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

RE: Mesozoic roots of parrots and passerine birds

  I have no time to really dig through the archives, but I recall having gone 
through virtually every single fully edentulous mandible of a stem-avian I 
could find, including *Apsaravis ukhaana* and the confuciusornithids, and 
reported on some of this. I assessed most of these taxa to determine not just 
their relative morphology, but to see whether a short dentary symphysis would 
arise and fuse, and the association among the bones when it did.

  One big thing to keep in mind when it came to the UCMP specimen is that there 
is no trace of the Meckelian canal, and there is no trace of any apparent facet 
for the medial mandibular bones, implying that, as in birds, they were reduced 
to splints that did not necessarily form articular surfaces with the lingual 
dentary. They were certainly nothing like caenagnathids in which these bones 
are very distinct and form contacts with the symphysis itself.

  It was once wondered if I even had the theropod ID correct, and so I took a 
look at elements that take the shape of the feature, such as symphyseal 
ossifications, fused paired first coronoid elements (I know, I know, but 
still), mentomeckelian ossifications, predentaries, what have you (possibly all 
the same homology). I even looked at rostral bones in ceratopsians. Like 
several of these elements, the bone is invaginated and partially hollow, with 
surficial vascular features. This resounded in me that aside from the shape of 
the bone, it could reasonably belong to these types of elements. What clinches 
this is, of course, the shape of the element, being a U-shape and having two 
obviously further-continuing colateral rami; there is no central or medial 
ramus that would sit between rami, and no animal that I know of has an 
abbreviated mesial element of the symphysis that completely separates the 
mandibles in such a fasion, especially without evidence of an articulation. So 
it's part of the fused lower jaw, and it's shape is clearly very abbreviated 
given proportions of the symphysis:mandible. So I started conceiving that if it 
could not be a lory, but was convergent to it, and it may not be an 
oviraptorosaur but was convergent to it, it might be a bird, and convergent to 
both. A third short-dentary-with-arched-tomial-margin type of theropod. It may 
be that I am correct in this prospect, which is my operating hypothesis coming 
out of the initial investigations. Resolving those initial questions first 
(lory, oviraptorosaur, something else) is required before I start trying to 
think it might be a highly transformed version of an enantiornithid, 
confuciusornithid, and so forth.


  Jaime A. Headden
  The Bite Stuff (site v2)

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 

> Date: Mon, 29 Aug 2011 10:57:59 +0200
> From: david.marjanovic@gmx.at
> To: dinosaur@usc.edu
> Subject: Re: Mesozoic roots of parrots and passerine birds
> My 0.02 € on the "Cretaceous parrot jaw"... anyone designing a
> phylogenetic analysis will have to keep in mind that "loriid" and
> "oviraptorosaur" aren't the only two possibilities. There are many
> Cretaceous clades of toothless birds, and their fossil record is bad
> enough that we hardly know anything about their distribution in space
> and time or, therefore, their morphological diversity. Off the top of my
> head, imaginable candidates for close relatives are the
> confuciusornithids (in particular *Changchengornis* with its slightly
> hooked beak), so far known _exclusively_ from Konservat-Lagerstätten,
> *Gobipteryx*, likewise only known from one site, and *Samrukia*, which
> may be closely related to the much smaller *Patagopteryx* (...no, I
> don't mean *Patagonykus* this time ;-) ).
> > The problem is exacerbated by the dating issue. "Eufalconimorphae"
> > are not entirely unreasonable, but Cretaceous? What about
> > Halcyornithidae
> > (http://www.tandfonline.com/doi/abs/10.1080/14772019.2010.505252
> > http://www.tandfonline.com/doi/abs/10.1080/14772019.2010.513703)?
> > Close enough to a "missing link" somewhere near the base of
> > Eufalconimorphae, but alive and kicking after 50 Ma including a
> > mega-extinction and near-complete ecological turnover (and
> > carnivorous to boot?) and still very much *looking* like the misssing
> > link you'd expect? It works too well in some aspects, and it
> > completely sucks in others. Those parts of the tree we *have*
> > resolved for good fit together more or less awkwardly, but overall in
> > a satisfying way.
> IMNSHO, the "dating" is bunk; fortunately, it's tacked on to the end of
> the study, not an integral part of it, so it can be disregarded without
> casting doubt on the other results.
> Indeed, as I've already mentioned, I think the phylogenetic tree they
> got is itself evidence for much younger dates. That huge unresolved
> Neoaves radiation which shows evidence of incomplete lineage sorting
> (contradictory distributions of retroposons)? That looks like it happend
> very, very quickly. The only time at which I can imagine such a thing
> happening is in the empty world after the K-Pg boundary mass extinction.
> Thanks a lot for the links. Evidently, somebody has now persuaded the
> university library of Vienna to use some of its nonexistent funds to buy
> the 2nd-ranked journal in paleontology (impact factor of 2010: 3.844 --
> the JVP had 2.241 and is the 8th-ranked journal in paleontology). Excuse
> me while I go on a downloading spree that will probably take all week.
> <bliss>