Lakes, streams and aquifers across North America are crawling with salamanders of all shapes and sizes. For most people, though, finding a 2-foot-long amphibian in the eastern United States might sound like a tall tale.
But giant salamanders are more common than you might think. The eastern hellbender (Cryptobranchus alleganiensis), which can grow up to 29 inches long, is the largest salamander native to North America, and the fourth largest in the world. And unlike most salamanders, it spends its entire life in the water.
Yet how did these giant salamanders evolve to grow several feet long when most of their kin only reach 4 to 6 inches in length? This question has long fascinated scientists — and the answer could lie in enormous amphibians’ evolutionary history.
While they share many genetic similarities with other amphibians, giant salamanders like the hellbender have developed unique genetic adaptations that allow them to be primarily aquatic. Some experts say these adaptations are what led them to grow as gigantic as they are today.
“You have these large-bodied animals that live in permanent aquatic stream-like environments and do quite well there,” says Dave Weisrock, a biology professor at the University of Kentucky who has spent years studying hellbenders in their natural habitat. “But it’s difficult for us to know exactly how and why that evolved.”
