The Lizard That Broke One of Evolution’s Most Sacred Rules

Key Points:

• Researchers traced 320 million years of reptile skin bone (osteoderm) evolution, finding that these bony plates evolved independently across multiple lizard lineages rather than from a single armored ancestor.
• The study analyzed 643 living and extinct species, identifying 13 independent acquisition events of osteoderms within squamate reptiles, with most acquisitions occurring around 140 million years ago during the Late Jurassic and Early Cretaceous.
• Once acquired, osteoderms were generally retained due to likely ecological advantages such as habitat versatility, temperature regulation, and water retention, though the exact functions remain uncertain.
• A notable exception is Australian monitor lizards (goannas), which lost their osteoderms about 72 million years ago but re-evolved them roughly 20 million years ago, challenging Dollo’s law that complex structures cannot be regained once lost.
• The findings pave the way for future research into whether osteoderm evolution is driven by convergent evolution under similar selective pressures or by a shared genetic predisposition for forming bony skin tissue.