Archaeorhynchus, new toothless beaked Liaoning ornithurine

[bh480@scn.org]

From: Ben Creisler bh480@scn.org

In case this paper has not been mentioned yet:

Zhou, Z. & Zhang, F. (2006). A beaked basal ornithurine 
bird (Aves, Ornithurae) from the Lower Cretaceous of 
China. ?Zoologica Scripta, 35, 363?373.

We report here one of the earliest known beaked 
ornithurine birds from the Lower Cretaceous deposits in 
Liaoning, northeast China. The new basal ornithurine, 
Archaeorhynchus spathula gen. et sp. nov., has a 
rhynchokinetic skull with toothless jaws. It also contains 
over three dozen preserved gizzard stones, suggesting an 
herbivorous diet. The distal end of the tibiotarsus is 
unfused, enabling recognition of the astragalus with a 
broad ascending process, generally similar to that of 
Archaeopteryx. The new discovery sheds new light on our 
understanding of the early radiation and diet 
diversification of early birds in the Lower Cretaceous.
 
Aves Linnaeus, 1758
Ornithurae Haeckel, 1866 (sensu Gauthier & de Queiroz 2001)
Archaeorhynchus spathula gen. et sp. nov.
Holotype. IVPP (Institute of Vertebrate Palaeontology and 
Palaeoanthropology, Beijing, China) collection number 
V14287; subadult individual, nearly complete skeleton with 
feather impressions.

Etymology. The generic name is derived from the Greek 
words archae and rhynch, meaning 'ancient beak'. The 
specific epithet is derived from the Greek word spatha, 
indicating the spathulate dentary.

Locality and horizon. Yixian, Liaoning Province, China; 
Yixian Formation, Lower Cretaceous.

Diagnosis. A basal ornithurine bird distinguishable from 
other Mesozoic ornithurines by the following combination 
of characters: beak present on both upper and lower jaws; 
premaxillae broad with slightly rounded tips; dentary 
spathulate, decorated with elongated foramina or grooves 
and a longitudinal ridge; sternum broad and strongly 
notched caudally with a pair of long lateral trabeculae; 
furcula with long and pointed acromion processes; 
metatarsals II and IV subequal in length; hindlimb 
shortened; ratio of femur to tibiotarsus 0.88; ratio of 
forelimb (humerus + ulna + major metacarpal) to hindlimb 
(femur + tibiotarsus + metatarsal III) about 1.35 
...........................
Archaeorhynchus is a medium-sized bird, represented by a 
partially articulated skull and nearly complete 
postcranial bones mainly preserved in ventral view, in 
association with feather impressions distributed on the 
whole body. ....

As one of the most basal ornithurines, Archaeorhynchus has 
retained several primitive features reminiscent of 
enantiornithines or more basal birds. For instance, the 
dentary is not strongly forked posteriorly as in 
Apsaravis; the sternum is broad but not as elongated as in 
Ambiortus (Kurochkin 1985) and Yanornis. The synsacrum 
comprises only seven sacrals, similar to Confuciusornis 
and the primitive enantiornithine Protopteryx, while both 
Yanornis and Yixianornis have nine and Apsaravis has ten. 
The fibula is long and nearly extends to the distal end of 
the tibiotarsus while it is much more reduced in both 
Yanornis and Yixianornis. The tarsometatarsus lacks a 
distinctive vascular foramen, which is present in 
Yixianornis, Yanornis and Apsaravis.
Archaeorhynchus is larger than most enantiornithines from 
the Lower Cretaceous, but smaller than more basal birds 
such as Archaeopteryx, Jeholornis, and Sapeornis. It has 
greatly shortened legs compared to the wings, a feature 
which bears some resemblance to the enantiornithine 
Longipteryx and the largest Lower Cretaceous bird 
Sapeornis, but is different from Archaeopteryx and other 
ornithurines such as Yixianornis (Table 1). The shortening 
of the leg in the basal ornithurine Archaeorhynchus 
obviously represents a parallel evolution independent of 
enantiornithines or more basal birds. Furthermore, the 
most basal ornithurines Archaeorhynchus, Hongshanornis 
(Zhou & Zhang 2005) and Liaoningornis (Hou et al. 1996) 
are smaller than more derived ornithurines such as 
Yanornis and Yixianornis, showing a trend of increasing 
body size among ornithurines in the Cretaceous. In 
contrast to the shorter legs in Archaeorhynchus, 
Hongshanornis had significantly elongated legs (Table 1).

..............................
The habit and possible diet of Archaeorhynchus are 
difficult to ascertain. Although the bill of 
Archaeorhynchus has some ostensible similarities to that 
of a duck, it lacks the characteristic latter's horny 
lamellae on the interior of the beak near the cutting 
edge. The bill of a bird is a key adaptation for feeding. 
The tip of the moderately long and flat bill of the new 
bird is not pointed; thus it was probably not suitable for 
grabbing fish or insects. The predentary bone, which is 
clearly present in Hongshanornis and in several other 
presumably fish-eating ornithurine birds (Zhou & Zhang 
2005), is absent in Archaeorhynchus. Since the specimen of 
Archaeorhynchus contains over three dozen preserved 
gizzard stones, it probably fed mainly on plants.

Also, I cnn't recall if this paper was mentioned yet. 
Sorry for the duplication if so:

Food remains in Confuciusornis sanctus suggest a fish diet
J. Dalsätt, Z. Zhou, F. Zhang and P. G. P. Ericson  Food 
remains in Confuciusornis sanctus suggest a fish diet. 
Naturwissenschaften advance online publication

Abstract: Despite hundreds of excellent fossils of 
Confuciusornis, the most abundant group of birds in the 
Early Cretaceous, ?Jehol Biota? in China, there is yet no 
indication of the food choice of these birds. Here, we 
describe fish remains preserved in the alimentary system 
of a specimen of Confuciusornis sanctus from the Jiufotang 
Formation. This find is about five million years younger 
than all previously published confuciusornithid birds from 
the Yixian Formation. Although it is unknown how common 
fish was in the diet of Confuciusornis, the find does not 
support previous hypotheses that it fed on plants or grain.