Euhelopodidae

["Nick Gardner" <ratites637@hotmail.com>]

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) -

Sauropoda
|--Vulcanodon
'--Eusauropoda
  |--Shunosaurus
  '--+--Barapasaurus
     '--+--Patagosaurus
        '--+--Omeisauridae
           |  |--Omeisaurus
           |  '--Mamenchisaurus
           '--+--Jobaria
              '--+--Diplodocoidea
                 '--Macronaria
                    |--Camarasaurus
                    '--Titanosauriformes
                       |--Brachiosaurus
                       '--Somphospondyli
                          |--Euhelopus
                          '--Titanosauria

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


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