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How Mesosaurs May Have Been Biters, Not Sifters

Pretto, F. A., Cabreira, S. F. & Schultz, C. L. in press. Tooth microstructure 
of the Early Permian aquatic predator *Stereosternum tumidum* and 
paleobiological implications. _Acta Palaeontologica Polonica_, posted online 4, 
July, 2012, doi: http://dx.doi.org/10.4202/app.2011.0121


"A histological investigation of the feeding apparatus of a *Stereosternum* 
specimen revealed a great number of adaptations in the structure and insertion 
of teeth, to deal with breakage risks. The tooth wall is composed of different 
layers of dentine, varying in orientation and composition. This mixed 
arrangement may have increased tooth resistance to lateral tension. The tooth 
insertion also involves more than one mechanism. The teeth are located inside 
shallow tooth sockets and are held in place by a tripartite periodontium 
(composed of alveolar bone, cementum and possibly soft periodontal tissue) and 
accessory structures, here termed anchorage trabeculae (mainly composed of 
cementum). Fully grown teeth are ankylosed to the bottom of the tooth socket. 
The recognition of alveolar bone and cementum (and the possible presence of a 
soft periodontal ligament) reinforces the idea that these tissues were 
widespread among Amniota, not being exclusive to mammals and archosaurs. The 
adaptations identified here reinforce the hypothesis that *Stereosternum* was 
an active aquatic predator."


As the paper details, various structures surrounding and comprising the thin, 
slender teeth of *Stereosternum tumidum* may have assisted prey acquisition 
through biting, rather than the commonly applied "straining" or "sifting" that 
has been suggested before. Mesosaurs lack true dental sockets, and are acrodont 
to ankylosed subthecodont in their tooth impantation, meaning they must 
overcome particular challenges when supposedly biting down into prey. Various 
adaptations of the periodontal and dental anatomy implies that they can, in 
fact, bite and thus would have been active predators instead of passive sifters.


Jaime A. Headden
The Bite Stuff (site v2)

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion