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Dino_Rampage wrote-
1) What is the status of the Euhelopodidae? Is it considered basal to the Neosauropoda? And are Euhelopus, Omeisaurus & Mamenchisaurus still considered a monophyletic clade? Would Shunosaurus be considered closely related to, or part of Euhelopodidae?

There seems to varying ideas as to its monophyly.

Upchurch (1995, 1998, 1999) supported a monophyletic Euhelopodidae (with Datousaurus, Euhelopus, Mamenchisaurus, Omeisaurus, & Shunosaurus) does not.

Refer to http://www.cmnh.org/dinoarch/1999Oct/msg00060.html for a listing of the characters. They appear to be often acquired in other clades. Maybe someone might comment on that post.

Sereno 1999 finds a paraphyletic Euhelopodidae with Omeisaurus basal to Neosauropoda and Euhelopus as the sistergroup to Titanosauria.

Omeisaurus was not considered to be a Neosauropod because of-

1. No preantorbital fenestra.
2. Postorbital ventral process transversely narrow.
3. Jugal-ectopterygoid contact present.
4. External mandibular fenestra present.
5. Marginal tooth denticles present.
6. 3 or more carpal bones.
7. Non-columnar metacarpus.
8. Metacarpals, shape of proximal surface gently curving, forming a 90 f arc.
9. Pelvis anterior width narrow, ilia longer anteroposteriorly than distance separating preacetabular processes.
10. Tibia proximal condyle is narrow and anteroposteriorly elongated.
11. Astragalar ascending process length limited to anterior two-thirds of astragalus
12. Astragalus rectangular.

Euhelopus was the sistergroup to Titanosauria based on-

1. Cervical vertebrae, neural arch laminaiton rudimentary, diapophyseal laminae only feebly developed if present.
2. Presacral vertebrae, bone texture spongy, with large, open internal cells.
3. Anterior and mid-cervical neural spines, orientation posterodorsally inclined, approximately 45? from vertical in lateral view.
4. Scapular glenoid, orientation strongly beveled medially.

I'm sure that individuals on list may wish to comment on Sereno's analysis, since it often find itself at the root of controversy in regards to method.

Holtz's (2000) discussion of the "Classification and Evolution of the Dinosaur Groups" says the following on the subject-

"Several Chinese sauropods (Euhelopus, Omeisaurus, and Mamenchisaurus) of the Middle Jurassic through the Early Cretaceous of China are characterized by extermely long necks that incorporate three or more extra vertebrae than found in typical groups. The analyses of Paul Upchurch of Cambridge University support a monophyletic grouping of these three taxa as the clade Euhelopodidae; those of Jeff Wilson (now at the University of Michigan) and Paul Sereno, instead, suggest that the "euhelopodids" are a polyphyletic group (if so, a remarkable example of convergence limited to a particular geologic span and geographic setting)."

Pisani et al. (2002) in their big supertree paper find Euhelopus as a titanosaur, and Shunosaurus and Omeisaurus as successive sistergroups to the Neosauropoda. But as we all know about supertrees now...

Wilson (2002) finds a paraphyletic Euhelopodidae in the following cladogram (based on Figure 13) -

           |  |--Omeisaurus
           |  '--Mamenchisaurus

Omeisauridae (Wilson, 2002 new taxon) is supported by the following 15 characters-

1. Marginal tooth denticles absent on posterior edge of crown.
2. Fifteen or more cervical vertebrae.
3. Anterior cervical centra height/width approximately 1.25.
4. Mid-cervical centra elongate, more than four times longer than the height of their posterior face.
5. Mid-cervical neural arches low, shorter than posterior centrum face.

Euhelopus is supported as the sistergroup to Titanosauria based on the following 6 characters-

1. Reduced cervical neural arch lamination.
2. Middle and posterior dorsal neural spines oriented posteriorly.
3. Six sacral vertebrae (one dorsosacral added).
4. Scapular glenoid strongly bevelled medially.
5. Scapular base flat in cross-section.
6. Humerus with well developed proximomedial corner.

That's all the information I can find on the subject. :-)

Nick Gardner Paleoartist AIM Eoraptor22