Euhelopodidae (was Re: Long Necks)

["Matthew Bonnan" <mbonnan@hotmail.com>]

Wish I had the refs in front of me so I could give you more details, but I'm 
at home and most of my refs are at the university.  Anyway, Paul Upchurch 
has done some excellent phylogenetic work on sauropods: a paper in 1995 with 
174 osteological characters, a paper in 1998 with over 200 characters, and a 
paper this year on the relationships between the Nemegtosauridae and the 
diplodocids and titanosaurids.

Unlike most other sauropod workers, Upchurch avoided higher lever taxa 
(Family level and higher) and instead put genus-level taxa into his 
cladograms (i.e., instead of taxon Camarasauridae, taxa Camarasaurus, 
Brachiosaurus, Mamenchisaurus, etc.).  When I get back to the university on 
Monday, I'll provide everyone with the exact refs and some more details, but 
here is the gist of his studies.  Again, I emphasize that I will fill in 
details later, so please don't write to tell me I have no details to back 
this stuff up! =)

Upchurch has concluded that there is something like the Euhelopodidae, and 
that all the Chinese sauropods are more closely related to one another than 
they are to other neosauropods.  Independent analysis of neck lengths in 
sauropods by my advisor, Mike Parrish, has shown that when you plot out neck 
length to body size, the Chinese sauropods cluster together as outliers to 
the general trend, and this would help add some weight to Upchruch's 
analysis.

Furthermore, Upchurch has shown that inclusion or exclusion of a single 
sauropod taxon can upset portions of a cladogram or change higher taxa 
relationships, hence his reason for using as many singular taxa as possible. 
 Even with the missing skeletal parts of sauropods, the consistency index 
of his cladograms are pretty decent (around .50, which is good considering 
how partial and scrappy some sauropod taxa are).

All things being equal, I tend to fall on the side of Upchurch with regard 
to Chinese sauropods -- they do share a number of characters that would 
place them closer together than to other sauropods and Upchurch has 
tentatively suggested that perhaps some of this was due to a kind of 
geographic isolation which he did not elaborate on.  Unlike Wilson and 
Sereno (1998) he included Mamenchisaurus in his data set.  As Upchurch has 
pointed out, because our record of sauropod material belowe higher level 
taxa is full of conspicuous absences, there is bound to be controversy over 
sauropod relationships for quite a while.  However, he feels that including 
as many taxa as possible, even while producing an incomplete data matrix, 
provides a clearer understanding of sauropod relationships.  And, hey, it's 
the best we've got right now anyway.

Matt Bonnan

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