It’s another transitional form, this time an amphibian from the Permian that shares characteristics of both frogs and salamanders — in life, it would have looked like a short-tailed, wide-headed salamander with frog-like ears, which is why it’s being called a “frogamander”.
For those of you with a more technical bent, here’s the list of diagnostic characteristics that bridge both amphibian groups.
Amphibamid temnospondyl with 21 tiny pedicellate teeth on the premaxilla, and 17 presacral vertebrae; shares with crown group salamanders a basale commune (combined distal tarsals 1 and 2) and tuberculum interglenoideum (‘odontoid process’) on atlas; shares with salientians and caudates an anteroposteriorly reduced vomer; shares with Triadobatrachus and crown group frogs a rod-like, laterally directed palatine; shares with Karaurus, Triadobatrachus and crown group frogs a broad skull, shortened presacral vertebral column; shares with most temnospondyls, frogs and basal salamanders a pedal phalangeal formula of ?-2-3-4-3; shares with frogs, Amphibamus, Doleserpeton, Platyrhinops and Eoscopus a large otic notch closely approaching the orbit; shares with frogs, salamanders, caecilians, Amphibamus, Tersomius and Doleserpeton pedicellate teeth; shares with Amphibamus, Doleserpeton and Platyrhinops a foreshortened supratemporal; shares with Amphibamus, Doleserpeton, frogs and salamanders a foreshortened parasphenoid basal plate with wide lateral processes.
Now maybe some of you paleontologically-minded people can help me out with something. Molecular evidence places the divergence point between frogs and salamanders at some point in the late Carboniferous, between 308 and 357 million years ago. This animal is from the Early Permian, so it’s more recent than that. Strangely, the authors claim that the discovery of Gerobatrachus places a lower bound on the divergence time, which I don’t see at all; Gerobatrachus could be a late representative of a significantly earlier common ancestor. Am I missing something here?
Anderson JS, Reisz RR, Scott D, FrÃ¶bisch NB, Sumida SS (2008) A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders. Nature 453(7194):515-518.