Scientists reveal face of 10-foot ‘killer tadpole’ that terrorized Earth long before the dinosaurs

With huge teeth and large eyes, Crassigyrinus scoticus was specially adapted to hunt in the coal swamps of Scotland and North America.

The discovery of fossils never ceases to amaze us, and scientists have made yet another incredible discovery. Researchers have revealed the face of a prehistoric amphibian dubbed the ‘killer tadpole’ that lived over 300 million years ago, long before the dinosaurs. With a length of up to 10 feet, this creature was a top predator in its environment, using its powerful jaws to feed on small animals and insects. The discovery of this terrifying creature is shedding new light on the history of life on Earth, and is opening up doors for new research and understanding of our planet’s past.

Crassigyrinus scoticus lived 330 million years ago in wetlands of what is now Scotland and North America.
Crassigyrinus scoticus lived 330 million years ago in wetlands of what is now Scotland and North America. © Bob Nicholls | Fair Use.

By piecing together fragments of an ancient skull, scientists have reconstructed the haunting face of a 330 million-year-old crocodile-like “tadpole” creature, revealing not only what it looked like but also how it may have lived.

Scientists have known about the extinct species, Crassigyrinus scoticus, for a decade. But because all known fossils of the primordial carnivore are severely crushed, it has been difficult to find out more about it. Now, advances in computed tomography (CT) scanning and 3D visualization have allowed researchers to digitally piece the fragments back together for the first time, revealing more details about the ancient beast.

The process of fossilisation has caused specimens of Crassigyrinus to become compressed.
The process of fossilisation has caused specimens of Crassigyrinus to become compressed. © The Trustees of the Natural History Museum, London | Fair Use.

Previous research has shown that Crassigyrinus scoticus was a tetrapod, a four-limbed animal related to the first creatures to transition from water to land. Tetrapods began appearing on Earth around 400 million years ago, when the earliest tetrapods started evolving from lobe-finned fishes.

Unlike its relatives, however, past studies have found Crassigyrinus scoticus was an aquatic animal. This is either because its ancestors returned from land to the water, or because they never made it to land in the first place. Instead, it lived in coal swamps – wetlands which over millions of years would turn into coal stores – in what is now Scotland and parts of North America.

The new research, carried out by scientists at University College London, shows the animal had huge teeth and powerful jaws. Although its name means “thick tadpole,” the study shows Crassigyrinus scoticus had a relatively flat body and very short limbs, similar to a crocodile or alligator.

“In life, Crassigyrinus would have been around two to three meters (6.5 to 9.8 feet) long, which was quite big for the time,” lead study author Laura Porro, a lecturer in cell and developmental biology at University College London, said in a statement. “It would probably have behaved in a way similar to modern crocodiles, lurking below the surface of the water and using its powerful bite to grab prey.”

Crassigyrinus scoticus was also adapted to hunt prey in swampy terrain. The new facial reconstruction shows it had large eyes to see in muddy water, as well as lateral lines, a sensory system that allows animals to detect vibrations in water.

3D reconstruction of the cranium and lower jaws of Crassigyrinus scoticus in articulation. Individual bones shown in different colors. A, left lateral view; B, anterior view; C, ventral view; D, posterior view; E, articulated lower jaws (no cranium) in dorsal view; F, cranium and lower jaw in dorsolateral oblique view; G, articulated lower jaws in dorsolateral oblique view.
3D reconstruction of the cranium and lower jaws of Crassigyrinus scoticus in articulation. Individual bones shown in different colors. A, left lateral view; B, anterior view; C, ventral view; D, posterior view; E, articulated lower jaws (no cranium) in dorsal view; F, cranium and lower jaw in dorsolateral oblique view; G, articulated lower jaws in dorsolateral oblique view. © Porro et al | Fair Use.

Although much more is known about Crassigyrinus scoticus, scientists are still puzzled by a gap near the front of the animal’s snout. According to Porro, the gap may indicate that scoticus had other senses to help it hunt. It may have had a so-called rostral organ that helped the creature detect electric fields, Porro said. Alternatively, scoticus might have had a Jacobson’s organ, which is found in animals such as snakes and helps to detect different chemicals.

In earlier studies, Porro said, scientists reconstructed Crassigyrinus scoticus with a very tall skull, similar to that of a Moray eel. “However, when I tried to mimic that shape with the digital surface from CT scans, it just didn’t work,” Porro explained. “There was no chance that an animal with such a wide palate and such a narrow skull roof could have had a head like that.”

The new research shows the animal would have had a skull similar in shape to a modern crocodile’s. To reconstruct what the animal looked like, the team used CT scans from four separate specimens and pieced the broken fossils together to reveal its face.

“Once we had identified all of the bones, it was a bit like a 3D-jigsaw puzzle,” Porro said. “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.”

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


The study was originally published in the Journal of Vertebrate Paleontology. May 02, 2023.