Bakiribu waridza: Fossilised Vomit Reveals a Filter-Feeding Pterosaur in Brazil

Two small pterosaurs flew over what is now north-eastern Brazil around 110 million years ago. Each was approximately the size of a seagull, and both eventually became food for a far larger animal.

The next events seem improbable, until nature’s untidiness is taken into account. The predator subsequently regurgitated the material it could not digest – principally the skulls – together with four fish from a more recent meal.

This expelled collection fossilised, remained in a museum collection for decades, and has now exposed an unexpected presence: a filter-feeding pterosaur in a location where researchers had not anticipated one.

The newly identified species has been named Bakiribu waridza. Its name translates as “comb mouth” in the Kariri language, referring to its unusual feeding apparatus.

Discovering Bakiribu waridza

Scientists have collected and investigated fossils from the Araripe Basin for generations. The area is renowned for preserving fragile remains, among them numerous pterosaurs.

For that reason, the find surprised the research team. Despite decades of investigation and an extensive catalogue of known flying reptiles, this type of pterosaur had never previously been recorded there.

Rubi Vargas Pêgas is a postdoctoral researcher at the Museum of Zoology of the University of São Paulo (MZ-USP).

“It was very unexpected, because fossils from the Araripe region have been studied for decades and almost 30 types of pterosaurs had already been found, none of them filter feeders,” said Vargas Pêgas. “We didn’t expect to find a new family for that region.”

The creature’s way of life set it apart. Filter-feeding pterosaurs are recognised by their fine, densely arranged, bristle-like teeth, which functioned more like a living sieve than the sharp teeth commonly associated with a predator.

They probably used these teeth to strain small aquatic prey, including tiny crustaceans, from the water.

Pterosaur fossil surprised scientists

At the relevant time, the Araripe Basin is generally characterised as an environment influenced by salt water. In contrast, filter-feeding pterosaurs have often been associated with freshwater habitats.

That apparent contradiction makes the fossilised regurgitation particularly important. It could account for how an animal linked to freshwater came to be preserved in a setting that seems inconsistent with its presumed habitat requirements.

Pêgas notes that Araripe was not a vast, uniform landscape. It was comparatively small and lay beside environments that may have left little trace in the fossil record.

“It was therefore an environment surrounded by others that weren’t necessarily preserved in the fossil record. This species might never have been known if it hadn’t been regurgitated in Araripe, known for the preservation of its fossils,” said Vargas Pêgas.

Put simply, the animal may have lived and fed in a nearby area. Its habitat might not have been suitable for fossil preservation, with the creature appearing in Araripe only because a predator transported it there.

Fossilised vomit tells all

The pterosaur fossil is classified as a “regurgitallite”, meaning fossilised vomit. The rock block holds remains from two pterosaurs as well as four fish.

The pterosaur bones bear erosion consistent with exposure to stomach acids, indicating that the predator began digesting its prey before abandoning the most difficult pieces.

By comparison, the fish were remarkably well preserved. This suggests they were consumed after the pterosaurs and spent less time being broken down.

The varied prey within the deposit also points to an opportunistic hunter capable of eating a diverse diet.

Clue in pterosaur fossil alignment

Researchers were particularly interested in one feature: all the remains were arranged in the same direction. Rather than being an odd coincidence, this may reveal how the predator ate.

“Today’s fish-eating birds swallow animals whole by the head to avoid choking on fins,” said study coordinator Aline Ghilardi, a professor at the Federal University of Rio Grande do Norte (UFRN).

“Whoever ate the Bakiribu and the fish probably did so in the same way, since they are all oriented in the same direction.”

This head-first arrangement cannot by itself establish the predator’s identity. However, it supports the view that the animal swallowed its prey whole instead of tearing it apart. It is also consistent with what is known about certain regional hunters.

Identifying the ancient eater

The team assessed two possible predators. A spinosaurid dinosaur, a group known for eating fish, is regarded as the most probable culprit.

One candidate is Irritator challengeri. This predator was sufficiently large to hold two small pterosaurs, four fish, and perhaps other prey in its stomach before later regurgitating the indigestible remains.

Another, less probable, explanation is that the predator was a pterosaur itself. With a wingspan of around eight metres, Tropeognathus mesembrinus was large enough to swallow smaller flying reptiles.

Nevertheless, the dinosaur interpretation appears to suit the wider evidence better, particularly the fish-rich meal and the established ecology of spinosaurids.

Rediscovering a forgotten fossil

The fossil was not a recent excavation. Instead, it was located in an established collection at the Câmara Cascudo Museum at UFRN, outside the Araripe region.

It came to light during a review of fish fossils, illustrating how routine research can become something much more significant when an unusual bone shape is noticed.

“Fish are very abundant organisms in the Araripe fossil record, which is perhaps why no one realized that among them was an animal that was still unknown,” said Vargas Pêgas.

After the material was identified as belonging to a pterosaur, Ghilardi assembled specialists and the group studied the fossil in Natal. Progress was rapid: the first paper draft was prepared within days.

Lessons from Bakiribu waridza

The rock block has been divided into two corresponding halves. One stayed in Natal, while the other was donated to the Plácido Cidade Nuvens Museum of Paleontology at the Regional University of Cariri (URCA), in Santana do Cariri, Ceará – nearer to the fossil’s original source.

“We incorporated an ethical and decolonial bias into this work. The transfer ensures the preservation of the piece in its territory of origin,” said Ghilardi.

Bakiribu waridza is part of the pterosaur family Ctenochasmatidae. Before this discovery, members of this family were known from Europe, East Asia and southern South America, including Argentina.

A tropical filter-feeding ctenochasmatid broadens the recognised distribution of these animals. It also suggests they were more adaptable to different habitats than previously thought. The discovery emerged only because a prehistoric predator could not keep down its meal.