Researcher from Ohio collaborates on new study about pterosaurs

December 5A reconstruction of a pterosaur (top) and a lagerpetid (bottom) from the Late Triassic period, around 215 million years ago. The 3D models on the right illustrate brain reconstructions based on computed tomography scans. (Image courtesy of Rodrigo Mller, Mario Bronzati, Matheus Fernandes)

Flight is a rare trait in the animal kingdom. It has only developed three times in vertebrates: in bats, birds, and the long-extinct pterosaurs. Pterosaurs were the first to conquer the skies more than 220 million years ago, long before early bird relatives like Archaeopteryx emerged. While scientists have gathered extensive information on how birds' brains adapted for flight, the neurological development of pterosaur flight has remained a mystery.

A groundbreaking study published in Current Biology and co-authored by Lawrence Witmer from Ohio University, along with international collaborators, now offers new insights into how pterosaurs evolved the necessary brain structures for powered flight. This marks a return to a research path Witmer began over twenty years ago, when his 2003 Nature paper revealed the complex brain and inner-ear structures that allowed pterosaurs to maneuver in the air. The new study expands on these early findings, providing the clearest view yet of how pterosaurs developed the neural "flight systems" that allowed them to soar.

Witmer, a professor of anatomy at the Ohio University Heritage College of Osteopathic Medicine, explains, "While we had plenty of information about early birds, which inherited their brain layout from theropod dinosaurs, pterosaur brains seemed to emerge out of nowhere. Now, with our first glimpse of an early pterosaur relative, we see that pterosaurs built their 'flight computers' independently."

The breakthrough came with the discovery of an ancient pterosaur relative, the lagerpetid archosaur Ixalerpeton, from 233-million-year-old Triassic rocks in Brazil. Mario Bronzati, lead author of the study and an Alexander von Humboldt fellow at the University of Tbingen, Germany, said, "This find was crucial in understanding how flight-related brain structures evolved in pterosaurs."

The researchers used high-resolution 3D imaging techniques, including microCT scanning, to reconstruct the brain shapes of more than thirty species. These included pterosaurs, their relatives like Ixalerpeton, early dinosaurs, bird ancestors, and modern animals like crocodiles and birds.

Coauthor Akinobu Watanabe, an associate professor at the New York Institute of Technology College of Osteopathic Medicine, said, "By analyzing the size and shape of the cranial endocasts, we mapped the evolutionary changes in brain anatomy that accompanied the development of flight."

Flight is a highly demanding form of movement, and it is believed to require major neurological adaptations, including an enlarged brain to coordinate the complex sensory and motor information needed for powered flight. Prior studies of pterosaur brain structure have shown that they shared some features with bird precursors like Archaeopteryx, such as the enlargement of brain regions related to sensorimotor integration and visual processing.

Ixalerpeton, the lagerpetid that is a close relative of pterosaurs, exhibited some, but not all, of the neurological traits found in pterosaurs. For instance, lagerpetids were likely tree-dwellers, and their brains already displayed features related to enhanced vision, like an enlarged optic lobe. Bronzati noted, "This adaptation may have helped pterosaurs take to the skies, but Ixalerpeton lacked other key neurological traits of pterosaurs."

Despite its similarities, Ixalerpeton's brain was intermediate in shape between more primitive archosaurs and pterosaurs, and it retained closer similarities to early dinosaurs. It also lacked the expanded flocculus seen in pterosaursan important structure in the cerebellum that processes sensory information from the wings to help maintain visual focus during flight. Instead, Ixalerpeton had a modest flocculus, similar to those found in other archosaurs, including early birds and nonavian theropods.

The study also revealed that pterosaurs had smaller brains than birds, a finding that suggests large brain size is not a prerequisite for flight. As coauthor Matteo Fabbri, assistant professor of Functional Anatomy and Evolution at Johns Hopkins University School of Medicine, explains, "Despite some similarities with birds, pterosaurs had much smaller brains, showing that a large brain is not necessary for flying."

Interestingly, the overall brain shape of pterosaurs resembled that of small, bird-like dinosaurs, such as troodontids and dromaeosauridsdinosaurs with little or no flight ability. The study reinforces that birds and pterosaurs represent two independent evolutionary experiments in flight. While birds inherited an already adapted brain from their non-flying dinosaur ancestors, pterosaurs developed their flight-ready brains concurrently with their wings.

A significant takeaway from the study, according to Witmer, is that "a large brain isn't necessary for flight, and the brain expansion in both birds and pterosaurs was likely more about enhancing cognition than the act of flying itself."

Another key insight is the importance of paleontological fieldwork in uncovering new discoveries. Rodrigo Temp Mller, a paleontologist at Universidade Federal de Santa Maria in Brazil, emphasized, "New fossils and studies from southern Brazil have drastically improved our understanding of the early relatives of dinosaurs and pterosaurssomething that was unimaginable just a few years ago."

Author: Ava Mitchell