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Title: Patterns of postnatal ontogeny of the skull and lower jaw of snakes as revealed by micro‐ CT scan data and three‐dimensional geometric morphometrics

We compared the head skeleton (skull and lower jaw) of juvenile and adult specimens of five snake species [Anilios(=Ramphotyphlops)bicolor,Cylindrophis ruffus,Aspidites melanocephalus,Acrochordus arafurae, andNotechis scutatus] and two lizard outgroups (Ctenophorus decresii,Varanus gilleni). All major ontogenetic changes observed were documented both qualitatively and quantitatively. Qualitative comparisons were based on high‐resolution micro‐CTscanning of the specimens, and detailed quantitative analyses were performed using three‐dimensional geometric morphometrics. Two sets of landmarks were used, one for accurate representation of the intraspecific transformations of each skull and jaw configuration, and the other for comparison between taxa. Our results document the ontogenetic elaboration of crests and processes for muscle attachment (especially for cervical and adductor muscles); negative allometry in the braincase of all taxa; approximately isometric growth of the snout of all taxa exceptVaranusandAnilios(positively allometric); and positive allometry in the quadrates of the macrostomatan snakesAspidites,AcrochordusandNotechis, but also, surprisingly, in the iguanian lizardCtenophorus. Ontogenetic trajectories from principal component analysis provide evidence for paedomorphosis inAniliosand peramorphosis inAcrochordus. Some primitive (lizard‐like) features are described for the first time in the juvenileCylindrophis. Two distinct developmental trajectories for the achievement of the macrostomatan (large‐gaped) condition in adult snakes are documented, driven either by positive allometry of supratemporal and quadrate (in pythons), or of quadrate alone (in sampled caenophidians); this is consistent with hypothesised homoplasy in this adaptive complex. Certain traits (e.g. shape of coronoid process, marginal tooth counts) are more stable throughout postnatal ontogeny than others (e.g. basisphenoid keel), with implications for their reliability as phylogenetic characters.

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Author(s) / Creator(s):
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Publisher / Repository:
Date Published:
Journal Name:
Journal of Anatomy
Page Range / eLocation ID:
p. 723-754
Medium: X
Sponsoring Org:
National Science Foundation
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