Palaeos Vertebrates: Coelurosauria: Oviraptorosauria

This is the teaching of Maryanska et al. (2002). This view has, thus far, met with a rather chilly reception among dinofolk. On initial reading of the paper, one may be suspicious. A number of key taxa, particularly alvarezsaurs, are scored, but not used in the analysis. Further, there is no comparison with neornithines or any other birds closer to neornithines than Confuciusornis. However, a little work suggests why. If neornithines are entered into the data matrix used by the authors, and the omitted taxa are included, the results are extremely strange. The overall topology is this:

Maniraptora
|--Alvarezsauridae
`--+--Therizinosauria
   `--Aves
      |--Archaeopteryx
      `--+--+--Troodontidae
         |  `--Dromaeosauridae
         `--+--Oviraptorosauria
            `--+--Confuciusornithidae
               `--Neornithes

Just as confusing, Avimimus and Caudipteryx are basal oviraptors. Undoubtedly, at some point, this will all be explained. After flirting briefly with this topology, we have returned to a more conventional view. ATW031103.

Oviraptorosauria

Oviraptor is frequently cited as an example of a bird-like dinosaur. Yet, for some reason, typical life reconstructions have missed one potential bird-like feature. The front surfaces of both jaws clearly show the typical rough, pitted markings of horn-like keratin material, quite possibly a beak. There is no reason to assume that the shape of the structure conformed closely to the shape of the bone. See, for example, the illustration at Oviraptor. While very good art, the bull-dog like cropped face that it shows would lose most of the nutritional value from whatever those odd jaws were designed to crack: nuts, eggs, fruit, or delicious crunchy lizards. Whatever it was, the good stuff would flow freely out the sides. What use is half a mouth? Would selection really favor an eye that was so close to things with sharp edges, whether egg shells or claws? Bone makes a very effective device for crushing and cutting. It would be completely superfluous to cover it with a layer of keratin merely to assume the same shape and function. It is more plausible to invent a long, tough curved beak from thin air (for, as usual, the keratin has dissolved without leaving fossil evidence) than to imagine otherwise.

Another problem with the available life reconstructions starts from the position of the arms girdles. Ingenia is a miniature (1.5 m) version of Oviraptor without some of the cranial bells and whistles. The body structures are very much the same. The Nakasota specimen shows a bony sternum (breast bone) like a bird. Above and/or in front of the sternum are the coracoid bones of the arm girdle, and above those the fused clavicles (furcula). The whole thing makes a rather neat package for both muscle attachment and at least some level of protection. The problem, when one does this, is that the big scapulas don't line up in a pretty way with the ribs and the vertebral column. See the close-up. Note how the scapulas stick up and away from the rib cage in the upper corners of the picture. Part of the problem here is that the anterior part of the spine may have been mounted too low (see the lateral view) for reasons that are not clear. Even so, Ingenia would have had remarkable shoulder blades.

A partial solution might be to give the beast a more vertical stance, leaning somewhat forward from the "shoulders." The clawed arms reach up in a natural position to protect the neck. The back bows outward and back, the neck swings forward somewhat, and the coracoids are raised slightly, which forces the scapulas to lie more closely with the body wall. This seems as if it would make reasonable fighting-threatening stance, with the chest armor facing the adversary. Running (and Oviraptorians would seem likely runners), the body assumes the forward, less balanced posture in which it is normally shown.

Descriptions

Characters: Small to medium (1-4 m) sized, lightly built, with a bizarre jaw. $ deep skull; skull strongly fenestrated; $ jaws toothless, forming large base for attachment of presumed horny beak; jaws deep & short; nares high; orbits fairly large; cranial domes or crests in some species which may have had additional horn sheaths; infratemporal fenestra large & square [M+02]; foramen magnum larger than occipital condyle [M+02]; maxilla and premaxilla form secondary palate which may bear a central projection articulating with a similar projection on the central articular process; $ strong medial process on articular; $ upper margin of lower jaw arched; $ dentaries with two long posterior processes; in effect, the lower jaw forms one narrow, centrally peaked (= "coronoid eminence" [M+02]), blade which may have articulated medially with the roof of the broader upper jaw; intramandibular joint absent; vertebral formula 10+13+6+~40; centra pneumatized, including anterior caudal vertebrae; hypapophyses present on caudal & dorsal vertebrae [M+02]; tail short overall (a 2000 article in Nature reports a specimen with a possible pygostyle, or at least a series of fused caudals); scapula thick, flat (in O. philoceratops, has process to articulate with clavicle); clavicles robust and fused (furcula); marked delto-pectoral crest on humerus; ectepicondyle more prominent than entepicondyle [M+02]; semilunate carpal present; three fingers with sharply curved , laterally compressed unguals; unguals with pronounced lip above articulation with penultimate phalanges; propubic; ilium deep in O. philoceratops but not others; pubis long, with small boot; ischium bears large obturator process; greater trochanter prominent, but 4th trochanter reduced; some species are arctometatarsalian; 4 toes, 3 weight-bearing; foot unguals relatively small & weakly curved. Several specimens found on nests with eggs, now believed to be their own.

Image: Profiles of all oviraptorids with known skull material, including identification key and scale bar. By Matt Martyniuk, via Wikipedia, Creative Commons Attribution

checkedATW040810

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Coelurosauria: Oviraptorosauria

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Oviraptors are Birds?!

Oviraptorosauria

Descriptions