[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Tiny dinosaur on verge of swearing off meat



Augusto Haro wrote:

<Except for the enlargement of the canines, the basal position within 
Ornithischia now hypothesized for Heterodontosaurus by Butler et al. (2007) 
suggests that these theropod-like tooth may be just plesiomorphic retentions, 
unless Silesaurus and Azendohsaurus (with basally constricted teeth) turn out 
to be successive outgroups of Ornithischia and Dinosauria. That the serrations 
of the crown are perpendicular instead of oblique would represent a further 
plesiomorphy.>

  Except that these perpendicularly oriented denticles are present despite 
other teeth displaying modifications of the crowns. Note that in *Goyocephale*, 
the cheek teeth are cingulate, possess a distinct lingual vertical ridge, and 
the denticulations are oblique to the carina, and very coarse, in effective 
being phyllodont in form. In *Heterodontosaurus*, the cingulum is less distinct 
but the vertical ridge still distinct, and the denticulations are restricted to 
the apical half of the crown with oblique orientations, with orthal processing 
helping produce a tooth with primarily apical and transverse wear instead of 
wear oblique to the crown axis, causing the teeth to take on a chisel-like 
appearance. This is a specialization, and as such the retention of the 
premaxillary form seems not in keeping with the specialization of the cheek 
teeth, especially as basal taxa, including *Azhendohsaurus*, have "coarse" 
oblique denticulations of the known crowns,
 and the basal ornithischian condition, as can be inferred from taxa like 
*Scutellosaurus*, *Agilisaurus*, and *Lesothosaurus*, agree that the oblique, 
phyllodont condition is the primitive condition for all teeth. This means that 
the premaxillary variation seen in Heterodontosauridae and Marginocephalia are 
unique to them as a clade. It is also important to note that that the basal 
condition for onrithischian denticulation density and orientation is coarse and 
oblique, rather than fine and perpendicular; it is then arguable that 
*Heterodontosaurus* developed the premaxillary modifications for the sake of 
rendering meat to some degree. They may even belong to the same clade as a 
result of this (although this seems to have gone under testing and been 
rejected, at least by Peyer and Butler).

  I am thinking here that a comparison is in order, and would bring attention 
to Darren Naish once calling this animal a sort of suine analogue. At one 
point, this animal was compared favorably with *Anthracotherium,* an animal 
that as a juvenile have finely serrated canines and ate meat, but matures into 
much more of an omnivore and opportunistic feeder, as are most extant suines.

  Cheers,

Jaime A. Headden

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