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-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of Mickey_Mortimer11 >Foster, Holtz and Chure, 2001.
Contrasting patterns of diversity and community structure in the theropod faunas
of the Late
>Jurassic and Late Cretaceous of
Western North America. JVP 21(3) 51A.
>The
main point of this talk was that the Morrison Formation has a wide size range of
theropods, with several taxa in the
>largest size range (500+ kg), while the Hell
Creek has fewer theropod taxa, only one of which is over 500 kg. Oddly,
>Ceratosaurus was said to be much smaller
than Allosaurus, presumedly based on the subadult holotype.
Nope. While
there are apparently fully adult Ceratosaurus out there (see Britt et
al.'s poster from 2000, for example), these are still smaller than the larger
(and, sadly, unmounted) Allosaurus fragilis
specimens.
>"What about Albertosaurus?!"
:-)
Quite. Incidentally, even if there were a
mid-sized tyrannosaurid in the Hell Creek, it doesn't make a difference to the
big pattern we were describing: namely, the extreme taxonomic diversity and even
size distribution in the Morrison versus the more restricted taxonomic diversity
and very uneven size distribution (all big carnivores being tyrannosaurids) in
the Hell Creek, Judith River, and the like.
>Holtz,
2001. Pedigree of the tyrant kings: New information on the origin and evolution
of the Tyrannosauridae. JVP 21(3) 62A-
>63A.
>Holtz had a phylogeny of theropods with 85
taxa and 642 characters with the following topology-
>|-Herrerasauridae
>`-+-Coelophysoidea > `-+-Ceratosauria > `-+-"Szechuanosaurus" zigongensis > `-+-Spinosauroidea > `-+-|-Monolophosaurus > | |-Lourinhanosaurus > | |-Sinraptor > | |-Allosaurus > | |-+-Fukuiraptor > | | `-Siamotyrannus > | `-+-Neovenator > | `-+-Acrocanthosaurus > | `-+-Carcharodontosaurus > | `-Giganotosaurus > `-+-Scipionyx > `-|-Compsognathus > |-Nqwebasaurus > |-Nedcolbertia > |-Proceratosaurus > |-Ornitholestes > `-+-|-Stokesosaurus > | |-Dryptosaurus > | `-+-Eotyrannus > | `-+-+-Alectrosaurus > | | `-Bayn Tsav material > | `-+-Alioramus > | `-+-+-Albertosaurus > | | `-Gorgosaurus > | `-+-+-Daspletosaurus > | | `-new long snout taxon > | `-+-Tarbosaurus > | `-Tyrannosaurus > `-|-Coelurus > |-Ornithomimosauria > `-+-+-Segnosauria > | `-+-Avimimus > | `-Oviraptorosauria > `-+-Alvarezsauridae > `-|-Protarchaeopteryx > |-Troodontidae > |-Dromaeosauridae > `-+-Rahonavis > `-+-Archaeopteryx > `-Pygostylia Actually, the Two Medicince Form (which comes out as the sister to
Daspletosaurus torosus) is not a particularly long-snouted form.
This is the form considered by Horner et al. (1992) to be transitional between
Daspletosaurus and T. rex.
>Notice the paraphyletic Ceratosauria sensu
lato, basal position of "Szechuanosaurus" zigongensis like Rauhut 2000, odd
>Siamotyrannus+Fukuiraptor clade,
Take
that one with a grain of salt: it is on just one character. However, it is
interesting given the somewhat similar distribution in time and
space...
>Dryptosaurus in the Tyrannosauroidea and
Coelurus being more derived than other "basal coelurosaurs". Also,
Avimimus is
>an oviraptorosaur, Protarchaeopteryx a
paravian and there is no evidence for secondary flightlessness. What an
interesting
>cladogram, I wish I could have copied the
rest of the taxa.
Actually, the rest just elaborates the ingroup relationships of the
various maniraptoriform clades, and these are being worked out in greater detail
by other scientists. Indeed, there are a few specimens and
analyses to be published within a few months (I expect) which will
really help to clarify some of these
relationships.
Thomas R. Holtz,
Jr. |