Where do turtles belong on the evolutionary tree? For decades, the mystery has proven as tough to crack as the creatures’ shells. With their body armor and retractable heads, turtles are such unique creatures that scientists have found it difficult to classify the strange animals in terms of their origins and closest relatives.
“We know turtles evolved from a common ancestor along with birds, lizards and snakes about 300 million years ago, but who modern-day turtles are most closely related to is one of the biggest and most controversial questions in the field of systematics,” said Tyler Lyson, a Yale University graduate student who studies the evolutionary relationships between different animal groups.
Some researchers have analyzed turtles’ genes and found they are most closely related to the group of animals that includes crocodiles and birds. Others, comparing turtles’ physical features to those of other reptiles, have placed them next to lizards or outside of the larger subclass of animals that includes lizards, crocodiles and birds altogether.
Now Lyson and his colleagues have used a novel approach involving microRNAs that strongly suggests turtles belong next to lizards.