Journeying back to the Jurassic era, scientists have unraveled fascinating insights into the evolutionary history of crocodilians through the study of Orthosuchus stormbergi, a small crocodile ancestor from about 200 million years ago. Unlike its modern descendants, which are often synonymous with immense size and aquatic dominance, Orthosuchus reveals a vastly different picture of early crocodilian life. This discovery, now published in the Journal of Anatomy, sheds light on the unique adaptations and evolutionary trajectory of one of Earth’s most resilient lineages.
The research team, spearheaded by Bailey Weiss, a Ph.D. student at the Evolutionary Studies Institute and School of Geosciences at the University of the Witwatersrand, brought together experts from South Africa and Europe. Collaborators included Kathleen Dollman of the European Synchrotron Radiation Facility (ESRF), Jonah Choiniere from the University of the Witwatersrand, Claire Browning from Iziko Museums of South Africa, and Jennifer Botha of the GENUS Center of Excellence in Palaeosciences. Together, they employed cutting-edge imaging techniques to unlock secrets embedded in the fossilized bones of Orthosuchus without causing any damage.
Orthosuchus stood out in the fossil record due to its small adult size and slow growth rate. Bailey Weiss explained that this creature was the smallest known adult archosaur (a group encompassing crocodiles and birds) from the Early Jurassic in South Africa. “It took three to four years to reach its maximum body size, and the specimens we studied were already eight and nine years old,” she said. This contrasts sharply with its fast-growing ancestors, marking a pivotal shift in crocodilian evolution.
The team used synchrotron radiation microcomputed tomography (SRµCT), a sophisticated imaging method akin to a highly advanced CT scan. This technique provided an unparalleled view of the internal bone structures while preserving the fossils. Conducted at the European Synchrotron Radiation Facility in Grenoble, France, the experiment utilized some of the most powerful X-rays available globally. “The ESRF allows us to image fossil bones at resolutions that were unimaginable just a few decades ago,” said Bailey. “By studying the microscopic features within the bone, we gain valuable insights into the life and environment of Orthosuchus.”
South Africa, a long-term partner of the ESRF, played a key role in enabling access to this state-of-the-art technology. This collaboration highlights the importance of international partnerships in advancing paleontological research. However, transporting a fossil of such historical and scientific value posed its own challenges. Bailey recalled the nerve-wracking experience of navigating international security with a briefcase containing priceless national heritage. Despite the anxiety, she described watching the fossil pass through the airport’s security X-ray scanner as oddly thrilling.
The importance of Orthosuchus extends beyond its physical characteristics. Its slow growth provides crucial context for understanding the evolutionary history of crocodilians. While modern crocodiles are slow-growing reptiles, their distant ancestors were known for rapid growth rates. This discovery suggests that the shift toward slower growth—a hallmark of today’s crocodilians—may have occurred much earlier than previously thought. Understanding this transition sheds light on how modern crocodiles evolved into efficient predators and explains their remarkable resilience through multiple mass extinction events.
Bailey elaborated on the evolutionary implications: “It’s critical to understand why, how, and when crocodiles transitioned from fast to slow growth. This shift may have equipped them with the adaptability needed to survive drastic environmental changes, including mass extinctions.”
The bone structure of Orthosuchus also revealed adaptations that point to a semi-aquatic lifestyle, straddling land and water. The bones were compact and thick-walled, features commonly found in aquatic animals. Yet, it lacked other hallmarks of aquatic specialization, such as a flattened tail, suggesting that Orthosuchus was equally at home on land and in water. Intriguingly, certain characteristics of its skeleton hinted at possible digging behavior. Modern crocodiles dig burrows to escape extreme temperatures, and it is plausible that Orthosuchus engaged in similar behavior, though it lacked specialized adaptations like thick claws for digging.
This dual lifestyle sheds light on the versatility of early crocodilians and their ability to exploit diverse ecological niches. Orthosuchus’ environment likely presented a mix of aquatic habitats and terrestrial landscapes, challenging it to navigate both realms effectively. Its compact bone structure, combined with its potential digging traits, underscores the ingenuity of evolutionary adaptations in the face of environmental pressures.
The study also opens the door to broader questions about the survival strategies of crocodilian ancestors during catastrophic events like the End-Triassic Extinction, a mass extinction that wiped out a significant portion of Earth’s species. Bailey expressed her desire to expand this line of inquiry: “I’d like to investigate whether the growth strategies of early crocodilians played a role in their survival through mass extinction events. Understanding these patterns could illuminate how certain species thrived while others perished.”
Orthosuchus serves as a time capsule, offering glimpses into ancient ecosystems and the challenges faced by early crocodilians. Its survival strategy of slow growth, adaptability to varied habitats, and potential burrowing behavior hints at the resilience and versatility that would eventually define modern crocodiles. This discovery underscores the importance of studying seemingly minor species to uncover the broader evolutionary narratives that shape life on Earth.
Through its innovative approach and collaboration between global institutions, this research not only enhances our understanding of crocodilian evolution but also demonstrates the transformative potential of technology in paleontology. The ability to study fossils at a microscopic level without damaging them opens new frontiers in the study of ancient life.
Orthosuchus stormbergi, though small in stature, casts a long shadow over our understanding of evolutionary biology. It bridges the gap between ancient and modern crocodilians, offering insights into how these formidable reptiles came to dominate their ecosystems. Its story is a testament to the resilience of life and the unrelenting pursuit of knowledge that drives modern science. By piecing together the past, researchers like Bailey Weiss and her team provide a richer, more nuanced picture of Earth’s evolutionary history, inspiring new questions and avenues of exploration.
Source: Wits University