Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom.
PLoS One. 2011;6(10):e24971. doi: 10.1371/journal.pone.0024971. Epub 2011 Oct 19.
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.
剑齿状犬齿显然有潜力造成严重的伤口，导致大量失血和迅速死亡。关于剑齿捕杀方式的假说包括攻击腹部或喉咙等柔软部位，在这些部位，深咬对于产生到达主要血管的打击至关重要。剑齿兽通常被解释为比现代非剑齿亲属更大、更强壮的猎物的猎手。然而，剑齿咬的精确功能优势，特别是与猎物大小的关系，尚不清楚。在这里，我们提出了一个新的点对点咬模型，并表明，对于剑齿兽来说，随着猎物大小的增加，致命咬伤的深度会急剧下降。剑齿兽的张口幅度只有在咬半径小于约 10 厘米的猎物时，才会导致咬深的显著增加。对于剑齿兽来说，这种与体型大小相反的功能优势表明，它们捕食的物种与现代肉食动物攻击的物种相似，而不是以前认为的“巨型草食动物”。剑齿兽条件的发展似乎代表了功能和捕杀行为的转变，而不是捕食者-猎物关系的转变。此外，我们的结果表明，剑齿兽的进化似乎沿着一条功能连续的轨迹发展：从现代猫科动物采用的一种由颚部驱动的致死咬伤开始，然后是由颈部驱动的咬伤，此后转变为颈部驱动的剪切咬伤。我们预计，这一新的见解将成为研究包括极端特化在内的进化途径的起点，例如，了解颈部驱动的咬伤如何转变为剪切咬伤及其对捕食者-猎物相互作用的意义。我们还期望我们的点对点咬伤模型和咬伤深度估计将为包括兽头亚目（gorgonopsian + 犬齿兽，剑齿兽状似哺乳动物的爬行动物）、蜥形纲（海洋爬行动物）和兽脚亚目恐龙在内的广泛灭绝捕食者的行为提供新的见解。
