Nemegtomaia
Nemegtomaia is a genus of oviraptorid dinosaur from what is now Mongolia that lived in the Late Cretaceous Period, about 70 million years ago. The first specimen was found in 1996, and became the basis of the new genus and species N. barsboldi in 2004. The original genus name was Nemegtia, but this was changed to Nemegtomaia in 2005, as the former name was preoccupied. The first part of the generic name refers to the Nemegt Basin, where the animal was found, and the second part means "good mother", in reference to the fact that oviraptorids are known to have brooded their eggs. Two more specimens were found in 2007, one of which was found on top of a nest with eggs, but the dinosaur had received its genus name before it was found associated with eggs.
Nemegtomaia is estimated to have been around 2 m (7 ft) in length, and to have weighed 40 kg (85 lb). As an oviraptorosaur, it would have been feathered. It had a deep, narrow, and short skull, with an arched crest. It was toothless, had a short snout with a parrot-like beak, and a pair of tooth-like projections on its palate. It had three fingers; the first was the largest, with a strong claw. Nemegtomaia is classified as a member of the oviraptorid subfamily ingeniinae, and it is the only known member of this group with a cranial crest. Though Nemegtomaia has been used to suggest that oviraptorosaurs were flightless birds, the clade is generally considered a group of non-avian dinosaurs.
The nesting Nemegtomaia specimen was placed on top of what was probably a ring of eggs, with its arms folded across them. None of the eggs are complete, but they are estimated to have been 5 to 6 cm (2 to 2.3 in) wide and 14 to 16 cm (5 to 6 in) long when intact. The specimen was found in a stratigraphic area that indicates Nemegtomaia preferred nesting near streams that would provide soft, sandy substrate and food. Nemegtomaia may have protected is eggs by covering them with its tail and wing feathers. The skeleton of the nesting specimen has damage that indicates it was scavenged by skin beetles. The diet of oviraptorids is uncertain, but their skulls are most similar to other animals that are known or thought to have been herbivorous. Nemegtomaia is known from the Nemegt and Baruungoyot Formations, which are thought to represent humid and arid environments that coexisted in the same area.
Description[]
Nemegtomaia is estimated to have been around 2 m (7 ft) in length, and to have weighed 40 kg (85 lb), a size extrapolated from more completely known relatives. As an oviraptorosaur, it would have been feathered. The neural spines of the neck (cervical) vertebrae were short, and the neural arches had an x-shaped appearance. The middle three of these vertebrae were the largest. The sacrum consisted of eight vertebrae. The scapula (shoulder blade) appears to have been 185 mm (7 in) in total length. The humerus (upper arm bone) had a fossa (depression) in a similar position as modern birds, but atypical among oviraptorosaurs, and appears to have been 152 mm (6 in) long. The radius of the lower arm was straight, oval in cross-section, and may have been 144 mm (5 in) long. The first finger was relatively large and had a strong ungual (claw bone), and was more massive than the two other fingers. The second finger was slightly longer than the first, and the third finger was smallest. The upper margin of the ilium of the pelvis was straight, and though both ilia were close to each other, they were not fused together. The pubic shaft was turned backwards. The femur (thigh bone) is estimated to have been 286 mm (11 in) long, and the tibia of the lower leg 317 mm long (12 in).
Compared to the rest of the body, the skull of Nemegtomaia was deep, narrow, and short and reached 179 mm (7 in) in length. It had a well-developed crest, formed by the nasal and premaxilla bones (mainly the latter) of the snout. The front margin of the crest was nearly vertical, and formed almost 90 degrees with the upper margin of the skull. Compared to other oviraptorids, the nasal processes (projections) of the premaxillae were barely visible when viewed from above (where they connected with the nasal bones on the highest points of the crest). The crest extended hindwards and down, forming a round arch at the highest point. The diameter of the orbit (eye opening) was 52 mm (2 in); the eyes looked large due to the shortness of the skull. The antorbital cavity in front of the eye consisted of two fenestrae (openings); a large antorbital fenestra at the back, and a small maxillary fenestra at the front. Nemegtomaia was distinct from other oviraptorids in that the frontal bone on the midline of the skull was about 25% the length of the parietal bone from front to back. The nares (external nostrils) were relatively small and placed high on the skull.[1][2]
The jaws of Nemegtomaia were toothless, and like other oviraptorid dinosaurs, it had a short snout with a deep, robust, and somewhat parrot-like beak. It had a hard palate formed by the premaxillae, vomers, and maxillae, like other oviraptorids. The palate was strongly concave (downwards-projecting), and had a cleft on the central part. As in other oviraptorids, the palatal parts of the maxillae each had a tooth-like projection that was directed downwards (a feature that has been called "pseudo-teeth"). Nemegtomaia had small foramina (openings) on the sides of the suture (joint) between the premaxillae at the front of the snout, which may have been nutrient openings (and which indicate the presence of a keratinous bill). The lower jaw was short and deep, with a convex lower surface, and reached 153 mm (6 in) in length. The dentary bone of the lower jaw reached 50 mm (2 in) at its highest point. The mandibular symphysis (where the two halves of the lower jaw connected) was short, deep, and very pneumatised (air-filled). The mandibular fenestra was large and was located at the front part of the lower jaw.[1][3][2][4] As in most other oviraptorids, the front part of the lower jaw was down-turned.
History of discovery[]
In 1996 the Japanese palaeontologist Yoshitsugu Kobayashi (as part of the "Mongolian Highland International Dinosaur Project" team) found an incomplete skeleton of an oviraptorid dinosaur in the Nemegt Formation of the Gobi Desert in southwestern Mongolia. The specimen (MPC-D 100/2112 at the Mongolian Palaeontological Center, formerly PC and GIN 100/2112), consists of a nearly complete skull and a partial skeleton, including cervical, dorsal, sacral, and caudal vertebrae, a left scapula, the lower ends of both humeri, the right radius, both ilia, the upper ends of both pubes, both ischia, and the upper end of a femur. The specimen was described as a new specimen of the genus Ingenia (referred to as I. sp.; of uncertain species) by the Chinese palaeontologist Junchang Lü and colleagues in 2002, and used to highlight the similarities between oviraptorosaurs and birds.
In 2004 Lü and colleagues determined that the skeleton belonged to a new, distinct taxon, and made it the holotype specimen of Nemegtia barsboldi. The genus name refers to the Nemegt Basin, and the species name honors the Mongolian palaeontologist Rinchen Barsbold, the leader of the team who found the specimen.[1] In 2005 the describers discovered (after being notified by a biologist) that the name Nemegtia had already been used for a genus of freshwater seed shrimp (Ostracoda) from the same formation in 1978, and was therefore preoccupied. They proposed instead the new genus name Nemegtomaia ("maia" means "good mother" in Greek, and the full name means "good mother of the Nemegt"), making reference to the then-recent discovery that oviraptorids brooded eggs rather than stealing them, though no trace of a nest or eggs had yet been found associated with Nemegtomaia itself.[6][7] The first known member of the oviraptorid family was found with a nest of eggs originally thought to have belonged to the ceratopsian genus Protoceratops, and was therefore named Oviraptor in 1924; this name means "egg-seizer". In the 1990s more oviraptorid specimens were discovered associated with nests and eggs, wherein oviraptorid embryos were found, thereby proving that the eggs belonged to the oviraptorids themselves.[8][9][10] Ingenia was similarly renamed as Ajancingenia in 2013, since the former genus name was preoccupied by a roundworm (Nematoda).
In 2007 two new specimens of Nemegtomaia were found by the "Dinosaurs of the Gobi" expedition, and were described by the Italian palaeontologist Federico Fanti and colleagues in 2013. The first specimen, MPC-D 107/15, was found by Fanti (who nicknamed it "Mary") in the Baruungoyot Formation, and consists of a nest with the presumed parent on top. As the fourth genus of oviraptorid found on top of a nest (after Oviraptor, Citipati, and cf. Machairasaurus), Nemegtomaia had therefore received a genus name referring to this feature before it was itself found associated with eggs. The specimen was excavated from a vertical cliff under "difficult circumstances", including heavy rain and collapsing sandstone blocks. The skeleton preserves parts of the skull, both scapulae, the left arm and hand, the right humerus, the pubes, the ischia, the femora, the tibiae, fibulae, and the lower portions of both feet. This specimen was found less than 500 m (1640 ft) from the holotype, and was of the same size; it was assigned to Nemegtomaia due to its similar morphology (anatomical features) and geographical proximity. It was collected in a single block so that the spatial relationship of the bones and eggs would be preserved. The second specimen, MPC-D 107/16, was found by the American palaeontologist Nicholas R. Longrich in the Nemegt Formation, and consists of the hands, a partial left ulna and radius, ribs, a partial pelvis, and both femora. This specimen was 35% smaller than the others, and was assigned to Nemegtomaia due to its hands having the same characteristics as those of specimen MPC-D 107/15. It is possible that the hands may have belonged to a different individual, as they were not found articulated with the rest of the skeleton (other oviraptorids are known from quarries with multiple skeletons), but this cannot be confirmed.