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>>n a proposed new family of sauropods, the Andesauridae? I am
>>familiar with the divison of sauropods into
>>Vulcanodontidae, Cetiosauridae, Camarisauridae, Brachiosauridae,
>>Diplodocidae and Titanosauridae, and the suggestion made several
>>years ago that the following classes should be added: Barapasauridae
>>(intermediate between Vulcanodontidae and Cetiosauridae), Dicraeosauridae
>>(sometimes trated a a subfamily
>>of the Diplodocidae: fairly similar but shorter necks), and Euhelopidae
>>(Chinese sauropods with diplodocid like tails and chevron bones but
>>Camarasaur like heads, e.g. Euhelopus, Mamenchisaurus, Omeisaurus.)

One note: that's "Euhelopodidae" (add an "od" between "p" and "i").

In Paul Upchurch's 1994 phylogeny (Phil. Trans. Roy. Soc.), Euhelopodidae is
the sister taxon to a group called "Neosauropoda" containing cetiosaurids, the
camarasaurid + brachiosaurid group (for which 'Camarasauroidea' would be the
proper name) and a titanosauroid + diplodocoid group.  Euhelopodids,
although they show many similarities to diplodocoids, lack many derived
characters of the neosauropods.

>  Now,  I
>>understand that a new family of (mainly South American Upper Cretaceous)
>>sauropods, all formerly classified as titanosaurids, has been proposed, the
>>Andesauridae.  All of these sauropods were formerly classed as Titanosaurids.
>> What is the justification for the new family; i.e. what special
>>characteristics set the Andesauridae apart from the Titanosauridae? Could
>>they be a subfamily of Titanosauridae?

Andesaurids lack the strongly procoelous caudal centra of true
Titanosauridae.  They may be the sister taxon to Titanosauridae, or even a
paraphyletic assemblage of basal members of Titanosauria (basically,
Titanosauridae + "andesaurids").
>>A related (maybe) question: where does Opithocoelicaudia fit in?

According to Paul Upchurch's phylogeny, Opisthocoelicaudia is the sister
group to Titanosauria within Titanosauridae.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661