpreted as: I?/?C1/1P3/3M3/3, but there is no evidence of dental replacement in the collection and alternative interpretations are possible. The largest tooth of the series is the multi-rooted, fully molarized last premolar (P/p3). The molar series diminishes progressively in size from the M/m1to the M/m3, with a noticeably reduced M3. The upper dentition is dominated by a central stylocone and a prominent lingual paracone; while in the lowers the protoconid, paraconid and metaconid are the dominant cusps. The M2 and M3 reduce the metastylar portion of the crown suggesting a strongly curved maxilla; also suggested by the strongly asymmetrical P2. In the lower dentition only the m3 reduces its distal cingulum. In Coloniathierium teeth are comparatively large and show a pronounced bunodont dentition, that is further complemented by large and elaborated cingula, building on a more primitive morphology like that present in the Late Cretaceous Mesungulatum. Peligrotherium from the Paleocene of Patagonia is even larger and further develops these traits with robust blunt cusps and cingula incorporated into the occlusal surface. Coloniatherium, Mesungulatum, Peligrotherium, and the more enigmatic Reigitherium form a monophyletic group of bunodont/herviborous meridiolestids that is first recorded in the Coniacian of Patagonia and represents a distinct clade of ungulate-like mammals that prospers during the Late Cretaceous surviving the K/T extinction event.