The phylogenetic position of Palaeosaniwa and the early evolution of the Platynotan (Varanoid) anguimorphs

Michael Joseph Balsai, University of Pennsylvania


Since 1928, when it was first described, Palaeosaniwa remained a very poorly known Late Cretaceous anguimorph taxon, despite a relatively wide distribution over northwestern North America. Originally named from a single dorsal vertebrae, most of its fossils have since consisted of assorted vertebrae, with associated jaw and limb fragments. Interestingly the taxon has a relatively extensive temporal range, from the latest Campanian right up to the end Cretaceous event (Maastrichtian). With the discovery of a new Museum of the Rockies semi-articulated specimen, considerably more material has now come to light and study of this fossil, combined with that of an undescribed University of California Museum of Paleontology specimen, sheds significantly more light on the morphology of this lizard as well as its phylogenetic affinities. Thought to have been an early varanid, it is now evident that this taxon is a member of the Monstersauria (Heloderma and its relatives) and may have possibly been venomous. A redescription of Palaeosaniwa and a reevaluation of its phylogeny is provided. In addition, the evolution of venom delivery and nest predation by monstersaurians is examined and the historical biogeography of platynotan anguimorphs is reexamined.

Subject Area


Recommended Citation

Balsai, Michael Joseph, "The phylogenetic position of Palaeosaniwa and the early evolution of the Platynotan (Varanoid) anguimorphs" (2001). Dissertations available from ProQuest. AAI3031637.