Gerobatrachus
Encyclopedia
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 caecilian
s. 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. The batrachian molecular clock, in other words, is ticking faster than had been thought.
, 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.
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."
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of amphibamid
Amphibamidae
Amphibamidae is an extinct family of dissorophoid euskelian temnospondyls. The earliest amphibamids such as Amphibamus are known from Early Permian strata in the United States, while the last known amphibamid, Micropholis, is known from the Early Triassic Karoo Basin of South Africa...
temnospondyl that lived in the Permian period
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
, approximately 290 million years ago, in the area that is now Baylor County, Texas
Baylor County, Texas
As of the census of 2000, there were 4,093 people, 1,791 households, and 1,156 families residing in the county. The population density was 5 people per square mile . There were 2,820 housing units at an average density of 3 per square mile...
. The animal has been interpreted as a concrete example for the hypothesis offered by many cladistic analyses
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
that frogs and salamanders had a common ancestor, and that they are only distantly related to the third extant order of amphibians, the caecilian
Caecilian
The caecilians are an order of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly...
s. Gerobatrachus has been considered to be the closest relative of Batrachia, the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
that includes modern amphibians.
The discovery provides a new setpoint for readjusting the molecular clock
Molecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
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.
Discovery
The type speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, Gerobatrachus hottoni ("Hotton's ancient frog") was described for the first time on May 22, 2008 in the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
. 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
National Museum of Natural History
The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. Admission is free and the museum is open 364 days a year....
, Washington DC, in 2004.
Comparative biologist Jason Anderson of the University of Calgary
University of Calgary
The University of Calgary is a public research university located in Calgary, Alberta, Canada. Founded in 1966 the U of C is composed of 14 faculties and more than 85 research institutes and centres.More than 25,000 undergraduate and 5,500 graduate students are currently...
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."