A delicate cast of a frog that lived 34 to 40 million years ago.
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Image modified from Laloy et al. 2013.
A delicate cast of a frog that lived 34 to 40 million years ago.

Fossil Frog Still Looks Gooey After Over 34 Million Years

In a blog posted late last year, paleontologist Sarah Werning made an important point that has stuck with me ever since – we need to stop apologizing for the fossil record. There are gaps and discontinuities and an astonishing amount of as-yet-undiscovered history, but a great deal of what has been found so far is truly exceptional. Werning picked prehistoric frogs as a prime example – several specimens of Liaobatrachus preserved in such detail that researchers were able to examine how the skeletons of the frogs transformed from cartilage to bone. A new look at a specific fossil amphibian discovered 140 years ago reminded me of her point. In a PLoS One paper, Fabien Laloy examine an Eocene frog that still looks gooey after over 34 million years.

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Views of the fossil frog Thaumastosaurus gezei. From Laloy et al. 2013.

The point of the study by Laloy and coauthors was the resolve the identity of this amazing find. In 1873, the French naturalist Henri Filhol briefly mentioned a fossil frog discovered among the Quercy Phosphorites of southwestern France that included an external cast of the amphibian’s soft tissues. The specimen, a head and body with an associated leg, looks less like a fossil and more like the crispy remains of a modern frog left out in the sun too long.

In his later writings, Filhol named the frog Rana plicata. This left later paleontologists with a taxonomic knot as the name was preoccupied, and no one really knew exactly where the frog fossil came from and therefore how old it was. When they CT scanned the fossil to see if there was anything inside the lovely exterior, Laloy and coauthors found the clues to finally resolve the mystery. Filhol’s frog had a skeleton “almost identical to that of Thaumastosaurus gezei“, another frog found in the same deposits. That narrows down the age of the beautiful cast to between 40 and 34 million years ago, and also helps constrain ideas about which frogs Thaumastosaurus gezei was most closely related to.

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Internal view of the bones inside the frog cast. From Laloy et al. 2013.

But the new study immediately caught my attention because the frog Filhol first described is so beautiful. Paleontologists often deal with scraps and fragments of prehistoric life; broken clues such as bits of dinosaur bone eroding out of a hill or tatters of an ancient leaf. These natural curiosities are pretty in their own way, but to be able to see the face of a frog that died over 34 million years ago is a stunning opportunity that is about as close as we may get to actually traveling back to the Eocene. The fossil record is incomplete, just as modern ecosystems are not recording every single jot and tittle of life, but the fact that such tender remains exist at all is an unfathomable source of wonder.