Evolution: Turtle ears may be bigger on the inside

An analysis of the inner ear shape of turtles and its connection to locomotion is presented in a paper published in Nature Communications. The findings may aid our understanding of vertebrate evolution. The inner ear, or bony labyrinth, senses movement and orientation and its shape and size have been used to infer agility in extinct animals. Turtles have evolved over 230 million years and both living and extinct species have a range of locomotor behaviours and ecological adaptations, however, little is known about the evolution of the turtle bony labyrinth. Serjoscha Evers and colleagues examined 163 specimens of turtles, representing 90 living and 53 extinct species, including softshell turtles, terrapins, and loggerhead sea turtles, which have a variety of locomotor behaviours. These include burrowing, walking on ground, walking underwater, and swimming to navigate terrestrial, freshwater, and marine habitats. The authors found that turtles have large inner ears relative to their head size and suggest this may have evolved during their adaptation to aquatic habitats. They also indicate that turtles have a relatively large bony labyrinth size compared to other vertebrates, and propose that inner ear size may not be as strongly related to agility as previously thought, but instead may be connected to visual acuity in turtles. The authors conclude that their findings suggest that there is greater diversity in bony labyrinth shape and size than previously thought and that further research is needed in understudied tetrapod groups and fishes to explore labyrinth evolution.