Feathered non-avian theropods discussion

Jeff Poling

From: "Thomas R. Holtz, Jr." <th81@umail.umd.edu>

Still a bit in awe over the critters. Given that the paper is now computer accessible (but NOT in the "public domain", as someone said: that is something different with regard to copyrights), here are some of the highlights:

Neither form has a distally placed retroverted pedal digit I: these were not perchers, and indeed had typical nonavian theropod feet. Protarchaeopteryx is fairly long-armed (Arm/Femur ratio of 2.5, comparable to the longest armed dromaeosaurs), whereas Caudipteryx is very short armed (Arm/F of 1.5, on the low end of oviraptorosaurs). The teeth of Protarchaeopteryx look like serrated versions of Archaeopteryx teeth, but Caudipteryx teeth are very unusual: long and slender. The ischium of Caudipteryx is very dromaeosaur or oviraptorosaur like: no sign of the posterodorsal process found in Archaeopteryx and more advanced birds. The dentary of Caudipteryx is reminiscent of oviraptorosaurs in shape, and to a certain degree resembles that of Shuvosaurus (!?!?!), but this does not necessarily imply close relationships with either.

The phylogenetic analysis Ji et al. published did not include any non-avian theropods other than velociraptorines, nor does it include Unenlagia or Rahonavis. It will be interesting to see where these guys fall out in a more inclusive analysis.

From: GSP1954@aol.com

Today I had quite the thrill of attending a historical event, the public unveiling of fully feathered Chinese dinosaurs.

The main presenters were Ji Qiang, Phil Currie & Mark Norell. Also attending were John Ostrom and Alan Brush. The July National Geographic and June 25 Nature cover and describe these fossils.

The two critical creatures were Protarchaeopteryx (one moderately good specimen, skull present but too damaged to restore) and Caudipteryx (two, one moderately good, the other very good with well preserved skull).

Both are peculiar theropod dinosaurs, quite advanced and bird-like (far more so than Sinosauropteryx). Skulls small and short in both. In both the complete tail is quite short, proportionally more so than in Archaeopteryx (although vertebral counts are not lower). Caudipteryx in particular seems to have affinities with oviraptorosaurs, including the skull. Yet is has many differences as well, a real mosaic animal. Hindlimbs are extremely long in both; these were clearly runners. Both are fairly large, as big as a turkey.

Claims by Martin (see below) and Feduccia that these are birds are incorrect. There are no avian skeletal features, many dinosaurian ones. Jugal is robust and triradiate. Quadratojugal contacts the squamosal. Coracoid short and broad. Ilium deep and subrectangular. Ischium lacks dorsal processes. Fibula reaches the calcaneum, which is seperate from the astragalus. Metatarsals are unfused. First toe is rather proximally placed and unreversed.

The reason that Martin & Feduccia want these to be birds is because of the feathers. In both large fans of long, fully avian type contour feathers radiate from the last few tail vertebrae. In Caudipteryx long primary feathers are anchored on the hands. These structures have the characters expected in complex bird feathers. Both have the Sinosauropteryx type bristle feathers on the body. (BTW, psittacosaurs from the same sediments have preserved scales, not feathers.)

The unsubstantiated nonsense that the fibers on Sinosauropteryx were internal collagen is of course refuted - again! Reality, theropods had feathers both simple and complex (how far back in theropods feathers go is now the question). Feathers no longer define birds. Indeed, as Padian emphasizes in a note in the Nature issue, most of what used to define Aves is now found in dinosaurs. It is now clear that the body covering of bristle feathers evolved as insulation, in that they thermally isolated the body from external heat. Ergo these were not ectotherms that relied primarily on the environment to provide internal heat.

It is the large arm and tail feathers that pose more of a question.

The arms of Caudipteryx (rather dull name - but easy to spell!) are very short, much too short to fly with. The primary feathers are symmetrical, which is not highly aerodynamic. Both forms appear to have been flightless.

The describers place these theropods less close to modern birds than Archaeopteryx, and before the advent of flight. Of course this is possible. However, I suspect these are secondarily flightless dinosaurs closer to birds than the urvogel. Consider some features one might expect in a secondarily flightless dinosaur, one closer to birds than Archaeopteryx. A shorter tail, perhaps stiffened in the manner of pterosaurs, to better control body orientation during flight. Large sternal plates and ossified sternal ribs, to support a flight musculature, and help ventilate high capacity lungs. Well developed primary and tail feathers symmetrically altered from larger, asymmetrical flight feathers. Caudipteryx has all these features. Andre Elzanowski has shown that the oviraptorosaur palate is more avian than that of Archaeopteryx. These dinosaurs could be early "ostriches", in that they evolved from fliers to become fast running, fairly large land herbivores (indicated by the presence of large bundles of gizzard stones in both Caudipteryx specimens), reducing the arms along the way. What were flight feathers were modified into display surfaces.

A lot of press was there, NBC & CBS news briefly covered the item, NPR had a nice piece on All Things Considered. Except that on the latter Larry Martin made a comment something to the effect that 'although it makes for a more exciting press conference to say that these are feathered dinosaurs rather than early birds, he was sure that more reasonable consideration will eventually show that these are birds'. Martin has yet to see these specimens, unlike Currie, Qiang & Norell who have carefully examined them and described the dinosaurs. I leave it to you to judge who was trying to make an unjustified - and insulting - splash with the press.

After the conference Ostrom - who has had the joy of seeing his notions erified by the fossils - turned to me and asked if I thought it had been an important even. I replied that we just saw history in the making.

On a related matter, the age of the Yixan beds is still up for grabs. Most important, two long tailed pterosaurs have been found, these are otherwise limited to the Jurassic. For that matter, Sinosauropteryx is a compsognathid of Jurassic type. The beds may be very early Jurassic in age. Leaves me scratching my head as to where the birds are in the Solnhofen.

The specimens, plus two Sinosauropteryx (including the type) and Confuciusornis will be on display at the Nationall Geographic Society for a month. Your big chance to see them in the USA!

From: "Thomas R. Holtz, Jr." <th81@umail.umd.edu>

A number of people seem to be distressed that Ji et al. make no mention of the possibility of secondary flightlessness in the newly described Chinese theropods. (The do address, albeit briefly, the evidence for flightlessness in general for these forms, particularly based on the shortness of their arms).

I do not wish to speak for Ji, Currie, Norell, and Ji in this matter. However, I can say what suggests, to me, that these are probably not secondarily flightless: namely, their phylogenetic position.

In the tree they provide, these taxa do not fall within a clade of taxa which are unambiguously volant (i.e., "known fliers" to those with a less-latinate vocabulary...). Instead, Caudipteryx is the sister taxon to a clade of known fliers, and Protarchaeopteryx forms a trichotomy with Velociraptorinae and Avialae.

Now, a few of you out there (and we know who you are...) strongly support particular scenarios where powered flight is, in your opinion, the only life habit sufficient to explain certain features of maniraptoran, or coelurosaurian, or dinosaurian anatomy. Okay, scenario-driven hypotheses (scenario first, phylogeny second) have a long tradition in evolutionary biology. Greg Paul has argued (in Predatory Dinosaurs of the World) that most of what are now called "maniraptoriforms" are secondarily flightless; George Olshevsky has argued here and elsewhere that even more inclusive clades of dinosaurs might be secondarily flightless.

However, Ji et al., and I, are operating under a different mode of evolutionary analysis. In phylogenetic-driven hypotheses (phylogeny first, scenario second), the position of a flightless form within a phylogeny generated by some means (parsimony, maximum likelihood, etc.) will help determine if its flightlessness is primary (i.e., it doesn't fly, nor did any of its ancestors) or secondary (i.e., it doesn't fly, but its ancestors did).

Under phylogenetic-driven hypotheses, all that would be required to convince me that Caudipteryx, Protarchaeopteryx, Mononykus, Velociraptor, Allosaurus, Apatosaurus, and/or Triceratops were secondarily flightless is to demonstrate that the most parsimonious phylogeny places these taxa within a clade whose ancestral state is unambiguously volant. This is the same standard which evolutionary biologists working on other groups of organisms employ.

(For example, a flightless wasp species is deeply nested within a clade of known flying insects, and so its flightlessness is regarded as secondary. Ring-tailed lemurs, however, are not so nested within known fliers, and its flightlessness is best regarded as primary).

However, as Alan Brush and others were talking about in the post-press conference milling about time, there are gradations in what we mean by "fliers", and it may be that one or both of the new Chinese forms had the ability to get off the ground for short pulses of airborn transport. Whether we call this "flight" is debatable.