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Re: Richardostesia teeth



Michael Mortimer (mickey_mortimer111@msn.com) wrote:

<Denticle shape is not uniform/distinct in the genus, as noted by Sankey et al.
(2002) for R. gilmorei- "Denticle tips can be slightly pointed, rounded, or
flattened."  While she describes R. isosceles as- "Denticle tips are straight
or slightly rounded, but not pointed." Similarly, all teeth referred to
Richardoestesia are not relatively straight.  Again, describing R. gilmorei-
"Isolated teeth vary in curvature from almost completely straight (0.1 mm
curvature) to strongly recurved (0.7 mm curvature)." The denticle size
distribution along the carinae for R. gilmorei ("Denticle size varies slightly
along the carinae, with smaller ones at the base and tip.") is not distinct
from Saurornitholestes ("Denticle size varies along the carina, they tend to be
smaller at the base and tip of teeth.").  R. isosceles has a different size
distribution though- "Posterior denticles are ... uniformly-sized along
tooth,">

  I did not mention the issue of potential conflation of sampling for *R.
gilmorei* as it appeared Tom Holtz had previously done so in this very thread,
and I had brought up the issue of possible taxonomic variability (as have
others in print) among the specimens in a previous incarnation of this topic.
The holotype jaws have teeth that are, on the other hand, very similar to one
another, have little recurvature, and have serrae that decrease in size toward
the base of the crown, as towards the apex.

<Indeed, Sankey later states "Richardoestesia isosceles is included in the
genus Richardoestesia because of the presence of small denticles. However, the
shape of the denticles in Richardoestesia gilmorei and isosceles is
different.">

  Which is only indicative perhaps of taxonomic variability. To wit, Sankey;'s
original diagnosis:

  "Diagnosis. -- (Modified from *Richardoestesia* sp. in Currie et al., 1990
and
   Baszio, 1997b). Teeth straight; narrow; shaped like an isosceles triangle in
   lateral view (as mentioned for *Richardoestesia* sp. in Currie et al., 1990
   and in Baszio, 1997b). Shape of tooth in basal cross-section is
   labio-lingually flattened oval. Denticles minute (0.1 mm in height and in
   antero?posterior width); square; uniformly-sized from base to tip of tooth;
   extend length of carinae. Anterior denticles, if present, often considerably
   smaller than posterior denticles. Interdenticle spaces usually minute and
   barely visible; denticles closely spaced. Denticle tips straight or faintly
   rounded, but not pointed. 7?11 denticles/mm."

  Teeth of *R. gilmorei* also possess these qualities, and may vary between
striaght to recurved, have limited to extensive mesial serrations, rounded to
flat-ended serrae, and some to no basal "waisting" in the crown. This
variability in the referred material, including that referred to *R. isoceles*,
makes it rather problematic to assume composition of a taxon based on the
specimens assumed to belong to it. It is, in essence, a self-fulfilling
prophecy. You make your own composition, and you can diagnosis it from that,
instead of the composition being self-evident (e.g., the *Hyphalosaurus* or
*Confuciusornis* slabs with multiple specimens). This is, rather, a prevalent
problem in diagnosing taxa based on isolated teeth, in that the observer must
make a large asusmption that the shape of a tooth MUST be consistent for the
diagnosis to be clear. There is little, in fact, to exclude the straighter *R.
gilmorei*-like teeth of *R. isoceles* in being mesial, less recurved crowns of
*R. gilmorei* itself, simply lack of tooth-bearing bones, something Tom Holtz
brought up this thread. Sankey's work so far has attempted to show that
distribution of her morphotype is not coincident with the type species', but
this does not provide information on the positioning or even variability in the
jaw of either animal, as only the type jaws of *R. gilmorei* can begin to
accomplish (and fail at, as there are no mesial crowns preserved).

  As even you, Mickey, wrote in this thread, variability of serrae extent
occurs in several taxa, but I will also remind the readers that not only can
serration presence vary, but so can their shape, size, the shape and/or size of
the tooth, its recurvature and/or recumbency, carination or position of the
carinae, etc., and does so within troodontids, dromaeosaurids, tyrannosaurids,
not to mention quite a few other non-theropod dinosaurs and non-dinosaurian
archosaurs present in the Late Cretaceous.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

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


 
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