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Re: Allosaur cladogram
Jaime Headden wrote-
> *Acrocanthosaurus* finds itself as an allosaurid, closer to
> *Allosaurus*, in various Holtz analyses,
Actually, Holtz has never found Acrocanthosaurus closer to Allosaurus than
to Carcharodontosaurus in a published analysis. To the contrary,
Acrocanthosaurus is a carcharodontosaurid in his 2000 and 2001 analyses.
> and this in the absence of any
> real carcharodontiform features, even to the absence of the wrinkles on
> the teeth.
Enamel wrinkles are known on many different tetanurines, as noted before.
Besides, just because Acrocanthosaurus isn't a member of the
Carcharodontosaurus + Giganotosaurus clade doesn't mean it can't be a
carcharodontosaurid. Far from "absent", Holtz (2001) found the following
carcharodontosaurid synapomorphies in Acrocanthosaurus (excluding those
considered invalid by Carpenter and Currie 2001)-
- lacrimal suborbital bar
- frontals fused
- basipterygoid processes moderately long
- anterior face of midcervical centra elevated
- cervicodorsal hypapophyses absent
- sacral pleurocoels
- humeral head offset and emarginated ventrally by groove
- deltopectoral crest expanded and offset from humeral shaft
- anterior ramus of maxilla shorter than tall
> In the same analysis by Garrido and Coria on *Giganotosaurus*'
> braincase, the braincase of *Acrocanthosaurus* is more similar to
> *Allosaurus* than to either *Carcharodontosaurus* or *Giganotosaurus*;
> this on top of the pelvic features Holtz recovered.
Assuming you mean Coria and Currie (2002), the braincases of
Acrocanthosaurus and Allosaurus are only more similar to each other in
plesiomorphic ways. Indeed, even abelisaurids are in a polytomy with these
two taxa and the sinraptorid-carcharodontosaurid clade. Of course, this
analysis only contained fifteen characters, which were so skewed towards
getting a (Sinraptor (Carcharo, Giganoto)) topology that Herrerasaurus and
Dromaeosaurus coded identically.
And just which pelvic characters of Holtz are you referring to that were
more similar in Acrocanthosaurus and Allosaurus than carcharodontosaurids?
> are united primarily on caudal anatomy, and while *Acrocanthosaurus* has
> large lateral caudal pleurocoels, *Giganotosaurus* lacks these [to my
> knowdlege, seeing the verts in poor photos and moving camera angles is
> hard to allocate precise details, just general ones].
Of the nine carcharodontosaurid characters listed from Holtz above, none are
caudal. Even Sereno et al. (1996) only had two caudal characters out of
their eight diagnosing Carcharodontosauridae.
> Other allosauroids
> have combinations of caudal and pelvic features with more basal tetanurans
> and each other that implies a basal "mosaic" of characters and a possibly
> step-wise evolution towards Coelurosauria in which traditional (i.e.,
> sensus Sereno et Holtz) Allosauroidea or Carnosauria is polyphyletic.
> Carnosauria, Allosauroidea, and Allosauridae may all be the same clade
> under some topologies.
Possible, but not found by any published phylogenetic analysis.