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Re: Koreanosaurus, new burrowing ornithopod [Meta]
John Conway <firstname.lastname@example.org> 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.