What bone scans reveal about a tiny crocodilian from the Jurassic era

Journeying back to the Jurassic era, scientists used cutting-edge tech to uncover the secrets about Orthosuchus stormbergi, a small, early crocodile ancestor. Their results are published in the Journal of Anatomy.

Unlike its modern relatives, which are renowned for their massive size and aquatic prowess, this tiny croc offers unique insights into the evolution of its lineage. Standing out for its slow growth and diminutive adult size, Orthosuchus paints a fascinating picture of ancient ecosystems and crocodilian history.

Led by Ph.D. student Bailey Weiss from the Evolutionary Studies Institute and School of Geosciences at the University of the Witwatersrand, the team included Kathleen Dollman (European Synchrotron Radiation Facility), Jonah Choiniere (University of the Witwatersrand), Claire Browning (Iziko Museums of South Africa), and Jennifer Botha (University of the Witwatersrand and GENUS Center of Excellence in Palaeosciences).

Their research highlights how advanced imaging technology can illuminate the lives of ancient creatures.

Bailey explains, “Orthosuchus grew relatively slowly. This research also confirms that it was a small-bodied adult—the smallest known archosaur (the group that contains birds and crocodiles) from the Early Jurassic in South Africa, about 200 million years ago. It took three to four years to reach maximum body size, and the specimens we examined were eight and nine years old.”

To delve into the inner workings of Orthosuchus’ bones, the team used synchrotron radiation microcomputed tomography, a powerful imaging technique that acts like a supercharged CT scan. This method allowed the researchers to examine the bone’s microscopic structures in extraordinary detail without damaging these rare fossils.

Bailey notes, “We conducted the experiment at the European Synchrotron Radiation Facility in Grenoble, France. This institution produces some of the most powerful X-rays in the world, allowing for high-quality imaging at high resolutions. The method allowed us to study the inner bone structure without destroying the specimen, which is the classical osteohistological method.”

South Africa is a Scientific Associate of the ESRF and has a long-standing partnership with the synchrotron facility, enabling local researchers and students to access this world-class technology at no cost to their institutions.

But why does it matter that Orthosuchus grew slowly? The answer lies in the evolutionary history of crocodiles. “Modern crocodiles are slow-growing reptiles; however, their ancestors were fast-growing,” Bailey explains.

“It’s important to understand why, how, and when this transition from fast to slow growth occurred. This helps us learn what makes modern crocodiles the apex predators they are today and how they survived multiple mass extinctions.”

The team’s findings suggest that the evolutionary shift to slow growth (a trait that now defines modern crocodiles) may have begun earlier than previously thought, offering clues about how these ancient reptiles adapted to changing environments.

The scans revealed that Orthosuchus’ bones were compact and thick-walled, traits typically seen in aquatic animals. However, it lacked other features commonly associated with water-dwelling creatures, such as a flattened tail. This suggests that Orthosuchus may have had a semi-aquatic lifestyle, navigating between land and water.

Adding to the intrigue, some of its bones bore characteristics often found in digging animals. Today’s crocodiles dig burrows to escape extreme temperatures and it’s possible that Orthosuchus did the same. However, without specialized adaptations like thick claws, the researchers stopped short of labeling it a true digger.

Transporting a priceless fossil to a cutting-edge research facility wasn’t without its nerve-racking moments. “Going through international security with priceless national heritage in a very conspicuous briefcase was a little nerve-wracking,” Bailey recalls. “However, seeing the specimen scanned on the airport security X-ray machine was exciting.”

Bailey is eager to build on this research to better understand how growth patterns may have influenced survival during mass extinction events. “I’d like to continue investigating the growth patterns of early crocodilians. This research will help us understand if growth strategies allowed specific groups of animals to survive mass extinctions, such as the End-Triassic Extinction.”