Prey hardness
As predicted, snakes eating hard prey have short, stout, blunt and less posteriorly and medially curved teeth, contrary to softer-prey eaters that have long, slender, and more curved teeth (Fig. 3 & 5). Compared to slender teeth, short and stout teeth undergo a relatively smaller maximal stress coming from the compression force and the stress is concentrated at the tip of the tooth (Bar-On, 2019; Rajabizadeh et al., 2020). This may reduce the risk of failure of the tooth while feeding on hard items but may cause fragmentation and wear of the tip. We noticed some tooth fragmentation in species such as Fordonia leucobalia .Fordonia is a peculiar species that feeds on crustaceans that are crushed and dismembered (Jayne et al., 2018). This behavior likely imposes high load on the teeth, thus aggravating the fragmentation. Most durophagous snakes do not use their teeth to dismember their prey, or to crush them like other vertebrates. They use their teeth to manipulate and swallow their prey (sometimes alive Arsovski et al., 2014). Consequently, they may not need to resist loads as high as other vertebrates. In fact, durophagous snakes generally do not pierce their prey, they only have superficial, but repeated contacts with it during capture and manipulation. These snakes may have evolved short and blunt teeth to limit fracture during capture and manipulation, but this tooth shape seems to be related with high prey escape rate, and the necessity for behavioral adjustments, such as coiling the body around the prey to limit losing the prey (Gripshover & Jayne, 2021). Some durophagous snakes have independently evolved hinged teeth that fold back when they swallow the prey but may rise up if the prey moves backwards, a strategy preventing escape as well (Jackson et al., 1999; Savitzky, 1981). Some legless lizards specialized on eating hard scaled lizards show a similar specialization suggesting a convergent evolution of hard-prey specialists in squamates (Patchell & Shine, 1986). On the other hand, the dentary teeth of snakes feeding on softer prey show morphological adaptations related to piercing and getting a grip on prey and preventing escape, such as an elbow-like configuration and a sharp tip.