RE: UCMP 143274 (RE: Leptorhynchos) & comments on Gibb et al. (2013) on Aequornithes

[evelyn sobielski <koreke77@yahoo.de>]

--- Jaime Headden <qi_leong@hotmail.com> schrieb am Sa, 27.4.2013:

> Von: Jaime Headden <qi_leong@hotmail.com>
> Betreff: RE: UCMP 143274 (RE: Leptorhynchos)
> An: "Eike" <koreke77@yahoo.de>, "Dinosaur Mailing List" <dinosaur@usc.edu>
[...]
> My intial hypothesis -- and note that this is preliminary --
> is that the specimen is particularly unique; should it be a
> bird, it is probably not a parrot, but should it be a
> nonavian dinosaur (barring identification as a turtle or
> whatever) it is likely to be a caenagnathid.
> Problematically, the size of the specimen lends an
> ontogoenetic spin on the identity of the specimen, as Eike
> notes; but as only TWO specimens have been described of
> caenagnathid-ish jaws (those of *Caenagnathasia
> martinsoni*), and the relative amount of fusion between them
> does not come with distinct size differences, it may be
> difficult to say anything as yet about relative ontogenetic
> state. There is no indication of "woven bone" surface
> texture, but this may not mean anything.
> 
> The basic assumption, that this specimen represents a
> near-adult animal, is tantalizing, and if so, would further
> support taxic uniqueness for the specimen, regardless of
> whether it was a bird or caenagnathid. There is also the
> option the specimen may be crocodilian (an identity only
> invoked because of *Macelognathus vagans*/*Hallopus
> victor*), testudinean, or even a teleostean or
> chondrichthyan! (I should note those last two are
> very unlikely.)

That sounds very good, hope you find something significant!

UCMP 143274 has the right scooped-out shape, but it *seems* (from Hope in 
Chiappe) not to be widening enough proximad - the rami/symphysis boundary 
region flares in Psittaciformes, in UCMP 143274 is looks almost parallel. If 
you expand the rami (the break is basically at the rami-symphysis boundary) 
assuming they were not notably kinked to midline or outsides, the resultant 
shape of the billtip (symphysis + distal rami) looks more like in Aequornithes 
or perhaps Galloanseres,
to anyone interested in UCMP 143274, don't know if we had them yet:


Milne-Edwards: Recherches sur la faune ornithologique éteinte des iles 
Mascareignes et de Madagascar, especially plates 2+3
http://www.biodiversitylibrary.org/item/50556#page/159/mode/1up
FWIW phylogeny for plate 2 AFAICT ( 3 ( (1(28)) ((45)67) ) ) For 3: ( (5(69)) 
((13)(24)78) ), with pl2 (1(28)) = pl3 (5(69)). Quite nice sampling considering 
this is the first post-Darwinian generation of researchers.

Olson & James: Descriptions of Thirty-two. New Species of Birds from the. 
Hawaiian Islands: Part I. Non-Passeriformes. 
http://sora.unm.edu/node/169
Ornithological Monographs 45: 1–88.
(Chelynechen, Ptaiochen, Thambetochen, fig.9&12, pp.28-42. Specimens are in 
USNM Paleo collection, database is here 
http://collections.mnh.si.edu/search/paleo/)

Mayr: Late Oligocene mousebird converges on parrots in skull morphology
http://dx.doi.org/10.1111/ibi.12034
Ibis Volume 155, Issue 2, pages 384–396, April 2013
"A new fossil stem group representative of Coliiformes (mousebirds) with a 
remarkable skull morphology is described from the late Oligocene of Germany. 
Oligocolius psittacocephalon sp. nov. for the first time preserves the skull of 
a post-Eocene fossil mousebird. 
This exhibits a combination of skull features unknown from any other bird and 
converges on the skull of parrots in that the beak is separated from the 
cranium by a marked nasofrontal hinge and in that the interorbital part of the 
frontal bones is very wide. 
In addition, the mandible of the new species exhibits long retroarticular 
processes, which are unexpected because unlike in other coliiform birds 
exhibiting this feature, the short beak was probably not used for probing in 
substrate. 
It is hypothesized that the retroarticular processes of O. psittacocephalon 
instead served for a particular wide and forceful opening of the beak. 
Eight large fruit stones are situated in the area of the digestive tract of the 
new species. Preservation of most of these in a well-delimited cluster i
 mousebirds, O. psittacocephalon had a crop. 
The new fossil shows that late Oligocene European stem group Coliiformes 
significantly differed from their extant relatives in morphology and probably 
also in feeding ecology."


Holliday & Nesbitt: Morphology and diversity of the mandibular symphysis of 
archosauriforms 
http://dx.doi.org/10.1144/SP379.2
In: Nesbitt, S. J., Desojo, J. B. and R. B. Irmis (eds) Anatomy, Phylogeny and 
Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, 
Special Publications, 379, 2013
"Archosauromorphs radiated into numerous trophic niches during the Mesozoic, 
many of which were accommodated by particular suites of cranial adaptations and 
feeding behaviours. The mandibular symphysis, the joint linking the mandibles, 
is a poorly understood craniomandibular joint that may offer significant 
insight into skull function and feeding ecology. 
Using comparative data from extant amniotes, we investigated the skeletal 
anatomy and osteological correlates of relevant soft tissues in a survey of 
archosauromorph mandibular symphyses. Characters were identified and their 
evolution mapped using a current phylogeny of archosauriforms with the addition 
of non-archosauriform archosauromorphs. 
Extinct taxa with the simple Class I condition (e.g. proterochampsids, 
‘rauisuchians’), rugose Class II (aetosaurs, protosuchians, silesaurids) and 
interdigitating Class III symphyses (e.g. phytosaurs, crocodyliforms) and 
finally fused Class IV (avians) build the joints in expected ways, although 
they differ in the contributions of bony elements and Meckel’s cartilage. 
Optimization of the different classes of symphyses across archosauromorph 
clades indicates that major iterative transitions from plesiomorphic Class I to 
derived, rigid Class II–IV symphyses occurred along the lines to phytosaurs, 
aetosaurs, a subset of poposauroids, crocodyliformes, pterosaurs and birds. 
These transitions in symphyseal morphology also appear to track changes in 
dentition and potentially diet.


Thank
niform and Ciconiiform Birds, and Long-Term Niche
Stability"! Brilliant, just what I needed. Their results are interesting and 
the divergence times look rather on the solid side. My only criticism is they 
left out loons+penguins from fig3 (the star phylogeny - very nicely done this 
one), would have been very interesting what they did to the unstable base; as 
you can see comparing fig.2/4/5 they mess things up a fair bit (as does Phaeton 
further "down" - the root with Galliformes is not at all stable, it basically 
LBAs somewhere according to algorithm used. The Phaeton case is discussed at 
length).
This is quite cool because it complements what I have been trying for "higher 
landbirds". There, the problem is if anything more widespread, tying in with 
the idea of an era of incomplete lineage sorting early in Neoaves radiation as 
suggested by retroposon data (see 
http://mbe.oxfordjournals.org/content/29/6/1497.abstract). 
If the calibration in Gibb et al. (2013) is good, that era would have been most 
likely a few Ma or less, after 70 Ma and before 60 Ma. (Gee wiz, I wonder what 
might have happened?)
Taxon sampling is quite satisfying. They might have tried enforcing Strisores + 
accipitrid monophyly just for shit & giggles tho, and/or thrown in some 
cranes&rails. But then again, this might only have confused things.

Anyone have the new Mayr paper cited above? 


Regards,

Eike


PS: re:Psittaciformes, it seems they do in fact have a striking AT base 
composition bias at least in major parts of their genome. In birds the general 
trend towards CG enrichment on the lineage towards passerines holds broadly 
true, but parrots are THE notable exception. Something happened there, their 
AT:CG ratio is more similar to paleognaths than to passerines.
IONO the ref, have the paper somewhere and could dig it out if someone wants to 
read it. Might have been in one of the Karger journals, Cytogenet. Genome Res. 
or sth.