Nemegtomaia

Nemegtomaia Temporal range:Late Cretaceous,
Specimen tentatively assigned toNemegtomaia,Central Museum of Mongolian Dinosaurs
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Oviraptoridae
Subfamily:	†Heyuanninae
Genus:	†Nemegtomaia Lüet al., 2005
Type species
†Nemegtomaia barsboldi (Lü et al., 2004)
Synonyms
Nemegtia barsboldi Lü et al., 2004

Nemegtomaiais agenusofoviraptoriddinosaurfrom what is nowMongoliathat lived in theLate CretaceousPeriod,about 70million years ago. The first specimen was found in 1996, and became the basis of the new genus and speciesN. barsboldiin 2004. The original genus name wasNemegtia,but this was changed toNemegtomaiain 2005, as the former name waspreoccupied.The first part of the generic name refers to theNemegt Basin,where the animal was found, and the second part means "good mother", in reference to the fact that oviraptorids are known to havebroodedtheir eggs. Thespecific namehonours the palaeontologistRinchen Barsbold.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.

Nemegtomaiais estimated to have been around 2 m (7 ft) in length, and to have weighed 40 kg (85 lb). As anoviraptorosaur,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 aparrot-like beak, and a pair of tooth-like projections on itspalate.It had three fingers; the first was largest and bore a strong claw.Nemegtomaiais classified as a member of the oviraptorid subfamilyHeyuanninae,and is the only known member of this group with acranialcrest. ThoughNemegtomaiahas been used to suggest thatoviraptorosaurswereflightless birds,thecladeis generally considered a group of non-aviandinosaurs.

The nestingNemegtomaiaspecimen 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 5to 6 cm (2to 2.3in) wide and 14to 16 cm (5to 6in) long when intact. The specimen was found in astratigraphicarea that indicatesNemegtomaiapreferred nesting near streams that would provide soft, sandy substrate and food.Nemegtomaiamay have protected its eggs by covering them with its tail and wing feathers. The skeleton of the nesting specimen has damage that indicates it wasscavengedbyskin beetles.The diet of oviraptorids is uncertain, but their skulls are most similar to other animals that are known or thought to have beenherbivorous.Nemegtomaiais known from theNemegtandBaruungoyot formations,which are thought to representhumidandaridenvironments that coexisted in the same area.

History of discovery

Maps showing theNemegtlocality (a, b) and whereNemegtomaiaspecimens have been found (c)

In 1996 the Japanese palaeontologist Yoshitsugu Kobayashi (as part of the "Mongolian Highland International Dinosaur Project" team) found an incomplete skeleton of anoviraptoriddinosaurin theNemegt Formationof theGobi Desertin southwesternMongolia.The specimen (MPC-D100/2112 at the Mongolian Palaeontological Center, formerly PC and GIN100/2112), 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 pubic bones, both ischia, and the upper end of a femur. The specimen was described as a new specimen of thegenusIngenia(referred to asIngeniasp.; of uncertain species) by the Chinese palaeontologistLü Junchangand colleagues in 2002, and used to highlight the similarities betweenoviraptorosaursand birds.

Nest diagram(A), bones of the nesting specimen that covered eggs (B–D), and a lower layer of eggs (E–G)

In 2004 Lü and colleagues determined that the skeleton belonged to a new, distinct taxon, and made it theholotype specimenofNemegtia barsboldi.The genus name refers to theNemegt Basin,and thespecific namehonours the Mongolian palaeontologistRinchen Barsbold,the leader of the team that found the specimen.In 2005 the describers discovered (after being notified by a biologist) that the nameNemegtiahad already been used for a genus of freshwaterseed shrimp(Ostracoda) from the same formation in 1978, and was thereforepreoccupied.They proposed instead the new genus nameNemegtomaia( "maia"means" good mother "in Greek, and the full name means" good mother of the Nemegt "), making reference to the then-recent discovery that oviraptoridsbroodedeggs rather than stealing them, though no trace of a nest or eggs had yet been found associated withNemegtomaiaitself.The first known member of the oviraptorid family was found with a nest of eggs originally thought to have belonged to theceratopsiangenusProtoceratops,and was therefore namedOviraptorin 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.Ingeniawas similarly renamed asAjancingeniain 2013, since the former genus name was preoccupied by aroundworm(Nematoda).

Assigned specimens

Skeletal diagrams showing the preserved elements of the three known specimens in grey, composite on right

In 2007 two new specimens ofNemegtomaiawere 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-D107/15, was found by Fanti (who nicknamed it "Mary" ) in theBaruungoyot Formation,and consists of a nest with the presumed parent on top. As the fourth genus of oviraptorid found on top of a nest (afterOviraptor,Citipati,andcf.Machairasaurus),Nemegtomaiahad 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 collapsingsandstoneblocks.

The nesting skeleton preserves parts of the skull, both scapulae, the left arm and hand, the right humerus, the pubic bones, 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 toNemegtomaiadue to its similaranatomical featuresand 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-D107/16, 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 toNemegtomaiadue to its hands having the same characteristics as those of specimen MPC-D107/15. 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.

Description

Size compared to a human

Nemegtomaiais 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.ThoughNemegtomaiadoes not possess any single feature that distinguishes it from other oviraptorids (autapomorphies), the combination of a crest, an enlarged first finger, and a high number ofsacral vertebrae(eight), is unique to thistaxon.

Skull

Preserved parts and reconstruction of specimen MPC-D107/15's skull

The skull ofNemegtomaiawas deep, narrow, and short (compared to the rest of the body), and reached 179 mm (7 in) in length. It had a well-developed crest, formed by thenasalandpremaxilla bones(mainly the latter) of the snout. The nearly vertical front margin of the holotype's crest formed an almost 90degree angle 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 theorbit(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 twofenestrae(openings); a largeantorbital fenestraat the back, and a small maxillary fenestra at the front.Nemegtomaiawas distinct from other oviraptorids in that thefrontal boneon the midline of the skull was about 25% the length of theparietal bonefrom front to back. Thenares(external nostrils) were relatively small and placed high on the skull.

The jaws ofNemegtomaiawere toothless, and like other oviraptorid dinosaurs, it had a short snout with a deep, robust, and somewhatparrot-like beak. It had a hardpalateformed by the premaxillae,vomers,andmaxillae,like other oviraptorids. The palate was strongly concave (downwards-projecting), and had a cleft on the central part. As in other oviraptorids, it had a pair of tooth-like projections on the palate that were directed downwards (a feature that has been called "pseudo-teeth" ).Nemegtomaiahad smallforamina(openings) on the sides of thesuture(joint) between the premaxillae at the front of the snout, which may have been nutrient openings (and which indicate the presence of akeratinousbill). The lower jaw was short and deep, with a convex lower surface, and reached 153 mm (6 in) in length. Thedentary boneof the lower jaw reached 50 mm (2 in) at its highest point. Themandibular symphysis(where the two-halves of the lower jaw connected) was short, deep, and verypneumatised(with air-spaces). The mandibular fenestra was large and was located at the front part of the lower jaw.As in most other oviraptorids, the front of the lower jaw was down-turned.

Postcranial skeleton

Life restoration

The neural spines of the neck (cervical) vertebrae were short, and theneural archeshad an x-shaped appearance. The middle three of these vertebrae were the largest. Thescapula(shoulder blade) appears to have been 185 mm (7 in) in total length. Thehumerus(upper arm bone) had afossa(depression) in a position similar to modern birds, but atypical among oviraptorosaurs, and appears to have been 152 mm (6 in) long. Theradiusof 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 strongungual(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 the smallest. The upper margin of theiliumof the pelvis was straight, and though both ilia were close to each other, they were not fused together. The pubic shaft was turned backwards. Thefemur(thigh bone) is estimated to have been 286 mm (11 in) long, and thetibiaof the lower leg 317 mm long (12 in).

Classification

Reconstructed skeleton,Henan Geological Museum

In their 2004phylogenetic analysis,Lü and colleagues classifiedNemegtomaiaas aderived(or "advanced" ) oviraptorosaur, and found it to be most closely related to the genusCitipati.In 2010 Longrich and colleagues determined thatNemegtomaiabelonged in the familyOviraptoridae,as part of the subfamilyIngeniinae,making it the only member of the latter group with a prominent crest. Members of the other recognised subfamily, Oviraptorinae, all possess crests. Members of this subfamily were distinguished by smaller size, short and robust forelimbs with weakly curved claws, the number of vertebrae in thesynsacrum,as well as certain features of the feet and pelvis. Longrich and colleagues suggested that the presence of a crest onNemegtomaiamakes it possible that this feature evolved or disappeared several times among oviraptorids, or that the animal may not have been an ingeniine.In 2010, the American palaeontologistGregory S. Paulsuggested that crestless oviraptorids were either the juveniles or females of otherwise crested species, and that the number of genera in the group was therefore exaggerated. He listedNemegtomaiaas "Citipati(=Nemegtomaia)barsboldi,considering it very similar to that genus, but in 2016, he instead listed it as "Conchoraptor(=Nemegtomaia)barsboldi".

In 2012 Fanti and colleagues also foundNemegtomaiato be part of Ingeniinae as a derived member, closest toHeyuannia,due to the proportions of the hands of the two new specimens (relatively short with a robust first finger). They stated that, though the presence of crests is generally associated with oviraptorines rather than ingeniines, the feature may be correlated with size and maturity. They pointed out that the nasal and frontal bones of the ingeniineConchoraptorwere pneumatic and could potentially have grown into a crest as the animal matured, though all known skeletons of that genus are of the same small size (and one specimen appears to have been fully grown).The subfamily name Ingeniinae has since been replaced by the name Heyuanninae (sinceIngeniawas preoccupied).Thecladogrambelow shows the placement ofNemegtomaiawithin Oviraptoridae, according to Fanti etal., 2012:

Restorations ofoviraptoridheads shown to scale; K (bottom middle) isNemegtomaia

Oviraptoridae	Oviraptor unnamed Rinchenia Citipati unnamed Khaan unnamed Conchoraptor unnamed Machairasaurus unnamed "Ingenia" (=Ajancingenia) unnamed Nemegtomaia Heyuannia

Evolution

Hand bones ofoviraptorosaurscompared; P (far right) is the hand ofNemegtomaia,grouped within Ingeniinae (=Heyuanninae)

ThecladeOviraptorosauria is generally regarded as a group of non-avian(or non-bird)theropoddinosaurs, and their similarity to birds (Aves) has often been noted. Fossils of oviraptorosaurs in the familyCaenagnathidaehave historically been confused with those of birds, and some researchers have gone so far as to consider oviraptorosaurs as a whole more closely related to birds than to other non-avian dinosaurs. In 2002 Lü and colleagues used the then unnamedNemegtomaiato show similarities between birds and oviraptorosaurs, and found the latter group to be closer to birds than to bird-like dinosaurs such asdromaeosaurs.They therefore concluded that oviraptorosaurs wereflightless birdsrather than non-avian dinosaurs, and noted that the boundary between birds and dinosaurs was becoming more and more difficult to delineate.Other researchers have instead found dromaeosaurs andtroodontidsto be most closely related to birds, together forming the groupParaves;oviraptorosaurs,therizinosaurs,andalvarezsaursare just outside this group. The wider group that includes oviraptorosaurs and Paraves is calledPennaraptora,and this group is defined by the presence ofpennaceous feathers(feathers with a stalk).

Oviraptorosaurs are known from Asia (where they may have originated) and North America, and are mainly known from deposits that date from theCampanian-Maastrichtianages of theCretaceous period.The group includes small to large members, and they are characterised by their short skulls and beaks, elongated fingers, and short tails.Basal(or "primitive" ) members had teeth, which disappeared in derived members of the group (those within the superfamilyCaenagnathoidea,which includes Oviraptoridae). They were at least partiallyherbivorous,and brooded their nests in a bird-like posture. Though they are all thought to have to been feathered, they appear to have been flightless.Cranialcrests appear to haveevolved convergentlyin differentlineageswithin the group.The family Oviraptoridae (to whichNemegtomaiabelongs) consisted of generally small members, and is exclusively known from theUpper Cretaceousof Asia, with most genera having been discovered in the Gobi Desert of Mongolia and China.IncludingNemegtomaia,at least nine oviraptorid genera have been discovered in a relatively small geographical area in the Gobi Desert.

Palaeobiology

Reproduction

Diagram showing the remains and body outline of the nesting specimen

TheNemegtomaiaspecimen MPC-D 107/15 was found associated with a nest with eggs; its feet were placed in the centre of what was probably a ring of eggs, with the arms folded across the tops of the eggs on each side of the body, a posture similar to what is seen in other fossils of brooding oviraptorids. The collected part of the nest is about 90 cm (35 in) wide and 100 cm (30 in) long; the skeleton occupies the upper 25 cm (10 in) of the block, whereas the remaining 20 cm (8 in) is occupied by broken eggs and shells. There is no evidence of plant material in the nest, but there are fragments of undetermined bones. The nest does not preserve any complete eggs or embryos, which prevents determination of the size, shape, number, and arrangement of the eggs in the nest. It is probable that there were originally two layers of eggs below the body, and there do not appear to have been eggs in the centre of the nest. Most eggs (seven distinct eggs have been identified) and egg fragments were recovered either in the lower layer of the nest or under the skull, neck, and limbs of the specimen, and the bones either rested directly on the eggs or were within 5 mm (0.2 in) of their surfaces. That the skeleton was directly positioned on top of it shows that the nest was not completely covered by sand. Though the placement of the eggs does not suggest a specific arrangement in the nest, most other oviraptorid nests show that the eggs were arranged in pairs in up to three levels of concentric circles. The eggs of MPC-D107/15 were therefore most likely displaced during burial, or by external factors, such as strong winds,sandstorms,or predators. This also supports the idea that the upper layer of eggs was not buried, as fully buried eggs would have been less likely to be transported by external factors.

Details of eggs preserved with the nesting specimen

Oviraptorid eggs appear to have been 17 cm (6 in) long on average, and the most complete eggs found with MPC-D107/15 are thought to have been 5to 6 cm (2to 2.3in) wide and 14 to 16 cm (5to 6in) long when intact. The eggs are nearly identical to some that have previously been found in Mongolia, and have therefore been assigned to theoofamily(egg-taxon family)Elongatoolithidae.The eggshells are relatively thin, between 1and 1.2 mm (0.03and 0.04in), and their outer surface is covered by ridges and nodes that rise about 0.3 mm (0.01 in) above the shell. Themicro-structureof the eggshells could not be properly studied, as thecalcitehas been heavily altered andre-crystallized.

The nesting specimen was found in astratigraphicarea indicating that oviraptorids preferred nesting near streams that provided soft, sandy substrate and food in environments that were otherwisexeric(receiving a small amount of moisture). Many oviraptorids have been found in brooding positions, indicating they may have brooded for relatively long periods, similar to modern birds such as theostrich,emu,andblack-breasted buzzard,which brood for more than 40 days with a limited supply of sustenance. Nesting in desert environments can be harmful to adults that stay in the nest for large parts of the day, and for eggs and nestlings, due toheat stress.The choice of nesting area may therefore have been a mechanism for successful incubation in extreme heat. It has also been suggested that the evolution of tail-feathers in oviraptorosaurs was an adaptation for shading and protecting eggs in their nests. That the second finger of heyuannine oviraptorids was reduced in size compared to the robust first finger may be explained by a change in function; it may be related to the presence of longwing feathersthat were attached to the second finger. These wing feathers were probably used to protect the eggs during nesting. When the second finger began functioning as a feather support, its ability to grasp was reduced, and this function was taken over by the first finger, which therefore became more robust. The third finger was reduced in size, too, probably because it was positioned behind the wing feathers in a way where it would not be effective for grasping.

Restoration of a nesting individual

In 2018, the Taiwanese palaeontologist Tzu-Ruei Yang and colleagues identifiedcuticlelayers on egg-shells of maniraptoran dinosaurs, including oviraptorids. In modern birds, such layers (which consist mainly oflipidsandhydroxyapatite) serve to protect the eggs from dehydration and invasion ofmicrobes.The researchers suggested that the cuticle-coated eggs would have been a trait adapted for enhancing their reproductive success in the variable environments whereNemegtomaiaand other oviraptorids nested.

Various studies have suggested that several individuals would gather eggs in a single nest, and arrange them so they could be protected by one individual, possibly a male.In 2010 the American palaeontologist David J. Varricchio and colleagues found that the relatively largeclutch-size of oviraptorids and troodontids is most similar to those of modernarchosaurs(birds andcrocodilians,the closest living relatives of dinosaurs) that practicepolygamousmating and extensive maleparental care(as seen inpaleognathssuch as ostriches and emus). Thisreproductive systempre-dates theorigin of birdsand would therefore be the ancestral condition for modern birds, with biparental care (where both parents participate) being a later development.Many oviraptorosaurs are known to have hadpygostyleson the end of their tails, which suggests the presence of feather-fans; the American palaeontologist W. Scott Persons and colleagues suggested in 2013 that these could have been used forintraspecific communicationsuch ascourtship rituals.

Diet and feeding

Lower jaw of the holotype specimen, with beak on the right

The diet of oviraptorids has been interpreted in various ways since the timeOviraptorwas wrongly thought to have been a predator of eggs. It has been suggested that oviraptorosaurs as a whole were herbivores, which is supported by thegastroliths(stomach stones) found inCaudipteryx,and the wear facets in the teeth ofIncisivosaurus.In 2010 Longrich and colleagues found that oviraptorid jaws had features similar to those seen in herbivoroustetrapods(four-limbed animals), especially those ofdicynodonts,an extinct group ofsynapsidstem-mammals.Oviraptorids and dicynodonts share features such as short, deep, and toothless mandibles; elongated dentary symphyses; elongated mandibular fenestrae; and a downwards-projecting bar in the palate. Modern animals with jaws that resemble those of oviraptorids include parrots and tortoises; the latter group also has tooth-like projections on their premaxillae.

Longrich and colleagues concluded that due to the similarities between oviraptorids and herbivorous animals, the bulk of their diet would most likely have been formed by plant matter. Oviraptorids are found at high frequencies in the formations they are known from, similar to the pattern seen in dinosaurs that are known to be herbivorous; these animals were more abundant than carnivorous dinosaurs, as more energy was available at their lowertrophic levelin thefood chain.The jaws of oviraptorids may have been specialised for processing food, such asxerophyticvegetation (adapted for environments with little water), that would have grown in their environment, but this is not possible to demonstrate, as little is known about the flora of the area at the time.A 2013 study by Lü and colleagues found that oviraptorids appear to have retained their hind limb proportions throughoutontogeny(growth), which is also a pattern mainly seen in herbivorous animals.In 2017, the Canadian palaeontologist Gregory F. Funston and colleagues suggested that the parrot-like jaws of oviraptorids may indicate afrugivorousdiet that incorporated nuts and seeds.

Diagrams showing the hands of specimen MPC-D 107/15 and 107/16

In 1977 Barsbold suggested that oviraptoridsfed on molluscs,but Longrich and colleagues rejected the idea that they practisedshell-crushingaltogether, since such animals tend to have teeth with broad crushing surfaces. Instead, the shape of the dentary bones in the lower jaws of oviraptorids suggests they had a sharp-edged beak used for shearing tough food, not for cracking hard food items such asbivalvesor eggs. The symphyseal shelf at the front of the dentary may have given some ability for crushing, but as this was a relatively small area, it was probably not the main function of the jaws. The fact that most oviraptorids have been found insedimentsthat are interpreted as having been xeric and arid or semi-arid environments also argues against them having been specialised eaters of shellfish and eggs, as it is unlikely there would have been enough of these items under such conditions to support them.

Longrich and colleagues pointed out that the robust forelimbs and enlargement of a single finger in heyuannine oviraptorids is similar to that seen in modern animals that eat ants and termites, such as anteaters andpangolins,but the morphology of heyuannine jaws does not support them beinginsectivorous.The researchers found that the function of heyuannine forelimbs was unclear, but suggested that they could have been used for scratching, tearing, or digging, though not prey capture.

In 2004 Lü and colleagues proposed that the articulation between thequadrateandquadratojugal bonesin the skull ofNemegtomaiasuggested that these bones weremovable in relation to each other,which would have affected how the jaws functioned. In 2015 the Belgian palaeontologist Christophe Hendrickx and colleagues found it unlikely thatNemegtomaiaand other oviraptords had bird-like kinesis in their skulls, due to the quadrate bone being immobile.

Palaeoenvironment

Map and diagram showing the relation between the interfingeringBaruungoyotandNemegt Formations

Nemegtomaiais known from the Nemegt and Baruungoyot Formations, which date to the upper Campanian–lower Maastrichtian ages of the Late Cretaceous period, about 70million years ago. Though this taxon is known only from the Nemegt locality, unidentified oviraptorid remains from other localities may belong to it. The Nemegtmassifhas numerous canyons or gorges, up to 45 metres (148 ft) deep, which have some of the best exposures of these formations. The rockfaciesof the Nemegt Formation are thought to represent a humid,fluvial(associated with rivers and streams) environment, whereas those of the Baruungoyot Formation are thought to represent an arid or semi-arid environment, withaeolian(affected by wind) beds. These two formations with their diverse fossils were historically thought to represent sequential time periods with different environments, but in 2009 the Canadian palaeontologist DavidA. Eberth and colleagues found that there was partial overlap across the transition between them. The two formations "interfinger" across a stratigraphic interval that is about 25 m (82 ft) thick, which suggests that the fluvial and aeolian environments coexisted when the area was sedimented.

Photos of the interfingering contacts between the formations

The environment of the Nemegt Formation has been compared to theOkavango Deltaof present-dayBotswana.The habitats in and around the Nemegt rivers provided a home for a wide array of organisms. Aquatic animals include molluscs, fish, turtles, and thecrocodylomorphShamosuchus.Fossils of mammals such asmultituberculateshave been found, and birds such asGurilynia,Judinornis,andTeviornisare known. Herbivorous dinosaurs of the Nemegt Formation includeankylosauridssuch asTarchia,thepachycephalosaurianPrenocephale,hadrosauridssuch asSaurolophusandBarsboldia,andsauropodssuch asNemegtosaurus,andOpisthocoelicaudia.Other theropods includetyrannosauroidssuch asTarbosaurus,Alioramus,andBagaraatan,troodontidssuch asBorogovia,Tochisaurus,andSaurornithoides,therizinosaurs such asTherizinosaurus,andornithomimosaurianssuch asDeinocheirus,Anserimimus,andGallimimus.

Other oviraptorosaur genera known from the Nemegt Formation include the basalAvimimus,the oviraptoridsRinchenia,Nomingia,ConchoraptorandAjancingenia,and the caenagnathidElmisaurus.In spite of the high number of oviraptorid taxa in these formations (the Nemegt has the highest known diversity of them anywhere), none of them were closely related. The Nemegt Formation is unique in having both oviraptorid and caenagnathid oviraptorosaurs, and in 1993 the Canadian palaeontologistPhillip J. Currieand colleagues suggested this diversity was due to the two groups preferring different environments in the area. In 2016 the Japanese palaeontologist Takanobu Tsuihiji and colleagues suggested that oviraptorids may have preferred drier environments, while caenagnathids preferred fluvial environments, based on the type of formations they have been found in.Funston and colleagues suggested that oviraptorids were found in both xeric andmesic environments(but were more abundant in the former), whereas the other oviraptorosaur groups avoided the xeric environments, and that the coexistence of the families can be explained byniche partitioningin diet. The environment of the Nemegt Formation may have acted as anoasisand thereby attracted oviraptorids.

Taphonomy

Feeding traces fromskin beetleson the nesting specimen

The nesting specimen MPC-D 107/15 has provided much information about thetaphonomic processes(changes during decay and fossilisation) in the Baruungoyot Formation. The specimen is preserved in facies that are thought to have been deposited through a sandstorm ordune-shift. It does not seem to have been transported after death, but the body appears to have shifted slightly to the right, indicating the sediment in which it was deposited came towards it from its left side. The neck is curved to the left, the left hand is folded backwards, and the legs are folded into a crouching position. The vertebral column, neck, and hips deteriorated during burial, and much of the damage to the skeleton is thought to have been caused by the activity ofinvertebrates.

Borings in the bones, burrows, and reworked sediments (perhaps caused by the construction ofpupal chambers) in the specimen indicate it wasscavengedupon by colonies ofskin beetles(Dermestidae) and perhaps other scavenging insects. There are many feeding traces in the joints of the skeleton, and almost all the surfaces where the bones articulated have been obliterated. There are also tunnels in the nest under the neck and skull, and no egg remains have been found in parts with such traces. Modern skin beetles mainly feed on muscle tissue but not on moist materials, and their activity is prevented by rapid burial. It is therefore thought that specimen MPC-D107/15 was only partially buried at first, with the upper part being exposed enough for a colony of skin beetles to develop. Some damage to the skeleton (especially in the vertebral column) may also have been caused by the scavenging of small mammals.

See also

• Timeline of oviraptorosaur research