A gap in the fossil record roughly 300 million years ago had scientists puzzling over the origins of modern frogs and salamanders. This gap has now been filled with a recent discovery by a University of Calgary assistant professor.
In 1995, the late Dr. Nicholas Hotton, with a group from the Smithsonian Institute, discovered the Gerobatrachus hottoni fossil in Texas. The fossil was forgotten until early 2004 when Dr. Jason Anderson, lead scientist on his study, decided to bring it to Calgary and see what it had to offer. What he found was unlike anything else.
"It has a mosaic of characteristics, some froggy, some salamandery, some remnant of the temnospondyls," said Anderson, explaining that temnospondyls are an extinct order of amphibians.
Until recently, there was disagreement among researchers about whether temnospondyls left any descendants. Anderson's research suggests that temnospondyls are in fact the ancient ancestors of modern amphibians.
"When you have a gap and no evidence, you're able to hypothesize any sort of arrangement," said Anderson. "But this fossil makes it fairly conclusive that frogs and salamanders come from temnospondyls."
Anderson explained that his research was further supported by molecular studies that place the timing of the splitting in the evolutionary lineage at approximately the same time the Gerobatrachus fossil was formed. However, past research supported the hypothesis that frogs, salamanders and caecilians--long worm-like amphibians--came from the same ancestor whereas Anderson's findings place caecilians in a field of their own.
"The question of the origin of all modern amphibians is now just a question of where caecilians come from," said Anderson.
The Gerobatrachus would have lived in bogs and was roughly 12 centimetres in length.
Funding for his project came from several different sources, including a discovery grant from the National Sciences and Engineering Research Council of Canada, another discovery grant which he shared with noted vertebrate paleontologist Dr. Robert Reisz from the University of Toronto and an initial grant from the government of France.
"I got to spend a month and a half in Paris, which is the hard side of research, I suppose," joked Anderson.
It was during previous work with Reisz when Anderson met one of the graduate students that would work on his project. McGill University PhD student Nadia FrÃ¶bisch is working on her thesis about other small amphibians, called branchiosaurs, which are closely related to salamanders. She and Anderson first became interested in paleontology for similar reasons.
"My parents took me to a large natural history museum in Frankfurt and ever since then I've been hooked," said FrÃ¶bisch. "A lot of little kids are interested in paleontology and then at some point they kind of lose it, but I never lost it."
FrÃ¶bisch went on to get her masters equivalent at the University of Bonne in Germany before coming to Canada. Anderson started university as a drama major before realizing his real interest lied in paleontology. He explained that the procedure he followed was typical of scientific research.
"It demonstrates the predictive nature of science," said Anderson. "If you were to take a look at the earliest frog and salamander fossils and you were to hypothesize what an ancestor for those might have been like, you wouldn't have been far off from what we discovered in Texas."