"Crooked" rhynchosaur described after 40 years

Based on a skull collected in the 1970s, scientists have published a description of Brasinorhynchus mariantensis, an herbivorous reptile thought to be an ancestor of today's crocodiles and birds.

By Peter Moon  |  Agência FAPESP – Brazilian paleontology’s most recent trophy is not a dinosaur, but a hitherto unknown species of rhynchosaur, a group of terrestrial herbivorous reptiles that were abundant in Triassic times and are thought to be among the ancestors of today’s crocodiles and birds. The discovery has been named Brasinorhynchus mariantensis.

Brasinorhynchus inhabited what is now Rio Grande do Sul, Brazil’s southernmost state, some 238 million years ago, in the Middle Triassic, approximately 7 million years before the first dinosaurs appeared. Large numbers of rhynchosaurs are known to have lived in the region, but none of them resembled Brasinorhynchus.

This makes the newly described species the oldest and most bizarre South American rhynchosaur, as well as the first to share unequivocal affinities with the rhynchosaurs that lived in Africa, offering additional evidence that these two continents were part of Gondwana before the supercontinent broke up.

The authors of the description are paleontologists Cesar Schultz, affiliated with the Federal University of Rio Grande do Sul (UFRGS), Max Langer from the University of São Paulo (USP), and Felipe Montefeltro from São Paulo State University (UNESP).

The article published in the journal Paläontologische Zeitschrift is the result of a study supported by FAPESP as part of the Thematic Project “The origin and rise of dinosaurs in Gondwana (late Triassic-early Jurassic)”.

The description of the new species is based on a somewhat deformed skull collected in the 1970s. “I’d known about the skull’s existence since 1980, when I saw it in the Department of Paleovertebrates at UFRGS,” Schultz said. “I first looked more attentively at that ‘crooked’ rhynchosaur in 1987 when I began working on my PhD. At the time, I was studying the way typical fossilization during the Triassic in Rio Grande do Sul deformed some fossils so much that they appeared to belong to different taxa. However, although it was clear that the skull had been laterally compressed, it wasn’t at all similar to the other rhynchosaurs from Rio Grande do Sul we were familiar with. It was longer than it was wide, exactly the opposite of the typical cranial morphology found in the region’s rhynchosaur fossils, which have broad skulls that aren’t particularly long.”

According to Schultz, the Brasinorhynchus fossil was found in Mariante, a district of Venâncio Aires, a small rural town in Rio Grande do Sul. It was almost discarded because there were many other rhynchosaur fossils, but the paleontologists eventually decided to dig it up. It came out whole and was taken to a laboratory.

In 1991, Schultz included the first studies of Brasinorhynchus in his doctoral thesis. “I produced a preliminary description,” he said.

Having later become a supervisor of graduate students in geosciences at UFRGS, in 1995 he began supervising his first master’s student, Max Langer, whose project unsurprisingly focused on rhynchosaurs. However, Langer set out to produce not an anatomical description of new specimens but a phylogenetic analysis.

As a result, the fossil then known as the “Mariante rhynchosaur” was analyzed along with the rest, but its description was not formally published. The task was given to a different masters student several years later. He made a start but eventually lost interest, so Brasinorhynchus was put back on the shelf and remained there for almost 20 years.

Meanwhile, Montefeltro completed his masters research with Langer as his supervisor. He again referred to the “Mariante rhynchosaur” and used it in comparisons, even though it had still not been formally identified.

Supportive Argentinians

This long scientific odyssey finally reached its conclusion in 2016. “Argentinian colleagues told me they’d found a similar animal and had started to describe it. They knew about the Brazilian fossil and said they’d wait for publication of our description before publishing theirs,” said Schultz, who made a point of stressing the Argentinians’ supportive attitude.

“The three of us met and worked flat out to finish the research, write up the description and have the paper published as quickly as possible,” said Langer, who heads the Paleontology Lab on USP’s Ribeirão Preto campus in São Paulo State.

“Brasinorhynchus must have been about the size of a large hog – some 3 m long including its tail. Its skull is elongated, narrow and deep, not unlike the cranium of a horse,” he added.

Like all rhynchosaurs, Brasinorhynchus had a bony beak (rhynchos in Greek), which it used to crop vegetation and cut it up as if with a knife. Its teeth were small, indicating that it ground its food up before swallowing. “None of today’s animals have similar dentition,” Langer said.

In the Middle Triassic, the pampa was home to animals we would find very strange. They were not dinosaurs, mammals, crocodiles, lizards, turtles or birds. All these life forms were yet to evolve.

This ancient landscape was dominated by primitive reptiles. According to the fossil record from Rio Grande do Sul in the Middle Triassic, 238 million years ago, there were dicynodonts and cynodonts, the latter possibly being the ancestors of all mammals.

There were also archosauromorphs, the lineage from which crocodiles and birds evolved. Rhynchosaurs belonged to this group, together with the largest predator at the time, Prestosuchus, a fearsome carnivore about the size of a large crocodile.

According to the fossil record from the same region, both the dicynodonts and Prestosuchus had disappeared by the Late Triassic, 231 million years ago. The rhynchosaurs, in contrast, had greatly multiplied. This was when a new group of animals destined to dominate the planet for the next 150 million years began to emerge, timidly at first.

They were the first dinosaurs, of which the oldest fossils have been found in Argentina and Rio Grande do Sul in Brazil. And the first carnivorous dinosaurs probably preyed on rhynchosaurs.

The article “A new rhynchosaur from south Brazil (Santa Maria Formation) and rhynchosaur diversity patterns across the Middle-Late Triassic boundary” (doi: 10.1007/s12542-016-0307-7) by Cesar Leandro Schultz, Max Cardoso Langer and Felipe Chinaglia Montefeltro, published in Paläontologische Zeitschrift, can be read at link.springer.com/article/10.1007%2Fs12542-016-0307-7.