[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
A new dromaeosaur from the Yixian Formation
++ 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 !
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...
Need a new email address that people can remember
Check out the new EudoraMail at