Science & Technology, South Africa (Commonwealth Union) – A recently uncovered, colossal prehistoric crocodylomorph species exhibited a notably slower growth rate when compared to other large reptiles of its era, such as dinosaurs. In contrast to the swift growth observed in their closest living relatives, birds, which can attain maturity in under a year (approximately 150 days for a chicken), contemporary crocodilians, including crocodiles and alligators, undergo a protracted growth process, spanning several years before they reach their full size. For many years, scientists have grappled with the enigma of when, how, and why crocodilians adopted this leisurely growth pattern. However, a fresh investigation titled “Origins of slow growth on the crocodilian stem lineage” in Current Biology is starting to illuminate this mystery.
A team of researchers scrutinized the internal composition of fossilized bones from 200-million-year-old ancestors of crocodiles, commonly referred to as crocodylomorphs, unearthed in South Africa. The examination revealed that these ancient creatures grew slowly, akin to their modern-day descendants. Professor Jennifer Botha, a co-author from the University of the Witwatersrand, indicated that, after scrutinizing the internal structure of these creatures’ bones, they were astounded to find that their bone tissues comprised a specific type known as parallel-fibred bone. This indicates that these crocodylomorphs had a growth rate falling between the rapid growth of their forebears and the slower development characteristic of contemporary crocodiles.
Researchers also pointed out that in stark contrast to the contemporary sprawling and aquatic ambush predators, these early crocodylomorphs were active terrestrial animals, boasting upright limb postures. This groundbreaking discovery challenges the conventional belief that the slow growth seen in modern crocodiles is tied to their sedentary, semi-aquatic lifestyles.
Moreover, the research team also examined fossils belonging to a colossal ancestral crocodilian species dating back 210 million years, discovered in the village of Qhemegha in Eastern Cape, South Africa. Professor Jonah Choiniere of the University of the Witwatersrand, a co-author of the study, says, “This fantastic specimen is one of dozens of new fossils we’ve recovered from our excavations in Late Triassic rocks at Qhemegha Village. The fossil area was initially discovered by local people and has developed into a superb example of integrating local knowledge with scientific enquiry”.
The researchers amalgamated this new data with information from previously amassed specimens housed in South African museums. By sectioning the bones and meticulously inspecting their attributes under a high-powered microscope, they were able to gauge the age at which these extinct forebears perished, the annual growth rate, and the properties of their bone tissue. Bailey Weiss, another co-author from the University of the Witwatersrand, indicated that when comparing this newly discovered specimen with other known species, they have identified it as an extremely early ancestor of modern crocodiles, possibly even the earliest within the group.
They discovered that the massive new species exhibited a notably slower growth rate in comparison to other large reptiles from its era, such as dinosaurs. Furthermore, the more recently evolved crocodylomorph species continued to embrace this deliberate slow-growth strategy, further decelerating it. This gradual growth approach eventually became a defining characteristic of all known crocodylomorphs descending from their ancient ancestor. Shortly after the advent of this slow-growth strategy within the crocodilian lineage, a mass extinction event occurred at the conclusion of the Triassic Period. Only those members of the group with a slower growth pattern managed to survive through this catastrophic event.
In contrast, it is theorized that dinosaurs survived the extinction event by adopting a fast-growth strategy. Following the extinction, the world was left with a dichotomy: fast-growing dinosaurs and slow-growing crocodylomorphs. This divergence in growth strategies laid the groundwork for the marked growth differences seen in their descendants today—the birds and crocodilians.
