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Re: New PaleoBios paper & Daanosaurus revisited


Mike Taylor wrote:

> Taylor, Michael P., and Naish, Darren (2005). The phylogenetic
> taxonomy of Diplodocoidea (Dinosauria: Sauropoda). PaleoBios 25 (2):
> 1-7.

I notice that the world seems to be a little underwhelmed by this contribution -- I has been expecting, at minimum, the Nobel Prize for Literature by now. But then I do admit that this is a pretty boring paper for people who are not particularly into sauropods or phylogenetic taxonomy.

The corollary is that it this paper is not at all boring for those of us that *are* into sauropods and/or phylogenetic taxonomy. Mike and Darren certainly did their homework, and I support their Recommendations (especially the one that genera rather than clades should be used as specifiers). These kind of housekeeping papers are indispensable. I'd like to see the same thing done for basal sauropodomorphs and non-neornithine birds (get out the antacid....).

The Diplodocoidea/Diplodicimorpha lends itself to this kind of PT study, given that (like the Titanosauriformes) the monophyly of this group is well-supported. One fly in the ointment was that Upchurch's original definition of Diplodocoidea originally included Nemegtosauridae (now universally regarded as titanosaurs); thus Taylor and Naish (2005) neatly excised _Nemegtosaurus_ (and its eponymous clade) from the definition. My only gripe is that the clade Diplodocoidea ends up as more inclusive than Diplodocimorpha; but this is not Mike and Darren's fault, and my objection lies solely on aesthetic grounds.

So much so that I didn't even require my wife to read it. 

I can relate to that.  :-)

From another post and another thread, Mike Taylor wrote:

> Once we get mature specimens, they should be correctly called Euhelopodidae....

Not necessarily. The name Euhelopodidae has been used for the clade of Chinese sauropods (_Euhelopus_, _Mamenchisaurus_, _Omeisaurus_ and _Shunosaurus_) recovered by Upchurch's (1995, 1998) analyses.

In her paper on Chinese sauropods, Martin-Rolland (1999) actually expanded the Euhelopodidae to include almost all Chinese sauropods known at the time, including _Zizhongosaurus_, _Bellusaurus_, _Datousaurus_ and _Tienshanosaurus_ (which she suggested might be synonymous with _Euhelopus_), as well as _Shunosaurus_, _Omeisaurus_, _Mamenchisaurus_, _Zigongosaurus (resurrected as a valid genus by Martin-Rolland) and _Euhelopus_. _Protognathosaurus_ was not considered to be a euhelopodid in this study, but a cetiosaurid. No phylogenetic analysis was included, and I found this paper to surprisingly unhelpful in resolving the status and relationships of Chinese sauropod taxa.

Martin-Rolland, V. (1999). Les sauropodes chinois, Revue de Paléobiologie. 18: 287-315.

In Wilson 2002, _Omeisaurus_ and _Mamenchisaurus_ together form a clade, the outgroup to (_Jobaria_ + Neosauropoda), so you _could_ define something like Mamenchisauridae =
(_Mamenchisaurus_ + _Omeisaurus_). However, Upchurch et al. 2004 recovered _Euhelopus_ as sister group to Neosauropoda, _Mamenchisaurus_ just outside the (_E._+Neo) clade, an
_Omeisaurus_-_Tehuelchisaurus_ clade outside that, and _Shunosaurus_ much more basal. So beware -- the definition above would amount to nearly all of Eusauropoda under that topology.

One way around this is to define Mamenchisauridae to be (_Mamenchisaurus_ + _Omeisaurus_, but not _Diplodocus_ or _Saltasaurus_), such that the definition includes an internal caveat. This way, if _Mamenchisaurus_ and _Omeisaurus_ are found to be paraphyletic relative to 'higher' sauropods, the clade self-nullifies. In other words, the clade Mamenchisauridae is only valid as long as _Mamenchisaurus_ and _Omeisaurus_ form a clade to the exclusion of most other sauropods, and we don't end up with a Mamenchisauridae that engulfs the entire Eusauropoda.

Not only that, but species-level taxonomy of both _Mamenchisaurus_ and _Omeisaurus_ is so
screwed up that some _M._ species may really be _O._ and vice versa, so basing a clade on either is asking for trouble.

Very true. I think it's fair to say that _Mamenchisaurus hochuanensis_ and _M. sinocanadorum_ are congeneric, but the type species _M. constructus_ needs further study. As noted by Upchurch et al. (2004), _Mamenchisaurus_ has tended to be used as a wastebasket for mid-Jurassic Chinese sauropods with very long necks. It might be better to use individual _Mamenchisaurus_ and _Omeisaurus_ species as separate OTU's in future phylogenetic analyses. There is also the issue of the validity of _Zigongosaurus_, which is usually referred to _Omeisaurus_ or _Mamenchisaurus_, but regarded by Martin-Rolland (1999) as a separate genus (see above).

Cheers

Tim