Fossil discovery shows the interaction between giant marine reptiles

By Steven Scarpa

Consider a moment from deep time.  

Approximately 160 million years ago, during the Age of Dinosaurs, giant marine reptiles ruled the seas. One such creature, an ichthyosaur, swam in a sea near present-day Peterborough, England. This huge animal, shaped like a dolphin, was a quick swimmer that chased around prey like ammonites and squid for its sustenance.  

However, on this day, luck was not on its side.  

A pliosaur, an even more imposing reptile with 5-inch-long, dagger-like teeth, attacked the ichthyosaur from underneath, biting with such force during the struggle that the tip of one of its teeth broke off in the middle of the ichthyosaur’s vertebra. The ichthyosaur’s body fell in pieces to the ocean floor, where the pliosaur finished its meal – a vivid scene inspired by the contents of a drawer in the Peabody’s Division of Vertebrate Paleontology. 

A paper by researchers Caleb Gordon and Daniel Brinkman of Yale and Giovanni Serafini of the University of Modena and Reggio Emilia published in the current issue of the Bulletin of the Peabody Museum of Natural History delves into the history of a unique fossil found in a drawer of “problematica” in the Peabody’s marine reptile collection. 

The fossil is an ichthyosaur vertebra punctured by the broken off tip of a tooth – a moment captured in time that fired Gordon’s curiosity.  

“I had initially thought when I saw this fossil that it was an ambush kill,” said Gordon, who was a PhD student at the time and currently serves as a postdoctoral researcher at the Florida Museum of Natural History. “These are intense force loads that are being exerted on the prey … That giant tooth in the giant jaw of a giant animal penetrated through the weakest, most fragile part of the vertebra, its very center, with enough force that the tip of the tooth broke off,” Gordon said.  

This triangular- shaped vertebra with a pointed tooth sticking out of its middle doesn’t just illustrate a moment of dramatic violence – it is a rare example of prehistoric animal interaction. The version of the encounter the scientists lean towards is the ambush theory, but there is also the possibility that the pliosaur scavenged an already dead creature, Gordon explained.  

“If it’s predation, which we lean towards, this was a chaotically violent moment for both of the creatures involved,” Gordon said.  

Gordon contacted Serafini, an expert on ichthyosaur carcasses, to get his take on whether this was an example of predation or scavenging. “What immediately caught my interest was how the tooth was piercing the vertebra in its exact center,” Serafini said. Serafini recognized that the fossil was from an ichthyosaur and that the bite must have occurred just above the tail.

Either way, the discovery is important to understanding life during the Late Jurassic of Europe.  

“It’s exciting to see a tooth punctured through a vertebra. Immediately, when you see a fossil like this, you think as a paleontologist, this captures a remarkable moment of interaction between two animals. They are vanishingly rare in the fossil record,” Gordon said.  

“This one-of-a-kind fossil is a direct window into the life of these extraordinary leviathans of the past,” Serafini said. 

Scientists had believed through indirect evidence that ichthyosaurs were likely fed upon by pliosaurs, and thanks to Gordon’s curiosity, they now have proof. “This can be really affirming for previous researchers to have their legitimate well-reasoned hypotheses validated by this more direct evidence,” Gordon said.  

The process began in September 2024 when Gordon rummaged through a drawer of mixed ichthyosaur fossils. He picked up a vertebra with a point in the middle. There was an information label with the specimen, but the six words on it weren’t particularly insightful.  

Enter Daniel Brinkman, the long-serving museum assistant in Vertebrate Paleontology at the Peabody.  

Using the specimen label as a starting point, Brinkman and Gordon investigated the vertebrate paleontology divisional archives to learn more about how the fossil was acquired and where it was from. Tracing the fossil’s complex archival history and knowing where it was collected was critical to identifying the two creatures involved. Brinkman and Gordon’s careful exploration of the divisional archives used history to help inform the science and vice versa.  

Their archival research showed that the fossil had to have been acquired by O.C. Marsh, Yale’s first professor of paleontology and the founder of the Peabody, sometime between 1863 and 1899. And that it was most likely collected around 1888 by Alfred Nicholson Leeds, a gentleman farmer and collector, from the Oxford Clay exposed at his family estate near Peterborough, England. The correspondence between Leeds and Marsh shows how paleontology was done during the field’s early days.  

“Marsh talked to a lot of people, went to a lot of places, and had a lot of professional correspondence. And he was acquiring specimens during the early days of the Peabody, when record keeping was not yet fully standardized,” Brinkman said. 

Thought to be acquired in 1888, the fossil was not catalogued until 1927 and then largely ignored for several decades. The original label for the specimen indicated only that the fossil was from Europe and that it had been donated by O.C. Marsh. Peabody curator John Ostrom, or a member of his team, sometime in the 1980s, created a new label for the fossil and attributed it to Leeds. It then went back into the drawer until catching Gordon’s eye.  

“This specimen highlights how human collections-based research can be,” Gordon said. “To figure out which animal this was, we needed to know when and where it was from, and to do that, we combed through old specimen tags and estate maps and 19th-century letters in barely legible cursive. We needed to learn more about the people who had handled this specimen before and the professional relationships they had.” 

This paper demonstrates how maintaining a historical collection can be a fluid enterprise, and one that might not readily yield its secrets.  

In this instance, modern technology allowed a level of understanding that would have eluded Marsh and Ostrom. The team analyzed the fossil using high-magnification microscopy and Micro-CT scans, giving them a look at the broken tooth’s anatomy and shape that would otherwise be obscured by ichthyosaur bone, thus helping them to identify Pliosaurus as the aggressor in the feeding frenzy. 

The team’s work demonstrates the importance of museum archives for collections-based paleontological research. 

Leeds likely found the fossil. Marsh secured it. And over a century later, Gordon, Serafini, and Brinkman used it to demonstrate a previously unverified but long-suspected behavior: that pliosaurs fed on ichthyosaurs in the Late Jurassic seas.  

“There are many more fossils than there are paleontologists to study them,” Gordon said. “And there is an enormous backlog of absolutely incredible and perspective-changing fossils waiting to be described in museum collections around the world.”