Scientists have spent nearly a century attempting to comprehend this 330 million-year-old species, which is related to some of the first animals to walk on land.

More information about the life of an ancient predator resembling a crocodile has been revealed by digital reconstructions of fossilised bones. Crassigyrinus scoticus, which lived over 300 million years ago, was well-suited to hunting prey in Carboniferous swamps thanks to its large teeth, large eyes, and variety of sensory enhancements.

Scientists have spent nearly a century attempting to comprehend this 330 million-year-old species, which is related to some of the first animals to walk on land. This has been particularly challenging, though, as all fossils of the Carboniferous carnivore that are known to exist are severely damaged.

Advances in CT scanning and 3D visualisation mean that a team of researchers have now been able to piece the fragments back together for the first time, revealing what Crassigyrinus’s skull would have looked like.

Dr. Laura Porro of UCL, the lead author of a new study, explains that the animal has previously been reconstructed with a tall skull similar to a Moray eel.

However, when trying to mimic that shape with the digital surface from CT scans, it just didn’t work. Instead, it would have had a skull similar in shape to that of a modern crocodile, with its huge teeth and powerful jaws allowing it to eat practically anything that crossed its path.

The paper, published in the Journal of Vertebrate Palaeontology, is dedicated to Professor Jenny Clack, a pioneering palaeontologist who revolutionised our understanding of early tetrapod evolution. Laura says it is bittersweet to finally see the paper published, as Jenny Clack worked on it as her PhD and was inspirational. Laura would have loved to continue working with her for years to come.

An animal with four legs known as a stem tetrapod, or Crassigyrinus, was one of the first to move from the water to the land.

However, unlike its relatives, Crassigyrinus was an aquatic creature, either because its forebears never left the water or because they never crossed the land. Instead, it inhabited coal swamps in parts of what is now Scotland and North America, which created the ideal environment for its post-mortem preservation.

Laura explains that the fine-grained rock in which these animals were preserved offers excellent contrast during CT scanning. Sadly, it doesn’t offer much structural integrity, so as more material was added on top of Crassigyrinus, the fossils were pressed down.

This indicates that all of the known specimens are broken and deformed, despite the fact that some of them are quite complete. The bones are broken up into numerous pieces, flattened, and stacked on top of one another, which has resulted in numerous different reconstructions in the past.

The team used CT scans from four Crassigyrinus specimens, including three at the Museum, to attempt to reconstruct this crushed specimen. All of the skull’s bones were present between these fossils, enabling scientists to begin reconstructing the tetrapod’s skull.

‘Once we had identified all of the bones, it was a bit like a 3D-jigsaw puzzle,’ Laura says. ‘I normally start with the remains of the braincase, because that’s going to be the core of the skull, and then assemble the palate around it.’

This provides a starting point from which I can begin to construct upwards using overlapping bone regions known as sutures that offer clues as to how the skull bones fitted together. We could confidently reconstruct the specimen because the bones were broken rather than bent.

The new assessment of the rest of Crassigyrinus’ body found that it was a relatively flat-bodied animal with very short limbs, which is consistent with the shallower skull shape that resulted from this. These reconstructions can help us learn more about Crassigyrinus’ life by working together. Crassigyrinus’s skull was digitally reconstructed from various coloured fragments.

Crassigyrinus scoticus, whose name translates to “shallow wriggler,” is not exactly a terrifying creature. But back then, it would have been a terrifying predator.

For its time, Crassigyrinus would have been about two to three metres long in life, according to Laura. It probably behaved similarly to modern crocodiles, lurking beneath the water’s surface and snatching prey with its potent bite.

There are several ridges in the shape of Crassigyrinus’ skull, which would have served to strengthen it and distribute the force of its bite among its numerous teeth.

Crassigyrinus scoticus had a suite of specialised senses that helped it track prey. These included large eyes to see in the dim coal swamps and lateral lines to detect vibrations in the water. A mysterious gap near the front of its snout may also be a sign that it had other senses as well.

One possibility is that Crassigyrinus may have had a rostral organ which helped it detect electric fields, or a Jacobson’s organ, which is found in animals such as snakes and helps to detect different chemicals.

Laura says, “Unfortunately, there is nothing preserved there, and nothing alive today is closely related enough to Crassigyrinus scoticus to definitely know,” so “we can’t be sure what was in this gap.”

It is obvious that these creatures had highly developed senses, so it makes sense that they might have had an additional sensory organ at the front of their snout. The skull has been meticulously recreated, and the researchers are now putting it to the test in a series of biomechanical simulations to determine its potential.