Clawed forelimbs allow northern seals to eat like their ancient ancestors

Funding for this project was provided by a Marie Skłodowska-Curie Global Postdoctoral Fellowship (656010/MYSTICETI) to F.G.M, by Marine Scotland to support the wild observations recorded by R.N.H., by an Australian Research Council Future Fellowship FT130100968 to A.R.E., and by an Australian Research Council Linkage Project LP150100403 to A.R.E. and E.M.G.F.Streamlined flippers are often considered the defining feature of seals and sea lions, whose very name ‘pinniped’ comes from the Latin pinna and pedis, meaning ‘fin-footed’. Yet not all pinniped limbs are alike. Whereas otariids (fur seals and sea lions) possess stiff streamlined forelimb flippers, phocine seals (northern true seals) have retained a webbed yet mobile paw bearing sharp claws. Here, we show that captive and wild phocines routinely use these claws to secure prey during processing, enabling seals to tear large fish by stretching them between their teeth and forelimbs. ‘Hold and tear’ processing relies on the primitive forelimb anatomy displayed by phocines, which is also found in the early fossil pinniped Enaliarctos. Phocine forelimb anatomy and behaviour therefore provide a glimpse into how the earliest seals likely fed, and indicate what behaviours may have assisted pinnipeds along their journey from terrestrial to aquatic feeding.Publisher PDFPeer reviewe

Is a blunt sword pointless? Tooth wear impacts puncture performance in Tasmanian devil canines

As teeth wear, their shapes change and functional features can be dulled or lost, presumably making them less effective for feeding. However, we do not know the magnitude and effect of this wear. Using Tasmanian devil canines as a case study, we investigated the impact of wear on puncture in pointed teeth. We measured aspects of shape impacted by wear (tip sharpness, height and volume) in teeth of varying wear followed by 3D printing of real and theoretical forms to carry out physical puncture tests. Tooth wear acts in two ways: by blunting tooth tips, and decreasing height and volume, both of which impact performance. Sharper tips in unworn teeth decrease the force and energy required to puncture compared with blunter worn teeth, while taller unworn teeth provide the continuous energy necessary to propagate fracture relative to shorter worn teeth. These wear-modulated changes in shape necessitate more than twice the force to drive worn teeth into ductile food and decrease the likelihood of puncture success.<br/

The killer's toolkit:remarkable adaptations in the canine teeth of mammalian carnivores

Pollock, Tahlia I, Hocking, David P, Evans, Alistair R (2022): The killer's toolkit: remarkable adaptations in the canine teeth of mammalian carnivores. Zoological Journal of the Linnean Society 196 (3): 1138-1155, DOI: 10.1093/zoolinnean/zlab064, URL: https://academic.oup.com/zoolinnean/article/196/3/1138/637023

Taking a stab at modelling canine tooth biomechanics in mammalian carnivores with beam theory and finite-element analysis

Canine teeth are vital to carnivore feeding ecology, facilitating behaviours related to prey capture and consumption. Forms vary with specific feeding ecologies; however, the biomechanics that drive these relationships have not been comprehensively investigated. Using a combination of beam theory analysis (BTA) and finite-element analysis (FEA) we assessed how aspects of canine shape impact tooth stress, relating this to feeding ecology. The degree of tooth lateral compression influenced tolerance of multidirectional loads, whereby canines with more circular cross-sections experienced similar maximum stresses under pulling and shaking loads, while more ellipsoid canines experienced higher stresses under shaking loads. Robusticity impacted a tooth's ability to tolerate stress and appears to be related to prey materials. Robust canines experience lower stresses and are found in carnivores regularly encountering hard foods. Slender canines experience higher stresses and are associated with carnivores biting into muscle and flesh. Curvature did not correlate with tooth stress; however, it did impact bending during biting. Our simulations help identify scenarios where canine forms are likely to break and pinpoint areas where this breakage may occur. These patterns demonstrate how canine shape relates to tolerating the stresses experienced when killing and feeding, revealing some of the form–function relationships that underpin mammalian carnivore ecologies

Assessing the biomechanics of sabre teeth through the trade-off between puncture performance and breakage resistance

peer reviewed“Sabre teeth” – elongate blade-like canines – have evolved repeatedly throughout mammalian history. However, the functional underpinnings of this reoccurring morphology remains unclear. To effectively bite into prey, all canine teeth must strike a balance between being slender enough to reduce puncture force, while being robust enough to resist breakage. We explored this trade-off in sabretooth canines by comparing these against teeth from living carnivores, integrating three-dimensional shape data with mechanical performance metrics within a functional optimality framework. Canine shape was captured via 3D geometric morphometrics in a sample representing 67 non-sabre and 20 sabretooth species. We then quantified two mechanical performance metrics in a subset of teeth, applying finite element analysis to model tooth stress and undertaking physical puncture tests to quantify puncture force. These data were combined using a Pareto rank approach, constructing an adaptive landscape to assess optimality. Extreme sabretooth forms, like Smilodon, Barbourofelis, and Thylacosmilus, exhibit a combination of curvature and slenderness not found in our extant dataset, resulting in the highest stress values and lowest puncture forces of all teeth. Interestingly, these forms occupy a small peak of optimality in the adaptive landscape which is separated by a valley from another larger peak of straighter canines with varying robusticity. Our combined approach reveals new aspects of sabretooth biomechanics, providing fundamental insights into the adaptive bases for morphological diversity in pointe

Hocking_tables_ESM.pdf from Clawed forelimbs allow northern seals to eat like their ancient ancestors

Supplementary tables for each subject animal detailing the number of behavioural bouts performed for each type of prey processing observed during these trials

Hocking_movie_ESM.mov from Clawed forelimbs allow northern seals to eat like their ancient ancestors

Prey processing in captive harbour seals (Phoca vitulina) and spotted seals (Phoca largha)