Limits...
Sabretoothed carnivores and the killing of large prey.

Andersson K, Norman D, Werdelin L - PLoS ONE (2011)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom. andersson.ki@gmail.com

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.

Show MeSH

Related in: MedlinePlus

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).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3198467&req=5

pone-0024971-g001: 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).

Mentions: The model for point-to-point killing bites presented here brings together two aspects, first the relationship between canine size and gape, and second, between prey size and bite depth, the latter ultimately the main factor behind the killing potency of the bite. The first and fundamental assumption of point-to-point biting is that there is a relationship between the size of the canines and the amount of clearance between the tips of the canines at maximum gape. This relationship, here referred to as “canine clearance” is optimised when the combined height of the upper and lower canines equals the amount of clearance between the tips of canines at maximum gape. Secondly, circular geometry closely approximates a strike into a curved outline of a prey animal (Fig. 1), and hence maximum theoretical bite depth is determined as the interaction of two circles, one representing the jaw of the predator with radius Rjaw and the other representing the prey with radius Rprey (Fig. 1a). In figure 1 the neck was chosen to illustrate prey radius. The model however is not restricted to neck-bites only nor does it assume it, on the contrary, it may equally well apply to any curved part of the body.


Sabretoothed carnivores and the killing of large prey.

Andersson K, Norman D, Werdelin L - PLoS ONE (2011)

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).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198467&req=5

pone-0024971-g001: 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).
Mentions: The model for point-to-point killing bites presented here brings together two aspects, first the relationship between canine size and gape, and second, between prey size and bite depth, the latter ultimately the main factor behind the killing potency of the bite. The first and fundamental assumption of point-to-point biting is that there is a relationship between the size of the canines and the amount of clearance between the tips of the canines at maximum gape. This relationship, here referred to as “canine clearance” is optimised when the combined height of the upper and lower canines equals the amount of clearance between the tips of canines at maximum gape. Secondly, circular geometry closely approximates a strike into a curved outline of a prey animal (Fig. 1), and hence maximum theoretical bite depth is determined as the interaction of two circles, one representing the jaw of the predator with radius Rjaw and the other representing the prey with radius Rprey (Fig. 1a). In figure 1 the neck was chosen to illustrate prey radius. The model however is not restricted to neck-bites only nor does it assume it, on the contrary, it may equally well apply to any curved part of the body.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom. andersson.ki@gmail.com

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.

Show MeSH
Related in: MedlinePlus