The early origin of a birdlike inner ear and the evolution of dinosaurian movement and vocalization

Abstract

Reptiles, including birds, exhibit a range of behaviorally relevant adaptations that are reflected in changes to the structure of the inner ear. These adaptations include the capacity for flight and sensitivity to high-frequency sound. We used three-dimensional morphometric analyses of a large sample of extant and extinct reptiles to investigate inner ear correlates of locomotor ability and hearing acuity. Statistical analyses revealed three vestibular morphotypes, best explained by three locomotor categories—quadrupeds, bipeds and simple fliers (including bipedal nonavialan dinosaurs), and high-maneuverability fliers. Troodontids fall with Archaeopteryx among the extant low-maneuverability fliers. Analyses of cochlear shape revealed a single instance of elongation, on the stem of Archosauria. We suggest that this transformation coincided with the origin of both high-pitched juvenile location, alarm, and hatching-synchronization calls and adult responses to them.

Ontogenetic variation in the crocodylian vestibular system

“…It is still under debate if, in reptiles, skull dimensions generally have more impact on inner ear size and shape than lifestyle and locomotion or phylogeny, and how all of these factors might interact to shape inner ear evolution across phylogeny and evolutionary time (e.g. Benson et al, 2017;Bronzati et al, 2021;Hanson et al, 2021).…”

“…It is still under debate if, in reptiles, skull dimensions generally have more impact on inner ear size and shape than lifestyle and locomotion or phylogeny, and how all of these factors might interact to shape inner ear evolution across phylogeny and evolutionary time (e.g. Benson et al, 2017; Bronzati et al, 2021; Hanson et al, 2021). Our results indicate that care must be taken when selecting specimens to include in broad comparative and deep‐time studies so that ontogenetic variation is not conflated with other potential influences on inner ear morphology.…”

“…Semicircular canal morphology has previously been associated with habitat, behaviour and locomotion in various vertebrate groups (e.g. Hanson et al, 2021; Neenan et al, 2017; Schwab et al, 2019, 2020; Spoor et al, 2002; see also Bronzati et al, 2021). More limited study has assessed labyrinth changes in an ontogenetic context, but only in a small sample of species, with most focus on mammals.…”

“…Semicircular canal morphology has previously been associated with habitat, behaviour and locomotion in various vertebrate groups (e.g. Hanson et al, 2021;Neenan et al, 2017;Schwab et al, 2019Schwab et al, , 2020Spoor et al, 2002; see also Bronzati et al, 2021).…”

Neuroanatomy of the nodosaurid Struthiosaurus austriacus (Dinosauria: Thyreophora) supports potential ecological differentiations within Ankylosauria

“… 36 ). Currently, it is a matter of debate to what extent the morphology of the semicircular canals is a proxy for certain ecological affinities within Archosauromorpha 37 , 38 . Few endosseous labyrinths of ankylosaur taxa are known, of which all possess relatively short and thick semicircular canals, as seen in the early-diverging ankylosaur Kunbarrasaurus ieversi 14 , the ankylosaurids B. archibaldi 13 , Euoplocephalus tutus 39 (and probably T. teresae 15 ), and the nodosaurid Pawpawsaurus campbelli 40 .…”