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Re: Long-necked stegosaur, head tail mimicry?

I don't have that much against Euhelopodidae applying to *Euhelopus* + *Erketu*, but...

This concept only came about fairly recently (c.1995),

Fourteen years ago is _not_ "fairly recently" in science. Really not.

and was not accepted by everyone.

Fine, but nobody used the name Euhelopodidae for anything else either, so whenever it was used, it was used for the assemblage Upchurch had found to be a clade.

Upchurch himself later abandoned his own Euhelopodidae, less than 10 years after. Euhelopodidae sensu Upchurch also differs slightly from Romer's original composition of the group (as Euhelopodinae), which also included _Tienshanosaurus_ and _Chiayusaurus_.

Is that so, or is that just because these two are so incomplete that they were never included in a phylogenetic analysis?

If you want to look at sauropods, then what about Cetiosauridae, which for most of its history was a dumping ground for "primitive" or poorly known Jurassic sauropods. But this nomenclatural history shouldn't preclude Cetiosauridae from being phylogenetically defined to include _Cetiosaurus_ and its closest relatives - as it was in fact used by Upchurch et al. (2004).

After it had not been used at all for ten years or more.

True. But I was referring specifically to the anatomical trait of increasing neck length by wholesale recruitment of dorsals into the cervical column. As you know, diplodocids and brachiosaurids lengthen the neck principally by elongation of pre-existing cervicals.

Not *Barosaurus*, which ended up with just nine dorsals -- an outright neornithean value.

_Euhelopus_ and mamenchisaurids go one better, and add extra vertebrae into the neck, at the expense of the anterior dorsals.

They _also_ add _really extra_ vertebrae into the neck that really are additional. Neomorphs -- perhaps genetic copies of neighboring vertebrae of something.