DOI: 10.5061/dryad.n50st0n
title: Data from: Cranial ontogeny of Thamnophis radix (Serpentes: Colubroidea) with a re-evaluation of current paradigms of snake skull evolution

description: Accurate knowledge of skeletal ontogeny in extant organisms is crucial in
 understanding important morpho-functional systems and in enabling
 inferences of the ontogenetic stage of fossil specimens. However, detailed
 knowledge of skeletal ontogeny is lacking for most squamates, including
 snakes. Very few studies have discussed postnatal development in snakes,
 with none incorporating data from all three major ontogenetic stages –
 embryonic, juvenile, and adult. Here, we provide the first analysis
 encompassing these three ontogenetic stages for any squamate, using the
 first complete micro-computed tomography (micro-CT)-based segmentations of
 any non-adult snake, based on fresh specimens of Thamnophis radix. The
 most significant changes involve the feeding apparatus, with major
 elongation of the tooth-bearing elements and jaw suspensorium causing a
 posterior shift in the jaw articulation. This shift enables macrostomy
 (large-gaped feeding in snakes) and occurs in T. radix via a different
 developmental trajectory than in most other macrostomatans, indicating
 that the evolution of macrostomy is more complex than previously thought.
 The braincase of T. radix is also evolutionarily unique among derived
 snakes in lacking a crista circumfenestralis, a phenomenon considered
 herein to represent paedomorphic retention of the embryonic condition. We
 thus present a number of important challenges to current paradigms
 regarding snake cranial evolution.
description: S1. Video of segmented
 adult T. radix skullThis supplementary video
 depicts the skull of an adult T. radix individual (see figure captions in
 main text for labelling of bones). This specimen is housed in the
 University of Alberta Museum of Zoology (UAMZ R636), and was scanned using
 a Bruker-SkyScan 1076 micro-CT scanner (see article text for details
 regarding methods). The micro-CT scans were visualized and segmented in
 Dragonfly 1.0, and the video was created using Dragonfly
 3.0.Adult.mp4S2. Video of segmented juvenile T. radix skullThis supplementary video depicts the skull of a juvenile T. radix individual (see figure captions in main text for labelling of bones). This specimen is housed in the University of Alberta Museum of Zoology (UAMZ R950), and was scanned using a Bruker-SkyScan 1076 micro-CT scanner (see article text for details regarding methods). The micro-CT scans were visualized and segmented in Dragonfly 1.0, and the video was created using Dragonfly 3.0.Juvenile.mp4S3. Video of segmented embryonic T. radix skullThis supplementary video depicts the skull of an embryonic T. radix individual (see figure captions in main text for labelling of bones). This specimen is housed in the University of Alberta Museum of Zoology (UAMZ R620), and was scanned using a Bruker-SkyScan 1076 micro-CT scanner (see article text for details regarding methods). The micro-CT scans were visualized and segmented in Dragonfly 1.0, and the video was created using Dragonfly 3.0.Embryo.mp4S4. 3D mesh files of all segmented skull bones of adult T. radixThis folder contains 3D mesh (.stl) files of all skull bones of an adult T. radix individual. This specimen is housed in the University of Alberta Museum of Zoology (UAMZ R636), and was scanned using a Bruker-SkyScan 1076 micro-CT scanner (see article text for details regarding methods). The micro-CT scans were visualized and segmented in Dragonfly 1.0. The mesh (.stl) files can be viewed in many 3D visualization programs (e.g., Avizo, Adobe Photoshop, etc).Mesh Files (Adult).zipS5. 3D mesh files of all segmented skull bones of juvenile T. radixThis folder contains 3D mesh (.stl) files of all skull bones of a juvenile T. radix individual. This specimen is housed in the University of Alberta Museum of Zoology (UAMZ R950), and was scanned using a Bruker-SkyScan 1076 micro-CT scanner (see article text for details regarding methods). The micro-CT scans were visualized and segmented in Dragonfly 1.0. The mesh (.stl) files can be viewed in many 3D visualization programs (e.g., Avizo, Adobe Photoshop, etc).Mesh Files (Juvenile).zipS6. 3D mesh files of all segmented skull bones of embryonic T. radixThis folder contains 3D mesh (.stl) files of all skull bones of an embryonic T. radix individual. This specimen is housed in the University of Alberta Museum of Zoology (UAMZ R620), and was scanned using a Bruker-SkyScan 1076 micro-CT scanner (see article text for details regarding methods). The micro-CT scans were visualized and segmented in Dragonfly 1.0. The mesh (.stl) files can be viewed in many 3D visualization programs (e.g., Avizo, Adobe Photoshop, etc).Mesh Files (Embryo).zip