Hongshanornis longicresta

[Tim Williams <twilliams_alpha@hotmail.com>]

Zhonghe Zhou and Fucheng Zhang.  (2005).  Discovery of an ornithurine bird 
and its implication for Early Cretaceous avian radiation.  Proc. Natl. Acad. 
Sci. USA.  Published online before print December 12, 2005.

Abstract: "An ornithurine bird, _Hongshanornis longicresta_ gen. et sp. 
nov., represented by a nearly complete and articulated skeleton in full 
plumage, has been recovered from the lacustrine deposits of the Lower 
Cretaceous Jehol Group in Inner Mongolia, northeast China.  The bird had 
completely reduced teeth and possessed a beak in both the upper and lower 
jaws, representing the earliest known beaked ornithurine.  The preservation 
of a predentary bone confirms that this structure is not unique to 
ornithischian dinosaurs but was common in early ornithurine birds.  This 
small bird had a strong flying capability with a low aspect ratio wing.  It 
was probably a wader, feeding in shallow water or marshes.  This find 
confirms that the aquatic environment had played a key role in the origin 
and early radiation of ornithurines, one branch of which eventually gave 
rise to extant birds near the Cretaceous/Tertiary boundary.  This discovery 
provides important information not only for studying the origin and early 
evolution of ornithurines but also for understanding the differentiation in 
morphology, body size, and diet of the Early Cretaceous birds."


The specimen (IVPP V14533; part and counterpart) comes from a small bird 
(skull around 30mm long) that was adorned with a head-crest (hence the 
species name).  Like _Liaoningornis_, _Hongshanornis_ comes from the Yixian 
Formation.  It had a sharp and slender toothless beak, short wings, and long 
legs; the toe proportions and relatively short, poorly recurved unguals 
suggest that it was not an arboreal bird.  The authors suggest that 
_Hongshanornis_ was a wading bird that fed on fish and invertebrates.

The phylogenetic analysis has _Hongshanornis_ as the most basal known member 
of the 'Ornithurae', below a clade comprising a _Liaoningornis_+ 
_Yanornis_+_Yixianornis_ clade, _Apsaravis_, _Hesperornithiformes, 
_Ichthyornis_ and Neornithes, and outside of the Enantiornithes.  
_Hongshanornis_ would be a member of the Ornithurae under Gauthier's (1986) 
stem-based definition (closer to Aves [=Neornithes] than to 
_Archaeopteryx_), followed by Taxon Search (emended to "closer to _Passer_ 
than to _Archaeopteryx_"); but not under Chiappe's (1995) node-based 
definition (all descendents of the most recent common ancestor of 
Hesperornithiformes and Neornithes).  I don't know what definition of 
Ornithurae Zhou and Zhang are using; their use of Ornithurae seems to be 
equivalent to Sereno's newly revised (2005) definition of Euornithes (the 
most inclusive clade comprising _Passer domesticus_ but not _Sinornis 
santensis_).  Thus, _Hongshanornis_ is the most basal known euornithine, 
under Zhou and Zhang's phylogeny.  _Hongshanornis_ is the most basal bird 
euornithine to lose its teeth (that we know of), and this loss would appear 
to be independent of modern birds.

The paper has a lot of stuff about the life habits of Mesozoic birds, but 
I'm not sure I go along with most of it.  For example: "Enantiornithines 
were mainly arboreal and had limited flight capability compared with 
ornithurines, and ornithurines were mainly terrestrial and possessed 
sophisticated flight skill nearly identical to modern birds."  And later: 
"Most early birds were arboreal, and only some ornithurines had become 
secondarily terrestrial and lived near the water."  The way I see it, the 
majority of non-neornithine euornithines (= 'ornithurines' of Zhou and 
Zhang) appear to have lived in or near water: _Yanornis_, _Yixianornis_, 
_Gansus_, _Ichthyornis_, Hesperornithiformes, and now _Hongshanornis_.  
Also, although it is true that some enantiornithines were probably expert 
perchers (e.g., avisaurids), and a medially oriented hallux appears to be be 
primitive for Confuciusornithidae and Enantiornithes, it is also true that a 
reversed anisodactyl hallux of the kind seen in modern birds has yet to be 
recorded outside of Neornithes (or even Neognathae).  The hallux _Apsaravis_ 
and _Ichthyornis_ is not preserved; _Yanornis_ and _Yixianornis_ were 
probably wading birds; and the foot of hesperornithiforms is highly derived 
for diving.  Nevertheless, there is no positive evidence that euornithine 
birds had a specialized perching foot prior to the evolution of the 
Neornithes.  Certainly, no non-ornithothoracine bird show a specialized 
perching pes (that of confuciusornithids is incipient at best), and nor do 
non-avisaurid enantiornithines.  So the idea that birds began their 
evolution as arboreal perchers, and that a non-arboreal lifestyle represents 
an aberration, seems hard to swallow.

Cheers

Tim