Main mechanical challenge
The results of the analyses focusing on the main mechanical challenge show that the teeth of durophagous species are different from those of species that need extensive manipulation of their prey (bulky, hard, hold). The hard prey group is characterized by teeth that are short, stout, with the smallest mean and maximal curvature (Fig. 3 & 5). Their pulp cavity is the short and the relative thickness of hard tissue is greater than for the other groups, making their teeth more robust. On the opposite, slippery prey eaters are characterized by long, slender, and highly curved teeth (Fig. 3 & 5). Their pulp cavity is long and provides the teeth with a relatively thin layer of hard tissue which may allow more bending, but this hypothesis remains to be tested.
This main mechanical challenge category shows us that the morphology of snake teeth can be divided into two groups. Slippery, bulky, and species holding their prey have similar teeth, and their distribution largely overlaps in the morphospace, while species feeding on hard and long prey are similar and overlap but they barely overlap with the other categories (Fig. 4). There are only two species that do not fit in their group: Atractaspis engaddensis and Atractus flammigerus .Atractaspis engaddensis falls within the durophagous group whereas it mostly feeds on small mammals (it would be classified as a bulky eater). Atractaspids are specialized fossorial snakes, they have developed a highly specialized envenomation strategy which consists of a highly mobile maxilla that can laterally protrude the fang, while the mouth remains closed, allowing the snake to stab its prey backwards. Its dentigerous bones are almost toothless and the hyper specialization of the envenomation system is associated with a loss of prey manipulation and transport efficiency (Deufel & Cundall, 2003). A high rate of prey loss in durophagous snakes also having short and stout teeth has been demonstrated (Gripshover & Jayne, 2021), suggesting that this tooth shape may not have evolved to manipulate the prey but rather to prevent breakage. Atractus flammigerus, on the other hand, is an earthworm specialist classified in the “long prey” group but falls into the “slippery” category in the morphospace (Fig. 4). We strictly defined our main mechanical challenges a priori and classified elongated prey as more constraining than slippery prey, butAtractus teeth look more like slippery prey feeders.