Whole feeding apparatus 3D landmarks

The kinetic skull is a key innovation that allowed snakes to capture, manipulate, and swallow prey exclusively using their heads using the coordinated movement of 8 bones. Despite these unique feeding behaviors, patterns of evolutionary integration and modularity within the feeding bones of snakes in a phylogenetic framework have yet to be addressed. Here, we use a dataset of 60 µCT scanned skulls and high-density geometric morphometric methods to address the origin and patterns of variation and integration in the feeding bones of aquatic-foraging snakes. By comparing alternate superimposition protocols allowing us to analyze the entire kinetic feeding system simultaneously, we find that the feeding bones are highly integrated, driven predominantly by functional selective pressures. The most supported pattern of modularity contains four modules, each associated with distinct functional roles: the mandible, the palatopterygoid arch, the maxilla, and the suspensorium. Further, the morphological disparity of each bone is not linked to its magnitude of integration, indicating that integration within the feeding system does not strongly constrain morphological evolution, and that adequate biomechanical solutions to a wide range of feeding ecologies and behaviors are readily evolvable within the constraint due to integration in the snake feeding system.

Methods
For each bone, anatomical and curve landmarks were placed by hand on each model. Surface semi-landmarks were placed on a template bone and then projected and slided onto the other specimens. After sliding, specimens from the same species were averaged to obtain 1 set of bones per species. The attached file is a TPS file of the mean shapes per species of all the bones (i.e. 8 bones for 1 species). 36 species of snakes are included in this dataset.

Landmarks number for each bone:

  dentary = 1:180  

  compound =181:368

  quadrate = 369:638

  supratemporal = 639:731

  pterygoid = 732:885

  ectopterygoid = 886:996

  palatine = 997:1108

  maxilla = 1109:1335