Re: theropod quibbles

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>I read Sereno et al's paper describing _Afrovenator_ last night, and a
>couple of things in it bothered me.  The first was probably just due
>to a bit of wording that could have been better, but it might also
>have been an indication that theory rather than observation was
>driving their description on this one point.  The authors state:
>
>   Unlike _Allosaurus_ and many other theropods, cranial crests and
>   rugosities are poorly developed.
>
>A quick look at figure 2A indicates that they found almost nothing of
>the top of the skull.  The only way I could salvage their comment was
>by accepting that the crests to which they're referring are always
>found as processes jutting off of the lacrimal bone, the one skull
>bone of which they seem to have discovered the dorsal surface.
>Looking through the sources I have at home, that seemed consistent at
>least with _Allosaurus_.  Is that what they probably meant?

Your objections are valid (most of the skull roof hasn't been discovered,
as far as I know).  However, the lacrimal (which is known) lacks the crest
found in some form in almost every other large theropod.

>>My second problem seems (to me at least) to represent a bit of
>careless scholarship on the part of the authors.  In delineating
>theropod phylogenetic relationships, they state:
>
>   Torvosauroids include _Afrovenator_, the Laurasion genera
>   _Torvosaurus_, _Eustreptospondylus_, and _Chilantaisaurus_ (13),
>   and tentatively the spinosaurids _Spinosaurus_ and _Baryonyx_
>   (6,14).
>
>The references in footnote 6 are dated 1915 and 1934, so they clearly
>refer to _Spinosaurus_ alone and not to _Baryonyx_.  Reference 14 is
>Charig and Milner's chapter in _Dinosaur Systematics_.  Since I
>recently read that book, it was fresh enough for me to know that
>Charig and Milner aren't cited accurately here.  In fact, if I were
>Charig or Milner, I'd be angered by the above statement.  From the
>conclusions in Charig and Milner, you find the most direct disavowal
>you could possibly expect to find of the above position:
>
>      The individual characters found in _Baryonyx_ (Fig. 9.7), some
>   of them unique, and its particular combination of characters,
>   indicate unequivocally that it cannot be assigned to any known
>   family of theropods; more specifically it is not a spinosaurid.  We
>   therefore believe that we were justified in placing it in a new
>   theropod family of its own (Baryonichidae Charig and Milner, 1986).
>
>Sereno et al may disagree with Charig and Milner, but if they do, then
>I think it was incumbent upon them to say so at least in the footnote.
>Better yet, if they want to disagree, they should state why.  My
>impression (based admittedly on little evidence) is that Charig and
>Milner's interpretations aren't popular, but that's not an excuse.  To
>cite that chapter as Sereno et al did, is *at best* misleading since
>it appears to indicate that Charig and Milner placed _Baryonix_ in
>Spinosauridae.

I agree that they probably should have quote any of the number of workers
who've shown that Baryonyx is more closely related to Spinosaurus than it
is to any other known theropod.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.