congresos y reuniones científicas
A NEW AND PECULIAR MORPHOTYPE OF SOUTH AMERICAN NATIVE UNGULATE
LÓPEZ, G.M.; BOND, M.
Congreso; 4th International Paleontological Congress; 2014
IANIGLA CCT CONICET
The highly endemic terrestrial fauna and flora of South America is mostly a result of the geographical isolation of this continent for much of the last 65 my. In this context the herbivorous mammals were mainly represented by native ungulates (five orders of extinct mammals) and xenarthrans. The South American native ungulates developed different morphotypes many of which are convergent with those present in phylogenetically unrelated groups of mammals. Notoungulates, the most diverse group, include a wide variety of animals: rodent-like ones, rhino and hippo-like ones, and even some ?chalicotherian-like? forms. The also varied litopterns include some ?camel-like? taxa and functionally monodactyl ?horse-like? ones. Astrapotheres are medium to very large mammals with tusks, some of them probably with a proboscis and perhaps semi-aquatic habits. Other ungulates such as pyrotheres are large-sized, elephant-like mammals with tusks, and xenungulates are large and comparable to tapirs. Here we report a new notoungulate recovered from the Divisadero Largo Formation (Mendoza province, middle Eocene?) which represents a novel and amazing morphotype so far unknown for this order. The specimen (MLP 87-II-20-40) consits of the anterior half of the skull (still unprepared) with both mandibles in occlusion that preserve two lower incisors, C-P4/c-p4 series of both sides, one broken M1 and one isolated m1. The most remarkable features observed in this skull are: (1) a strong shortening of the rostral region; (2) large orbits tending toward frontalization; (3) a relatively large cranial height; (4) robust mandibular rami with a long and fully fused symphysis. These peculiar features are reminiscent of a small primate, although according to an analysis of its anterior cranial proportions it would be ecologically comparable to some arboreal marsupials (e.g. phalangerids). Of what can be observed, the occlusal morphology of the molariforms is reminiscent of that of the putative oldfieldthomasiids of Divisadero Largo. Consequently, this new taxon is referred to the notoungulates and tentatively to the Oldfieldthomasiidae s.l. This taxon, probably arboreal, represents a new morphotype, so far unknown of native ungulates. Up to now, in the South American Paleogene, the mammals of presumed arboreal habits were restricted to the marsupials and especially to Groeberia, a form that has been compared favorably to some primates, and which until now is only known from the Divisadero Largo Formation. This new and peculiar small notoungulate illustrates the incomplete knowledge about the history of the Paleogene mammals outside Patagonia.