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

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

Feeding traces left by colonies of dermestid beetles in specimen MPC-D 107/15.

<p>Articular surfaces have been completely obliterated in the left forearm (A), left leg and pes (B), as well as in the right forearm (C). Circular borings are particularly evident in the left side of the skull (D–F). G, Bone-chip burrow found under the skull of the specimen. H, large traces of reworked sediment under the skeleton.</p

Hands of <i>Nemegtomaia barsboldi</i>.

<p>A, preserved elements and reconstructed manus of MPC-D 107/15 in dorsal (a1) and lateral (a2) views: B, right manus of MPC-D 107/16 in dorsal (b1) and medial (b2) views; C, left manus of MPC-D 107/16 in medial (c1) and dorsal (c2) views, with the preserved distal portions of radius and ulna. <b>lr</b>, left radius; <b>lu</b>, left ulna. Scale bar 5 cm. Illustration by Marco Auditore.</p

Phylogeny of Oviraptoridae.

<p>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.</p

Eggs of <i>Nemegtomaia barsboldi</i>.

<p>Details of eggs preserved in the upper layer of eggs in specimen MPC-D 107/15. Scale bar A–E 5 cm.</p

Nest and preserved elements of <i>Nemegtomaia barsboldi</i> (MPC-D 107/15).

<p>A, dorsal view; B, left lateral view; C, right lateral view; D, posterior view. <b>lf</b>, left femur; <b>lfi</b>, left fibula; <b>lh</b>, left humerus; <b>lm</b>, left manus; <b>lp</b>, left pes; <b>lpu</b>, left pubis; <b>lr</b>, left radius; <b>ls</b>, left scapula; <b>lt</b>, left tibia; <b>lu</b>, left ulna; <b>rf</b>, right femur; <b>rfi</b>, right fibula; <b>rh</b>, right humerus; <b>rp</b>, right pes; <b>rpu</b>, right pubis; <b>rs</b>, right scapula; <b>rt</b>, right tibia; <b>sk</b>, skull. Scale bar 10 cm. Reconstruction by Marco Auditore.</p

The paleoenvironments of Tugrikin-shireh (Gobi Desert, Mongolia) and aspects of the taphonomy and paleoecology of Protoceratops (Dinosauria: Ornithishichia)

Tugrikin-shireh, south-central Gobi Desert, Mongolia, consists of about 1.5 km of west- and northwest-facing exposures that produce a rich vertebrate fauna dominated by the ornithischian dinosaur Protoceratops. The sandstones of Tugrik are thick-bedded (2-9 m) and are distinguished by large-scale (10\u27s to 100\u27s of meters in cross-section), high-angle (28°-34°) trough-cross stratification. The axes of the cross stratification dip east-northeast. These and other sedimentary features indicate eolian deposition, driven by westerly winds. At Tugrik, bedding planes as well as inferred slip faces, are dominated by a complex calcite- and iron-oxide-cemented ichnofauna. At least three different trace fossil types are preserved. A biologically active ecosystem is reflected by the vertebrate body fossil and invertebrate trace fossil assemblages. Protoceratops specimens are commonly found articulated and semi-articulated, and oriented parallel to the maximum dip direction of the sediments in which they are entombed. Limbs are commonly contracted and necks are pulled back, in poses indicative of dessication. In some cases, death probably occurred by suffocation during sand storms, but in other cases, by less dramatic processes. Turgik may constitute the basinward continuation of a nearby braid plain-to-eolian suite of depositional environments. Penecontemporaneous deposits in northern China reveal similar suites of environments, suggesting a uniform depositional response in the region to Late Cretaceous climates

Skull of <i>Nemegtomaia barsboldi</i> (MPC-D 107/15).

<p>A, preserved elements of the right side; B, preserved elements of the left side; C, reversed elements of the left side superimposed to those of the right side (where elements of both sided overlap, the grey is darker); D, reconstruction of the skull. <b>an</b>, angular; <b>d</b>, dentary; <b>ec</b>, ectopterygoid; <b>eo</b>, exoccipital; <b>f</b>, frontal; <b>j</b>, jugal; <b>l</b>, lacrimal; <b>m</b>, maxilla; <b>n</b>, nasal; <b>p</b>, parietal; <b>pm</b>, premaxilla; <b>po</b>, postorbital; <b>q</b>, quadrate; <b>qj</b>, quadratojugal; <b>sa</b>, surangular; <b>sq</b>, squamosal; <b>sr</b>, sclerotic ring. Scale bar 10 cm. Illustration by Marco Auditore.</p