A single partial pelvic bone has revealed that one of the earliest large meat-eating dinosaurs survived a major change in its ancient community—and may be the youngest member of its group ever found. Herrerasauridae were the oldest large-bodied predatory dinosaurs known from the Late Triassic of South America.

Their remains had been found in communities dominated by rhynchosaurs, but not in younger layers where Exaeretodon was abundant. Then a partial pelvic bone was recovered from those Exaeretodon-dominated layers in southern Brazil. Its distinctive combination of features, including expanded ends on the lower bone, identifies it as a herrerasaurid.

That matters because the animal was still present after the community changed. The find expands the known variety of large predators there and suggests these dinosaurs could keep the top predator role under changing conditions.

The missing fossils had suggested a possible problem: perhaps these predators depended on rhynchosaurs for food, so the decline of those herbivores might have prevented the predators from surviving. But rhynchosaurs became less common rather than disappearing. That means their decline alone may not explain why herrerasaurid fossils seemed absent from the younger deposits.

The new bone changes that picture. It shows that herrerasaurids persisted through the major shift from rhynchosaur-dominated communities to communities dominated by Exaeretodon, extending the known time range of the group. The bone is extremely fragmentary, but it has particular features found in only a few groups of ancient reptiles.

That made it possible to place the specimen more precisely despite its poor condition. To test that placement, the specimen was compared with a broad range of Triassic relatives using many skeletal features. The analysis was designed to assess where the material belongs among these animals.

The analysis placed the new specimen within Herrerasauridae in every resulting evolutionary arrangement, with that placement holding across all most parsimonious trees. In other words, the surrounding herrerasaurid clade was supported by several shared skeletal features identified in the evolutionary analysis.

The specimen was grouped with several known herrerasaurids in the consensus tree, including Gnathovorax cabreirai, Herrerasaurus ischigualastensis, and Sanjuansaurus gordilloi. The wider group was placed within Herrerasauria, close to the split between the lineages that later included meat-eating dinosaurs and long-necked plant-eaters.

The discovery was unexpected in one specific setting: no herrerasaurid had previously been recorded from the Exaeretodon-dominated layers. The new specimen shows that these predators remained part of those ecosystems as rhynchosaurs declined and other animals became more abundant.

This may mean the group could live in ecosystems different from those usually associated with it. The exact prey remains uncertain because there is no direct evidence showing which animals these predators attacked. The find also increases the known variety of relatively large predators at the site.

Because herrerasaurids could reach large body sizes, they were likely the largest predators there when fully grown and may have occupied the top position in the food web. The specimen may also be the youngest known herrerasaurid record worldwide.

That possibility comes from evidence that Exaeretodon-rich layers in a better-studied Argentine sequence are younger than layers containing other herrerasaurids. If the Brazilian layers follow the same pattern, this specimen would be younger than several other known herrerasaurids, including Gnathovorax cabreirai, Staurikosaurus pricei, and previously reported indeterminate herrerasaurid remains.

But the rocks still need direct age measurements before that proposed timeline can be established securely across the Brazilian fossil localities. The timeline makes the gap visible: herrerasaurids appear in both rock intervals, while the newly highlighted upper interval also contains the plant-eating Exaeretodon.

The bone carries a combination of pelvic features shared only with herrerasaurids, and both its shape and its placement among related animals support that identification. It is the first herrerasaurid record from the Exaeretodon-dominated layers of the Hyperodapedon zone.

That means these predators lived in ecosystems unlike the ones where they had usually been found. The specimen may also represent the youngest known record of Herrerasauridae worldwide, although the study presents that conclusion cautiously here.

The finding also indicates that herrerasaurids persisted in ecosystems distinct from those typical of the Hyperodapedon Acme Zone, rather than disappearing. The find shows that these predators could persist as familiar herbivores declined and different animals became abundant.

For scientists, it redraws the ancient food web and may extend the group’s known history.