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New specimens of Nemegtomaia from the Baruungoyot and Nemegt Formations (Late Cretaceous) of Mongolia.

Fanti F, Currie PJ, Badamgarav D - PLoS ONE (2012)

Bottom Line: Nemegtomaia represents the fourth known genus of oviraptorid for which individuals have been found on nests of eggs.All other known oviraptorids from Mongolia and China are known exclusively from xeric or semi-arid environments.However, this study documents that Nemegtomaia is found in both arid/aeolian (Baruungoyot Formation) and more humid/fluvial (Nemegt Formation) facies.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Scienze della Terra e Geologico-Ambientali, Alma Mater Studiorum, Università di Bologna, Via Zamboni, Bologna, Italy. federico.fanti@unibo.it

ABSTRACT
Two new specimens of the oviraptorid theropod Nemegtomaia barsboldi from the Nemegt Basin of southern Mongolia are described. Specimen MPC-D 107/15 was collected from the upper beds of the Baruungoyot Formation (Campanian-Maastrichtian), and is a nest of eggs with the skeleton of the assumed parent of Nemegtomaia on top in brooding position. Much of the skeleton was damaged by colonies of dermestid coleopterans prior to its complete burial. However, diagnostic characters are recovered from the parts preserved, including the skull, partial forelimbs (including the left hand), legs, and distal portions of both feet. Nemegtomaia represents the fourth known genus of oviraptorid for which individuals have been found on nests of eggs. The second new specimen, MPC-D 107/16, was collected a few kilometers to the east in basal deposits of the Nemegt Formation, and includes both hands and femora of a smaller Nemegtomaia individual. The two formations and their diverse fossil assemblages have been considered to represent sequential time periods and different environments, but data presented here indicate partial overlap across the Baruungoyot-Nemegt transition. All other known oviraptorids from Mongolia and China are known exclusively from xeric or semi-arid environments. However, this study documents that Nemegtomaia is found in both arid/aeolian (Baruungoyot Formation) and more humid/fluvial (Nemegt Formation) facies.

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The nest of Nemegtomaia barsboldi, MPC-D 107/15.A, disposition of preserved eggs within the nest. Eggshells have been recovered under the skull (B), left pes (C) and leg (D), suggesting the direct apposition of the oviraptorid on top of the eggs. During the early excavation of the nest, it was possible to document a lower layer of eggs lying approximately 10 cm below the body (E–G).
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pone-0031330-g009: The nest of Nemegtomaia barsboldi, MPC-D 107/15.A, disposition of preserved eggs within the nest. Eggshells have been recovered under the skull (B), left pes (C) and leg (D), suggesting the direct apposition of the oviraptorid on top of the eggs. During the early excavation of the nest, it was possible to document a lower layer of eggs lying approximately 10 cm below the body (E–G).

Mentions: 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.


New specimens of Nemegtomaia from the Baruungoyot and Nemegt Formations (Late Cretaceous) of Mongolia.

Fanti F, Currie PJ, Badamgarav D - PLoS ONE (2012)

The nest of Nemegtomaia barsboldi, MPC-D 107/15.A, disposition of preserved eggs within the nest. Eggshells have been recovered under the skull (B), left pes (C) and leg (D), suggesting the direct apposition of the oviraptorid on top of the eggs. During the early excavation of the nest, it was possible to document a lower layer of eggs lying approximately 10 cm below the body (E–G).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3275628&req=5

pone-0031330-g009: The nest of Nemegtomaia barsboldi, MPC-D 107/15.A, disposition of preserved eggs within the nest. Eggshells have been recovered under the skull (B), left pes (C) and leg (D), suggesting the direct apposition of the oviraptorid on top of the eggs. During the early excavation of the nest, it was possible to document a lower layer of eggs lying approximately 10 cm below the body (E–G).
Mentions: 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.

Bottom Line: Nemegtomaia represents the fourth known genus of oviraptorid for which individuals have been found on nests of eggs.All other known oviraptorids from Mongolia and China are known exclusively from xeric or semi-arid environments.However, this study documents that Nemegtomaia is found in both arid/aeolian (Baruungoyot Formation) and more humid/fluvial (Nemegt Formation) facies.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Scienze della Terra e Geologico-Ambientali, Alma Mater Studiorum, Università di Bologna, Via Zamboni, Bologna, Italy. federico.fanti@unibo.it

ABSTRACT
Two new specimens of the oviraptorid theropod Nemegtomaia barsboldi from the Nemegt Basin of southern Mongolia are described. Specimen MPC-D 107/15 was collected from the upper beds of the Baruungoyot Formation (Campanian-Maastrichtian), and is a nest of eggs with the skeleton of the assumed parent of Nemegtomaia on top in brooding position. Much of the skeleton was damaged by colonies of dermestid coleopterans prior to its complete burial. However, diagnostic characters are recovered from the parts preserved, including the skull, partial forelimbs (including the left hand), legs, and distal portions of both feet. Nemegtomaia represents the fourth known genus of oviraptorid for which individuals have been found on nests of eggs. The second new specimen, MPC-D 107/16, was collected a few kilometers to the east in basal deposits of the Nemegt Formation, and includes both hands and femora of a smaller Nemegtomaia individual. The two formations and their diverse fossil assemblages have been considered to represent sequential time periods and different environments, but data presented here indicate partial overlap across the Baruungoyot-Nemegt transition. All other known oviraptorids from Mongolia and China are known exclusively from xeric or semi-arid environments. However, this study documents that Nemegtomaia is found in both arid/aeolian (Baruungoyot Formation) and more humid/fluvial (Nemegt Formation) facies.

Show MeSH
Related in: MedlinePlus