Fierce ‘hell heron’ dinosaur puts new wrinkles in Spinosaurus origin story

Today, the southwestern coast of the U.K.’s Isle of Wight is a picturesque seascape framed by sandstone cliffs. But more than 125 million years ago, this vista was a savanna-like valley cut through with rivers and floodplains—a fitting home for two new hulking dinosaurs with sleek, crocodile-like skulls.

Described in the journal Scientific Reports, fossils found on the island belong to two new types of spinosaurid, an enigmatic group of large predatory dinosaurs famed for their croc-like appearance. Based on the proportions of close cousins, the two dinosaurs would have been intimidating to behold. Each was about 26 feet long, snout to tail, and roughly 6.6 feet tall at the hip.

Scientists gave them names to match: Ceratosuchops inferodios roughly translates to “horned, crocodile-faced hell heron,” drawing inspiration from proposals that spinosaurids were riverbank predators like today’s herons. Riparovenator milnerae means “Milner’s riverbank hunter” in tribute to U.K. spinosaurid expert Angela Milner.

The bones of both species are fragmentary, but they add crucial diversity to the ranks of spinosaurids, which are poorly understood and had bizarre anatomical features, such as croc-like snouts and the occasional giant sails on their backs.

The fossil discoveries may also shed light on spinosaurids’ evolutionary origins by pinning down the group’s family tree with greater accuracy. That, in turn, can help paleontologists studying the iconic dinosaur Spinosaurus, which made its home in the river systems of what is now northern Africa more than 95 million years ago.

For lead study author Chris Barker, a Ph.D. candidate at the University of Southampton, the study is the pinnacle of a lifetime of fascination with carnivorous dinosaurs. As a young child, he regularly visited London’s Natural History Museum, staring in awe at a cast of the spinosaurid Baryonyx—one of the closest relatives of Barker’s new discoveries.

“Being able to study something which as a kid you almost idolized—I recognize how privileged I am today,” he says.

The newly described fossils underscore just how many more dinosaurs there are still left to find. Ceratosuchops and Riparovenator hail from the Wessex Formation, part of a broader set of rock layers that paleontologists have combed over since the early 1800s.

“We are still, in many ways, in our infancy in our knowledge of the diversity of ancient dinosaurs,” says University of Maryland paleontologist Tom Holtz, an expert on spinosaurids who wasn’t involved with the new study. “We haven’t plateaued, even for what we think of as well-studied formations!”

Hunting for spinosaurs

Although fossils of spinosaurids have been known for more than a century, reconstructing the animals has been a decades-long slog. Fossils are rare and often fragmentary; the first known bones of Spinosaurus were destroyed in World War II, hindering efforts to study the creature.

In 1986, British paleontologists Alan Charig and Angela Milner announced that the rocks of Surrey, England, had yielded a largely complete spinosaurid that lived about 129 million to 125 million years ago. This fossil, named Baryonyx walkeri, confirmed that spinosaurids had sleek, crocodile-like skulls, large front claws, and long, slender necks. Baryonyx now serves as a key spinosaurid reference, helping to fill in the details of others that have since been found in Spain, Brazil, Thailand, Morocco, Niger, and Australia.

In the decades since, the rocks of southern England have yielded hints that Baryonyx wasn’t the only spinosaurid around. For instance, spinosaurid teeth found in the region’s rocks came in a variety of forms and shapes—perhaps consistent with variation from individual to individual, but perhaps also a sign of multiple species kicking around in the rocks.

Enter Neil Gostling, an evolutionary biologist at the University of Southampton. Gostling had been working to form a partnership with the Isle of Wight’s Dinosaur Isle Museum when he caught word that the museum had acquired some fossils found at Chilton Chine, a nearby coastal gully ringed by ancient sandstone cliffs. In 2019, Barker started his Ph.D. under Gostling and decided to take on the bones for his research.

Over several years, Barker carefully noted many different anatomical traits across the bones and compared those traits with those of known spinosaurids. When he and his colleagues ran computer models on these data, they found that the Isle of Wight remains probably represented two different types of spinosaurid, both of which were close relatives of Baryonyx and a spinosaurid from Niger called Suchomimus.

Near the project’s end, Barker, Gostling, and their colleagues put together an email chain to workshop the new dinosaurs’ names. Milner had died in August at the age of 73, following a distinguished career at the U.K.’s Natural History Museum. The team agreed that honoring her “just seemed like the right thing to do,” says Gostling. “She was the person who really brought it forward and made spinosaurs a group that people understood and were aware of.”

Strange migrations

For now, it’s not clear whether Ceratosuchops and Riparovenator overlapped in time with each other or with Baryonyx. The new dinosaurs’ bones fell out of the exposed cliffsides, making it that much harder to know which exact rock layers entombed them—information that would more accurately date the bones. The best estimate is that both new species lived roughly 129 million to 125 million years ago during the early Cretaceous period.

Still, the new study sheds light on spinosaurids’ movement across ancient Earth. When Barker and his colleagues made an updated family tree for the group, they found that most of the oldest species near the base of the tree lived in what’s now Europe.

That discovery strengthens the idea that spinosaurids’ ancestral homeland was in the Northern Hemisphere, possibly within Europe. If so, spinosaurids migrated into what’s now Africa at least twice: one wave that yielded Niger’s Suchomimus, and a second, later wave that gave rise to Spinosaurus and its North African kin.

But if spinosaurids arose in Europe, a major dino-mystery deepens. Throughout much of the age of dinosaurs, Europe, Asia, and North America were connected. Spinosaurid remains have been found in Europe and Asia, but no clear fossil evidence of the group has ever been found in North America.

The absence of North American spinosaurids is all the more puzzling because other dinosaur groups clearly had no problem moving between North America and Asia during this time. There are no obvious signs that spinosaurids would have lacked North American real estate. Rock formations in Montana, Wyoming, Utah, Texas, and Maryland all date to when spinosaurids lived elsewhere, and they preserve spinosaurids’ preferred coastal or river habitats.

“There’s nothing really super-special that might have excluded them—so yeah, this is a curious fact,” Holtz says. “All we need to do is discover one tooth.”

Back on the Isle of Wight, Barker and Gostling’s work on spinosaurids is only just beginning. Barker notes that the fossils of Ceratosuchops and Riparovenator include portions of the dinosaurs’ braincases, which means that future scans of the fossils could provide data on the animals’ brain shapes.

They add that the Isle of Wight has yielded more spinosaurid fossils that are waiting to be described—material that will stay with Ceratosuchops and Riparovenator in the Dinosaur Isle Museum, providing a scientific destination and a cultural landmark for the Isle of Wight.

“We cannot stress how important having a dinosaur museum—a functional, proper dinosaur museum—on the Isle of Wight is for the Isle of Wight dinosaurs,” Gostling says. “They’re not being sent somewhere else around the world. They’re in the place where they were found.”