k = 0.83, r2 = 0.95). The length of the femur is 10% longer (305 mm) in MPC-D 100/42 (Citipati sp.), which has similar dimensions in other parts of the skeleton to MPC-D 107/15. This suggests that the humerus was roughly half the length of the femur. The shaft width of the tibia, when compared with 23 other oviraptorids and dromaeosaurids (selected because they are not arctometatarsalian; b = 1.55, k = 0.64, r2 = 0.87), produces an estimated length of 317 mm for the tibia. This makes sense because it suggests that the tibia in the folded legs of MPC-D 107/ 15 (Fig. 4B) is about 5–10% longer than the femur as in other oviraptorids. Posture MPC-D 107/15 shows no evidence of post-mortem transpor- tation. It is preserved in a facies hypothesized to have been deposited in a single sandstorm or dune-shifting event. The body had shifted slightly to the right of center, rather than being exactly symmetrical across the midline of the skeleton; the right forearm and part of the right foot are obscured in dorsal view (Figure 3). This shift of the body suggests that the sediment deposited upon the skeleton may have come toward the animal from its left side. A similar assumption was made by Clark et al. [6] for another nesting oviraptorid (Citipati osmolskae, MPC-D 100/979) from Ukhaa Tolgod. Overall, MPC-D 107/15 shares several similarities with the brooding Citipati (MPC-D 100/1004) of Erickson et al. [8]. The neck curves toward the left and downward, and the skull is facing the outside of the nest in a position lower than much of its body (Fig. 3A,B). The humeri are oriented down and back, the radius and ulna of the left side are oriented forward and down (the right side is partially obscured by matrix), and the left hand is folded backwards. The forelimbs do not extend laterally as much as observed in other known nesting oviraptorid dinosaurs [4–6,8]. The legs are folded up into a crouching position. The feet are upright and are medial to the position of preserved broken eggs. The tail, ischia, and presumably a large portion of the nest have been eroded away (Fig. 3C,D,E). In addition, the vertebral column and the neck, parts of the pelvic bones, ribs, and the vast majority of articular surfaces were scavenged before fossilization by saprophagus insects and/or other small scavengers such as small theropods or mammals. However, considering the overall preservation of the skeleton, the absence of all cervical, dorsal and sacral vertebrae is puzzling. Taphonomy Specimen MPC-D 107/15 is a terrific source of information on taphonomic processes in the semi-arid environments of the Baruungoyot Formation. In fact, a combination of different factors resulted in the final preservation of the body: 1. lateral shift of the body due to mono-oriented sediment accumulation; 2. partial burial and subsequent deterioration (and possibly predation by scavengers) of vertebral column, neck, and hips; 3. gradual decomposition under xeric conditions; 4. intense scavenging by insect colonies and; 5. final burial. In addition to minor deformation caused by vertical compression during and after burial, much of the damage observed in the skeleton and nest were caused by intense activity of invertebrates. A number of studies have dealt with insect traces on fossil bone and their implication in constraining the reconstruction of the taphonomic history of a specimen [42–48]. Such studies also document bone modification during early stages of fossilization and indicate a common pattern in areas where damage is more extensive, and in particular in the cranial and dorsal vertebrae [49,50]. Traces of dermestid beetles and possibly other saprophagus insect activity are documented by bone borings, bone-chip-lined burrows, and reworked sediment in New Specimens of Nemegtomaia from Mongolia specimen MPC-D 107/15 (Figure 4), some of which may have been caused by the construction of pupal chambers. Nearly circular borings passing completely through thin bones are preserved in the left side of the skull and range between 3 and 6 mm in diameter (Fig. 4D,E,F,G). Similar borings have been previously reported from the Baruungoyot Formation and coeval Djadokhta Formation [30,49] on Bagaceratops, Pinacosaurus, Proto- ceratops, Velociraptor, and other ankylosaurid skeletons [6,51–54]. Feeding traces are also abundant in the joints of the skeleton and nearly obliterate all articular surfaces (Fig. 4A,B,C). Bone-chip- lined burrows have been found around the skeleton, and the largest of these are approximately 35 mm in diameter and contain fragments of bone up to 7 mm wide (Fig. 4G). Furthermore, a large section of the nest revealed reworked sediment in the form of a light colored, elongate tunnel under the neck and the skull: interestingly, such larger traces are found only in the part of the nest where neither eggs nor egg fragments have been recovered (Fig. 4H). Similar to several specimens collected in the Gobi desert of Mongolia and China [48,55], no pupal chambers or similar structures have been observed. As pointed out by Hasiotis et al. [44], dermestid beetle activity implies specific environmental conditions. Present day dermestids, for instance, feed primarily on dried muscle tissue and they do not eat moist materials; furthermore, rapid burial prevents any activity [56]. The presence of such intense damage to bones supports the hypothesis that the carcass was partially buried with the upper part of the body exposed and subject to rapid exsiccation and deterioration for long enough to allow a dermestid colony to develop. If skeletons are kept in dermestid colonies for long enough, depending on environmental and seasonal conditions, articular surfaces and thinner bones (such as skull, ribs, scapulae, etc.) are totally destroyed by the beetles [44,57]. Recently, Saneyoshi et al. [49] suggested that some of the largest borings found on a Protoceratops skeleton collected from the aeolian beds of the Djadokhta Formation at Tugrikin Shire can be referred to scavenging activities of small mammals. Similarly, remains of small mammals have been found in the Baruungoyot and Nemegt formations of the Trans-Altai Gobi [35,58]. Thus, it is possible to consider small mammals as responsible for bone damage observed in MPC-D 107/15, and in particular for the damage observed in the vertebral column. Description and taphonomy of specimen MPC-D 107/16 MPC-D 107/16 is a partial skeleton of another oviraptorid from the Baruungoyot Formation. Most of the skeleton had eroded away before it was discovered, but half a dozen ribs, the anterior edge of the right ilium, the distal ends of the left radius and ulna, both hands, and most of both femora (Figs. 6, 7) were recovered. The specimen can be identified as Nemegtomaia on the basis of its hands, which have all the same ingeniine characteristics as MPC- D 107/15. The diagnostic features of the hand that these two specimens share include the relatively large first digit with a strong ungual, and a third digit that is so small that the third metacarpal is reduced to a splint. The specimen is significant in that it provides information on the anatomy of Nemegtomaia that is not available with either the holotype or MPC-D 107/15. It is also approximately 35% smaller than either of the other two specimens. The rib fragments all appear to be from the right side, and the spacing suggests that they were buried during the Cretaceous as part of a fully articulated skeleton. The positions of the anteroventral edge of the right ilium, and the right femur also suggest that this is true. However, in the same block of sandstone is the articulated right hand, but it is far enough behind the right leg PLoS ONE | www.plosone.org 8 February 2012 | Volume 7 | Issue 2 | e31330