[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Our current understanding of Mesozoic bird phylogeny



> Interesting.  A Confuciusornithidae+Enantiornithes
> clade would explain the 
> similar hallucal morphology between
> confuciusornithids and certain 
> enantiornitheans (like _Concornis_ and _Sinornis_). 
> In all these taxa, the 
> hallux is medially/posteromedially oriented to form
> an incipiently or weakly 
> perching foot.  Avisaurids show a more advanced
> condition, presumably 
> derived from this; while the perching foot of
> ornithuromorphs evolved 
> independently.

What about _Yungavolucris_? The specimen does not look
like it walked a lot but IIRC it's neither too well
adapted for perching. Is there anything Mesozoic
around which has similar proportions? (Is there
*anything* with similar proportions?)

Crown avisaurids -> functional convergence to gripping
feet of Falconiformes maybe?

> Good call, the position of Lectavis differed as
> well.  Upon rerunning the 
> analysis with a few modifications, Lectavis was back
> inside Enantiornithes, 
> though barely.  This is based on four characters-
> tibiotarsal distal 
> condyles equal in anterior projection (absent in
> Sazavis; unknown in 
> Aberratiodontus); plantar surface of metatarsus
> excavated (absent in 
> Yungavolucris and Gobipteryx; also in Confuciusornis
> and Patagopteryx; 
> unknown in Aberratiodontus); tubercle on midshaft of
> metatarsal II (also in 
> Confuciusornis and Yanornis+Passer; unknown in
> Aberratiodontus); metatarsal 
> IV much narrower than II and III (absent in
> Iberomesornis and 
> Liaoningornis+Vorona).
> As you can imagine, a position in
> Confuciusornithidae isn't many steps 
> longer (as there are no ornithothoracine hindlimb
> characters known / 
> included), nor is a position in basal Euornithes 
> (especially since Lectavis 
> has a hypotarsus, otherwise only present in
> euornithines).

Mmmh, it certainly would expand confuciornithine
diversity to a point where one would have to assume
the fossil record to be VERY imperfect/misassigned
and/or _Confuciusornis_ itself to be a crown member of
its clade (which could push back the latter's origin
to a point where things would get really interesting
and/or ugly).

Geography suggests against it though, or else
ocean-crossing ability would have been present before
the full mobility of the shoulder girdle evolved (it
was not yet present in _Confuciusornis_, preventing an
effective, modern-bird-type recovery stroke).

And then there is the question of size - if Lectavis
was simply scaled up, the issue of whether it wasn't
actually flightless arises. But it seems to have been
long-legged rather than big - and this, in turn, would
suggest a cursorial lifestyle, meaning that the
hypotarsus (which certainly is an autapomorphy as
regards to other avian hypotarsi) might have high
adaptational value and thus be of limited phylogenetic
value*.

(Given the fact that the trochleae are missing, it
could be possble, with not too much deliberate ill
character choice, to achieve a
Lectavis+Recurvirostra+Presbyornis+Phoenicopterus
clade. This could then go party with the "monophyletic
foot-propelled divers" clade
Hesperornis+Gavia+Podiceps ;-P )

* Useful insofar as to set it apart from the other
Lecho Fm. taxa, which certainly is a most welcome
find. Indeed, Walker's infamous "New Subclass" paper
uses the diverse morphology of the El Brete material
to argue for the Enantiornithes being a major and
diverse lineage, which is certainly correct.


Many thanks for the work (finally we seem to be
getting *somewhere* as regards Enantiornithes internal
phylogeny!)

Eike


                
___________________________________________________________ 
Telefonate ohne weitere Kosten vom PC zum PC: http://messenger.yahoo.de