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.
Highlights
Oviraptorid dinosaurs have long been a source of information and speculation about the behavior of non-avian theropods [1,2]
They retrieved Conchoraptor and Ingenia in a monophyletic clade defined by a scapula to humerus ratio greater than 0.7, a deltopectoral crest that extends for 40%–50% of the length of humerus, a metacarpal II to metacarpal III ratio that is less than 0.5, and a postacetabular process of the ilium that has a truncated distal end
Specimen MPC-D 107/15 was collected from the red sandstones of the Baruungoyot Formation in the Northern Sayr of the Nemegt locality (N 43u30.3539, E 101u03.3839) (Figure 2)
Summary
Oviraptorid dinosaurs have long been a source of information and speculation about the behavior of non-avian theropods [1,2]. The first detailed phylogenetic analysis of the Oviraptoridae was published by Maryanska et al [13] They retrieved Conchoraptor and Ingenia in a monophyletic clade defined by a scapula to humerus ratio greater than 0.7, a deltopectoral crest that extends for 40%–50% of the length of humerus, a metacarpal II to metacarpal III ratio that is less than 0.5, and a postacetabular process of the ilium that has a truncated distal end. The type specimen (MPC-D 100/2112) was collected in 1996 in southern Mongolia at the Nemegt locality (sensu [15]) by the Mongolian Highland International Dinosaur Project [14] It included the skull and partial skeleton (thirteen cervical, six dorsal, eight sacral and two caudal vertebrae, left scapula, distal ends of both humeri, right radius, both ilia, proximal ends of both pubes, both ischia, and proximal end of a femur). Nemegtomaia (‘‘good mother of Nemegt’’) refers to the stratigraphic and geographic location of the discovery (early Maastrichtian Nemegt Formation, Nemegt locality, southern Gobi, Mongolia) and to the idea that oviraptorid dinosaurs were brooding, rather than stealing, eggs [4,5,7,8,9,20,21,22,23]
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