Monitor lizards, also known as goannas, are iconic reptiles in Australia, famed not only for their remarkable survival through the mass extinction event that wiped out non-avian dinosaurs but also for being the largest living lizards on the planet.
In a pioneering study published in the Zoological Journal of the Linnean Society, researchers have uncovered previously hidden bone structures in these lizards that may explain their evolutionary success on the continent.
Understanding osteoderms, the small bony plates embedded in the skin tissue of certain reptiles, has been an ongoing challenge in the scientific community.
Similar to the armor-like plates found in crocodiles and armadillos, osteoderms vary widely in size and function across different species.
For instance, some reptiles use these structures primarily for defense, while others may utilize them for thermoregulation, aiding mobility, or even as a calcium reserve during reproduction.
Despite extensive research, the precise reasons for the evolution of osteoderms remained obscure until now.
The research team began by recognizing a significant gap in knowledge regarding which species possess these intriguing features.
An international consortium of specialists carried out a comprehensive study on osteoderms found in lizards and snakes, examining specimens from renowned collections across institutions like the Florida Museum of Natural History, the Natural History Museum in Berlin, and Museums Victoria.
However, investigating osteoderms proved to be more complicated than anticipated.
The presence of these bony structures can differ greatly among individual members of the same species, and they are often not preserved adequately in every specimen examined.
Adding to the complexity, osteoderms are located deeply within skin tissues, making them mostly invisible and traditionally requiring the destruction of specimens to identify them.
To address these issues, the researchers employed micro-computed tomography (micro-CT), an advanced imaging technique akin to a conventional medical CT scan but with superior resolution.
This method enabled the team to assess even the smallest anatomical structures while keeping the specimens intact.
Utilizing computer-generated 3D models, the researchers explored the anatomy of lizards and snakes from around the globe and integrated data from previously published works, generating a vast sample size of nearly 2,000 specimens to locate osteoderms.
To visually present their findings, they developed a novel technique called radiodensity heatmapping, which highlights bone structures’ locations within the bodies of the examined specimens.
The results were surprising, as it became clear that the number of lizard families with osteoderms was nearly double what was previously expected.
In fact, the study revealed that almost half of all lizards possess some form of osteoderm.
Perhaps the most astonishing discovery involved goannas, long believed to lack osteoderms with the exception of rare cases like the Komodo dragon.
Researchers identified previously undocumented osteoderms in 29 Australo-Papuan goanna species, thereby increasing the known prevalence of these structures fivefold.
This revelation goes beyond mere anatomical curiosity.
The newfound presence of osteoderms in Australian goannas paves the way for exciting future research opportunities.
As these goannas first arrived in Australia approximately 20 million years ago, their adaptation to a new and often harsh environment raises pertinent questions about the evolutionary pressures they faced.
If the emergence of osteoderms in goannas coincided with their arrival, it could provide invaluable insights into the functional evolution of these complex bone structures.
This study not only brings to light crucial information about goannas but also enhances our broader understanding of the evolutionary forces that have shaped Australia’s unique reptiles over millennia.
As scientists continue to explore the role of osteoderms, they may uncover further secrets of these remarkable creatures that thrive in diverse Australian ecosystems.
image source from：theconversation
