Under the Noses of Dinosaurs, a New Species of Early Cretaceous Amphibian is Described
A small, fragmentary fossil found in an outcrop of the Kuwajima Formation, in western Central Japan has been identified as a new species of albanerpetontid amphibian. This tiny animal, measuring just six centimetres in length inhabited a wide floodplain, that was crossed by meandering rivers in a humid environment some 130 million years ago. The fossils represent the oldest example of this type of Tetrapod found in Asia, they predate the only other specimens known from Asia (Uzbekistan), by tens of millions of years.
A Life Reconstruction of the Little Albanerpetontid Amphibian (S. isajii)
An illustration of Shirerpeton – an Early Cretaceous amphibian.
Picture Credit: Takumi Yamamoto
The Ancient Albanerpetontidae Family
Superficially resembling modern-day Salamanders, these ancient amphibians are only distantly related to their modern counterparts. They evolved in the Middle Jurassic and persisted until very recently, finally becoming extinct during the Pleistocene Epoch. Several genera are known and they are characterised by their unique skulls and the presence of bony scales on their skin. The tiny specimen consists of a partial skull, vertebrae and elements from a hind limb, a total of forty-three bones. The only Asian examples of this clade of amphibian have been found in Uzbekistan. These fossils date from the very end of the Cretaceous, so the Japanese specimen is some sixty million years older.
High resolution X-ray computed microtomography was used to identify the shape of the bones which remain partially buried in the part-prepared fossil.
The Rock Containing the Partially Exposed Fossil Bones Along with a Computer Image Tracing the Outline of the Individual Bones
A new Early Cretaceous amphibian from Japan (Shirerpeton).
Picture Credit: The Education Board of the city of Hakusan, (Ishikawa Prefecture, Japan)
The picture (above) shows the holotype fossil of the new albanerpetontid amphibian, which has been named Shirerpeton isajii. Image (A) shows the fossils in the 2.5 by 1.5 cm square slab of rock, whilst image (B), is a digital photograph with various bones from the skull highlighted. Abbreviations: Br, braincase elements; Fr, frontal; L.La, left lacrimal; L.Mx, left maxilla; L.N, left nasal; L.Pa, left parietal; LPf, left prefrontal; L.Sm, left septomaxilla; L.Sq, left squamosal; R.La, right lacrimal; R.Pa, right parietal; R.Pf, right prefrontal; R.Sq, right squamosal; ?, unidentified element. Scale bars in both images = 5 mm.
Writing in the open-access academic journal PLOS One, the researchers, Susan Evans, a professor of vertebrate morphology and palaeontology (University College London) and Ryoko Matsumoto, a curator with the Kanagawa Prefectural Museum of Natural History were able to identify the specimen as a member of the Albanerpetontidae from the shape of the lower jaw. The distinctive frontal bone of the skull, along with several other identified autapomorphies (unique traits), enabled the scientists to erect a new species.
The scientists named the species in honour of Shinji Isaji, the head of the Tetori Group fossil investigation commission, a body under the Hakusan city government in charge of studying the Kuwajima fossil location where the fossil was found.
A spokesperson from Everything Dinosaur commented:
“There are about twenty of these amphibians known in the fossil record, currently assigned to five genera. They were globally widespread during the Mesozoic, but this is the first time an albanerpetontid has been recorded from East Asia. Their fragmentary record makes understanding their evolution and their phylogeny very difficult, scientists are not even sure how closely related these ancient lissamphibians are to extant amphibians. Small animals like Shirerpeton are just as important as larger animals like dinosaurs when it comes to considering ancient environments and habitats. In fact, this amphibian is probably more important than larger vertebrates in helping scientists to understand the localised climate in the Barremian of Japan.”