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VERY DIVERSE ENANTIORNITHINES



Little thread going about enantiornithine birds. Nick Pharris, our 
favourist linguist, wrote...

> Careful.  There was a time not long ago when almost any Mesozoic 
> bird might be referred to as an "enantiornithine".  More recently, 
> the term has been restricted to a single, natural group of early 
> birds, a branch of the Ornithurae ["bird tails", since in members of 
> this group, which includes modern birds, the tail vertebrae are 
> fused into a stump].

Whoops Nick, enantiornithines are emphatically not ornithurines and 
never have been.

I'm not about to mail in a big listing of all enantiornithine taxa - 
others on the list could do a more competent job of that than I, but 
I would like to say a few things about our changing perception of 
what an enantiornithine IS.

When Cyril Walker first created 'subclass' Enantiornithes in 1981 
(Cyril is one of those vehement anti-cladist types), he did not 
create a hierarchical subdivision of the group, and only just about 
made the taxon valid by including one species (_Enantiornis leali_) 
as a caption in a table. Though this procedure allowed following 
workers to then regard Enantiornithes as valid (i.e. because it had 
at least one constituent taxon (arguments about monotypic higher 
taxa being redundant are not universal (especially in ornithology) 
and have only come in very recently anyway)), he did get a lot of 
criticism from other palaeornithologists (see Olson 1985). 
Conversely, he also got loads of credit as subsequent work has shown 
how insightful he was in recognising a major new avian clade based on 
only a few bits and pieces. Though Cyril and his long-time colleague 
Colin Harrison have been getting a lot of stick recently (because 
many of their proposed identifications are dubious or 
non-supportable), it should always be recognised how tremendously 
competent they were at recongising and identifying avian material, 
often of very scrappy nature. Hats off to them.

A trend in the 1980s was to regard all or nearly all Cretaceous birds 
as enantiornithines. This is carried to its extreme by Feduccia and 
co-workers who have proposed a model whereby, though 'modern type' 
(ornithurine) birds supposedly originated at the same time as 
enantiornithines, it was the latter than dominated Mesozoic avian 
diversity, supposedly thriving at massive diversity right up 
to the Maastrichtian (see Feduccia 1994, 1995). _Confusiornis_ was 
regarded as part of this assemblage (or very close to it) and 
Feduccia (1996) even lists _Patagopteryx_ as worthy of an 'order' 
within the Enantiornithes. 

Working with empirical, rather than intuitive, data, other 
palaeornithologists agree that Enantiornithes were a monophyletic 
radiation of birds that represent the sister-group to ornithurines 
(_Patagopteryx_, Hesperornithiformes, Ichthyornithiformes, 
Neornithes) - this clade has been called Pygostylia. Pygostylia 
+ _Iberomesornis_ is the clade Ornithothoraces. Confuciusornithids 
are the sister-group to the Ornithothoraces (Ji et al. 1999).

The most important point I want to make here is the diversity of the 
enantiornithines, much of which goes generally unappreciated. 
Work by Chiappe and others has shown that avisaurid enantiornithines 
(_Avisaurus_, _Neuquenornis_ etc.) have anisodactyl feet with 
moderately long tarsomets, sharp, recurved pedal claws, and a large, 
fully reflexed hallux. They look to have been good perchers and were 
probably arboreal/scansorial. Meanwhile, Walker was the first to 
propose that some enantiornithines - such as the_Enantiornis_ in his 
original assemblage - had such short tarsometatarsi that they 
appeared to be most like penguins, and perhaps may have been aquatic 
and with limited or absent flight abilities. Larry Martin elaborated 
on this idea in his big review of enantiornithines, though if I 
remember correctly he did not reconstruct _Enantiornis_ as 
flightless. _Yungavolucris_, a Chiappe taxon based on an unusual, 
strongly asymmetrical tarsomet, has also been proposed as aquatic, 
and as a foot-propelled diver. A diving enantiornithine! Why has 
no-one other than Chiappe drawn attention to this? I find it amazing. 
Chiappe further suggested that _Lectavis_, another tarsomet-based 
taxon, was aquatic. In this genus, the tarsomet is incredibly 
elongate and gracile, and would suit a wader (though I wonder if 
tarsomet structure distinguishes long-legged cursors from waders 
amongst birds).

Bottom line here, then, is that enantiornithines may have been very 
diverse, at least ecologically. They may have dwelt in trees, like 
modern songbirds and rollers, may have waded in shallow waters, like 
modern shorebirds, and may have dived and swam under water, like auks 
and penguins. It has further been suggested that the enantiornithine
_Boluochia_ may have been a hawk-like predator (though the evidence 
for this is open to other interpretations).

"...a theropod origin of birds is clearly inextricably coupled with 
the biophysically difficult cursorial theory" 
Oh really?

DARREN NAISH
darren.naish@port.ac.uk