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Re: Caudipteryx not a bird and more from APP



My understanding is that caudpteryx and some other close relatives of birds
are controversial as to whether they are birds.    It is also sometimes
argued that they are evidence that archeopteryx are not birds' direct
ancestor but a dead end.

It would be really good to be able to do genetic studies to determine if all
modern birds are really descended from teh same lineage of dinosaurs - I see
real cause to wonder.    More than one line of dinosaurs were evolving in
birdlike directions.

Yours,
Dora Smith
Austin, Texas
villandra@austin.rr.com
----- Original Message -----
From: "Mickey Mortimer" <Mickey_Mortimer111@msn.com>
To: <dinosaur@usc.edu>
Sent: Wednesday, February 02, 2005 3:18 PM
Subject: Caudipteryx not a bird and more from APP


> Dyke, G.J. and Norell, M.A. 2005. Caudipteryx as a non?avialan theropod
> rather than a flightless bird. Acta Palaeontologica Polonica 50 (1):
> 101-116.
>
> Caudipteryx zoui is a small enigmatic theropod known from the Early
> Cretaceous Yixian Formation of the People's Republic of China. From the
time
> of its initial description, this taxon has stimulated a great deal of
> ongoing debate regarding the phylogenetic relationship between non?avialan
> theropods and birds (Avialae) because it preserves structures that have
been
> uncontroversially accepted as feathers (albeit aerodynamically unsuitable
> for flight). However, it has also been proposed that both the relative
> proportions of the hind limb bones (when compared with overall leg
length),
> and the position of the center of mass in Caudipteryx are more similar to
> those seen in extant cusorial birds than they are to other non-avialan
> theropod dinosaurs. This conclusion has been used to imply that
Caudipteryx
> may not have been correctly interpreted as a feathered non?avialan
theropod,
> but instead that this taxon represents some kind of flightless bird. We
> review the evidence for this claim at the level of both the included
fossil
> specimen data, and in terms of the validity of the results presented.
There
> is no reason - phylogenetic, morphometric or otherwise - to conclude that
> Caudipteryx is anything other than a small non-avialan theropod dinosaur.
>
> Salgado, L., Coria, R.A., and Chiappe, L.M. 2005. Osteology of the
sauropod
> embryos from the Upper Cretaceous of Patagonia. Acta Palaeontologica
> Polonica 50 (1): 79-92.
>
> Exceptionally well?preserved embryonic skulls of Upper Cretaceous
(Campanian
> Anacleto Formation) sauropods from Auca Mahuevo (Neuquén Province,
> Argentina) provide important insights into the ontogeny and evolution of
> titanosaurian neosauropods. The most important cranial modifications
> occurring during titanosaurian ontogeny appear to be centered on the
> infraorbital and narial regions, which exhibit a substantial degree of
> "mosaic" evolution. On one hand, the Auca Mahuevo embryos show a large
jugal
> that forms part of the lower margin of the skull and unretracted external
> nares, as indicated by the position and orientation of the lacrimals as
well
> as the anterior extension of the frontals. Both of these features are
> ancestral for neosauropods, being present in prosauropods. On the other
> hand, the embryonic skull exhibits a large ventral notch, tentatively
> interpreted as homologous to the neosauropod preantorbital fenestra, that
> opens ventral to the jugal and between the maxilla and the quadratojugal,
> and a temporal region that closely resembles the adult neosauropod
> condition. This mosaic of character states indicates that different
regions
> of the skull of titanosaurian neosauropods acquired their characteristic
> morphology at substantially different rates during their ontogenetic
> development.
>
> Schubert, B.W. and Ungar, P.S. 2005. Wear facets and enamel spalling in
> tyrannosaurid dinosaurs. Acta Palaeontologica Polonica 50 (1): 93-99.
>
> Numerous paleontologists have noted wear facets on tyrannosaurid lateral
> teeth over the past century. While several workers have proposed
> explanations for these features, there remains to this day no consensus
> concerning their etiology. Here we report on an examination of wear
surfaces
> on these teeth from the Upper Cretaceous (mid-Campanian) Judith River
Group
> of southern Alberta, Canada. This study reveals two distinct types of wear
> features on the labial and lingual sides of tyrannosaurid lateral teeth:
> irregular "spalled" surfaces and wear facets. The irregular spalled
surfaces
> typically extend to the apex of the tooth, which evidently reflects
flaking
> of enamel resulting from forces produced during contact between tooth and
> food. These surfaces are often rounded, presumably from antemortem wear
> following spalling. Wear
> striations on these surfaces are oriented heterogeneously. The wear
facets,
> in contrast, occur on only one side of the tooth and are typically
> elliptical in outline and evince parallel wear striations. Similar
patterns
> of parallel wear striations in extant mammals reflect tooth-tooth contact.
> We therefore propose that wear facets in tyrannosaurids were formed by
> repeated tooth-tooth contact between the lingual side of maxillary teeth
and
> labial side of dentary teeth. It remains unclear whether this contact was
> serendipitous or adaptive, though it appears to be unusual for reptiles,
as
> we have found no evidence for wear facets in extant varanids and
> crocodilians.
>
> Also, Burgess Shale chaetognaths in this issue...