Yandangornis

["Timothy Williams" <twilliams_alpha@hotmail.com>]

The whole reference for the paper is:

Cai Zhengquan and Zhao Lijun (1999).  A long-tailed bird from the Late 
Cretaceous of Zhejiang.  _Science in China (Scientia Sinica) Series D_: 
42(4): 434-441.

Name: _Yandangornis longicaudus_ (not _Yangdangornis_ like I wrote in the 
last post - that's my typographical error.  There's lots and lots of others 
in the paper).  Named after Yandang Mountains; fossil was collected on the 
northeast foot, associated with the pterosaur _Zhejiangopterus_.

Holotype: Zhejiang Museum of Natural History (M1326).  Near-complete 
skeleton.  Preserved (it appears) in two dimensions, so a lot of detail is 
obscured.  Much of both forelimbs (including carpus and metacarpus) is 
missisng altogether.

Locality: Aoli Village, Shangpan Town, Linhai City, Zhejiang Province. 
China.

Horizon: Tangshang Group; early Late Cretaceous (81.4 MYA)


Entire body length: around 60cm.
Only the underside of the head (47mm long, 20mm across) is preserved; the 
skull bones are lightly built.  The premaxilla has no teeth, and its not 
clear if the maxilla and mandible are toothed since these are squashed 
together.  The authors say _Yandangornis_ has a beak, but I don't know if 
they know this or it's inferred (I think the latter).

There are nine vertebrae in the neck (80mm long), with biconcave centra.  
The tail is 305mm long and made of 20 vertebrae (19 preserved, anterior ones 
are amphicoelous).  Caudals are not ossified (no dromaeosaur-like stiff 
tail) with no hemal arches.

The forelimbs are not reduced (so it says in the Diagnosis, although later 
on the authors are not all that sure on this point - maybe the legs got 
longer?) and are much like those of _Archaeopteryx_.  The humerus (80mm) has 
no pneumatic fossa or foramen and the shaft is rather sigmoid.  The authors 
state the manus has two free digits, but judging from the pictures I'm sure 
they mean that only two are preserved; _Yandangornis_ could have at least 
three digits.  The forelimb between the distal radius+ulna and these digits 
is missing.  The unguals are small and curved.  The estimated length of the 
ulna is 60mm.

The sternum is broad (max. width at lateral processes 38mm; c.50mm long) and 
not keeled (although the authors imply that a "markedly expanded middle 
posterior portion" may be an incipient carina).

The pectoral girdle is crushed, and the pelvic girdle largely unpreserved 
except for the well-preserved pubis (the authors interpret it as 
opisthopubic).  There is no pubic "boot".  The authors also interpret the 
three pelvic elements as unfused to each other.  Abdominal ribs are present. 
 A furcula is present (incompletely preserved).

The femur (106mm) is straight, prominently expanded at both articular 
condyles.  Fourth trochanter is reduced, distal intercondylar foss is 
prominent.  Tarsometatarsus (70mm) is partially fused.  I think the fibula 
is separate.  Tibiotarsus is 132mm long with a good cnemial process.  Pes is 
tetradactyl, middle of the three longer toes is the longest.  No 
sickle-claw.  No adaptations to perching.

Te best evidence that _Yandangornis_ is a bird seems to come from the shape 
of the sternum (broad and expanded anterolaterally, although there is no 
carina) combined with a few characters of the pubis and femur.  Cai and Zhao 
think it was a flightless bird, although evolving from a volant ancestor.

The authors give _Yandangornis_ its own (misspelled) family and own 
(misspelled) order within the Sauriurae: Yandagithidae and -iformes.

There is one interesting comment from the authors regarding 
_Sinosauropteryx_ and _Caudipteryx_: "If they have real feathers, they 
should be referred to birds" (p.440).  Uh-huh.  If you say so.


Tim

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