After 100 years, scientists solve the mystery of the skull of an ancient predator

Scientists have managed to piece together the crushed fragments of the skull of a 330-million-year-old species into a fossilized puzzle that has puzzled many for 100 years, according to a new study published in the peer-review Journal of Vertebrate Paleontology.

Several skulls believed to have belonged to the ancient predator known as Crassigyrinus scoticus, have been found in Scotland. The first specimen was recorded by David Meredith Seares Watson in 1929 and was named Crassigyrinus, but the specimen only showed parts of the right side of the skull, only the cheek region and the side of the snout, making it difficult to decipher the skull when viewed as a whole.

Crassigyrinus is known for being a bit odd and having some unusual traits.

The species was a stem tetrapod, a group of four-limbed animals that were among the first to move from water to land. Unlike its relatives, Crassigyrinus remained an aquatic animal, although it is unclear whether this is because its ancestors returned to the water from land or never moved to land.

3D reconstruction of the skull and mandible of Crassigyrinus scoticus (Credit: Laura B. Porro, Emily J. Rayfield, and Jennifer A. Clack/Journal of Vertebrate Paleontology)

A feared predator

Crassigyrinus would probably have been a feared predator in its time, as it would have been around two to three meters long and behaved somewhat like a modern crocodile. The species’ skull contains several ridges that would have helped strengthen its skull and spread the force of its bite across many teeth.

The species also likely had large eyes that could see in the murky surroundings of the coal swamps, and an odd gap near the front of its snout that may have had an as yet unknown purpose, with one possibility being that the gap was used to close it help to detect electric fields or chemicals.

“Many early tetrapods have midline gaps at the front of their snouts, but the gap in Crassigyrinus is much larger and has smoothly formed edges,” explained Dr. Laura Porro of University College London, the study’s lead author, in a press release from the Natural History Museum. “The nostrils were elsewhere, so there was a lot of speculation as to what that opening might have been.”

The species lived in coal swamps in what is now Scotland and parts of North America, which preserved their skeletons but did not offer much structural integrity, resulting in the fossils being crushed over time, with the fossils being shattered into many pieces, flattened and laid flat were on top of each other. However, the rock in which they were kept provides great contrast for CT scans.

Modern technology paints a new picture

While early studies suggested that Crassigyrinus had a very tall eel-like skull with a short and broad snout, advances in CT scans and 3D visualization have created a different picture.

“When I tried to mimic this shape with the digital surface of CT scans, it just didn’t work. There was no way an animal with such a wide palate and such a narrow skull could have a head like that,” Porro explained. “Instead, it would have had a skull similar to a modern crocodile, with its huge teeth and powerful jaws that enabled it to eat virtually anything that came its way.”

The researchers used CT scans of four Crassigyrinus specimens, which together contained all of the skull bones. Then they started what Porro called a “3D puzzle.”

“I usually start with the remains of the cranium, because that’s going to be the core of the skull, and then build the palate around it,” Porro explained. “This gives me a base to start building up from, using overlapping areas of bone known as sutures, which provide clues to how the skull bones fit together. Because the bones were broken rather than bent, we were able to reconstruct the specimen with a good degree of confidence.”

Porro noted that the new study is dedicated to co-author Prof Jenny Clack, a paleontologist who revolutionized the field’s understanding of the early evolution of tetrapods (four-limbed vertebrates).

“It’s bittersweet to finally see this paper published,” Porro said. “Jenny Clack worked on this as a PhD student and I’m glad she got to see the final reconstructions of Crassigyrinus. She was so inspirational and I would have loved to work with her for years to come.”


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