This lizard shrinks its own skeleton to survive famine, then regrows it

Galapagos marine iguanas can reabsorb bone material and shrink up to 20% of their body length during El Nino years when their algae food vanishes, then regrow to full size once feeding conditions recover. It's the only vertebrate confirmed to reversibly shrink its own skeletal length as an adult.

— Martin Wikelski, Corinna Thom, Marine iguanas shrink to survive El Nino — Nature, vol. 403, 2000