A NEW SPARASSODONTA (METATHERIA, MAMMALIA) FROM THE MIOCENE OF LA GUAJIRA, COLOMBIA

SUAREZ GOMEZ, C.; FORASIEPI, A.M.; GOIN, F.J.; JARAMILLO, C

Mendoza

Congreso; 4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS; 2014

CCT-Mendoza, CONICET

In 2009 the Smithsonian Tropical Research Institute initiated a series of field trips to prospect deposits in the northernmost areas of the La Guajira Peninsula in northern Colombia. As a result of these efforts, hundreds of fossil vertebrates have been collected, including reptiles, mammals, fishes, and birds. Here, we report the first record of a Sparassodonta (Metatheria, Mammalia) from the Castilletes Formation in the La Guajira Peninsula. Preliminary geochronological and stratigraphical data indicate that the age of the Castilletes Formation is ~ 17.5 to 14.5 My (early to middle Miocene). The Castilletes Formation was deposited in a very shallow marine environment intermixed with coastal plain environments. It is characterized by marly limestones, clays, calcareous and noncalcareous sandstones, and conglomerates. The specimen is represented by a left maxilla with the M1?M4 series and fragments of the lacrimal and jugal bones. The presence of four molars is indicative of its belonging to the Metatheria. Unlike most extinct and extant metatherians except borhyaenoid sparassodonts, it is relatively large-sized. At least one feature of its molars is diagnostic of Sparassodonta: the orientation of the preparacrista, which is anterobucally placed regarding the long axis of the tooth. Some characters shared by Hathliacynidae and Borhyaenoidea sparassodonts are also present in the specimen from La Guajira: 1) marked increase in molar size from M1 to M3; 2) fused metacone and paracone bases; 3) very low protocone. At least two characters are not shared with most other sparassodonts, probably representing autapomorphies for this taxon: on one side, presence of two lacrimal foramina instead of one; on the other, the jugal-maxillary suture shows a unique pattern, running dorsally sub-parallel to the frontal plane of the skull, centrally being subvertically displayed, while ventrally running sub-horizontally again. Preliminary comparisons suggest that the La Guajira specimen could be referred to the genus Lycopsis, a basal borhyaenoid not referable to the Borhyaenidae, the Proborhyaenidae or the Thylacosmilidae. Actually, the unusual jugal-maxillary suture of the La Guajira specimen is also present in Lycopsis longirostrus, from the middle Miocene of Colombia. Research in the La Guajira Peninsula offers the opportunity of increasing our knowledge about neotropical Neogene faunas and allows us to recognize aspects of the South American biota prior to the Great American Biotic Interchange (GABI). The specimen reported here constitutes the northernmost record of an extinct metatherian mammal in South America.