In 2019, a team of researchers uncovered a 70-million-year-old dinosaur in a Patagonian province of Argentina. The dinosaur, a hunter, was a 23-foot-tall predator whose long, powerful arms were tipped with massive claws. And it came with an unexpected bonus.
As the team led by Lucio Ibiricu, a paleontologist at the Patagonian Institute of Geology and Paleontology, worked on the remains, they realized that a bone tucked between the jaws was not from the skeleton: it was, instead, the upper arm bone of a crocodile relative. The dinosaur’s teeth were actually touching the crocodile bone.
It was such a bizarre discovery that team members joked that the dinosaur had “choked on a croc leg,” said Matt Lamanna, a paleontologist at the Carnegie Museum. “We don’t believe that, but we also don’t think it’s impossible.”
He added, “Either it was feeding on this animal, or it’s nature playing one hell of a cruel joke on us.”
The group to which the dinosaur belonged, the megaraptors, is typically known only from scrappy remains that don’t include the bones of their dinner. But in a paper published Tuesday in the journal Nature Communications, a team including Ibiricu and Lamanna announced that their discovery is the most complete member of the megaraptor family. They named it the Joaquinraptor, after Ibiricu’s son, and argue that it shows that the megaraptors were some of Earth’s most powerful predators right up to the time of dinosaur extinction.
The first megaraptor was discovered in 1996 by Fernando E. Novas, an Argentine paleontologist. He spotted scattered bones — including a giant claw — and named the animal assuming it belonged to the same group as the velociraptors. As more bones came to light in South America, Asia and Australia, researchers wrangled over which dinosaurs the group was closest to in the broader family of predatory dinosaurs.
Some said they were related to allosaurs, tall powerful bipedal predators. Others pointed to the spinosaurs, wading hunters known for the sail-like spines on their backs. More recently, said Cassius Morrison, a paleontologist at University College London, many researchers have begun to converge on the idea that megaraptors are an older offshoot of the group that gave rise to other great hunters of the Cretaceous period, the tyrannosaurs.
With their relatively slender snouts and lengthy arms, the group seems like a mirror opposite of the terrifying but tiny-armed T. rex, Lamanna said. But members of the family seem to have had unusually light and air-filled bones, so they rarely fossilize well. That makes understanding them a tricky puzzle.
Over a series of years starting in 2019, Argentine paleontologists prospecting in the Chubut Province in Patagonia found 20% of a megaraptor skeleton, including an articulated forelimb, hind limbs, ribs and vertebrae. The most critical find was a skull with parts of the jaw and braincase, Ibiricu said.
As soon as they found that, he said, “We knew that this discovery was going to be a very important one.”
While 20% of a skeleton might not sound like much, Lamanna said, it makes Joaquinraptor one of the most complete megaraptor specimens ever found. Up to this point, researchers haven’t had much skull material to go on, and few megaraptor skeletons had only the same assortment of bones preserved, making comparisons difficult.
With several areas of the skeleton represented, Joaquinraptor is “the Rosetta stone” for the megaraptor family, Lamanna added.
None, up to this point, have come with a bonus crocodile bone. That discovery particularly amused Novas, a paleontologist at the Bernardino Rivadavia Natural Sciences Argentine Museum.
“It’s funny that Ibiricu’s team found this kind of extinct croc being chopped by Joaquinraptor,” said Novas, the first researcher to describe a megaraptor, and a member of a separate team that recently announced Kostensuchus, a large, fearsome land crocodilian, from similar deposits.
He added that the discovery suggests that megaraptors and land crocodiles interacted regularly in their ecosystem, much like the fearsome competition between modern jaguar and caiman in South American wetlands.
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