Research Describes New Fossil Frogs from the Late Cretaceous of Alberta

 

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Frogs are the most familiar of living amphibians. Adults are distinctive; having a squat body, no tail, and powerful hind limbs. They also are entirely carnivorous, typically eating insects and other small invertebrates, although larger frogs will also consume bigger prey such as snakes, rodents, and even other frogs. Most frogs begin life in fresh water, where their gelatinous eggs hatch into a fully aquatic and herbivorous larval form called a “tadpole.” The tadpole feeds, grows, and eventually undergoes a dramatic metamorphosis that culminates in it changing into the adult form. Although frogs are constrained by being cold-blooded and having skin that can dry out, they are the most diverse and widespread of living amphibians. Today over 6,550 living species are found on most continents, except Antarctica. They occur in a variety of ecosystems including temperate forests, semi-arid grasslands, and lush tropical forests. Some frogs are fully aquatic, whereas others live in trees, alongside the margins of ponds and streams, or in burrows.

The fossil record of frogs extends back to the earliest Triassic (about 240 million years ago) alongside the earliest appearances of dinosaurs and mammals. Some spectacular frog fossils are known, including tadpoles in various stages of development and complete skeletons of adult frogs; however, the most common frog fossils are isolated bones. Thanks to the distinctive structure of the frog skeleton, most of their bones are easily identifiable and can be informative for identifying species.

In Alberta, vertebrate microfossil localities, which are accumulations of small fossil bones, teeth, and scales from many kinds of vertebrate species, are a rich source of frog bones from the latter part of the Late Cretaceous (about 85 to 65 million years ago). Frog fossils have been known in Alberta since the mid-1960s. The accumulation of specimens and research over the past fifty years from isolated bones collected from those microfossil localities, led Museum researchers to formally describe two new species of Late Cretaceous frogs earlier this year. These are the first fossil frogs to be named from Alberta.

The first species, named Hensonbatrachus kermiti in honour of the muppeteer Jim Henson and his Kermit the Frog™ muppet, was described by Dr. Jim Gardner, Curator of Palaeoherpetology, and Dr. Donald Brinkman, Director of Preservation and Research. Hensonbatrachus is known from skull bones, ilia, and a humerus. It was a moderate-sized frog, with an estimated body length of 75 to 115 mm. The external surfaces of its skull bones are ornamented with bony ridges and its upper jaws bore many small teeth.

The second species was described by Dr. Jim Gardner and was named Tyrrellbatrachus brinkmani in honour of the 30th anniversary of the Royal Tyrrell Museum of Palaeontology and Dr. Donald Brinkman, one of the founding researchers at the Museum. Tyrrellbatrachus is known only by a half dozen upper jaws, distinctive because they are considerably smaller, have a nearly smooth external surface, and are entirely toothless. Loss of teeth is a common feature among frogs and its occurrence in Tyrrellbatrachus represents one of the oldest (about 76. 5 million years ago) instances of this phenomenon. The presence of additional frog bones in the same localities that yielded these two new frogs indicates that a number of different frog species lived alongside dinosaurs during the Late Cretaceous of Alberta.

RTMP blog_fossil frogs_fossil jaws figure_Jim ver_2015-11-27

Incomplete upper jaws (maxillae) of two new species of fossil frogs from the Late Cretaceous (ca. 76.5 million years ago) of Alberta, described this year by researchers at the Royal Tyrrell Museum of Palaeontology: Hensonbatrachus kermiti (top: specimen number UALVP 40167, holotype) and Tyrrellbatrachus brinkmani (bottom: specimen number TMP 1985.066.0035, holotype). Both specimens are shown at same sizes for ease of comparison; the smaller image of the Tyrrellbatrachus maxilla at left shows its actual size compared to the much larger Hensonbatrachus maxilla. The Hensonbatrachus fossil is courtesy of the University of Alberta Laboratory for Vertebrate Paleontology.

References:

Gardner, J.D. 2015. An edentulous frog (Lissamphibia; Anura) from the Upper Cretaceous (Campanian) Dinosaur Park Formation of southeastern Alberta, Canada. Canadian Journal of Earth Sciences, 52: 569–580.

Gardner, J. D., and Brinkman, D.B. 2015. A new frog (Lissamphibia, Anura) from the Late Cretaceous of Alberta, Canada. In: All Animals are Interesting: a Festschrift in Honour of Anthony P. Russell. Edited by: O.R.P. Bininda-Emonds, G.L. Powell, H.A. Jamniczky, A.M. Bauer, and J. Theodor. BIS Verlag, Oldenberg, pp. 35–105.

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