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Re: Koreanosaurus, new burrowing ornithopod [Meta]

John Conway <john.a.conway@gmail.com> wrote:

> Ah the DML, a potential BURROWING
> FREAKIN DINOSAUR turns up, and we get 5 posts about
> nomenclature, 5 posts requesting PDFs, 3 truncated messages,
> and exactly O on any other aspect. Oi.
> ...okay, and 1 complaining about the lack of topic
> diversity on the DML.

Hang on to your horses, John.  Give some of us a chance to actually READ the 
paper before we start commenting on the actual dinosaur.

Regarding the anatomy of _Koreanosaurus_, one very interesting thing is that 
the postcranium is said by the authors to indicate that it walked on all-fours. 
 Specifically, the relatively long and robust scapula and humerus, the 
relatively short hindlimb (especially the femur), and the orientation of the 
femoral head, all suggest to Min &c that _Koreanosaurus_ was a quadruped, and 
not a cursorial biped.  The long neck may also lend support a quadrupedal 
posture, if it was a way of increasing the elevation of the head when all four 
feet were on the ground.

In contrast, the description of _Oryctodromeus_ by Varicchio &c explicitly 
mentions that this digging ornithopod has the hindlimb proportions of a 
cursorial biped - typical of hypsilophodont-grade ornithopods.  So if 
_Koreanosaurus_ is related to hypsilophodont-grade ornithopods, then (as 
pointed out by Min &c) this would be quite a departure from the impressive 
cursoriality of other hypsilophodont-grade ornithopods (including _Orodromeus_ 
and _Oryctodromeus_ - hence the 'dromeus' part).

Note that although the _Koreanosaurus_ paper includes a cladogram, the 
relationships of this taxon were never actually tested.  As the authors put it: 
"_Koreanosaurus was simply placed by hand on this cladogramme [sic], on the 
base of the characters that can directly be observed on the _Koreanosaurus_ 
material at hand."  IMHO, this approach should not be encouraged, because the 
figured cladogram gives the misleading impression that a sister-taxon 
relationship was recovered between _Orodromeus_ and _Koreanosaurus_.  In fact, t
esis that _Koreanosaurus_ belonged to the 'zephyrosaur' clade 
(_Zephyrosaurus_-_Orodromeus_-_Oryctodromeus_) was not tested, and the precise 
affinities of _Koreanosaurus_ to other ornithischians remain an open question.

The relationships of _Koreanosaurus_ are of critical importance, because if 
this ornithischian is indeed a hypsilophodont-grade ornithopod, then the 
inferred quadrupedal gait is secondary.  If _Koreanosaurus_ lies outside the 
'zephyrosaur' clade, then its fossorial adaptations either evolved 
independently; or the fossorial adaptations common to these four taxa are 
primitive (symplesiomorphic) for a larger ornithischian clade.  The latter 
hypothesis might explain the jugal bosses shared by _Changchunsaurus_,  
heterodontosaurids, zephyrosaurs, and basal marginocephalians; and also the 
(unverified) reports of little _Drinker_ being discovered in burrows.