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Re: sauropods and abelisaurids



>I have 2 questions; 1 from me and 1 from my son that I could't answer.
>1) can someone provide me with a sauropod lineage? Who came first sort of
>thing. This is a result of browsing through dinosaur books with my son
>and he noted that frequently different types of sauropods are shown
>together. While this is most likely for convenience, what is the timeline
>for sauropods?

A sauropod phylogeny, huh?

Sauropods have the WORST resolved phylogeny in the Dinosauria, currently,
and even the number and membership of families within the group are poorly
known.

Basically, some really primitive sauropods show up in the Early Jurassic,
some more advanced ones in the Middle Jurassic, and by the Late Jurassic
there are many different specialized groups: titanosaurians,
brachiosaurids, camarasaurids, euhelopodids, dicraeosaurids, and
diplodocids.  All of these seem to survive into the Early Cretaceous.
During the Late Cretaceous only titanosaurids, dicraeosaurids, and whatever
the hell Opisthocoelicaudia is, have been documented.

>2) can someone explain more about the abelisaur(ids) mentioned by Stan
>and others while discussing S American dinos? They were related to the
>ceratosaurs, which were an early line of theropods...were abelisaurs the
>last in this line, more advanced, or what?
>Thank you, and someday (hopefully soon) I'll have enough free cash to buy
>some of these references you folks always mention.

Abelisaurids are one of the most interesting groups of dinosaurs to be
discovered in the 1980s.  The first two recognized were Abelisaurus and
Carnosaurus, the former known only from a skull, the latter from a nearly
complete skeleton (lacking feet - sorry, Jim ;-) ).  Some other theropods
which might be abelisaurids are Xenotarsosaurus (from Argentina),
Majungasaurus (from Madagascar), Indosaurus and Indosuchus (from India),
and Tarascosaurus (from Provencal, France).  Abelisaurids seem to have a
Eurogondwanan distribution (i.e., Europe and the southern continents).

Since most are known only from fragments, it is hard to make
generalizations about the abelisaurids.  They do seem to be large
theropods, comparable in size range to the allosaurids and tyrannosaurids,
which appear to be closely related to Ceratosaurus.

Note: the ceratosaurs are not a particularly *early* group of dinosaurs,
since the evidence suggests that tetanurines (the other major group of
advanced theropods) are equally old.  Coelophysoid ceratosaurs were an
important early group, including Dilophosaurus, Syntarsus, Coelophysis,
etc.  Neoceratosaurians are known from fossils from the Middle Jurassic to
the end of the Cretaceous.  The abelisaurids, and related groups like
Noasaurus, were the latest and most advanced known neoceratosaurs.

                                
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.