Some eighty-three million years ago, a large meat-eating dinosaur roamed what is now northern Patagonia in Argentina, and its scattered remains, found near Cerro Overo, have now been given a name: Rinconraptor pipoae. The find is modest, a handful of tail bones and fragments of limbs, yet it adds a new voice to a family of predators whose fossil story has been faint and disputed for years. It also hints at an older question of how two kinds of apex hunters, megaraptorids and abelisaurids, managed to share the same land, perhaps by dividing its resources between them.
Newly Described Megaraptorid Rinconraptor pipoae Adds Predatory Dinosaur Diversity to Late Cretaceous Patagonia
Two groups of apex predators sharing time and space
Mark
So what exactly was found at Cerro Overo?
Mimi
An incomplete skeleton: 10 tail vertebrae, part of a bone from the underside of the tail, the lower end of a left upper-arm bone and the upper end of a right shinbone. The shinbone was still in rock; the rest lay across about 4 square meters.
Mark
And that's enough to name a new species?
Luke
The team says so, by comparing the vertebrae with better-known relatives. But it's worth remembering the length of about 7 meters is an estimate from that comparison, not a measured skeleton.
Mimi
Same for the tail count. They calculate more than 40 to 45 segments; they didn't find them all.
Mark
Why do megaraptorids matter?
Mimi
They've turned up in Argentina, Brazil, Australia, Thailand and Japan, but the record is scarce and fragmentary, so how they relate to other dinosaurs is still debated.
Mark
The paper also talks about competition with abelisaurids. What's the claim?
Mimi
Both groups of apex predators were present in the same area during the Santonian, in medium and large sizes. That could mean competition, or some division of ecological roles.
Luke
Careful there. The researchers say it "may have" led to competition and the record "could indicate" partitioning. Those are hypotheses, not findings.
Mark
Is there anything beyond the predators?
Mimi
Titanosaurs and several kinds of ornithopods lived there too, which is why they call it a high-biodiversity ecosystem.
Luke
And we don't know yet how the other megaraptorid bones relate to Rinconraptor; the authors couldn't assign them to a species.
Le Pouls
- A new predator of roughly seven meters has emerged from a small, incomplete skeleton, unsettling the thin record of its family.
- Scattered bones across about four square meters of rock near Cerro Overo were pieced together by a team led by Ariel Hernán Méndez.
- Several other megaraptorid bones from the same site, some suggesting animals up to 8.5 meters, crowd the picture with more large hunters.
- Abelisaurids shared the landscape, so researchers are working out whether these rival predators competed or carved out separate niches.
- The findings, published in Palaeontologia Electronica, await further fossils from the Bajo de la Carpa Formation to confirm the niche-partitioning idea.
Some eighty-three million years ago, a large meat-eating dinosaur roamed what is now northern Patagonia in Argentina, and its scattered remains, found near Cerro Overo, have now been given a name: Rinconraptor pipoae. The find is modest, a handful of tail bones and fragments of limbs, yet it adds a new voice to a family of predators whose fossil story has been faint and disputed for years. It also hints at an older question of how two kinds of apex hunters, megaraptorids and abelisaurids, managed to share the same land, perhaps by dividing its resources between them.
On a patch of ground at Cerro Overo, about 50 kilometers southwest of Rincón de los Sauces in northern Patagonia, bones lay scattered across roughly four square meters. One shinbone was still locked in rock. Together they belonged to a predator now named Rinconraptor pipoae, a new genus and species of megaraptorid dinosaur that lived around 83 million years ago.
The skeleton is incomplete. It includes ten tail vertebrae, part of an underside tail bone, the lower end of an upper-arm bone and the upper end of a shinbone. Paleontologist Ariel Hernán Méndez and his CONICET colleagues read these modest remains as something new. Megaraptorids, known for curved, 8-shaped teeth and large clawed hands, have been recognized for about a decade across Argentina, Brazil, Australia, Thailand and Japan, but their fossil record remains sparse and their relationships are still debated.
Comparing the vertebrae with better-known relatives, the team estimates the animal was about seven meters long. The site also yielded other megaraptorid bones, suggesting medium and large individuals shared the same ground.
That shared ground held more than one kind of apex hunter. Abelisaurids, another group of carnivorous dinosaurs, also lived there, along with titanosaur sauropods and ornithopods. The researchers suggest these predators may have competed, or may have divided the ecosystem's resources to coexist. For now that idea rests on an incomplete skeleton and a scattering of other bones, and further finds from the Bajo de la Carpa Formation will be needed to test it.
On a patch of ground at Cerro Overo, roughly 50 kilometers (30 miles) southwest of the city of Rincón de los Sauces in northern Patagonia, Argentina, bones lay scattered across about 4 square meters (43 square feet). One of them, a shinbone, was still locked in rock. Together they belonged to a predator that paleontologists have now named Rinconraptor pipoae, a new genus and species of megaraptorid dinosaur.
The animal lived in the Late Cretaceous, around 83 million years ago. The skeleton is incomplete. The main specimen includes 10 tail vertebrae, part of a bone from the underside of the tail, the lower end of a left upper-arm bone and the upper end of a right shinbone. It is a modest set of remains, but enough for the team led by CONICET paleontologist Ariel Hernán Méndez to recognize something new.
Megaraptorids are medium- to large-sized theropods. Méndez and colleagues describe them as having strongly curved teeth with an 8-shaped outline, long and slender hind-limb bones, highly pneumatic skull and vertebral elements, and large, trenchant claws on the hands. The group was recognized a decade ago. Its remains have turned up in Argentina, Brazil, Australia, Thailand and Japan, yet the researchers note that the fossil record is scarce and fragmentary, which has left the group's evolutionary relationships a matter of debate among specialists.
By comparing the vertebrae with those of better-known relatives, the team estimates that Rinconraptor was about 7 meters (23 feet) long. They also calculate that it had more than 40 to 45 tail segments, a pattern similar to that of Tyrannosaurus.
The bones come from the Bajo de la Carpa Formation, part of the Río Colorado Subgroup within the Neuquén Group, in the Upper Cretaceous of the Neuquén Basin. The researchers say this formation records a variety of paleoenvironments shaped by wind-driven and river-driven deposition across the basin.
Rinconraptor was not the only megaraptorid in the paper. Méndez and co-authors also describe several other megaraptorid bones from the same area that they could not assign to a species. Estimated body lengths for these animals range from about 6 to 8.5 meters (20 to 28 feet), so the area held both medium and large individuals.
That matters because of who else lived there. During the Santonian, the Cerro Overo-La Invernada area also has a record of medium- and large-sized abelisaurids, another group of carnivorous dinosaurs. The scientists write that two groups of apex predators sharing time and space may have competed for resources. But the theropod fossil record there could also point to some partitioning of ecological niches, a way of avoiding direct competition and allowing coexistence.
The researchers call this especially relevant because the area represents an ecosystem with high faunal biodiversity. Besides the predators, it included titanosaur sauropods, elasmarian ornithopods and other indeterminate ornithopods, among other species.
The work was published online this month in Palaeontologia Electronica, under the title on expanding the dinosaur diversity of the Cerro Overo-La Invernada area. What to watch is whether further finds in the Bajo de la Carpa Formation can test the niche-partitioning idea, which for now rests on an incomplete skeleton and a scattering of other bones.
Citations marquantes
The presence of two groups of apex predators sharing time and space may have led to competition for resources.— Ariel Hernán Méndez and colleagues
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