Paleontology & Fossils

Scottish fossils that were crushed were rebuilt to reveal an ancient predator’s head.

Meet Crassigyrinus scoticus, also known as the “tadpole from hell” species. This ancient predator that looked like a crocodile has been better understood thanks to digital reconstructions of broken fossils.

With enormous teeth, huge eyes, and a scope of tactile variations, Crassigyrinus scoticus was appropriate to hunting prey in Carboniferous marshes quite a while back.

For nearly a century, researchers have attempted to comprehend this 330 million-year-old species, which is related to some of the earliest animals to walk on land. However, this has been particularly challenging due to the severe crushing of all known fossils of the Carboniferous carnivore.

A group of researchers has now been able to put the pieces back together for the first time thanks to advances in CT scanning and 3D visualization. This lets us see what Crassigyrinus’ skull would have looked like.

“Based on the type specimen in Edinburgh, which has been flattened from side to side, this animal has previously been reconstructed with a very tall skull, similar to a Moray eel.”

Dr. Laura Porro of UCL, the lead author of the new study,

“This animal has previously been reconstructed with a very tall skull, similar to a Moray eel, based on the type specimen in Edinburgh, which has been flattened from side to side,” says Dr. Laura Porro of UCL, the lead author of the new study.

“However, it just didn’t work when I tried to mimic that shape with the digital surface from the CT scans.” “It was impossible for an animal with a palate that wide and a skull roof that narrow to have a head like that.”

“Instead, it would have had a skull that was similar to the shape of a modern crocodile, and it would have had huge teeth and strong jaws that allowed it to eat almost anything that came in its way.”

Co-author Professor Jenny Clack, a pioneering paleontologist who revolutionized our understanding of early tetrapod evolution and died in 2020, is honored in the paper, which was published in the Journal of Vertebrate Palaeontology.

“It is clashing to at long last see this paper distributed,” Laura says. “As part of her Ph.D., Jenny Clack worked on it, and I’m glad she got to see the final Crassigyrinus reconstructions. I would have loved to continue working with her for many years because she was such an inspiration.

Exemplars of Crassigyrinus have become compressed as a result of the fossilization process.  Credit: The Trustees of the Natural History Museum, London.

How to rebuild a fossil that has been flattened

Crassigyrinus is a stem tetrapod, a group of animals with four legs who were among the first to move from water to land. Crassigyrinus, on the other hand, was an aquatic animal, unlike its relatives. This could be because Crassigyrinus’ ancestors moved back to the water from land or because they never moved to land in the first place.

Instead, it lived in coal swamps in Scotland and other parts of North America, which made it possible for it to stay alive after it died.

Laura explains, “These animals were preserved in fine-grained rock that provides excellent contrast during CT scanning.” Since it lacks structural integrity, it squashed the fossils as more material piled on top of Crassigyrinus.”

This indicates that all of the known specimens are broken and deformed, despite the fact that some of them are quite complete. The bones have been broken up into many pieces, flattened, and laid on top of each other, resulting in a number of different reconstructions in the past.

To attempt to reconstruct this crushed example, the group utilized CT examinations of four Crassigyrinus examples, including three at the historical center. They were able to begin rebuilding the tetrapod’s skull because all of the skull’s bones were present between these fossils.

“Whenever we distinguished the bones, it was all a piece like a 3D jigsaw puzzle,” Laura says. “Since the braincase is going to serve as the core of the skull, I typically begin by putting together the palate around it.

“Using overlapping areas of bone known as sutures, which provide hints about how the skull bones fit together, I can start building upwards from this base. We were able to confidently reconstruct the specimen because the bones were broken rather than bent.

A recent reevaluation of the rest of Crassigyrinus’ body reveals that it was a relatively flat-bodied animal with very short limbs, which is consistent with the resulting shallower skull shape. These reconstructions can provide additional insight into Crassigyrinus’ life.

Bone sections from various examples were utilized to decipher how the skull would have looked. Credit: Porro et al.

What information about Crassigyrinus has been uncovered?
Crassigyrinus, whose name translates to “thick tadpole,” is not exactly frightening. However, it would have been a terrifying predator in its day.

According to Laura, “Crassigyrinus would have been approximately two to three meters long in life, which was quite big for the time.” It would probably have behaved similarly to modern crocodiles, lurking beneath the surface of the water and grabbing prey with its powerful bite.”

The shape of Crassigyrinus’ skull has a number of ridges, which would have spread the force of its bite between its many teeth and helped to strengthen the skull.

Any prey crossing its way would likewise need to fight with a set-up of specific detects that assisted Crassigyrinus with following them. These included lateral lines to detect water vibrations and large eyes to see in the dim coal swamps. It could also indicate that it had additional senses by having a baffling gap near the front of its snout.

According to Laura’s explanation, “The gap in Crassigyrinus is much larger and features smoothly sculpted edges.” “A lot of early tetrapods have midline gaps at the front of their snout,” she says. There has been a lot of speculation about what this opening might have been because the nostrils were elsewhere.

One possibility is that Crassigyrinus, like other living fish, had a rostral organ that helped it detect electric fields. Alternately, it might have had a Jacobson’s organ, which helps detect various chemicals and is found in animals like snakes.

Laura states, “Unfortunately, we can’t be sure what was in this gap because nothing has been preserved there, and nothing alive today is closely related enough to Crassigyrinus to know for sure.” What is clear is that these creatures had very advanced faculties, so it makes sense that it could have had one more tactile organ at the front of its nose.”

The researchers are testing the reconstructed skull through a series of biomechanical simulations to determine what it might have been able to do.

More information: Laura B. Porro et al, Computed tomography and three-dimensional reconstruction of the skull of the stem tetrapod Crassigyrinus scoticus Watson, 1929, Journal of Vertebrate Paleontology (2023). DOI: 10.1080/02724634.2023.2183134

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