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Sabretoothed Carnivores and the Killing of Large Prey; Andersson K, Norman D, Werdelin L (2011) PLoS ONE 6(10): e24971. https://doi.org/10.1371/journal.pone.0024971
Topic Started: Jan 9 2018, 04:02 PM (225 Views)
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Journal Reference:
Andersson K, Norman D, Werdelin L (2011) Sabretoothed Carnivores and the Killing of Large Prey. PLoS ONE 6(10): e24971. https://doi.org/10.1371/journal.pone.0024971

Abstract
Sabre-like canines clearly have the potential to inflict grievous wounds leading to massive blood loss and rapid death. Hypotheses concerning sabretooth killing modes include attack to soft parts such as the belly or throat, where biting deep is essential to generate strikes reaching major blood vessels. Sabretoothed carnivorans are widely interpreted as hunters of larger and more powerful prey than that of their present-day nonsabretoothed relatives. However, the precise functional advantage of the sabretooth bite, particularly in relation to prey size, is unknown. Here, we present a new point-to-point bite model and show that, for sabretooths, depth of the killing bite decreases dramatically with increasing prey size. The extended gape of sabretooths only results in considerable increase in bite depth when biting into prey with a radius of less than ∼10 cm. For sabretooths, this size-reversed functional advantage suggests predation on species within a similar size range to those attacked by present-day carnivorans, rather than “megaherbivores” as previously believed. The development of the sabretooth condition appears to represent a shift in function and killing behaviour, rather than one in predator-prey relations. Furthermore, our results demonstrate how sabretoothed carnivorans are likely to have evolved along a functionally continuous trajectory: beginning as an extension of a jaw-powered killing bite, as adopted by present-day pantherine cats, followed by neck-powered biting and thereafter shifting to neck-powered shear-biting. We anticipate this new insight to be a starting point for detailed study of the evolution of pathways that encompass extreme specialisation, for example, understanding how neck-powered biting shifts into shear-biting and its significance for predator-prey interactions. We also expect that our model for point-to-point biting and bite depth estimations will yield new insights into the behaviours of a broad range of extinct predators including therocephalians (gorgonopsian + cynodont, sabretoothed mammal-like reptiles), sauropterygians (marine reptiles) and theropod dinosaurs.

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Figure 1. The outline of the prey modelled as a circle.
In the canine clearance model bite is restricted by what can be fitted between the tips of the canines at maximum jaw extension. (a) Basic circle geometry determines the depth of the bite (h = Sprey+Sjaw) into a prey of radius (Rprey) for canine clearance (c) and jaw size (Rjaw). (b) Illustrating the geometry of biting into prey of different sizes - a sabretooth may deliver a fatal wound when biting the neck of the prey. (c) At twice the prey size the same sabretooth is capable of delivering a superficial bite only. Showing veins (blue), arteries (red), trachea (grey).

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Figure 2. Canine size follows gape for carnivorans with canine killing bite habits.
Measured gape plotted against gape predicted from canine size, for fossil sabretooths (white symbols and dash-dot regression line), present day non-sabretoothed carnivorans (Felidae, light gray symbols and dashed regression line; all other carnivoran families, dark grey symbols and dotted regression line). The solid line marks isometry (y = x) between measured and predicted gape and bubble diameters represent Rshift values (not to scale). Gape is measured as the angle formed between the craniomandibular-joint and the tips of the incisors. Gape is predicted assuming canine clearance equal to the combined height of the upper and lower canine and calculated as the sum thereof.

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Figure 5. The prey size threshold around which bite depth changes.
The prey radius (Rshift) around which bite depth alters plotted against jaw length. Sabretooths, with the exception of Amphimachairodus giganteus has Rshift values similar to extant felids of similar size. Extant Felidae, light grey circles; all other extant carnivoran families, dark grey circles; Sabretooth Felidae open circles and labelled. Linear regression (y0 = −3.103, a = 0.3553, R2 = 0.940, SEE = 3.4839, P = <0.0001) of all extant carnivoran families (sabretooths excluded). Confidence line (dashed) and prediction line (dotted) at 99%. Jaw length is the distance from the tip of the lower canine to the posterior end of the mandibular condyle.

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