Grad Publication: Dave DeMar

The earliest crown group frog, Prosalirus, from the Early Jurassic
Kayenta Formation of Arizona. Prosalirus retains some tell tale
features of its shared ancestry with salamanders.
(From Shubin & Jenkins, 1995)
        A paper coauthored by UW Biology graduate student Dave DeMar was recently published online in the journal Palaeobiodiversity and Palaeoenvironments. Dave's paper with coauthor James (Jim) Gardner of the Royal Tyrrell Museum of Palaeontology stemmed from a symposium entitled "Insights from the Fossil Record into the Evolution of Extant Amphibians and Reptiles", which was part of the Seventh World Congress of Herpetology held in August 2012 in Vancouver, British Columbia. Jim and Dave's paper is a comprehensive chronological review of fossil lissamphibians (frogs, salamanders, caecilians, and albanerpetontids) from North America that lived during the age of dinosaurs (Mesozoic) and the first epoch (Paleocene) following the demise of non-avian dinosaurs at the end of the Cretaceous. Their review, which is based on more than 400 published and unpublished accounts from 61 geological formations, is complemented by two plates illustrating several impressive lissamphibian fossils and a series of maps, time scales, and annotated faunal lists supplemented by several online appendices to aid in summarizing the geographic and stratigraphic distributions of fossil localities and the lissamphibian taxa found within them.
The earliest stem member of the odd clade of living amphibians,
the caecilians. Eocaecilia is also from the Early Jurassic Kayenta
of Arizona. Illustration by N. Tamura.
        Several of those published accounts derive from Dave's undergraduate research while at the University of Wyoming and his ongoing dissertation project here at UW with Dr. Gregory Wilson. Those accounts include his recent description of the fossil proteid salamander Paranecturus garbanii (see Science Positive post from May 8, 2013), geographic range extensions of some rare and poorly known Late Cretaceous frogs (e.g., Theatonius lancensis), and recognition of several undescribed new salamander species, all from the Upper Cretaceous Hell Creek Formation of Montana.        

Jim and Dave highlight the importance of the North American lissamphibian fossil record as it documents the origins, radiations, and extinctions prior to the establishment of the more modern aspect of the clade and the initial phases of that modernization on the continent during the Late Cretaceous and into the Neogene. For example, the North American record includes the oldest global occurrence of a crown frog (Prosalirus) and a stem caecilian (Eocaecilia), both from the Early Jurassic of Arizona. From the fossil occurrence data compiled in their study Jim and Dave created the first species richness curve for North American lissamphibians from the Mesozoic and Paleocene. Their plots demonstrate a general increase in species richness leading up to the Cretaceous-Paleogene boundary (~66 million years ago) and a decline thereafter, but caution that the curves are highly influenced by factors such as research bias and uneven temporal sampling. Jim and Dave end their review by stating:

"While compiling this review, it became glaringly obvious to us that we have barely scratched the surface of the North American Mesozoic and Palaeocene lissamphibian record. If the surge of new localities, specimens, taxa, and ideas that have come to light in the last five decades since Estes' (1964) monograph on non-mammalian vertebrates from the Lance Formation is any indication, the future holds many exciting new opportunities for the study of Mesozoic and Paleocene lissamphibians in North America."

Here's the link!
For a pdf of the paper (and its impressive figures) contact Dave!


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