Crushed Fossil Pieces Used to Reconstruct Killer ‘Tadpole from Hell’

What was 3 meters (10 feet) long, had huge teeth, big eyes and chased prey in ancient Scottish exchanges more than 300 million years ago? The answer: an extremely ferocious crocodile-like predator called Crassigyrinus scotiscus. Now a team of scientists has managed to digitally reconstruct the skull of this beast, which not only provides new insights into what it looked like, but also how it may have lived.

Crassigyrinus meaning “fat tadpole”, is known as an early tetrapod (from the Greek Tetrapoda “four legs”) and was a large aquatic carnivore that lived in the coal moors of Scotland and parts of North America during the Lower to Middle Carboniferous. However, it is closely related to some of the first species to make the transition from water to land Crassigyrinus it did not reach the ground itself.

Although scientists have studied the remains of the aquatic animal for nearly a century, they have had difficulty understanding the 330-million-year-old species because all known fossils have been badly crushed. It is this way because Crassigyrinus tend to be preserved in a fine-grained rock that, as more layers of material accumulate, subsequently crushes the remains.

So what scientists have to deal with so far is a lot of broken and deformed bones and flattened fragments. Many of these pieces are also out of order and stacked on top of each other. This has made it extremely difficult for researchers to reconstruct what it might have actually looked like.

However, advances in computed tomography (CT) scanning and 3D imaging have allowed a team of researchers to reassemble the fragments for the first time. They used pieces from four specimens where all the bones of the skull were present.

The reconstructed skull of four specimens of Crassigyrinus scoticus. Image credit: Porro et al., Journal of Vertebrate Paleontology, 2023 (CC BY 4.0)

“Once we identified all the bones, it was a bit like a 3D puzzle,” Dr Laura Porro of University College London, the lead author of the new study, said in a statement. “I usually start with the remains of the braincase, because that will be the core of the skull, and then I assemble the palate around it.”

“This animal,” added Porro, “was previously reconstructed with a very high skull, similar to a moray eel, based on the type specimen in Edinburgh, which was flattened from side to side.”

“However, when I tried to mimic that shape with the digital CT surface, it just didn’t work. There was no way an animal with such a wide palate and such a narrow skull roof could have such a head.”

Instead, Poro discovered that the animal had a skull similar to modern crocodiles, as well as large teeth and powerful jaws, the better to eat anything that crossed its path. This information, combined with recent research by Crassigyrinus‘ body, shows that the animal had a rather flat body with short limbs. This sheds important light on how the predator would have lived and helps explain how it would have been a fearsome predator.

“In life,” Porro explained, “Crassigyrinus it would be about 2 to 3 meters [6.5 to 10 feet] long, which was quite large for the time,” says Laura. “It probably would have behaved in a manner similar to modern crocodiles, lurking beneath the surface of the water and using its powerful bite to grab prey.”

interesting Crassigyrinus it also had a set of specialized senses to help it track its prey. These included his large eyes that allowed him to see in the overwhelming darkness of the coal swamps, but also lateral lines that detected vibrations in the water. There is also a strange hole in the front of his skull that may have given him other senses as well.

“Many early tetrapods have midline gaps in the front of their snouts, but the gap in Crassigyrinus is much larger and has smoothly sculpted edges,” Porro explained. “The nostrils were elsewhere, so there was a lot of speculation as to what that opening might have been.”

One possibility is that Crassigyrinus, like some extant fish, may have had a rostral organ for detecting electric fields. It may also be an early example of a Jacobson’s organ, which allows species such as modern snakes and amphibians to detect various chemicals. Although this is all speculation as whatever was in this gap is not preserved.

With the new reconstructions, the researchers experimented with a series of biomechanical simulations to see what it was capable of doing.

The paper is dedicated to co-author Professor Jenny Clack, “a pioneering paleontologist who revolutionized our understanding of early tetrapod evolution” and who died in 2020.

The research is published in the Journal of Vertebrate Paleontology.

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