Plicidentine and the repeated origins of snake venom fangs

Snake fangs are an iconic exemplar of a complex adaptation, but despite striking developmental and morphological similarities, they probably evolved independently in several lineages of venomous snakes. How snakes could, uniquely among vertebrates, repeatedly evolve their complex venom delivery apparatus is an intriguing question. Here we shed light on the repeated evolution of snake venom fangs using histology, high-resolution computed tomography (microCT) and biomechanical modelling. Our examination of venomous and non-venomous species reveals that most snakes have dentine infoldings at the bases of their teeth, known as plicidentine, and that in venomous species, one of these infoldings was repurposed to form a longitudinal groove for venom delivery. Like plicidentine, venom grooves originate from infoldings of the developing dental epithelium prior to the formation of the tooth hard tissues. Derivation of the venom groove from a large plicidentine fold that develops early in tooth ontogeny reveals how snake venom fangs could originate repeatedly through the co-option of a pre-existing dental feature even without close association to a venom duct. We also show that, contrary to previous assumptions, dentine infoldings do not improve compression or bending resistance of snake teeth during biting; plicidentine may instead have a role in tooth attachment.

Computational biomechanical modelling of the rabbit cranium during mastication

Although a functional relationship between bone structure and mastication has been shown in some regions of the rabbit skull, the biomechanics of the whole cranium during mastication have yet to be fully explored. In terms of cranial biomechanics, the rabbit is a particularly interesting species due to its uniquely fenestrated rostrum, the mechanical function of which is debated. In addition, the rabbit processes food through incisor and molar biting within a single bite cycle, and the potential influence of these bite modes on skull biomechanics remains unknown. This study combined the in silico methods of multi-body dynamics and finite element analysis to compute musculoskeletal forces associated with a range of incisor and molar biting, and to predict the associated strains. The results show that the majority of the cranium, including the fenestrated rostrum, transmits masticatory strains. The peak strains generated over all bites were found to be attributed to both incisor and molar biting. This could be a consequence of a skull shape adapted to promote an even strain distribution for a combination of infrequent incisor bites and cyclic molar bites. However, some regions, such as the supraorbital process, experienced low peak strain for all masticatory loads considered, suggesting such regions are not designed to resist masticatory forces.

DISTRIBUTION OF THE EFFORTS OF THE MUSCLE MUSCLES HUMAN DENTAL SYSTEM AT ASYMMETRIC TONE SURFACE MASKING MUSCLES

The dentofacial system is closely related to the musculoskeletal, digestive, nervous, cardiovascular systems, etc. The functioning of the dentofacial system affects nutrition, breathing, swallowing, speech, hearing, etc., where occlusion is one of its main parameters. Many pathologies in the dentofacial system are also associated with a change in the efforts of the masticatory muscles, where hypertonicity of the superficial masticatory muscle is most common. The article considers an example of her hypertonicity by biomechanical modelling. For this, the problem of determining of the masticatory muscle efforts was solved at the maximum value of the force of compression of the jaws, which was 600 N. The cases were considered when the minimum possible value of the force of the superficial masticatory muscle was 70%, 80% and 90% of the maximum value. It was found that for the case while the minimum values of the efforts of all masticatory muscles do not exceed 50% of their maximum possible values, then the distribution of muscle efforts remains unchanged, i.e. the values of muscle efforts do not change. When at least one of the muscles exceeds its half of the maximum possible effort, it is observed that the efforts of the remaining muscles on the same side of the face decrease or remain approximately at the same level, and on the opposite side, the muscle efforts initially decrease, and at 80% and 90% of the maximum possible magnitude of the effort of the superficial chewing muscle increases again. In further works, various combinations of hypertonicity of the masticatory muscles, as well as the hypotonia of these muscles, are assumed.

Assessing bite force estimates in extinct mammals and archosaurs using phylogenetic predictions

ABSTRACTBite force is an ecologically important biomechanical performance measure is informative in inferring the ecology of extinct taxa. However, biomechanical modelling to estimate bite force is associated with some level of uncertainty. Here, I assess the accuracy of bite force estimates in extinct taxa using a Bayesian phylogenetic prediction model. I first fitted a phylogenetic regression model on a training set comprising extant data. The model predicts bite force from body mass and skull width while accounting for differences owning to biting position. The posterior predictive model has a 93% prediction accuracy as evaluated through leave-one-out cross-validation. I then predicted bite force in 37 species of extinct mammals and archosaurs from the posterior distribution of predictive models.Biomechanically estimated bite forces fall within the posterior predictive distributions for all except four species of extinct taxa, and are thus as accurate as that predicted from body size and skull width, given the variation inherent in extant taxa and the amount of time available for variance to accrue. Biomechanical modelling remains a valuable means to estimate bite force in extinct taxa and should be reliably informative of functional performances and serve to provide insights into past ecologies.