HUEHUECUETZPALLI MIXTECUS GEN. ET SP. NOV - A BASAL SQUAMATE (REPTILIA) FROM THE EARLY CRETACEOUS OF TEPEXI DE RODRIGUEZ, CENTRAL MEXICO

Huehuecuetzpalli mixtecus gen. et sp. nov. is characterized by a combi nation of characters unlike those of any of the previously described L ate Jurassic or Early Cretaceous lizards. It has most of the synapomor phies common to modern squamates, but still retains primitive features rare in living taxa. Autapomorphic characters include an anteroposter iorly elongated premaxilla that results in the elongation of the snout and the apparent retraction of the external nares. A small rounded po stfrontal and a parietal foramen on the frontoparietal suture suggest affinities with iguanians, but the retention of divided premaxillae, a mphicoelous vertebrae, thoracolumbar intercentra, entepicondylar foram en, and a second distal tarsal supports the hypothesis that Huehuecuet zpalli has a more basal position relative to the extant squamates. Alt hough its appearance is late in the fossil record of lizards, Huehuecu etzpalli is the first report of a basal squamate. It provides importan t information on early transformation of characters in lizard evolutio n. Many primitive characters present in some modern squamates are usua lly explained by paedomorphosis; however, these characters are common in early lizards suggesting that derived states may have been fixed la ter in lizard evolution. If Huehuecuetzpalli is an iguanian, then it w ould be the earliest known representative of this lineage and extends their fossil record into the Albian. This paper presents an extensive review of the characters and character states used in previously publi shed cladistic analyses of the Squamata.