New Specimens of Nemegtomaia from Mongolia Figure 8. Phylogeny of Oviraptoridae. Phylogenetic analysis of Oviraptoridae was performed by adapting the matrix of Longrich et al. (3) and using the exhaustive search algorithm of PAUP* 4.0b10. Numbers next to clades indicate bootstrap support value/decay value. doi:10.1371/journal.pone.0031330.g008 The Nest The collected portion of the nest is approximately 90 cm wide and 100 cm long (Figs. 3, 9A). If we consider as paleo-ground level the virtual plane where feet and head lie, the skeleton occupies the upper 25 cm, whereas the remaining 20 centimeters of the block are entirely occupied by broken eggs and eggshells. Within the nest there is no obvious variation in sedimentary structures nor changes in micro- and macroscopic details. There is also no evidence of plant material, whereas several undetermined bone fragments were recovered within the sediment in the nest and immediately above the skeleton. Similar to several nests collected from the Gobi desert of China and Mongolia [4–8,60,61], specimen MPC-D 107/15 does not preserve a single complete egg, nor have any embryonic skeletal elements been recovered [20,21]. Such poor preservation prevents one from estimating the size and shape of a single egg; determining the number of eggs laid, and observing specific orientations or patterns in the arrangement of the eggs within the nest. Overall thickness of the block, and field observations of the specimen suggest that two layers of eggs were originally preserved below the body. Most of the center of the nest is not exposed; nevertheless, there is no evidence of eggs in the center at the same level as the exposed eggs. The plaster and burlap jacket protecting the specimen precludes direct observation of parts of the nest that were observable in the field. A total of seven distinct eggs were identified in the lower layer where damage by dermestid activity is assumed to be minor (Fig. 9E, F, G). Large fragments of eggs were recovered under the skull, left side of the neck, left humerus, left femur, and both feet: in all cases, the bones rest directly on or within 5 mm from the surfaces of the eggs (Figure 9). The direct apposition of the skeleton on the nest in MPC-D 107/15 shows that the nest was not completely covered by sand. It is important to note that the majority of egg fragments are located in three distinct sections of the nest—beside the left and right legs, and in front of the shoulder girdle and neck. In the majority of known oviraptorid nests, eggs are arranged in pairs at different levels in up to three concentric circles [60,62]. This is not the case of MPC-D 107/15, where the positions of the eggs do not suggest a specific arrangement. Eggs were likely displaced during early stages of burial by external factors (such as strong winds, sediment transport associated with sandstorm events or small predators). This supports the conclusion that the upper layer of eggs was not buried (or was only partially buried) because it is unlikely that endogenous factors were able to interfere with fully buried eggs. Previous studies [4,9,23] proposed the hypothesis that several individuals gathered eggs into a single nest and arranged them so they could be protected by one individual, possibly a male. Although it is possible that Nemegtomaia laid eggs with no particular arrangement within the nest, this seems unlikely given the large numbers of oviraptorid nests that have been found in Cretaceous deposits of China and Mongolia. Specimen MPC-D 107/15 is a Nemegtomaia individual associated with a nest of eggs and therefore Nemegtomaia represents the fourth known genus of oviraptorids (Citipati, 8; cf. Machairasaurus, 5; Oviraptor, 1; Nemegtomaia, this paper), the first within the Ingeniinae clade, found on nests. PLoS ONE | www.plosone.org 11 February 2012 | Volume 7 | Issue 2 | e31330