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FEATURED ARTICLE
The Adapted Ears of Big Cats and Golden Moles: Exotic Outcomes of the Evolutionary Radiation of Mammals
Edward J. Walsh and JoAnn McGee
Through the process of natural selection, diverse organs and organ systems abound throughout the animal kingdom. In light of such abundant and assorted diversity, evolutionary adaptations have spawned a host of peculiar physiologies. The anatomical oddities that underlie these physiologies and behaviors are the telltale indicators of trait specialization. Following from this, the purpose of this article is to consider a number of auditory “inventions” brought about through natural selection in two phylogenetically distinct groups of mammals, the largely fossorial golden moles (Order Afrosoricida, Family Chrysochloridae) and the carnivorous felids of the genus Panthera along with its taxonomic neigh- bor, the clouded leopard (Neofelis nebulosa).
In the Beginning
The first vertebrate land invasion occurred during the Early Carboniferous period some 370 million years ago. The primitive but essential scaffolding of what would become the middle and inner ears of mammals was present at this time, although the evolution of the osseous (bony) middle ear system and the optimization of cochlear fea- tures and function would play out over the following 100 million years. Through natural selection, the evolution of the middle ear system, composed of three small articu- lated bones, the malleus, incus, and stapes, and a highly structured and coiled inner ear, came to represent all marsupial and placental (therian) mammals on the planet thus far studied. The consequences of this evolution were extraordinary. The process of natural selection enabled an extension of the highly restricted low-frequency hearing range that tops out around 12 kHz for most nonmamma- lian vertebrates (although there are notable exceptions in some frogs and fishes) into the greatly expanded high-fre- quency space of the mammal that reaches an upper limit of about 90 kHz in some terrestrial mammals and exceeds
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https://doi.org/10.1121/AT.2020.16.2.65
150-200 kHz in some echolocating bats and aquatic mam- mals. All of this was accomplished, at least partially, by the selection-driven repurposing of elementary components of the reptilian jaw into the osseous middle ear and the reconfiguration of the amphibian and basilar papillae into
Figure 1. Schematics of the outer, middle, and inner ears (A) and the organ of Corti in cross section (B) of a placental mammal.
Volume 16, issue 2 | Summer 2020 • Acoustics Today 65