A new dromaeosaur from the Yixian Formation

["Nick Gardner" <paleo_otaku95@eudoramail.com>]

++ Citation ++

Xu, X. and Wang, X.-L. (2004). A new dromaeosaur (Dinosauria: Theropoda) from 
the Early Cretaceous Yixian Formation of Western Liaoning. Vertebrata 
PalAsiatica 42(4): 111-119.

++ Abstract ++

A specimen collected from the Early Cretaceous lowest part of Yixian Formation 
of Liaoning, northeastern China, represents a new genus and species of 
dromaeosaurid theropod. It comprises a fragmentary maxilla with some teeth, a 
few caudals, almost complete fore limbs, and partial hind limbs and is here 
named Graciliraptor lujiatunensis gen. et sp. nov. Distinctive characteristics 
of the new species include a laminal structure connecting the postzygapophyses 
of middle caudals, middle caudals extremely long and slender, small manual 
ungual I, proximal end of metacarpal III strongly expanded, proximal 
tibiotarsus shaft rectangular in cross section, astragalar medial condyle 
significantly expanded posteriorly, metatarsal II distally much wider than 
other metatarsals and long and slender pedal phalanx III-1. Being the earliest 
definitive dromaeosaurid species known to date, G. lujiatunensis provides new 
information important for understanding the early evolution of the group. On !
 on!
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e
 hand, G. lujiatunensis displays a few features similiar to those of basal 
birds, such as caudals significantly elongated, semilunate carpal small and 
primarily contacting metacarpal II, and manual digit I short, providing further 
evidence for a close relationship between the Dromaeosauridae and the Aves; on 
the other hand, it is similiar to troodontids in some features on the caudals. 
The discovery of G. lujiatunensis also indicates a high diversity of the 
Dromaeosauridae in the Early Cretaceous Jehol Biota. Combined with other lines 
of evidence, it is inferred that the Dromaeosauridae rapidly diversified 
taxonomically but remained relatively stable morphologically in the early 
evolution of the group.

++ Some thoughts ++

Graciliraptor appears to have teeth similiar to "velociraptorines" (i.e. 
posterior serrations are significantly larger than the anterior serrations). 
It's been mused on list before that perhaps "Velociraptorine" is paraphyletic, 
and that they are more bird-like basal members of the group, but perhaps that 
is more on observations of Bambiraptor than anything else.

The third metatarsal is compressed in the "subarctometatarsalian" fashion, like 
other basal dromaeosaurids, and basal troodontids. Who was surprised by that? 
;-)

It's suggested in the paper that the Liaoning dromaeosaurids form their own 
clade, but there's no mention of Cryptovolans. They're united by:
1) Radius significantly thinner than ulna.
2) Ungual of manual digit III much smaller.
3) Manual digit I significantly shortened.
4) Manual phalanx III-2 extremely short.
5) Presence of a proximoventral heel on manual phalanx III-2.

Correct me if I'm wrong, but I'm pretty sure that most of these are present in 
basal birds too...

Anyway, the cladistic analysis is apparently from Xu's Ph.D. dissertation which 
the authors note that details can be found in. Perhaps I'm wrong here, but I 
don't think that most have access to that. Does anyone know how one might even 
begin to go about ordering such a thing? It's also frustrating, because 
alvarezsaurids are found to be the sistergroup to all other "enigmosaurs" and 
I'm sure a lot of people would like to know why...

If anyone wants this paper, they can e-mail me offlist...

Nick Gardner


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