Echimyid

About Chaetomys

The bristle-spined rat, Chaetomys subspinosus, has sometimes been classified in Echimyidae, although traditionally considered a member of the New World porcupine family Erethizontidae. The classification with Echimyidae is supported by similarities in the cheek teeth structure. Like all living caviomorphs except erethizontids, Chaetomys seems to lack posterior carotid foramina, and together with all echimyids and in contrast to all other caviomorphs, Chaetomys seems to retain the otherwise deciduous premolars (dP4). Some of these characters have been, however, reinterpreted as evidence for affinities between Chaetomys and the Erethizontidae. A molecular phylogeny based on the mitochondrial gene coding for cytochrome b combined to karyological evidence actually suggests Chaetomys is more closely related to the Erethizontidae than to the Echimyidae, although it branches as the sister group to the rest of the Erethizontidae.