| Gerobatrachus Temporal range: Early Permian |
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| Restoration | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Craniata |
| Superclass: | Tetrapoda |
| Class: | Amphibia |
| Subclass: | Labyrinthodontia |
| Order: | Temnospondyli |
| Superfamily: | Dissorophoidea |
| Family: | Amphibamidae |
| Genus: | Gerobatrachus Anderson et al., 2008 |
| Species | |
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Gerobatrachus, also referred to as a frogamander, is an extinct genus of amphibamid temnospondyl that lived in the Permian period, approximately 290 million years ago, in the area that is now Baylor County, Texas. The animal has been interpreted as a concrete example for the hypothesis offered by many cladistic analyses that frogs and salamanders had a common ancestor, and that they are only distantly related to the third extant order of amphibians, the caecilians.[1] Gerobatrachus has been considered to be the closest relative of Batrachia, the clade that includes modern amphibians.
The discovery provides a new setpoint for readjusting the molecular clock of this amphibian lineage, since this new data revises the best estimate of the date when frogs and salamanders separated from each other sometime between 240 and 275 million years ago, much more recently than previous molecular data had suggested, according to Prof. Robert Reisz, University of Toronto at Mississauga, one of the paper's co-authors.[2] The batrachian molecular clock, in other words, is ticking faster than had been thought.
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The type species, Gerobatrachus hottoni ("Hotton's ancient frog") was described for the first time on May 22, 2008 in the journal Nature. The "frogmander" fossil, as journalists swiftly dubbed it, was collected in the mid-1990s, then rediscovered in the collections of the National Museum of Natural History, Washington DC, in 2004.[1]
Comparative biologist Jason Anderson of the University of Calgary led the new analysis of the fossil, claiming he recognized the "froggy salamander-y sort of look" of the fossil.[1] Anderson judges that the animal would have looked like a stubby-tailed salamander with froglike ears and that it "pretty convincingly settles the question [that the] frog and salamander shared origins from the same fossil group."[1]
The analysis is not yet complete, though. National Geographic News reported that the Field Museum’s John Bolt, a curator for fossil amphibians and reptiles, cautioned that it is difficult to say for sure whether this creature was itself a common ancestor of the two modern groups, given that there is only one known specimen of Gerobatrachus, and an incomplete one at that. "At this point I would say it is by no means certain that this is representative of a common ancestor to frogs and salamanders, although it might be," Bolt said.[1] Bolt also says, "The most astonishing thing to me about this study is that this animal is far more froglike than I would ever have expected from its age. Nothing this nonprimitive has ever been described from this age. It's just amazing."[1]
Gerobatrachus combines features found later in frogs, such as a large space for a tympanic ear— an "ear drum"— and two ankle bones that are fused together, a typical salamander trait. Its backbone and teeth show features common to both frogs and salamanders, with a wide, lightly built skull similar to that of a frog.[2]