Australian Monitor Lizards Challenge Evolutionary Principles with Osteoderm Re-evolution
A recent study has revealed a significant evolutionary development in Australian monitor lizards, challenging a long-standing principle known as Dollo's law. This principle posits that complex biological structures, once lost, cannot be regained. However, researchers have documented a rare reversal in these lizards, which lost their bone armor and then re-evolved it. The study, published in the Biological Journal of the Linnean Society, analyzed 643 living and extinct species to trace the evolutionary history of osteoderms, bony plates embedded in the skin of many reptiles. The findings indicate that these structures evolved independently across multiple lizard lineages rather than from a single armored ancestor. The re-evolution of osteoderms in goannas, a type of monitor lizard, represents a unique case where the ancestral lineage lost its osteoderms approximately 72 million years ago, only to regain them during the Miocene epoch, roughly 20 million years ago. 
