A New Fossil Iguanid From Late Pliocene South America

As impressive as their current diversity may be, anoles have a rather pathetic fossil record. Aside from a smattering of subfossils that are less than a million years old, all we have to work from are a few amber specimens from the Dominican Republic preserved over a narrow temporal window (15-20 mybp). This lack of fossils is problematic because molecular genetic data suggest that that Anolis may be more than 50 million years old. The fossil record for anole relatives isn’t much better, with only a handful of well-characterized fossils that are greater than 10 or 20 million years old existing across Iguania. Although they are relatively uncommon, previous reports of iguanian fossils have occasionally been sloppy about assignment to extant clades. Daza et al. (2012) have done a remarkable job of clarifying our understanding of fossil iguanians by providing not only a remarkably detailed and nuanced description of a new fossil iguanian from the Late Pliocene, but also by conducting quantitative phylogenetic analyses that place this fossil in a large tree that includes a diverse range of other fossil and extant iguanians.

Publishing in a recent issue of the Journal of Herpetology, Daza et al. (2012) provide a comprehensive study of a new fossil iguanian found in the Late Pliocene middens of predatory birds in northwestern Argentina. Although these fossils are fragmentary and highly incomplete, they include the tooth-bearing maxilla and pre-maxilla that are particularly important to assigning fossil lizards to modern clades. Daza et al. (2012) describe this material as a new genus: Uquiasaurus.

Ultimately, Daza et al. (2012) are able to score 54 character from these fossils and include this data in a larger phylogenetic dataset that includes 396 morphological characters scored from across other iguanians (including both extant species and fossils). Phylogenetic analyses of this dataset using parsimony result in new phylogenetic trees for the Iguania, which place the new fossils with the Liolaemidae, Leiocephalidae, and Tropiduridae. Daza et al.’s (2012) phylogenetic tree for major iguanian groups suggests that iguanids are roughly 80 million years old and that the Polychrotidae arose approximately 40-50 million years ago. Hopefully we’ll see more such well done work soon.

PS – Daza et al.’s report begins with an effort to clarify taxonomic names that have complicated histories (e.g., Iguanidae, Iguaninae). We’re going to need to have another post on this topic because Daza et al. have proposed an entirely new name that I’m worried will lead to more confusion than clarification moving forward.

Juan D. Daza, Virginia Abdala, J. Salvador Arias, Daniel García-López, and Pablo Ortiz (2012). Cladistic Analysis of Iguania and a Fossil Lizard from the Late Pliocene of Northwestern Argentina Journal of Herpetology DOI: 10.1670/10-112