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RE: Megalosaurids



Greetings, everyone,

I'm back from an education conference in Vermont, and have seen many
interesting things pop up on the list!  I'm VERY VERY VERY happy to see that
the spiky _Psittacosaurus_ sp. (so noted as the skull is exposed primarily
in ventral view, so the specific diagnostic characters are not easily
visible) has been published.

As for the present questions:
> From: Nicholas Gardner [mailto:n_gardner637@hotmail.com]

> 1.How many species are valid within Megalosaurus?

Only one: _M. bucklandi_.  Even for that material, it is not at all certain
if we can fairly include all the Stonesfield Slate fossils within that
taxon.  There is variation among them, and (quite possibly) some of that
variation may represent the presence of multiple non-_Megalosaurus_ taxa.
(Indeed, _Iliosuchus_ definitely comes out of there: if it turns out that
the type ilia are juveniles, then it is not inconcievable that some of the
big femora and so forth are from _Iliosuchus_). Urgh.

Other referred species are not referred on the basis of shared derived
features, and so are not demonstrably closer to _M. bucklandi_ than they are
to other theropods.

> 2.What horizon does it hail from?

Stonesfield Slate, Middle Bathonian, Middle Jurassic.

> 3.What type of ecosystem was that horizon?

The Stonesfield Slate (an OLD name for it: it is a limestone, not a slate)
does not represent the environment in which _Meg._ lived, simply where the
body washed into and sank.  It is a near-shore marine enivornment.  It is in
the lower part of the Great Oolite Series (stratigraphically right above the
original Fullers Earth), and represents a shallow subtidal zone.

> 4.What type of flora would have been present?

Cleal, C.J. & Rees, P.M. in press. The Middle Jurassic flora of Stonesfield,
Oxfordshire, UK. Palaeontology.

When it comes out, we'll know...

> 5.What other species of amniotes were present?

Other dinos in the quarry are _Iliosuchus incognitus_ and indeterminate
hypsilophodont-grade ornithopod.  Pterosaurs are being worked on by Whalley
(see http://members.aol.com/Pterodata3/LMJur/stone.htm).  Not certain about
crocs, lepidosaurs, or turltes. Mammals include _Amphilestes broderipi_,
_Phascolotherium bucklandi_, _Amphitherium prevostii_.

> 6.What is the estimated length and mass of Megalosaurus?

Guesstimated length is 6-9 m and guesstimated mass is 1-2 tonnes, based on
rough comparisons to other theropods.  Very tentative values, though.

> 7.How much material has been assigned to the valid species?

See above.  Minimally a dentary; maximally add a few other fragmentary skull
elements, verts from parts of the column (esp. sacrals), scauplae,
coracoids, humeri, ulnae, ilia, pubes, ischiae, femora, tibiae, metatarsals,
phalanges.

> 8.Is Megalosauridae a valid grouping?  If so, what supports it?

As the existence of _Megalosaurus_ as a valid group (of bones) is
questionable, I think you can see why the next step up is even more
tentative.  I have a contribution forthcoming that does support a grouping
of _Meg._, _Torvo._, _Poekilo._, _Eustrep._, _Piatnitzky._, _Afrovenator_,
and someone else (heh, heh, heh...), to the exclusion of all other
theropods.  One the other hand, if you do NOT consider the non-dentary _M.
bucklandi_ material as belonging to a single taxon, the monophyly of
Megalosauridae falls apart relative to other basal tetanurines.  As for what
supports it: wait for the paper... :-)

> 9.Should Torvosaurus and Poekilopleuron be sunk into Megalosauridae?

See above.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796