Allometry of bony sound reception structures

The origin of sensory structures provides an excellent framework for studying how constraints and selective pressures affect the evolution of complex features. The evolution of the mammalian middle ear from the jaw hinge of non-mammalian synapsids offers a deep time perspective on sensory evolution but is limited by a poor understanding of early synapsid hearing. This work tests hypothesis that the reflected lamina of the angular in non-mammalian synapsids followed a strict, negative allometric trend that may be expected for a sound reception structure. Allometry is first investigated in the pterygoid of chameleons, which was co-opted for hearing in some species and represents a possible analog for the synapsid reflected lamina. Results indicate that chameleons with a pterygoid ear converge on a similar allometric slope, while other species have variable slopes, suggesting an optimum allometric pattern in sound receivers. In the reflected lamina, we find reduced variation around the all..., We photographed museum specimens of chameleons in ventral, lateral, and ventromedial views, and synapsids were photographed in lateral view with a Nikon D3100 camera. Additional photographs of inaccessible synapsid specimens were graciously provided by other researchers and museum staff. 59 synapsid specimens were also 3D surface scanned using an Artec Space Spider blue light scanner with a voxel size of 0.3 mm.
For chameleons, ImageJ V1.51j (Schneider et al., 2012) was used to measure basal skull length, pterygoid plate area, orbit diameter, and coronoid process height from photographs. In synapsids, we measured reflected lamina area in ImageJ and mandible length and orbit diameter using a Neiko digital caliper. Area was measured by outlining each structure with the “polygons selection” tool in ImageJ. When photographs and/or caliper measurements were unavailable, comparable measurements were taken using Meshmixer V3.5.474 (©Autodesk, San Rafael, CA, U.S.A) and the R package molaR (Pam..., , # Allometry of bony sound reception structures

Dataset DOI: [10.5061/dryad.nvx0k6f0f](10.5061/dryad.nvx0k6f0f)

## Description of the data and file structure

Data on the allometric scaling of the pterygoid plate of chameleons with basal skull length, as well as the reflected lamina of the angular in synapsids with jaw length. Please note that most of these are raw data files that were not directly input to our analysis. The files that were reorganized for more direct use in our analyses can be found along with our code on our Github repository at [https://github.com/savannaholroyd/EarBoneAllometry](https://github.com/savannaholroyd/EarBoneAllometry).

### Files and variables

#### On Zenodo - Supplemental Information

The images included with the dataset illustrate how measurements were taken, and the \"Supplementary information\" pdf file provides details about how measurements were taken, which institutions the specimens were housed in, and how missing data was estimated. It also incl...,