On having a closer look, abelisaurid functional morphology is not all that uniform, despite sharing some major features.
These are:
• short arms, most likely useless for prey acquisition
• brevirostry
• a robust neck with enlarged epipophyses and reduced neural spines
• Large spaces for muscle insertion above the occiput
Some differences include:
•
Majungasaurus’ skull is strongly coossified (Sampson & Witmer 2007), while that of
Carnotaurus is characterised by many loose connections (Mazzetta et al. 1998). The skull of
Majungasaurus was designed to be rigid, that of
Carnotaurus to be flexible.
• In
Carnotaurus the neck is more robust for its lenght, and the reduction of the neural spines in favour of the epiphyses is more extreme than in
Majungasaurus (Méndez 2014). Whatever it was doing, it needed it’s
musculus compexus even more, which would imply dorsolateral movements.
• The skull of
Carnotaurus is comparatively shorter, deeper and narrower than in
Majungasaurus (Sampson & Witmer 2007)
• Carnotaurines have highly cursorial adaptions (Bonaparte et al. 1990, Mazzetta et al. 1998, Persons & Currie 2011),
Majungasaurus obviously doesn’t (Hartman 2012 [online])
All in all, I’m not really buying into the idea that either used its skull for striking as proposed by Bakker (1998). I’ve already posted my thoughts on that; there’s no evidence of a downward shift of major head depressors in any abelisaur to improve their leverage, and the skull and neck are ill-proportioned (short skull, thick neck) and built (stiffening by long, interlocked cervical ribs) for performing a striking motion with high velocity at the tooth row).
What I’m wondering about is why there’s this difference in kineticism between the two types, and whether that means they did entirely different things. It’d also be conceivable that both basically did the same, but on prey of various sizes.
Majungasaurus’ teeth are short-crowned and laterally compressed (Smith et al. 2005). I don’t know about
Carnotaurus tough.
Anyway, presumably
Majungasaurus has its robusticity in order to hold onto prey for prolonged periods of time, while using the slicing teeth to slowly tear it apart with some sort of laterally curving sawing motion similar to a komodo dragon, but probably with more bite force involved.
––
References:
Bakker, Robert T.: Brontosaur killers: Late Jurassic allosaurids as sabre-tooth cat analogues. Gaia, Vol. 15 (1998); pp. 145-158
Bonaparte, José F.; Novas, Fernando E.; Coria, Rodolpho A.: Carnotaurus sastrei Bonaparte, the Horned, Lightly Built Carnosaur from the Middle Cretaceous of Patagonia. Natural History Museum of Los Angeles County Contributions in Science number 416 (1990); pp. 1-41
Mazzetta, Gerardo V.; Fariña, Richard A.; VizcaĂno, Sergio F.: On the Palaeobiology of the South American horned Theropod Carnotaurus sastrei Bonaparte. Gaia, Vol. 15 (1998); pp. 185-192
Méndez, Ariel H.: The cervical vertebrae of the Late Cretaceous abelisaurid dinosaur Carnotaurus sastrei. Acta Palaeontologica Polonica, Vol. 59 (2014); 3; pp. 569-579
Persons, W. Scott; Currie, Philip J.: Dinosaur Speed Demon: The Caudal Musculature of Carnotaurus sastrei and Implications for the Evolution of South American Abelisaurids. PLoS ONE, Vol. 6 (2011); 10; pp. 1-11
Sampson, Scott D.; Witmer Lawrence M.: Craniofacial Anatomy of Majungasaurus crenantissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Memoir (Society of Vertebrate Paleontology), Vol. 8 (2007); pp. 32-102
Smith, Joshua B.; Vann, David R.; 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
Hartman, Scott (2012): Majungasaurus – redux.
scotthartman.deviantart.com/art/Majungasaurus-redux-87892198 (acessed 07 September 2014)
