Serpentes

Conrad, J. L., 2008, Phylogeny And Systematics Of Squamata (Reptilia) Based On Morphology, Bulletin of the American Museum of Natural History 2008 (310), pp. 1-182 : 106

Amphisbaenia + Serpentes

(figs. 54C, 55C, 56B)

DIAGNOSIS: Amphisbaenians and snakes are hypothesized to form a clade exclusive of other squamates in this analysis; a clade diagnosed by 28(0) midpoint/apex of maxillary nasal process at or anterior to the midpoint of the maxilla, 79(0) absence of a midline parietal flange, 110(0) absence of medial ‘‘step’’ to the palatine, 114(0) no development of the secondary palate, 117(0) absence of ventromedial processes (basipterygoid buttresses) on the pterygoid, 131(1) occipital condyle bipartite and constructed primarily by the exoccipital portions of the otooccipitals, 134(1) absence of an epipterygoid, 182(1) absence of a dentary shelf, 254(2) chevrons fused to the vertebrae, 284(2) pelvic bones with nonsutural contacts, 289(2) absence of a femur (note that this is reversed both within Amphisbaenia and Serpentes ), and 317(4) foretongue divided for more than 50 percent of its length.

COMMENTS: The sister-group relationship between amphisbaenians and snakes was recently recovered by Evans and Wang (2005), a result duplicated here. Other recent studies have suggested that amphisbaenians and dibamids form the sister-taxon to snakes ( Evans and Barbadillo, 1997, 1998, 1999; Evans et al., 2005). This hypothesis is consistent with the terrestrial origin of snakes, a hypothesis further supported by the recent discovery of Najash rionegrina (Apestiguía and Zaher, 2006) ; a taxon that will be included in future versions of this analysis.