Data from: What makes a fang? phylogenetic and ecological controls on tooth evolution in rear-fanged snakes

Background: Fangs are a putative key innovation that revolutionized prey
capture and feeding in snakes, and – along with their associated venom
phenotypes – have made snakes perhaps the most medically-significant
vertebrate animals. Several snake clades are known for their
forward-positioned fangs, and these clades (Elapidae; Viperidae) contain
the majority of snakes that are traditionally considered venomous.
However, many other snakes are "rear-fanged": they possess
potentially venom-delivering teeth situated at the rear end of the upper
jaw. Quantification of fang phenotypes – and especially those of
rear-fanged species – has proved challenging or impossible owing to the
small size and relative rarity of many such snakes. Consequently, it has
been difficult to understand the evolutionary history of both venom and
prey-capture strategies across extant snakes. We quantified variation in
the dentition of 145 colubriform (“advanced”) snake species using microCT
scanning and compared dental characters with ecological data on species’
diet and prey capture method(s) to understand broader patterns in snake
fang evolution. Results: Dental traits such as maxilla length, tooth
number, and fang size show strong phylogenetic signal across
Colubriformes. We find extreme heterogeneity and evolutionary lability in
the rear-fanged phenotype in colubrid (colubrine, dipsadine, and natricine
lineages) and lamprophiid snakes, in contrast to relative uniformity in
the front fanged phenotypes of other groups (vipers and, to a lesser
extent, elapids). Fang size and position are correlated with venom-use in
vipers, elapids, and colubrid snakes, with the latter group shifting fangs
anteriorly by shortening the entire maxillary bone. We find that maxilla
length and tooth number may also be correlated with the evolution of
dietary specialization. Finally, an ancestral state reconstruction
suggests that fang loss is a widespread phenomenon in colubrid snakes,
likely accompanied by shifts in diet and prey capture mode. Conclusions:
Our study provides a framework for quantifying the complex morphologies
associated with venom use in snakes. Our results suggest that fang
phenotypes, and particularly the rear-fanged phenotype, in snakes are both
diverse and labile, facilitating a wide range of ecological strategies and
contributing to spectacular radiations of these organisms in tropical and
subtropical biomes worldwide.