A single bone from southern Brazil indicates that herrerasaurids, among the first large meat-eating dinosaurs, persisted after the fauna around them changed.
An artistic representation of the CAPPA/UFSM 0539 herrerasaurid dinosaur in life. Image credit: Johnny Pauly V. Mingau.
Herrerasaurid dinosaurs lived during the Carnian age of the Late Triassic epoch, roughly 230 million years ago.
They were bipedal hunters with serrated teeth and large claws on their hands, and some grew longer than 5 m (16 feet).
The group is known only from South America, from fossils found in Argentina and Brazil.
Until now, herrerasaurids in both countries had come only from rock layers dominated by rhynchosaurs, stocky plant-eating reptiles.
Younger layers, where a pig-sized cynodont relative of mammals called Exaeretodon became more abundant and rhynchosaurs declined, had produced none.
The absence raised the possibility that herrerasaurids died out when the fauna shifted.
“The absence of herrerasaurid records from strata characterized by abundance of Exaeretodon could reflect faunal changes that ultimately prevented the persistence of the group,” said Dr. Rodrigo Temp Müller, a paleontologist at the Universidade Federal de Santa Maria.
“For example, if herrerasaurids were ecologically specialized for preying upon rhynchosaurs, the decline of these herbivores may have negatively affected their survival.”
“However, although rhynchosaurs become less abundant in these younger assemblages, they are not absent from the fauna.”
“Consequently, this alone may not adequately explain the apparent absence of herrerasaurids from these deposits.”
In the study, Dr. Müller examined a fragment of a herrerasaurid pubis (hip bone) that was collected at a site near the town of Agudo in Rio Grande do Sul, Brazil.
Catalogued as CAPPA/UFSM 0539, the fossil is the first herrerasaurid record from rock layers where Exaeretodon is abundant.
“The specimen was collected from the Várzea do Agudo site, located in the municipality of Agudo, Rio Grande do Sul, Brazil,” Dr. Müller said.
“The fossil-bearing strata at this site belong to the Santa Maria Formation, Paraná Basin.”
The author suggests that herrerasaurids were adaptable enough to survive in changed ecosystems, and that they may have been the top predators at the site.
He also raises the possibility that this is the youngest herrerasaurid known, but only if the Brazilian rocks are younger than other herrerasaurid-bearing layers, as they are in Argentina.
“Absolute dating of the Brazilian strata remains essential to establish a more reliable chronological framework for the different Triassic fossil-bearing localities,” the researcher said.
The study was published on October 19, 2026 in The Science of Nature.
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R.T. Müller. 2026. First occurrence of a herrerasaurid dinosaur in a traversodontid cynodont-dominated Late Triassic fauna of southern Brazil. Sci Nat 113, 133; doi: 10.1007/s00114-026-02185-1
