Background Crocodilians show a spectrum of rostral shape from long snouted (longirostrine), through to short snouted (brevirostrine) morphologies. shaking and twisting loads. The best predictors of overall performance for biting and twisting lots in FE models were overall size and symphyseal size respectively; for shaking lots symphyseal size and a multivariate measurement of shape (Personal computer1C which is definitely strongly but not specifically correlated with symphyseal size) were equally good predictors. Linear measurements were better predictors than multivariate measurements of shape in biting and twisting lots. For both biting and shaking lots but not for twisting, simple beam models agree with best overall performance predictors in FE models. Conclusions/Significance Combining beam and FE modelling allows hypotheses about the importance of morphological qualities on biomechanics to be statistically tested. Short mandibular symphyses perform well under loads utilized for feeding upon large prey, but elongate symphyses incur high strains under equal lots, underlining the structural constraints to prey size in the longirostrine morphotype. The biomechanics of the crocodilian mandible are mainly consistent with beam theory and may be expected from simple morphological measurements, suggesting that crocodilians are a useful model for 482-39-3 investigating the palaeobiomechanics of additional aquatic tetrapods. Intro Large aquatic predators run inside a physical environment that has driven impressive morphological convergence, notably the self-employed evolution of a tunniform body form in ichthyosaurs (reptiles), lamnids (sharks), thunnids (bony fish) and odontocetes (mammals) , , , , . In addition to 482-39-3 swimming, feeding behaviour works under strong constraints based on the fundamental fluid dynamics of water that apply to ram, filter, and suction feeders . For ram memory feeding, a spectrum of skull morphology runs from elongate, thin pincer jaws (longirostrine) to shorter, more robust jaws (brevirostrine). This spectrum of jaw morphologies is present in a wide range of secondarily aquatic amniotes, including crocodilians, ichthyosaurs, plesiosaurs, and odontocetes (Number 1). Number 1 Spectrum of rostral proportions in marine tetrapods. Among the 24 extant varieties of crocodilians, head shape ranges from your hyper-long snouted animals such as the gharial and false gharial through to broad-snouted brevirostrine taxa such as the spectacled caiman and dwarf crocodile (Number 2). Rostral shape correlates consistently with feeding behaviour; very long slender-snouted crocodilians tend to concentrate on small, agile, aquatic prey (fish), whilst shorter and more robust-snouted animals often take much larger prey , , . The Gharial is the longest snouted form and is described as a SLC7A7 specialist fish eater , , whilst the saltwater and Nile crocodiles have shorter, more robust snouts and are capable of taking terrestrial prey much larger than themselves . This relationship between head shape and diet has been considered reliable plenty of to serve as a basis to infer diet in fossil varieties of marine reptiles and mammals , , . Number 2 Range of skull shape in crocodilians. Longirostrine aquatic predators consistently have an elongated mandibular symphysis, which in longirostrine crocodilians such as and makes up half the space of the lower jaw. In general, longirostrine taxa have proportionally longer mandibular symphyses than do mesorostrine or brevirostrine relatives (Numbers 2 and ?and3).3). As the longirostrine condition correlates having a preference for small agile prey (e.g. fish), an elongate symphysis can consequently act as a proxy for feeding ecology in some extinct organizations . The presence of elongated mandibular symphyses in longirostrine varieties in many unrelated organizations suggests possible physical constraints on prey capture. The spectrum of jaw morphology in crocodilians has been interpreted as the practical trade-off between hydrodynamic agility and strength, with longirostrine skulls reflecting a low drag-high rate morphotype suited for capturing small agile prey, and meso- to brevirostrine skulls becoming low speed-high strength jaws better suited for killing and processing slower but larger or harder foods , , , . In longirostrine forms, the elongated jaws provide extra reach and higher tip velocity, factors which likely contribute to success rates of taking 482-39-3 small agile prey. However, the quick sideways sweeping of the jaws during feeding incurs high pull, a cost that raises quadratically with snout size for a given profile , and the reduced height and width of the jaws in longirostrine taxa may serve to minimise pressure and pores and skin drag respectively, especially in the anterior portion of the jaw. Additionally, the reduction of rostral width and height in longirostrine crocodilians may reduce angular momentum and mass instant of inertia () of the snout, reducing the energy required to accelerate the jaws towards prey (which also increases the acceleration possible for a given muscular effort); it may also be a means of minimising pull.