Early spinosaur bones reveal the rise of an unusual dinosaur dynasty

Spinosaurs were dinosaurs that broke all the rules. Instead of a skull optimized for biting power like T. rex, these Cretaceous carnivores evolved crocodile-like jaws, better suited to holding on to struggling prey. Many sported impressive sails on their backs, and at least a handful of species made a living catching fish along ancient shorelines instead of chasing down prey on land.

And now, thanks to a smattering of fossils from the 130-million-year-old rocks of Spain, scientists are revealing the beginnings of this unusual dinosaur dynasty. A new species, described in a study in Scientific Reports, is among the oldest spinosaurs known.

The new dinosaur is named Protathlitis cinctorrensis, which roughly translates to “champion of Cinctorres” in honor of a nearby town and the 2021 victory of the local football team in the UEFA Europa League. In life, the animal was likely more than 30 feet long and snapped at its prey with long, shallow jaws brimming with conical teeth. Whether Protathlitis had a huge thumb claw or an elaborate sail on its back, like other related species, will have to wait for additional fossils to turn up. Only a small collection of the dinosaur’s bones have been found since paleontologists started searching the site in 2002: part of the upper jaw and five vertebrae from the tail.

Working from a small number of bones makes identifying a new dinosaur species tricky. The Protathlitis fossils show a particular feature on the jaw not seen in other spinosaurs, says Field Museum paleontologist Matteo Fabbri, who was not involved in the new study. This subtle trait isn’t as obvious as a crest or horn, but still distinguishes Protathlitis as a new spinosaur distinct from known relatives.

The rocks where Protathlitis was found reveal that this area was once a prehistoric estuary where salt and fresh water mixed. The animal likely shared the region with others of its kind, such as the similarly sized Baryonyx, which favored wetland habitats where fish would have been plentiful and smaller prey dinosaurs would have come to drink. Protathlitis may have led a similar life stalking the ancient shorelines, but more fossils are needed to puzzle out what it looked like and how it behaved.

Another mysterious spinosaur also lived around the same time called Vallibonavenatrix—although it is possible that this dinosaur, also known from a handful of fossil fragments, was actually the same animal as the newly discovered Protathlitis.

Nevertheless, the discovery of yet more spinosaur remains from Spain underscores that western Europe was the crucible of early spinosaur evolution. “What’s surprising to me is the sudden explosion of new spinosaur species that have been described from Portugal, Spain, and the U.K. in the last years,” Fabbri says.

The ancient bones help piece together how these fish-eaters were beginning to diversify before spreading to what is now Brazil, Morocco, Laos, and other locales, ultimately becoming some of the largest land predators to stalk the Earth.

A river monster’s origins

Paleontologists split spinosaurs into two groups, one that was somewhat smaller and tended to lack sails, called baryonychines, and the larger, sail-bearing spinosaurines. The abundance of early spinosaur species in western Europe indicate that these major branches of the animal’s family tree originated on the continent long before the evolution of later giants like the famous Spinosaurus—a monstrous carnivore that could grow to more than 45 feet in length and had a five-foot-tall sail jutting from its back.

When Protathlitis lived, most of North America, Europe, and Asia were bound up in a supercontinent continent called Laurasia. “During the Early Cretaceous in Laurasia, the two spinosaur subfamilies occupied the western part of Europe,” says Andrés Santos‑Cubedo, a paleontologist at Jaume I University in Spain and lead author of the new study. The baryonychines, likely including Protathlitis, went on to become common in Europe, while the larger spinosaurines thrived in ancient Africa.

Precisely when spinosaurs began to evolve their aquatic abilities will require more research. For one thing, Fabbri notes, it’s likely that the very first spinosaurs evolved in the earlier Jurassic period but have not yet been discovered. Paleontologists are working backwards from the oldest definitive spinosaurs to find how the group split from other dinosaurs.

Just how well spinosaurs fared in the water is also under debate, and recent research has concluded that some species likely hunted near riversides while others may have dived completely underwater to chase prey. Everything from dense bones that acted as biological ballast to gut contents containing fish have underscored how important a semiaquatic life was to at least some spinosaurs.

Not enough of Protathlitis is known to determine whether the dinosaur was snapping after fish or preferred more terrestrial fare. “Adequate evaluation of the aquatic hypothesis requires biomechanical tests, as well as body and limb comparisons,” Santos‑Cubedo says.

Such studies are difficult because spinosaur fossils are “not very abundant,” he notes, but future discoveries may provide the necessary bones to investigate why some spinosaurs preferred to hunt on land while others lurked along the water’s edge.