With yesterday’s publication in PLoS ONE, Federico Fanti, Philip Currie and Badamgarav Demchig add more information to an otherwise unknown oviraptorosaur, Nemegtomaia barsboldi. That taxon, described in 2004 by Lü Junchang and colleages and, in Lü’s PhD thesis once called Ingenia, is now more substantially known than it was before. Of the two new specimens, the best is MPC-D 107/15, preserving not just a partial skull, but a partial forelimb resembling Machairasaurus leptonychus, “Ingenia” yanhsini, and Heyuannia huangi in having a thumb (pollex) nearly as long as the second digit. While this point is intriguing, and has other implications, I will focus instead right now on the posture of the MPC-D 107/15.
This specimen was found laying in a posture not unlike that of MPC-D 100/979 (Clark et al., 1999), squatting down with its feet in the middle of a ring of eggs, arms splayed out to the sides. This makes the third named taxon found atop a nest, but there is reason to think that this might be the fourth.
The first, of course, was Oviraptor philoceratops (Osborn, 1924) AMNH FR 6517, which was found adjacent to a nest catalogued as AMNH FR 6508, from Shabarakh Usu, in the Djadokhta Formation of southern Mongolia. Images of the eggs collected with AMNH FR 6517 may be found here.
The second, found during the Chinese-Canadian Mongolian expeditions, was IVPP V9608 (Dong & Currie, 1996), from Bayan Mandahu, in the Wulansuhai Formation (roughly equivalent to the Djadokhta), in Inner Mongolia, People’s Republic of China. This specimen, covered in part by Longrich et al. (2010), as suggested as being not necessarily Oviraptor philoceratops, to which Dong and Currie had referred it, and they suggested that phalangeal proportions may exclude it. Barring further analysis, Longrich et al. focused on two other specimens recovered at Bayan Mandahu, naming a new huge-thumbed “ingeniine”-like oviraptorid, Machairasaurus leptonychus. However, given the potential of more than one oviraptorid species in the same formation, just as there are several in the Djadokhta, Baruungoyot, and Nemegt Formations, it is premature to suggest that this nesting specimen represents Machairasaurus leptonychus, and Longrich et al. do not waste time considering this option. Fanti et al., however, list IVPP V9608 as a specimen of Machairasaurus leptonychus in their supplemental online material (measurements table), which seems to suggest that they feel it is, rather, a specimen of that species. I will return to this eventually, but would like to point out that the minimum here is a single taxon, one on a nest, and that taxon — potentially a new species — is distinct from other taxa described as nest layers so far.
edit: I previously proposed that the “minium” was two taxa, but looking through the Fanti et al. supplemental data has me revising this statement somewhat, so the syntax is differing to incorporate different numbers.
The third was MPC-D 100/979, one of many recovered with bits and pieces and referred to Citipati osmolskae (Clark et al., 2001). Other specimens referred to Citipati osmolskae, including the holotype (MPC-D 100/978), and a more complete specimen than previously discussed, MPC-D 100/1004 (Varricchio et al., 2008), indicate that full body size may not have been reached by the time the animal was fertilizing eggs, nesting, or brooding, a feature that may be relevant in distinguishing “full” ontogenetic maturity (or adult) from sexually mature animals. It may, rather, blur the line in what we are willing to accept as “adult” characteristics. This also has implications with Fanti et al. (2012) where the cranial ontogeny may include developed crests in more mature adults, although the implications are not all that clear. There’s even more to say on this, including coverage of work by Dave Hone and Darren Naish on sexual selection, as well as Horner and Padian on use of visual features for species identification rather than sexual selection.
And so the forth becomes Nemegtomaia barsboldi (Lü et al., 2004). This taxon, largely based on specimen lacking the tail, ribs, lower pelvis or any pectoral material, and virtually none of the limbs, becomes supplemented by much of that material in two new specimens, especially in the manus. The skull of MPC-D 107/15 bears several uncanny resemblances to MPC-D 100/2112; the other referred specimen, MPCD-D 107/16, was recovered very close to the site where MPC-D 100/2112 was recovered, although still 500m apart and lower in the stratigraphic column than the holotype.
There are, of course, many other specimens found on nests, some of them not even from Ukhaa Tolgod, and their description may add to the species for which nests are known, and that further the eggs may be compared between them and thus allow isolated eggs to be qualified to taxa.
Recent analysis implies, however, that the Nemegt “Mother” may actually be a Nemegt “Daddy,” and so too all of the other oviraptorosaurs on nests might actually be males, who supervised or tended communal nests in the absence of the females (Varricchio et al., 2008), due to lack of recovery of medullary bone in “sitting” specimens, and comparison of egg volume to individuals.
Barsbold R. 1981. Беззубйе жыщнйе динозаврй Монголий (Edentulous carnivorous dinosaurs of Mongolia). Трудй – Совместная Совестко-Монгольской Палеотологыческая Зкспедитсия — Joint Soviet-Mongolian Paleontological Expedition, Transactions 15: 28-39, 124. (in Russian, w/ English summary)
Clark, J. M., Norell, M. A. & Barsbold R. 2001. Two new oviraptorids (Theropoda: Oviraptorosauria), Upper Cretaceous Djadokta Formation, Ukhaa Tolgod, Mongolia. Journal of Vertebrate Paleontology 21(1):209–213.
Clark, J. M., Norell, M. A. & Chiappe, L. M. 1999. An oviraptorid skeleton from the late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avian-like brooding position over an oviraptorid nest. American Museum Novitates 3265:1–36.
Dong, Z.-M. & Currie, P. J. 1996. On the discovery of an oviraptorid skeleton on a nest of eggs at Bayan Mandahu, Inner Mongolia, People’s Republic of China. Canadian Journal of Earth Sciences — Revue canadiene des sciences de la Terre 33:631–636.
Fanti, Federico, Currie, Philip J. & Badamgarav Demchig. 2012. New specimens of Nemegtomaia from the Baruungoyot and Nemegt Formations (Late Cretaceous) of Mongolia. PLoS ONE 7(2):e31330.
Longrich, N. R., Currie, P. J. & Dong Z.-M. 2010. A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia. Palaeontology 53(5):945–960.
Lü J.-c., Tomida Y., Azuma Y., Dong Z.-m. & Lee Y.-N. 2004. New oviraptorid dinosaur (Dinosauria: Oviraptorosauria) from the Nemegt Formation of southwestern Mongolia. Bulletin of the National Science Museum of Tokyo, Series C 30:95–130.
Osborn, H. F. 1924. Three new theropods, Protoceratops zone, central Mongolia. American Museum Novitates 144:1–12.
Varricchio, D. J., Moore, J. R., Erickson, G. M., Norell, M. A., Jackson, F. D. & Borkowski, J. J. 2008. Avian parental care had dinosaur origin. Science 322:1826-1828.