Inner Ear Biology Reveals the Origin of Birdlike Features in Dinosaurs
Two detailed evaluations of the anatomy of inner ears and for some, scleral eye rings, from 124 extinct and 91 living species reveal new insights into the evolution of dinosaur sensory biology and behavior, including their ability to fly, hunt at night, and hear the high-pitched chirps of their offspring. The two separate studies - by Michael Hansen and colleagues and Jonah Choiniere and colleagues, respectively - leverage cutting-edge imaging techniques and sophisticated statistical analyses.
"Documenting life's history with fossil discoveries remains the core of paleontology, but these two studies typify a new wave of paleontologist, armed not with a pick and shovel but with a CT scanner and R code," writes Lawrence Witmer in a related Perspective. Hansen et al evaluated the inner ear structures across extinct and living archosaurs, a group that includes non-avian dinosaurs, crocodilians, and birds. They discovered clear patterns relating the shape of the semi-circular canal and cochlea to movement ability, including walking on two or four feet, and flying, as well as to the ability to hear high-frequency sound. According to the authors, the analysis reveals the earliest instances of flight ability in dinosaurs and potentially the earliest emergence of parent-offspring vocal communication. Choiniere et al. also examined the inner ear, as well as aspects of the visual system, in living and extinct theropods. They found that the hearing and visual adaptations required for nocturnal, owl-like predation evolved early, particularly within the Late Cretaceous alvarezsaurids. The findings suggest that nocturnal sensory adaptations evolved independently in dinosaurs long before the origin of modern birds and demonstrate convergence for these traits across non-avian dinosaurs, birds and mammals and over millions of years. "Until recently, the advances presented by these teams of authors were unthinkable, in that many aspects of internal anatomy and certainly their connection to habits like parental care and daily activity patterns had been out of reach," Witmer writes.