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By News Staff | May 21st 2008 09:45 AM | 6 comments | Print | E-mail | Track Comments
The description of an ancient amphibian that millions of years ago swam in quiet pools and caught mayflies on the surrounding land in Texas has set to rest one of the greatest current controversies in vertebrate evolution. The discovery was made by a research team led by scientists at the University of Calgary.

The examination and detailed description of the fossil, Gerobatrachus hottoni (meaning Hotton’s elder frog), proves the previously disputed fact that some modern amphibians, frogs and salamanders evolved from one ancient amphibian group called temnospondyls.

“The dispute arose because of a lack of transitional forms. This fossil seals the gap,” says Jason Anderson, assistant professor, University of Calgary Faculty of Veterinary Medicine and lead scientist in the study.

Artistic rendition of Gerobatrachus hottoni lunging at the mayfly Protoreisma between stands of Calamites and under a fallen Walchia conifer. Credit: Michael Skrepnick


The Gerobatrachus fossil provides a much fuller understanding of the origin and evolution of modern amphibians. The skull, backbone and teeth of Gerobatrachus have a mixture of frog and salamander features—the fossil has two fused bones in the ankle, which is normally only seen in salamanders, and a very large tympanic ear (ear drum). It also has a lightly built and wide skull similar to that of a frog. Its backbone is exactly intermediate in number between the modern frogs and salamanders and more primitive amphibians.

The new fossil also addresses a controversy over molecular clock estimates, or the general time salamanders and frogs evolved into two distinct groups.

“With this new data our best estimate indicates that frogs and salamanders separated from each other sometime between 240 and 275 million years ago, much more recently than previous molecular data had suggested,” says Robert Reisz, professor, University of Toronto Mississauga and second author on the paper.

Gerobatrachus was originally discovered in Texas in 1995 by a field party from the Smithsonian Institution that included the late Nicholas Hotton, for whom the fossil is named. It remained unstudied until it was “rediscovered” by Anderson’s team. It took countless hours of work on the small, extremely delicate fossil to remove the overlying layers of rock and uncover the bones to reveal the anatomy of the spectacular looking skeleton.

“It is bittersweet to learn about frog origins in this Year of the Frog, dedicated to informing the public about the current global amphibian decline,” continues Anderson. “Hopefully we won’t ever learn about their extinction.”

Article: Jason S. Anderson, Robert R. Reisz, Diane Scott, Nadia B. Fröbisch & Stuart S. Sumida, 'A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders',Nature 453, 515-518 (22 May 2008) doi:10.1038/nature06865

Comments

Missing link? A "missing link" between Anura and Caudata should be between the two. This appears to be the sister group to Batrachia, therefore I don't think "missing link" is really appropriate.

Response from AiG

"...supposedly 290 million years old, the frogamander fossil was collected in Texas a decade ago, then “rediscovered” in the National Museum of Natural History in 2004. Comparative biologist Jason Anderson of the University of Calgary led the new analysis of the fossil, claiming he recognized the “froggy slamander-y sort of look” of the fossil— now dubbed Gerobatrachus hottoni.

The creature is said to fit a “noted gap” in the amphibian fossil record—one of those gaps the media never reports on until it’s filled! 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.”

A couple of thoughts for creationists. First, although the find has been reported with typical evolutionary fanfare and certainty on the surface, that’s not to say everyone agrees with the complete analysis. For example, read what National Geographic News reported from the Field Museum’s John Bolt, a curator for fossil amphibians and reptiles:

Bolt, the Field Museum expert, 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, intriguingly, “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.” (Emphasis added.)

Our second thought is that it is possible that, assuming the incomplete fossil has been interpreted accurately and truly shares frog and salamander features (and such assumptions often fail to hold true), frogs and salamanders descended from the same amphibian kind—that is, selective pressures gradually exploited the genetic variation in an original amphibian kind, resulting in the two modern groupings. If not, it is possible God created an amphibian kind with features in common with both salamanders or frogs.

As always, though, Christians must separate the actual finding from the interpretation. There are several creation-based explanations for an incomplete fossil with salamander and frog features, but all too often, well-meaning Christians swallow the evolutionary propaganda whole, facts and worldview, without trusting God over man’s often-foolish speculation."

Hank's picture
We are a spin-free science site so we call 'em like they say they threw 'em.

Jason Anderson - “The dispute arose because of a lack of transitional forms. This fossil seals the gap.”

From Nature - "Here we report the discovery of an amphibamid temnospondyl from the Early Permian of Texas that bridges the gap between other Palaeozoic amphibians and the earliest known salientians and caudatans from the Mesozoic."

To go and put our own take on it (pro- or con-) in absence of obvious logical or methodological flaws would be the kind of thing that partisan sites, including a few science ones, do. If someone comes along tomorrow and makes a compelling argument that this is completely wrong we'll print that too.

Rockstar, What you fail to realize is the fact that the study showed that Gerobatrachus is the sister group to Batrachia. Proving it is the ancestor is not possible. That is what, I believe Bolt, meant. There is no reason to question the current sister taxon relationship. As for the possibility that God created theses, completely untestable therefore unscientific. Creationism offers nothing to scientific discovery. Sorry.

Sounds like someone is unable to accept other view points and explanations. Last time I checked, evolution also can neither be proven or refuted. So close-minded Anonymous...

Actually we can and most often will accept other view points and explanations if backed up with scientific evidence and the proposed counter theory better fits the scientific evidence given. As for your erroneous statement that evolution cannot be proven or refuted well evolution has already been observed (in action) several times in both nature and controlled test. If you would like to take a look as some of those studies yourself you can find a very nicely put together page of several of these here (http://www.talkorigins.org/faqs/comdesc/). All of the examples and work are properly referenced so that if you feel that anything is being taken out of context you can examine the original work for yourself. And yes evolution could be refuted, if you were to find a fossil record that consistently showed all forms of life appearing at the same time it would call into question the theory of evolution but that has not happened yet and at the risk of sounding overly confident I believe never will happen. And finally as for your addressing those that subscribe to the theory of evolution as close minded well I would think that somebody in the face of so much evidence to the contrary still believes in creationism or ID and won’t even consider evolution because it goes against what is taught in a very old book is more close minded than somebody who relies on science to form their beliefs around. If you are a creationist would you accept evolution if we could show you all the evidence that indicates that species came into being at different times in history (the fossil record all over the world shows this). Or if you are an ID proponent would you accept evolution if you were shown evidence of some very unintelligent biological designs (In African locusts, the nerve cells that connect to the wings originate in the abdomen, even though the wings are in the thorax. This strange "wiring" is the result of the abdomen nerves being co-opted for use in flight. A good designer would not have flight nerves travel down the ventral nerve cord past their target, and then backtrack through the organism to where they are needed. Using more materials than necessary is not good design.). And please if you have evidence that shows your theories stand up to scientific scrutiny then for all that is good’s sake let us know, we will be more than happy to review it. BUT if you have no scientific evidence to support your theories then PLEASE stop trying to force your beliefs on our children by masquerading them as science, keep them in the theology class where they belong.

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