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Re: Long-necked stegosaur, head tail mimicry?




Speaking of long sauropod necks... there's a new paper in the pipeline on 
_Euhelopus_.  Although Wilson & Upchurch break up the clade of long-necked 
Chinese sauropods ("Euhelopodidae", containing _Euhelopus_, _Mamenchisaurus_, 
and _Omeisaurus_), they baulk at erecting (or defining) a new Euhelopodidae, 
which would include _Euhelopus_ and _Erketu_. 

Nevertheless, it's clear that *very* long necks evolved at least twice in the 
Sauropoda - in the non-neosauropods (_Mamenchisaurus_, _Omeisaurus_) and basal 
titanosauriforms (_Euhelopus_, _Erketu_).  Given the uncertainty surrounding 
the taxonomy and relationships of the many named _Mamenchisaurus_ and 
_Omeisaurus_ species, the evolution of an extra-long neck (with dorsal 
vertebrae recruited into the cervical series) may have occurred multiple times. 
 

As discussed here, the stegosaur _Miragaia_ shows this strategy happened 
outside the Sauropoda too.  It's fun to think that _Miragaia_ could have given 
rise to some super-long-necked stegosaurs of the Cretaceous.

-------------------------------

Jeffrey A. Wilson and Paul Upchurch.  Redescription and reassessment of the 
phylogenetic affinities of _Euhelopus zdanskyi_ (Dinosauria: Sauropoda) from 
the Early Cretaceous of China.  Journal of Systematic Palaeontology , First 
View article doi:10.1017/S1477201908002691, Published Online by Cambridge 
University.

SYNOPSIS: 

_Euhelopus zdanskyi_ was the first dinosaur described from China. Both 
traditional and modern cladistic assessments have found support for an endemic 
clade of Chinese sauropods (Euhelopodidae) that originated during an interval 
of geographic isolation, but the monophyly of this clade has remained 
controversial. The phylogenetic affinity of the eponymous genus _Euhelopus_ is 
central to this controversy, yet its anatomy has not been completely restudied 
since the original German-language monograph in 1929.

We jointly re-examined the cranial and postcranial anatomy of the holotypic and 
referred materials of _Euhelopus_ to provide a new diagnosis for the ge
 phylogenetic affinities. Diagnostic features of _Euhelopus_ include: postaxial 
cervical vertebrae that have variably developed epipophyses and more subtle 
âpre-epipopophysesâ below the prezygapophyses; cervical neural arches with 
an epipophysealâprezygapophyseal lamina separating two pneumatocoels; 
anterior cervical vertebrae with three costal spurs on the tuberculum and 
capitulum; divided middle presacral neural spines, which in anterior dorsal 
vertebrae bear a median tubercle that is as large or larger than the 
metapophyses; middle and posterior dorsal parapophyseal and diapophyseal 
laminae arranged in a âKâ configuration; and presacral pneumaticity that 
extends into the ilium. Following this morphological study, we rescored 
_Euhelopus_ for the two most comprehensive
 sauropod data matrices (Wilson 2002; Upchurch et al. 2004a), which previously 
yielded vastly different hypotheses for its relationships. Both matrices 
decisively demonstrate that _Euhelopus_ is closely related to Titanosauria; 
traditional and cladistic claims that _Euhelopus_, _Omeisaurus_, 
_Mamenchisaurus_ and _Shunosaurus_ formed a monophyletic âEuhelopodidaeâ 
endemic to East Asia are not supported. These results suggest that there were 
at least two clades of very long-necked sauropods in East Asia, occurring in 
the Middle Jurassic (i.e. _Omeisaurus_ + _Mamenchisaurus_) and Early Cretaceous 
(e.g. _Euhelopus_, _Erketu_), with the latter group perhaps also occurring in 
Europe (Canudo et al. 2002). It is probable that the _Euhelopus_ + _Erketu_ 
lineage invaded East Asia from another part of Pangaea when isolation ended in 
the Early Cretaceous. The large number of basal titanosauriforms from East Asia 
has been interpreted to mean that this area may
 represent their centre of origin (You et al. 2003), but the titanosaur fossil 
record and phylogenetic studies indicate that the group probably originated 
prior to the Middle Jurassic and acquired a virtually global distribution 
before Pangaean fragmentation.