Under Armor 

Australia’s iconic goannas (monitor lizards) have been hiding a secret under their scaly skin: A layer of tiny bony plates known as osteoderms.  

Long overlooked, these structures may help explain how these ancient reptiles adapted to one of the harshest environments on Earth millions of years ago. 

In a new study, an international research team conducted the first large-scale global survey of osteoderms in lizards and snakes.  

They examined nearly 2,000 reptile specimens from major museum collections, using high-resolution micro-computer tomography scans to peer beneath the skin without damaging the samples. 

Until now, osteoderms in monitor lizards were thought to be rare and mostly limited to the Komodo dragon, but the new findings suggest otherwise. 

“We were astonished to find osteoderms in 29 Australo-Papuan monitor lizard species that had never been documented before,” lead author Roy Ebel said in a statement. “It’s a fivefold increase in known cases among goannas.” 

Osteoderms are seen in crocodiles, armadillos, and even dinosaurs like Stegosaurus. While they may act as armor, scientists now suspect they also serve other important functions, such as regulating body heat and supporting movement.  

The study shows that these skin bones are present in nearly half of all lizard species worldwide – an 85 percent increase over previous estimates. It also challenges previous assumptions about reptile evolution and opens new lines of inquiry into how skin structure relates to survival in extreme environments. 

Ebel wrote in The Conversation that their widespread presence across Australo-Papuan goannas also raises new questions about when and why they evolved.  

Goannas arrived in Australia about 20 million years ago and had to adapt to a tough environment, Ebel noted. If osteoderms emerged around this time, they may have done so in response to environmental pressures. 

“What’s so exciting about this finding is that it reshapes what we thought we knew about reptile evolution,” Jane Melville, a senior curator at Museums Victoria Research Institute who contributed to the study, said in the statement.  

“It suggests that these skin bones may have evolved in response to environmental pressures as lizards adapted to Australia’s challenging landscapes.”