Polyglyphanodontia

Polyglyphanodontia Temporal range: Late Cretaceous
Skeleton of the polyglyphanodontian Polyglyphanodon sternbergi
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Clade:	†Polyglyphanodontia Alifanov, 2000
Synonyms
Borioteiioidea Nydam et al., 2007

Polyglyphanodontia is an extinct clade of lizards from the Late Cretaceous that includes around a dozen genera. Polyglyphanodontians were the dominant group of lizards in North America^[1] and Asia^[2] during the Late Cretaceous. They produced a remarkable range of forms. Chamopsiids, including Chamops, were characterized by large, blunt, crushing teeth, and were most likely omnivores. Macrocephalosaurus, from the Gobi Desert, was a specialized herbivore; it grew to roughly a meter long and had multicusped, leaf-shaped teeth like those of modern iguanas. Polyglyphanodon, from the Maastrichtian of Utah, was another herbivore, but its teeth formed a series of transverse blades, similar to those of Trilophosaurus. Peneteius had remarkable, multicusped teeth, similar to those of mammals. The polyglyphanodontids first appear in the latter part of the Early Cretaceous in North America, and became extinct during the Cretaceous-Paleogene extinction event. Polyglyphanodontians closely resembled the teiid lizards, and purported teiid lizards from the Late Cretaceous appear to be polyglyphanodontians.^[3]

A large-scale phylogenetic analysis of squamates conducted by Conrad (2008) found polyglyphanodontians (called Polyglyphanodontidae by Conrad) to be closely related to teiid lizards. In the strict consensus tree recovered in the analysis, polyglyphanodontids were part of a polytomy (unresolved evolutionary relationship) with teiids, gymnophthalmids, Chamops and lacertids; in the Adams consensus tree polyglyphanodontids were the sister group to teiids.^[4] (Some other studies that recognize a close relationship between polyglyphanodontians and teiids use the name Borioteiioidea rather than Polyglyphanodontia, although Borioteiioidea encompasses only North American polyglyphanodontians.)^[5] Conrad's analysis also recovered Sineoamphisbaena, a Cretaceous lizard that resembles legless amphisbaenian lizards, as a member of Polyglyphanodontidae.^[4] On the other hand, a later large-scale phylogenetic analysis of fossil and living squamates published in 2012 by Gauthier et al. found that Polyglyphanodontia was not particularly closely related to teiids, but rather that it was the sister taxon of the clade containing the extinct marine mosasaurs, their closest relatives and the major lizard group Scleroglossa. Because the first scleroglossans appear in the Late Jurassic, polyglyphanodontians must also have originated in the Late Jurassic if this phylogeny is correct. However, polyglyphanodontians are limited to the Late Cretaceous, meaning that a long ghost lineage may exist.^[3] The primary analysis of Gauthier et al. (2012) did not find polyglyphanodontians and Sineoamphisbaena to be closely related; however, the authors noted that when all snake-like squamates and mosasaurs were removed from the analysis, and burrowing squamates were then added individually to it, Sineoamphisbaena grouped with polyglyphanodontians. Gauthier et al. (2012) considered it possible that Sineoamphisbaena was a burrowing polyglyphanodontian.^[3]

References