Evolutionary pattern of Eumysops (Rodentia, Echimyidae) from the Pliocene of southern South America

OLIVARES, A.I.; VERZI, D.H.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

International Palaeontologica Association

Echimyidae is the most diverse family of hystricomorph rodents, which is currently distributed mainly in tropical forests and occasionally more open, xeric habitats in northern South America. However, part of its modern history (late Miocene to Pleistocene) took place in open habitats of southern South America. Eumysops is part of these modern lineages and the only echimyid with a long evolutionary history in southern South America (central Argentina). In a phylogenetic analysis, obtained from both morphological data and combined molecular and morphological evidences, Eumysops was recovered as a monophyletic clade, sister to the extinct Pampamys and the living Thrichomys. The position of this grouping in a major clade including non-eumysopine echimyids constrains the traditional taxon Eumysopinae only to these three genera. The stratigraphic distribution (assessed by locality and level) reveals a probable coexistence among species of Eumysops, a unique pattern among the octodontoid genera from the Pliocene of the Pampasia: E. laeviplicatus and E. formosus in the Montehermosan; E. chapalmalensis and E. gracilis in the Chapadmalalan; E. chapalmalensis, E. gracilis and Eumysops sp. nov. in the Vorohuean and Sanandresian. Such distribution and phylogenetic relationships suggest a predominant cladogenetic pattern for the genus. Beyond this, a gradual directional change is shown by E. chapalmalensis from the Chapadmalal Formation to the overlying San Andrés Formation. This trend includes an increase in the size and robustness of the skull and jaw, and in the height of molars. Similar features are present in Eumysops sp. nov. from the Vorohuean-Sanandresian, or even are acquired by other octodontoid lineages during this lapse. According to numerical ages, and magnetostratigraphic and biochronological data, the interval Vorohuean-Sanandresian is a local representation of the global cooling and drying trend recorded between ~3.0 and 2.5 Ma. Changes detected in Eumysops during this interval integrate an important faunal turnover which involves the sudden first appearance of the caviomorph extinct fauna most clearly indicative of arid environments so far recorded. Distinctive skeletal and dental anatomy of Eumysops, including cranial and postcranial specializations, and marked hypsodonty, would be a result of its southern history related to a particular palaeoclimatic context.