On Carnotaurus sastrei:I’ve got some doubts about the proposed "sledgehammer hypothesis".
When people use it (e.g. Bakker 1998), usually
Allosaurus comes up as an analogy, but this is problematic, because they are actually very different in a number of features:
Firstly, the cranial muscle insertions:
Carnotaurus doesn’t have downturned paroccipital processes to enhance the ventroflexive ability of its head as is the case in
Allosaurus (Bakker 1998, Antón et al. 2003, Snively et al. 2007, 2013). Rather its paroccipital processes are directed laterally (Bonaparte 1990) as is the case with basal ceratosaurs. That alone already implies major differences in muscle arrangement between the two (but there’s far more to it than that).
Secondly, the proportions of their skulls: It is true neither of them has a particularly large head and both are deep-skulled, but the similarities end there. Compared to
Allosaurus (Madsen 1976), the skull of
Carnotaurus is completely differently proportioned, being almost as tall as it is long, having a much shorter rostrum and being proportionately wider. This is not a morphology that would be particularly suitable for relying on impact feeding, as it reduces the velocity which could be reached at the tooth row with such a strike.
Thirdly, their necks:
That of
Allosaurus has been described as particularly flexible (Snively et al 2007, 2013), that of
Carnotaurus was likely rather rigid (Méndez 2014). The supposed slashing and striking for
Allosaurus is a motion that would require a fair degree of flexibility–this was even one of the key points of criticism brought forth against it (Antón et al. 2003).
That’s not everything though. The neck of
Carnotaurus is a highly unusual structure with huge, dorsally tall epipophyses but tiny, atrophied neural spines. Again, the muscle arrangement between these two is completely different. Whereas Allosaurus shows a specialization for ventroflexion,
Carnotaurus rather seems to have a specialization for dorsi- and lateroflexion (plus a much stiffer neck overall).
So with all these differences I would highly doubt we can really compare them. There is more of course, for example the entire postcranium, but I’m focusing on the head and neck here.
Carnotaurus’ wide, robust neck, proportionately shorter and more brevirostrine skull, differences in basicranial muscle insertions and the large epipophyses suggest it held onto prey with its jaws, not that it slashed at it. It is plausible it did that in a very explosive motion of course, but I don’t think it was suited for dealing considerable damage with a powerful strike alone.
It should be noted that the skull and mandible of
Carnotaurus are very kinetic (Mazzetta et al 1998)
1. I don’t think this would have served to ingest large prey whole as I’m sure most people would be thrilled to envision, since the mechanism used for this in snakes requires palatal teeth and independent action of both sides of the jaw and the quadrates to work, but I think it may be linked to absorbing the stresses of struggling prey.
1. They even proposed kineticism of the quadrate. However Hendrickx et al 2014 did not acknowledge this even though they studied theropod quadrates including the one of
Carnotaurus, and it seems hard to conceive in a taxon that has a quadratojugal. Instead, the supposed "joint" may be a growth zone.
REFERENCES:
Antón, M.; Sánchez, I.; Salesa, M.; Turner, A.: The muscle-powered bite of Allosaurus (Dinosauria; Theropoda): an interpretation of cranio-dental morphology. Estudios Geológicos, vol. 59 (2003); 5-6; pp. 313-323
Bakker, Robert: Brontosaur killers: Late Jurassic allosaurids as sabre-tooth cat analogues. Gaia, vol. 15 (1998); pp. 145-158
Bonaparte, José; Novas, Fernando; Coria, Rodolpho: Carnotaurus sastrei Bonaparte, the Horned, Lightly Built Carnosaur from the Middle Cretaceous of Patagonia. Natural History Museum of Los Angeles County Contributions in Science vol. 416 (1990); pp. 1-41
Hendrickx, Christophe; Araújo, Ricardo; Mateus, Octávio (2014): The nonavian theropod quadrate I: standardized terminology and overview of the anatomy, function and ontogeny.
peerj.com/preprints/379/ accessed 13.09:2014
Madsen, James: Allosaurus fragilis: a revised Osteology. Salt Lake City (1976)
Mazzetta, Gerardo; Fariña, Richard; Vizcaíno, Sergio: On the Palaeobiology of the South American horned Theropod Carnotaurus sastrei Bonaparte. Gaia, vol. 15 (1998); pp. 185-192
Méndez, Ariel: The cervical vertebrae of the Late Cretaceous abelisaurid dinosaur Carnotaurus sastrei. Acta Palaeontologica Polonica, vol. 59 (2014); 3; pp. 569-579
Smith, Joshua; Vann, David; Dodson, Peter: Dental Morphology and Variation in Theropod Dinosaurs: Implications for the Taxonomic Identification of Isolated Teeth. The Anatomical Record, vol. 285 (2005); A; pp. 699-736
Snively, Eric; Cotton, John; Ridgely, Ryan; Witmer, Lawrence: Multibody dynamics model of head and neck function in Allosaurus (Dinosauria, Theropoda). Palaeontologia Electronica, vol. 16 (2013); 2; pp. 1-29
Snively, Eric; Russell, Anthony: Functional Variation of Neck Muscles and Their Relation to Feeding Style in Tyrannosauridae and Other Large Theropod Dinosaurs. The Anatomical Record, vol. 290 (2007); pp. 934-957