Biology subjects

Evans, A. R.

Publications and source records attributed to Evans, A. R..

3 recordsLinked to original sources

bioRxiv2026

The origin and evolution of amphibious hearing in pinnipeds

Seals (pinnipeds) are the only mammals that can hear in both air and water. How and when they achieved the ability to negotiate such contrasting auditory media remains unknown. Here, we apply 3D shape and phylogenetic comparative analyses to a large dataset of caniform carnivorans (119 species, 217 specimens) to study the emergence of amphibious hearing in pinnipeds despite significant evolutionary constraints. We find support for the cavernous tissue as a functional and evolutionary mechanism for amphibious hearing. This tissue, which fills with blood during diving to equalise air pressure in the ear, enables a shift from in-air to underwater hearing by matching the acoustic impedance of the ear to that of the surrounding water. Early diverging freshwater pinnipeds had impaired hearing underwater. The first marine pinnipeds could hear amphibiously but were limited by a functional tradeoff between hearing abilities and the need to prevent damage from loud underwater sounds. Subsequently, otariids (eared seals) and phocids (true seals) independently acquired middle ear adaptations that expanded their underwater hearing range. This iterative evolution likely facilitated the exploration of novel auditory adaptive zones by crown pinnipeds, resulting in rare acoustic abilities like ultrasonic singing, vocal learning, and keeping rhythm.

evolutionary biology↗

bioRxiv2025

Microevolutionary trends of tooth complexity in the Ibiza wall lizard, Podarcis pityusensis, mirror macroevolutionary trends in squamates

Tooth complexity has long been known as a powerful indicator of feeding in mammals and reptiles, often used to infer diets of long-extinct species. However, how these trends are established below the species level remains unclear. Here, we use Orientation Patch Count Rotated (OPCR) to quantify tooth complexity across eight populations of Podarcis pityusensis, an insular omnivorous lizard endemic to the Pityusic Islands of the Western Mediterranean. These populations vary widely in their extent of herbivory and specialisation, which we use to assess the link between complexity and diet. We find that increasing herbivory is matched with increasing dental complexity, with comparable effect sizes to those found on the macroevolutionary scale. We do not, however, find clear evidence of divergence of tooth complexity between sexes within populations (in a way that would be consistent with niche divergence), meaning that the extent to which this trait is plastic remains controversial. Our results suggest that dental complexity is a highly powerful metric to infer diet, and an informative candidate for linking micro- and macroevolutionary patterns.

evolutionary biology↗

bioRxiv2021

Getting out of a mammalian egg: the egg tooth and caruncle of the echidna

In the short-beaked echidna, Tachyglossus aculeatus, after an initial period of in utero development, the egg is laid in the pouch and incubated for 10 days. During this time, the fetuses develop an egg tooth and caruncle to help them hatch. However, there are only a few historical references that describe the development of the monotreme egg tooth. Using unprecedented access to echidna pre- and post-hatching tissues, the egg tooth and caruncle were assessed by micro-CT, histology and immunofluorescence, to map the changes at the morphological and molecular level. Unlike mammalian tooth germs that develop by invagination of a placode, the echidna egg tooth developed by evagination, similar to that of the first teeth in some reptiles. The egg tooth ankylosed to the premaxilla, rather than forming a mammalian thecodont attachment, with loss of the egg tooth post-hatching associated with high levels of odontoclasts, and apoptosis. The caruncle formed as a separate mineralisation from the adjacent nasal capsule, and as observed in birds and turtles, the nasal region epithelium expressed markers of cornification. Together, this highlights that the monotreme egg tooth shares many similarities with reptilian teeth, suggesting that this tooth is conserved from a common ancestor of mammals and reptiles.

evolutionary biology↗