The return of Najash: New, better preserved specimens change the face of the basalmost snake

APESTEGUIA, S.; GARBEROGLIO, FERNANDO F.

Los Angeles

Congreso; 73 rd Annual Meeting of the Society of Vertebrate Paleontology; 2013

Los Angeles County Museum of Natural History

La Buitrera is a fossiliferous locality from northern Patagonia, Argentina. It preserves superb small to mid-sized skeletons in a Gobi style, but evidencing subaereal exposure, scavenging, disolution and shallow disarticulation. Skeletons are commonly well-defined and clearly separated from other. Lag deposits are present too, but as consequence of disarticulation of complete skeletons. Najash rionegrina is the only snake found in this locality. The phylogenetic approach positioned this species as the basalmost snake, bringing it into the large debate of snake origins. The species was described after one main specimen consisting in a quite complete vertebral sequence of 122 vertebrae from axis to caudals, including pelvis, limbs and a dentary. As frequent in La Buitrera style, this specimen was mainly articulated except for some moved vertebrae (isolated within the jacket), the dentary some milimeters in front of the axis, and the fibula at less than one centimeter from the tibia. A recent work discussing the position of Najash proposed the exclusion of these elements for not being in anatomical contact. We reject this opinion. Full anatomical contact is rare in vertebrate paleontology. Concerning other elements, found isolated and at about 3 km (i.e., an isolated partial skull, a quadrate, an additional dentary and several vertebrae), included as referred material, debate is understandable. A recent visit to the locality resulted in the finding of two additional specimens, both provided with skull and bearing vertebrae that are indistinguishable from those described for the holotype. One of them bears an incomplete skull preserved almost exactly as the published one. The second skull, although still unprepared, bears an ?anilioid? general aspect and it preserves premaxilla, nasal, vomer, prefrontal, frontal, maxilla, postfrontal and jugal (both clearly differentiated), ectopterygoid, parietal, prootic, otoccipital, supraoccipital, supratemporal and quadrate. The lower jaw includes compound bone, angular and a dentary with two foramina. This new specimen makes a substantial contribution to make Najash rionegrina one of the better known basalmost snakes.