Gerobatrachus

taxobox
name= "Gerobatrachus"


image_width=250px
fossil_range = Early Permian
regnum = Animalia
phylum = Chordata
subphylum = Craniata
superclassis = Tetrapoda
classis = Amphibia
order = Temnospondyli
superfamily = Dissorophoidea
family = Amphibamidae
genus = "Gerobatrachus"
genus_authority=
subdivision_ranks=Species
subdivision=
*"G. hottoni"

"Gerobatrachus", also referred to as a frogamander, is an extinct genus of early, toothed amphibian, a stem-batrachian that lived in the Permian period, approximately 290 million years ago, in the area that is now Baylor County, Texas. The animal is considered to be a missing link that supplies a concrete example for the hypothesis offered by cladistics, that frogs and salamanders had a common ancestor, and that they are only distantly related to the third extant order of amphibians, the caecilians. [http://news.nationalgeographic.com/news/2008/05/080521-frog-fossil.html "National Geographic", "'Frog-amander' Fossil May Be Amphibian Missing Link"] ]

The fossil, named "Gerobatrachus hottoni" ("Hotton's ancient frog") was described for the first time in "Nature", 22 May 2008. It combines features found later in frogs, such as a large space for a tympanic ear— an "ear drum"— with 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. [http://www.sciencedaily.com/releases/2008/05/080521131541.htm "Science Daily", "Ancient Amphibian: Debate Over Origin Of Frogs And Salamanders Settled With Discovery Of Missing Link"] Accessed 22 May 2008.]

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. The batrachian molecular clock, in other words, is ticking faster than had been thought.

The "frogamander" 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. 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. 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.”

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. 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.”

Notes

References

* Anderson J.S., Reisz R.R., Scott D., Fröbisch N.B., & Sumida S.S. 2008. A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders. "Nature" 453: 515-518.
* [http://news.nationalgeographic.com/news/2008/05/080521-frog-fossil.html "National Geographic", "'Frog-amander' Fossil May Be Amphibian Missing Link"]