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UCMP 143274 (RE: Leptorhynchos)




--- Jaime Headden <qi_leong@hotmail.com> schrieb am Do, 25.4.2013:

> Von: Jaime Headden <qi_leong@hotmail.com>
> Betreff: RE: Leptorhynchos, new caenagnathid theropod from Late Cretaceous of 
> North America
> An: "Dinosaur Mailing List" <dinosaur@usc.edu>
> Datum: Donnerstag, 25. April, 2013 19:04 Uhr
> In my post below, I argued that ICZN
> Art. 70.1 allowed automatic type fixation. I am incorrect on
> this score, as explained in the comments here: 
> http://qilong.wordpress.com/2013/04/25/an-oviraptorosaur-worth-the-name/
> .


Seeing the material of "L." gaddisi brought me back to 
http://qilong.wordpress.com/2011/03/02/a-cretaceous-parrot/ ... anything the 
new study (or other recent studies) adds on this case? Any indications in the 
presently-known caenagnathid hypodigm whether the 
presence/absence/structure/shape/pattern of surface ornamentation may be 
ontogenetic?
Or in the absence of material evidence (the hypodigm of very young 
caenagnathids is, IIRC, still marginal or zero), is there any indication of 
ontogenetic dietary shifts in caenagnathids? Evidence in favor of a dietary 
shift is not proof of change in surface ornamentation, but it can argue in 
favor of it, even strongly so (in cases of extreme shifts that demand gross 
ontogenetic changes in morphology).
(IF the beak of caenagnathids was an adaptation to shear through strongly 
sclerotized plant tissue, a dietary shift is perhaps more likely than not, as 
such food would doubtfully be nutritious enough to sustain a theropod growing 
to moderate or largish size. Juveniles would probably have fed on 
easier-digested, softer plant tissues... or have been extremely slow-growing, 
but that makes the lack of caenagnathid growth series in the hypodigm puzzling. 
And if juvies ate softer food, the null hypothesis would be their jaws had a 
less structured surface than those of adults.)



FWIW the latest phylogenetic studies on stem Psittaciformes, eg 
http://www.bioone.org/doi/abs/10.1080/02724634.2012.641704, virtually rule out 
a psittaciform identity of UCMP 143274
ot jaw was a late Paleogene or early Neogene apomorphy postdating crown 
psittaciform TMT apomorphies - and ecologically building on these, nut-gripper 
foot opening a niche for evolution of nut-cracker beak -, as far as anyone can 
tell ATM. 

The general shape, particularly the outer curvature of UCMP 143274 is 
remarkably *un-*parrot-like in fact; if this was avian, the entire mandible 
would have been closer to that of Aequornithes in shape (ie narrow and 
elongated)... in Psittaciformes with rounded mandibular tips, the length of the 
symphysis is subequal to (at most) barely superequal to its width. On the other 
hand, in UCMP 143274 it is almost twice as long as wide and the rami ran almost 
parallel at least in the the distal part; if they were not exceptionally short, 
a parrot-like bill shape (short and blunt) in UCMP 143274 can be rejected by 
these two features combined already: it is simply too narrow for its length.



TL;DR: 
What did the mandibular symphysis of a *hatchling* or "fledgling" FMNH PR 2081* 
(http://qilong.wordpress.com/2012/01/22/the-hell-creek-oviraptorosaur-should-or-shouldnt-it-be-chirostenotes-pergracilis/)
 look like? In gross morphology and size at least, UCMP 143274 would be the 
closest match there is in the fossil record, if I'm not mistaken.


* Or maybe the smaller coeval and sympatric caenagnathid, if that was not just 
a subadult of the same taxon as FMNH PR 2081.



(FWIW, the standards of evidence and sweepingness of conclusions in Stidham 
(1998) are simply scary 15 years in hindsight... stuff you only see in 
high-priced high-impact low-quality-of-peer-review journals:

"The discovery of this parrot [sic] in the Lance Formation indicates that the 
lineage leading to the parrot crown group was present by the end of the 
Cretaceous. If this parrot were a lory [sic], as suggested by its morphology 
[sic], ..."

Eerily recalls of studies 25 years older, when K-Pg boundary avians were still 
routinely assigned to crown "families".
Stidham may be excused a bit for the second gaffe, because the
ption at that time still was that "Loriidae" was basal or almost basal among 
crown Psittaciformes. They are not; on the contrary, the origin of lorikeets 
cannot be realistically pushed back much further than mid-Neogene.
So in the light of present-day phylogenetic knowledge and fossil record, the 
argument of Stidham (1998) for a psittaciform identity of UCMP 143274 is 
entirely demolished; it is a rather funny (or sordid; you decide) case of 
verification bias. To draw any conclusions from a comparison of UCMP 143274 
with lories is as meaningless as to argue an unusually rounded mammalian 
calvaria from the Danian were "proof" for crown Hominidae in the late 
Cretaceous.)


Thus, at the present time I can only conclude that a thorough comparison of 
UCMP 143274 with any and all caenagnathid material pertinent to its identity, 
and inferring what can be inferred from the rest re: ontogeny, diet, and 
Maastrichtian caenagnathid diversity in North America, would be more warranted 
than ever.


Regards,

Eike