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Re: Megalosaurids



Sean Carroll wrote-

> So, granting that Paul was not even working with a cladistic system but
> with a Linnaean one, this is roughly something around the sequence he
> saw in the fossils available at the time:
>
> Theropoda
>   |--Procompsognathidae
>   `--+--+--Coelophysoidea (incl Spinosauridae)
>      |  `--Ceratosauridae
>      `--+--Megalosauridae (incl Abelisaurinae, Noasaurinae)
>         `--+--Eustreptospondylidae (incl Metriacanthosaurinae)
>            `--Tetanurae
>
> I am not sure what cladistic analyses have been done to support or
> refute this basic concept. I know that Paul's visions of the
> Ceratosauria and Avetheropoda (=Tetanurae) have essentially been borne
> out and supported by the currently accepted cladistic model (aside from
> a few details, like the exact placement of the Spinosauridae and
> Tyrannosauridae), but the information I have been able to find on
> megalosaurs, abelisaurs/noasaurs, eustreptospondyls, and
> metriacanthosaurs, relative to other theropod groups, seems to be spotty
> and tentative at best. It is my opinion that a working out of the exact
> relationships among these groups and their placement relative to the
> main flow of theropod evolution will be probably the most interesting
> and exciting development to watch for in the field of theropod
> phylogenetics over the next decade or 2, possibly even more than the
> sorting out of relationships within the Maniraptora.

Of course, Paul wrote all this in 1988, so it's not expected to be
considered valid today.  He did come up with some very good ideas (eg.
ceratosaurids closer to tetanurines than coelophysoids; a Tetanurae only
missing spinosaurids and incorrectly including abelisauroids; putting
Metriacanthosaurus and Yangchuanosaurus together) at a time when people were
just throwing things into Carnosauria or Coelurosauria.
Procompsognathus seems to be a coelophysoid (Sereno and Wild, 1992; Rauhut,
2000).
Spinosaurids are definitely closer to birds than coelophysoids and
dilophosaurids are.
Ceratosaurids are probably closer to tetanurines than coelophysoids are,
which I think Paul (1988) intended as well.
A megalosaurid-abelisaurian link has not been demonstrated in any cladistic
analysis, though some have proposed a carcharodontosaurid-abelisaurid link.
Rather, megalosaurids are more derived than abelisaurids (Holtz, 2001;
Rauhut, 2000).
Paul's Eustreptospondylinae includes a spinosauroid (Eustreptospondylus), a
basal tetanurine or spinosauroid (Piatnitzkysaurus), a probable sinraptorid
(Gasosaurus) and a possible coelurosaur (Marshosaurus).  His
Metriacanthosaurinae includes sinraptorids, though his Metriacanthosaurus?
sp. has been named by Chure (2001)-
http://www.cmnh.org/dinoarch/2001Nov/msg00118.html .  There is some
confusion regarding his new name and "Szechuanosaurus" zigongensis however.

> I might as well list them since it is at least
> quite possible some or any of them could end up to be related to the
> megalosaurs or eustreptospondyls, or otherwise somewhere between the
> ceratosaurs and tetanurans:
>
> *_Megalosaurus? nethercombensis_
> *_Megalosaurus? hesperis_
> *_Xuanhanosaurus qilixiaensis_
> *_Iliosuchus incognitus_
> *_Stokesosaurus clevelandi_
> *_Segisaurus halli_

Magnosaurus nethercombensis is very close if not congeneric with
Eustreptospondylus, so is a spinosauroid (Rauhut, 2000).  "Walkersaurus"
hesperis is a non-avetheropod tetanurine (Holtz, 2000).  Xuanhanosaurus is a
non-coelurosaur tetanurine (Rauhut, 2000).  Iliosuchus just might be a basal
tyrannosauroid, as Stokesosaurus probably is (Holtz, 2001).  Segisaurus is a
coelophysoid (Rauhut, 2000).

Stephen Pickering wrote-

> NOTE: There are 4 species of Megalosaurus:
>     Megalosaurus nethercombensis
>     Megalosaurus bucklandii
>     Megalosaurus phillipsi
>     Megalosaurus tanneri

While I have yet to see M. "phillipsi", and sinking Torvosaurus into
Megalosaurus is largely subjective assuming they are closer to each other
than either is to spinosaurids or other distinctive spinosauroids, I think
that Rauhut (2000) did a good job showing Magnosaurus nethercombensis is
very closely related to Eustreptospondylus.  Thus, I would not recommend
sinking it into Megalosaurus.

Mickey Mortimer