|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)
|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.
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!