CONRAD, J L; Univ of Chicago: Evolution of ‘necrosaurids’ (Reptilia, Squamata) and their utility for reconstructing ancestral character states

More than 20 years of cladistic work has yielded virtually no consensus regarding the phylogenetic relationships of the anguimorph groups (Xenosauridae, Anguidae, Monstersauria, Varanidae, and Mosasauroidea). The �Necrosauridae� have been particularly problematic due to their poorly understood morphology and the omission of individual taxa in phylogenetic analyses. Some researchers have suggested necrosaurid affinities lie with Anguidae, whereas others placed them within Platynota. The constituent taxa of the group have also been variable with most researchers now agreeing that necrosaurids probably represent a non-monophyletic assemblage. Often only fossil taxa have been referred to Necrosauridae, but at least one historical study suggested affinity between extant Shinisaurus and some �necrosaurids.� Most necrosaurid specimens are very incomplete or under-described and they often possess a combination of apomorphic and plesiomorphic character states, further complicating any understanding of their evolutionary history. However, these problematic taxa represent an important window into the historical anguimorph morphology. My work suggests that Necrosaurus cayluxi and Paravaranus may be close to mosasauroid ancestry; Necrosaurus eucarinatus is close to the base of the varanid-mosasauroid clade; Eosaniwa, Shinisaurus, Parasaniwa, and Colpodontosaurus are close to the base of Platynota. Inclusion of these taxa in an analysis of Anguimorpha changes the polarization of characters at various levels within the cladogram. Further, these data add evidence to the argument that even incompletely known taxa may be very important for inclusion in reconstructing phylogenies.