Skeletal specializations of the extinct South American echimyid rodent †Eumysops (Hystricognathi)

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

Punta del Este

Congreso; 9th International Congress of Vertebrate Morphology; 2010

International Society of Vertebrate Morphology

The South American caviomorph rodents (Hystricognathi) exhibit wide ecomorphologicaldiversity, especially evident among the Neotropical Echimyidae (spiny rats) which includearboreal, terrestrial, semi-aquatic, and fossorial species. The skeletal specializations of thepeculiar Plio-Pleistocene echimyid †Eumysops were assessed and compared with those of 24genera of living caviomorphs with varied habits, belonging to Octodontoidea, Cavioidea, andChinchilloidea. Cranial features of †Eumysops, such as orbital, zygomasseteric and jawmorphology, indicated epigean habits. In the postcranium, morphology of the humeral deltoidcrest, proximal radial head, neural spines of thoracic and lumbar vertebrae, femoral greatertrochanter, tibial spine, and pes, indicated mainly terrestrial habits, with postcranialspecializations favorable for jumping as suggested in previous hypotheses. Quantitativeanalyses of morphofunctional indexes supported these interpretations, although the intermembral index was similar to that of terrestrial caviomorphs and greater than in ricochetalforms. Because of its unique combination of skeletal specializations, †Eumysops is unlike anyother echimyid; instead, the desert-adapted caviid Microcavia is a reasonable modern analogue.This is consistent with hypotheses that consider †Eumysops as a lineage related to openenvironments in southern South America.