Roedores caviomorfos (Rodentia Hydrochoeridae) del Blancano temprano-tardío – Irvingtoniano de los estados de Guanajuato, Jalisco y Sonora, México: relación con Phugatherium dichroplax

Abstract

The Caviomorphs rodents collected in the late Blancan sedimentary sequence of San Buenaventura, in the Tecolotlán Basin, Jalisco, are described. The study and comparison with Neochoerus cordobae fossils collected in the early Blancan San Miguel Allende region have revealed that the Buenaventura specimens have more progressive characters than N. cordobae. Distinguishing features of the new species are: 1) the secondary internal flexid (h.t.i.), in the second prism of m2, divides the prism in two isolated plates; 2) the secondary external flexid (h.s.e.), in m3 exceeds 50% of the prism, and 3) the secondary internal flexid (h.s.i.), in both m1 and m3 has a 90% depth of the prism. These characters are shared with a specimen collected from late Blancan-Irvingtonian sedimentary deposits exposed at Golfo de Santa Clara, Sonora, which is referred to Neochoerus occidentalis. The taxonomic position of Neochoerus cordobae and Phugatherium dichroplax from the late Blancan fauna of 111 Ranch, Arizona is also discussed. The presence of Neochoerus occidentalis in Tecolotlán and in the Golfo de Santa Clara faunas is evidence that the western part of Mexico was a corridor where mammals migrated toward the northern region of Mexico and in general to the SW portion of North America.