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Re: Megalosaurids



Stephen Pickering (StephanPickering@cs.com) wrote:

<I cannot stress this enough: Buckland was describing a partial skeleton
of one individual, confirmed by Sam Welles's detailed examinations of each
specimen, including measuring and photographing; to restrict the Buckland
name to the rostral right dentary is an error.>

  Not really. In condition that association is questionable, and where
material is not articulated and though it comes from the same quarry is of
possible dissassociation to a single individual, it is prudent to select a
single element as a lectotype, which is the type specimen. At the time the
material was uncovered, only the the dentary with one erupted crown and
several germ teeth was known, and given the designation *Megalosaurus
bucklandii*. Further Stonesfield material which we now consider to belong
to a large-ish megalosaur has been referred to *M. bucklandii*, but for a
few elements, none of this material is associated, the original position
of the dentary is unknown from the quarry and thus is of questionable
association to the postcrania present. It is also likely, as in the Bara
Simla material of the Lameta Formation, that many vertebrae from a single
quarry can pertain to more than one individual, despite 1) lack of overlap
of left vs. right elements (there are several sacra from the Stonesfield
quarry, as well as otyher pelvic and hindlimb material) or 2) any size
discrepancy (unlike the Stonesfield). In the Stonesfield, it is clear that
there are several individuals represented based on overlap, and this is a
condition that is permitted as in the various Morrison quarries and Bara
Simla quarry where multiple specimens of more than one theropodan taxon
are present, even if they are related (several allosaurines are present in
the Morrison, often split into up to three species, with another on the
way, and several are present in the same levels, meaning IT CAN HAPPEN).
If there are several megalosaur specimens in one level, this does not mean
there can only be ONE megalosaur in that level ... but nor does it mean
there cannot be.

  However, *M. bucklandi* is a specific case. The lectotype (of which the
type is not a "holotype" per se) is a lower jaw, rostral half of the left
dentary, and this does not permit comparison to *Poekilopleuron* as yes,
as the type of _that_ species lacks cranial material. No further
Stonesfield material associate both cranial with postcrania material, and
only location is used to associate the material historically, which does
not permit the taxa to be reasonably synonymized. Use of more articulated
*Torvosaurus* material to associate both the *Megalosaurus* and
*Poekilopleuron* material to itself is a matter of second-handedly
associating the postcrania to *Megalosaurus*, but this is questionable
still for reasons detailed about, and as I second Holtz on the matter,
this is "walking on eggshells" when it comes to producing a diagnosis of
disparate and disarticulated material.

  However, apart from the destroyed *Poekilopleuron* material, the most
complete postcranial skeleton of a megalosaur is Siegwarth et al.'s
unnamed Nail Quarry animal, which may actually call into doubt the variety
of megalosaur material that Britt and Jensen and Jensen & Galton refered
to *Torvosaurus*, or that Bakker et al., referred to *Edmarka*, or even
the nature of *Edmarka* (commented on previously on the DML concerning
Siegwarth et al.'s "new" taxon).

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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