Details on Nomingia

Description-

The holotype was discovered in 1994, illustrated in Sloan (1999) and described briefly by Barsbold et al. (2000) before its official publication. The species was originally called "Nomingia brevicaudia", but was changed shortly before publication. The specimen was a subadult based on the unfused sutures between presacral neural arches and centra. Based on comparison to oviraptorids and adjusting for the shorter tail, it may have been about 1.8 meters long.

The first three preserved vertebrae are cervicals. They have a single pair of pleurocoels and low neural spines, although not as low as Microvenator. The last has a moderate-sized epipophysis overhanging the postzygopophysis, which are much shorter than Microvenator. The second to last cervical centrum has a ventral ridge, while the last has a large hypapophysis. Cervical ribs were not fused to centra.

The ten dorsal vertebrae also have pairs of pleurocoels and neural spines grading from moderate to tall (about twice as tall as centra). The first two dorsals have large hypapophyses, the next next five have ventral ridges and the last three are flat ventrally. The centra are short compared to Microvenator. The ninth dorsal vertebra has a bipartite transverse process; one part contacts the rib tuberculum, the other contacts the ilium's preacetabular process. The tenth dorsal vertebra is sutured to the sacrum and the neural spine contacts the first sacral neural spine. The transverse process does not contact the ilium however. The ribs and gastralia are not described or illustrated.

Five sacral vertebrae are fused and have transverse processes in contact with the ilia. Their neural spines are in contact and project slightly above the ilium. Ventrally, the centra are subequal in width and the second through fourth centra are grooved.

Twenty-four caudal vertebrae are present, the last five fused into a pygostyle. The first caudal vertebra is sutured to the sacrum. The centra gradually decrease in length, until the last ten before the pygostyle are 60-65% the length of the first. Pleurocoels are present in the first ten centra. The first two and the eleventh and twelfth centra are flat ventrally, but the others have a pair of ridges bounding a median groove. Sixteen caudals have neural spines and eighteen have transverse processes. The fifteenth through nineteenth have elongate prezygopophyses, though not comparable to dromaeosaurs. The postzygopophyses join to form a continuous midline crest from the fourteenth onward and the prezygopophyses join it after the eighteenth caudal. The last five caudals are fused indistinguishably. Seventeen caudals have chevrons (only fifteen are preserved), ending after the eighteenth. The first fourteen chevrons are dorsoventrally elongate, none are distally expanded. Instead, the last several arectangular, while the proximal six are tapered distally.

The pelvis is slightly propubic (~20 degrees to the vertical). The ilium has an expanded preacetabular process, with a blunt anteroventral corner. The dorsal margin is convex until the acetabular midpoint, where it becomes straight. It is then angled posteroventrally to take part in the rounded postacetabular process. The preacetabular process is about 15% longer than the postacetabular process. The pubic peduncle is vertically oriented, extends ventrally as far as the ischial peduncle and has a concave ventral edge. There is a shallow elongate cuppedicus fossa, no supracetabular crest and a short shallow brevis fossa. A low antitrochantor is present on the ischial peduncle. Dorsally, the iliac blades converge medially to contact the sacral neural spines. The pubis is very slightly concave anteriorly and lacks any proximal foramina or processes. The foot is slightly larger anterior than posteriorly and acutely pointed in both directions. The symphysis extends for half of the pubic length. The ischium is 60% of the pubis in length and has a triangular obturator process placed halfway down the shaft. There may be a small mid-dorsal ischial process, although this could just be a broken area.

The femur has a horizontal head that is separated from the greater trochantor. There is a slight neck. The lesser trochantor is either fused to the greater trochantor or separated by a small groove. No fourth trochantor is visible, but a posterior trochantor may be present. A pronounced tibiofibular crest is present. The tibia is similar to Ingenia. The fibula reaches the calcaneum, is weakly concave proximomedially and has a craniolaterally projecting tibiofibularis tubercle. The astragalocalcaneum is unfused and the ascending process is 20% of tibial height.

Relationships-

The authors classify this as an oviraptorosaur based on- three cervicodorsal vertebrae with large hypapophyses; pneumatic proximal caudal centra; tail short; ischium with posterior profile. The first character is difficult to validify as the entire sequence of anterior dorsals is needed. Nomingia does have three large hypapophyses, and oviraptorids are said to (contra Barsbold et al. 1990). Chirostenotes has at least two large hypapophyses, Microvenator has at least one small hypapophysis. Avimimus only as two large hypapophyses, Mononykus and Velociraptor have one. Tyrannosaurids, ornithomimids, segnosaurs, Alvarezsaurus and Archaeopteryx have no large hypapophyses. This character may be a synapomorphy of oviraptorosaurs, but I'm hesitant to agree with this until more dorsal series are described. Pneumatic caudal centra are absent in Caudipteryx and Microvenator (see below). The tails of oviraptorosaurs are less than 2.5 times the femur in length. This is also probably present in Protarchaeopteryx, a possible oviraptorosaur sister group. Finally, the posteriorly concave ischium is probably primitive for coelurosaurs, as Gorgosaurus, Compsognathus, the Santana compsognathid? and probably Scipionyx also exhibit it. It should also be mentioned pygostylians have three or more large hypapophyses and very short tails. The authors don't place Nomingia in a family, but think the strong posterior curve to the ischium, long preacetabular process and straight pubis might suggest caenagnathid affinities. Compsognathus is very similar to Nomingia in ischial curvature, while Caudipteryx and Ingenia are not very different either. "Rinchenia" and Caudipteryx also have elongate preacetabular processes. Finally, the pubis of Chirostenotes may be straightened by postmortem crushing (Sues 1997), and this would be symplesiomorphic in any case.

This taxon is a member of the segnosaur-oviraptorosaur group based on the presence of- posterior dorsal pleurocoels; caudal vertebrae shorten posteriorly; concave ventral mergin of pubic peduncle; anterior pubic foot larger than posterior foot. Oviraptorosaurian characters include- three dorsals with large hypapophyses?; tail less than 2.5 times femoral length. It is the sister group to Caudipteryx based on- less than eleven dorsal vertebrae; tail less than twice as long as femur; less than twenty-five caudal vertebrae; some distal caudal prezygopophyses elongate; ischium less than 70% of pubic length. It's more basal than Microvenator + Caenagnathoidea because of- one pair of cervical pleurocoels; no transverse processes on distal caudal vertebrae. On the other hand, a single character supports it as the sister group to Microvenator + Caenagnathoidea- proximal caudal pleurocoels. This is most parsimoniously seen as a convergence. Phylogenetic analysis of 318 characters and 47 taxa supports this conclusion, as does Holtz' most recent unpublished analysis. Perhaps Nomingia should be placed with Caudipteryx in the unfortunately named Caudipteridae.

Anyone who wants the figures can see them online at-

http://www.paleo.pan.pl/acta/45-2-97.htm . The only other figures in the paper are a schematic drawing of the pelvis and a ventral view of the ilium. If anyone wants scans of these, they can contact me offline as usual. Questions and comments are welcome. Next comes Caudipteryx, with a few suprises. After that, probably Masiakasaurus. Hope you enjoy!

references- Barsbold, R., Osmólska, H., Watabe, M., Currie, P.J., & Tsogtbaatar, K -. A new oviraptorosaur (Dinosauria, Theropoda) from Mongolia: The first dinosaur with a pygostyle, pp. 97-106.

Barsbold R.; Currie, P.J.; Myhrvold, N.P.; Osmólska, H.; Tsogtbaatar K.; and Watabe M. 2000. A pygostyle from a non-avian theropod. Nature 403: 155-156.

Mickey Mortimer