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New Specimens of Nemegtomaia from the Baruungoyot

and Nemegt Formations (Late Cretaceous) of Mongolia

Federico Fanti1*, Philip J. Currie2, Demchig Badamgarav3

1 Dipartimento di Scienze della Terra e Geologico-Ambientali, Alma Mater Studiorum, Universita` di Bologna, Via Zamboni, Bologna, Italy, 2 Department of Biological

Sciences, University of Alberta, Edmonton, Alberta, Canada, 3 Paleontological Center, Mongolian Academy of Sciences, Ulaan Baatar, Mongolia

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.

Citation: Fanti F, Currie PJ, Badamgarav D (2012) New Specimens of Nemegtomaia from the Baruungoyot and Nemegt Formations (Late Cretaceous) of

Mongolia. PLoS ONE 7(2): e31330. doi:10.1371/journal.pone.0031330

Editor: Carles Lalueza-Fox, Institut de Biologia Evolutiva - Universitat Pompeu Fabra, Spain

Received June 14, 2011; Accepted January 6, 2012; Published February 8, 2012

Copyright: © 2012 Fanti et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits

unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This work was supported with funding by the Dinosaur Research Institute (Calgary), the Museo Geologico Giovanni Capellini (Bologna, Italy), and

NSERC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

* E-mail: federico.fanti@unibo.it

Introduction

Oviraptorid dinosaurs have long been a source of information

and speculation about the behavior of non-avian theropods [1,2].

Known since the Third Central Asiatic Expedition led by Roy

Chapman Andrews [3] and for decades mistakenly referred to as

exemplary egg thieves, this group of edentulous maniraptoran

dinosaurs is now studied for its sophisticated social structure and

behavior, which includes the brooding and care of eggs in specially

prepared nests [4–9]. The family Oviraptoridae, known to date

from the Late Cretaceous of Asia where multiple complete or

nearly complete skeletons have been recovered, includes two

widely accepted clades, Ingeniinae and Oviraptorinae [10,11].

Barsbold [12] established the subfamily Ingeniinae, and separated

ingeniines from oviraptorines on the basis of their smaller size and

reduced manual digits II and III. The clade included both

Conchoraptor and Ingenia. 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.

Osmólska et al. [10] defined ingeniines as Conchoraptor gracilis and

Ingenia yanshini, their most recent common ancestor, and all

descendants. The three synapomorphies they used to define the

subfamily are: the synsacrum includes seven to eight vertebrae; the

deltopectoral crest extends for 40%–50% of the length of

humerus; and the postacetabular process of the ilium has a

truncated distal end. Khaan mckennai was included in the

Ingeniinae, and is clearly similar to Conchoraptor. Nemegtomaia

barsboldi [14] is unusual in that it is the only ingeniine that has a

cranial crest, and is the only oviraptorid that was collected from

fluvial (instead of xeric) deposits. The type specimen (MPC-D

100/2112) was collected in 1996 in southern Mongolia at the

Nemegt locality (sensu [15]) by the Mongolian Highland Interna-

tional 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). However, characters of the forelimbs and hands

that are diagnostic for determining interspecific variation [11,16],

were unknown. Furthermore, no eggs or eggshells were found in

association with the specimen. The specimen was originally

referred to as Ingenia sp. by Lü et al. [17] but a detailed revision of

the specimen led to it being renamed Nemegtia barsboldi [14].

However, the genus had to be renamed Nemegtomaia when it was

realized that the name was preoccupied by a freshwater ostracod

from the Nemegt Formation [18,19]. Nemegtomaia (‘‘good mother

of Nemegt’’) refers not only to the stratigraphic and geographic

location of the discovery (early Maastrichtian Nemegt Formation,

Nemegt locality, southern Gobi, Mongolia) but also to the idea

that oviraptorid dinosaurs were brooding, rather than stealing,

eggs [4,5,7–9,20–23].

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Nomadic Expedition’s ‘‘Dinosaurs of the Gobi’’ 2007 party

recovered two new specimens of oviraptorids from the Baruun-

goyot Formation (or ‘‘Barun Goyot’’ in older literature; strati-

graphic terminology in this paper follows [24]) beds at the Nemegt

locality (Figure 1). Specimen MPC-D 107/15 is a nest of eggs with

the presumed mother lying on top. In addition to being found less

than 500 m from the holotype of Nemegtomaia, the new specimen

shares diagnostic characters of the skull and has the same absolute

body size. It provides new anatomical information about the front

limbs that conclusively shows that Nemegtomaia should be referred

to the subfamily Ingeniinae. The second new specimen, MPC-D

107/16, consists of hands, ribs, a partial pelvis and both femora of

a smaller individual. The two new specimens are described here

with a focus on diagnostic and previously unknown characters

(especially in the skull and hands), the association of the skeleton

with the eggs, and the taphonomy, stratigraphic range, and

paleoecology of the taxon.

Institutional Abbreviations

AMNH, American Museum of Natural History, New York,

USA; IVPP, Institute of Vertebrate Paleontology and Paleoan-

thropology, Beijing, People’s Republic of China: MPC-D,

Paleontological Center of the Mongolian Academy of Sciences,

Ulaan Baatar, Mongolia ( = GIN, Geological Institute, Mongolian

Academy of Sciences); UALVP, University of Alberta, Laboratory

of Vertebrate Paleontology, Edmonton, Canada.

Geology and Stratigraphy

Since its discovery in 1946, the Nemegt locality (sensu [15]) has

been recurrently investigated for the rich and diverse fossil fauna

preserved in the exposed Upper Cretaceous sediments (Figure 1).

Several major sayrs (canyons, gorges) and numerous side-canyons

cut the pediment that slopes toward the south beneath the Nemegt

massif. The cuts are up to 45 meters deep and provide some of the

best exposures of the upper Campanian - lower Maastrichtian

Baruungoyot and Nemegt formations, which have been largely

discussed in the literature [25–33]. Specimen MPC-D 107/15 was

collected from the upper Baruungoyot Formation deposits that

crop out extensively along the Northern Sayr. These upper beds

are barren of mudstone and consist of a stacked succession of

tabular redbeds. Abundant extraformational clasts, well-developed

caliches, and invertebrate feeding traces characterize these

primarily aeolian deposits (Figure 2). Wedging out of single beds

is fairly common, even though individual tabular beds can be

traced laterally for tens or hundreds of meters. Prospecting

activities carried out in Northern Sayr revealed the lateral

variation of such beds, even within the cliff in which the nest

was discovered (Fig. 2B). A short distance (150 meters) to the north

of the nest, the distinctive Baruungoyot facies interfinger with light

grey, trough cross-bedded channel deposits that are typical of the

Nemegt Formation. The basal contact is sharp and erosive,

juxtaposing fine- to medium-grained sandstone with a medium-

grained, 5 cm thick conglomerate that fines upward into cross-

bedded sandstones. Such beds form an approximately four meter

thick, fining-upward tongue that is conformably overlaid by red,

massive, aeolian deposits (Baruungoyot facies). Finally, the channel

fill sandstone deposits of the Nemegt Formation cap this interval

(Fig. 2F). The two formations and their different fossil assemblages

have historically been considered to represent sequential periods of

time and different environments [26,27,34–36]: the Baruungoyot

Formation is indicative of semi-arid or arid environments with

recurrent aeolian beds, and the Nemegt Formation has been

interpreted as representing a dominantly fluvial environment with

most fossils being recovered from channel fills, point bars, and

some overbank deposits laid down under more humid conditions

[33]. However, new data collected in the Northern Sayr at the

Nemegt locality document an approximately 25meter thick

stratigraphic interval where the two formations interfinger, and

Figure 1. The Nemegt locality the Gobi Desert, southern Mongolia. A, map showing the location of the study area within southern Mongolia;

B, the Nemegt area is located a few kilometers south of the massif of the same name; C, a detail of the Nemegt locality (sensu 5), showing the exact

locations of specimens described in this study.

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New Specimens of Nemegtomaia from Mongolia

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support previous studies suggesting that aeolian and fluvial

environments coexisted at the beginning of Nemegt sedimentation

[33].

Methods

Specimen MPC-D 107/15 was collected from the red

sandstones of the Baruungoyot Formation in the Northern Sayr

of the Nemegt locality (N 43u30.353!, E 101u03.383!) (Figure 2).

In order to preserve the spatial relationships of the bones and eggs,

the specimen was collected in a single block delimited by the last

occurrence of preserved eggs. The lower side of the block is only

partially prepared to expose mostly egg fragments, whereas the

upper surface has the articulated partial skeleton of an oviraptorid

dinosaur overlying the nest (Figure 3). It includes the skull, both

scapulae, the left arm and hand, right humerus, pubes, ischia,

femora, tibiae, fibulae, and the distal portions of both feet. Much

of the skeleton was subjected to intense scavenging by small

predators and dermestid coleopterans during an early stage of

burial (Figure 4).

The second specimen (MPC-D 107/16) was collected from the

uppermost layers of the Baruungoyot Formation in the eastern

portion of the Nemegt locality from the Red Walls (N 43u30.327!,

E 101u04.706!) (Figure 1). It includes a complete right hand, the

left hand with partial ulna and radius, a few ribs, both femora, and

a partial ilium.

Results

Description of MPC-D 107/15

The oviraptorid affinities [10] of MPC-D 107/15 are

unquestionable with its relatively short snout, and its deep,

edentulous, beaklike lower jaws (Figure 5). Similarly, there are

many characters in the postcranial skeleton as well as in the eggs

that clearly show it is an oviraptorid (Figure 3). Much of MPC-D

107/15 was damaged by post-mortem, pre-burial insect activity,

crushing during burial, and most recently by erosion; it is

nevertheless rich in morphological and phylogenetic information.

Similar to other nests of brooding oviraptorids [4,8,37,38], the

animal had its feet in the center of what was probably a ring of

eggs, and the arms were folded across the tops of the eggs on either

side of the body. Although the individual bones have been

damaged by borings and other scavenging, their shapes and

lengths can be reconstructed because of the fact that the bones

were held immobile in the sediments while they were being eaten

by insects, and because their margins are often preserved. The

Figure 2. Location map showing the position of the measured section discussed in the text. A, Northern Sayr, where specimen MPC-D

107/15 was collected. B, lithostratigraphic logs showing the relative stratigraphic occurrence of the interfingering Baruungoyot and Nemegt

formations. C, In-situ and partially reworked caliche glaebules and concretions, Baruungoyot Formation. D, tubular burrow fills interpreted as

nonmarine invertebrate feeding traces, Baruungoyot Formation. E, cross-bedded deposits in the basal deposits of the Nemegt Formation. F,

photograph showing the interfingering contact between the Baruungoyot and Nemegt formations in the Northern Sayr (litho-log c). MPC-D 107/15

was collected just below the Nemegt tongue deposits.

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Figure 3. Nest and preserved elements of Nemegtomaia barsboldi (MPC-D 107/15). A, dorsal view; B, left lateral view; C, right lateral view; D,

posterior view. lf, left femur; lfi, left fibula; lh, left humerus; lm, left manus; lp, left pes; lpu, left pubis; lr, left radius; ls, left scapula; lt, left tibia; lu,

left ulna; rf, right femur; rfi, right fibula; rh, right humerus; rp, right pes; rpu, right pubis; rs, right scapula; rt, right tibia; sk, skull. Scale bar 10 cm.

Reconstruction by Marco Auditore.

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front of the premaxilla and the posterior margin of the paroccipital

process are preserved on each side of the skull, and both sides show

that the skull was 172 mm long. The dorsal and posterior margins

of the orbit are preserved on the right side of the skull, whereas the

anterior, ventral and ventroposterior margins of the orbit are

preserved on the left side. The skull length is slightly shorter than

that of the holotype of Nemegtomaia (179 mm), whereas the

diameter of the orbit is approximately the same size (52 mm).

Other overlapping measurements of the two specimens are also

similar, including jaw length (153 mm in holotype, 152 mm in

MPC-D 107/15), and maximum dentary height (49 mm in

holotype, 50 in MPC-D 107/15). Equivalent measurements (skull

and jaw lengths) in MPC-D 100/42 (Citipati sp.) suggest that this

virtually complete individual is also approximately the same size as

the two Nemegtomaia specimens. The femur length in MPC-D 100/

42 is 305 mm and its shaft circumference is 95 mm (which

suggests the animal weighed 40 kg using the formulae of [41]), and

the length of the skeleton is 1.95 meters. It is therefore likely that

MPC-C 107/15 was an individual with a total length of about

2 meters, and that it weighed approximately 40 kg. The edges of

the premaxilla, nasal, frontal and parietal clearly show that MPC-

D 107/15 was a crested oviraptorid like Citipati, Nemegtomaia and

Rinchenia [10,17,39]. The crest is similar to those of both Citipati

and Nemegtomaia in that it is relatively low and is centered above the

antorbital region, in contrast with the much taller crest of Rinchenia

that is centered more posteriorly. Whereas crest development

extends posteriorly to thicken and pneumatize the frontals in

Citipati [40], this region is thin, flat and not pneumatized in MPC-

D 107/15 and the holotype of Nemegtomaia. Like the holotype of

Nemegtomaia, the ventral part of the anterior margin of the

premaxilla of MPC-D 107/15 is nearly vertical to the main axis

(as seen in lateral view) of the suborbital portion of the jugal. This

is in contrast with known specimens of Citipati, where the anterior

margin of the premaxilla slopes anterodorsally. The jugal process

of the postorbital (Fig. 5a) forms the upper two thirds of the

posterior border of the orbit in MPC-D 107/15 and most other

oviraptorids, but Citipati is unusual in that the jugal process extends

to the ventral margin of the orbit. As in Nemegtomaia, the ventral

end of the exoccipital of MPC-D 107/15 (Fig. 5B) is level with the

suborbital process of the jugal, which is considerably lower than in

Citipati. Whereas Citipati is from Djadokhtan-aged strata of

Dzamyn Khond and Ukhaa Tolgod, the holotype of Nemegtomaia

came from the Nemegt Formation less than 500 m from where

MPC-D 107/15 was collected. Similar morphology, similar size,

Figure 4. Feeding traces left by colonies of dermestid beetles in specimen MPC-D 107/15. 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.

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geographic proximity, and the interfingering nature of the

Baruungoyot and Nemegt formations make it most parsimonious

to identify MPC-D 107/15 as Nemegtomaia.

Like all oviraptorids, the skull of MPC-D 107/15 is relatively

short compared with other parts of the body (Figure 5). It is, for

example, almost half the estimated length of the femur, whereas in

other theropods the skull can be more than 90% the length of the

femur. Oviraptorid skulls are short overall because of a significant

reduction in the length of the antorbital region [10]. The eyes of

oviraptorids look large because of the relatively small sizes of most

species, but also because of their short skulls. If orbit length is

plotted against femur length (logarithmically transforming the

measurements) for 76 theropods (Currie, unpublished data), the

resulting regression is defined by y=0.6517x+0.0931 where y

represents orbit length, x is femur length and 0.6517 is the

allometric coefficient. The allometric coefficient shows that orbit

length (roughly equivalent to the size of the eyeball) shows strong

negative allometry with size increase. Adding the data for nine

oviraptorosaurs where both these dimensions are known clearly

demonstrates that the orbit length of each oviraptorid individual is

not significantly different from what is expected in any theropod.

The orbit of MPC-D 107/15 is 55 mm high, which suggests that

the length was 50 mm (compared with 55 mm in the holotype).

The anterior margins of the premaxillae are well preserved, and

show that the external nares would have been relatively small and

positioned high as in the holotype. The lateral temporal opening

was clearly large and quadrangular (Figure 5). The antorbital

length of MPC-D 107/15 is 78 mm, which is almost ten percent

longer than in the holotype. A difference of this scale can be easily

accounted for as individual variation or taphonomic distortion,

and is not significant.

The anterior (premaxillary) and dorsal (nasal) margins of the

skull show that MPC-D 107/15 had a prominent crest like many

other oviraptorids, including the holotype of Nemegtomaia (MPC-D

Figure 5. Skull of Nemegtomaia barsboldi (MPC-D 107/15). 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. an, angular; d, dentary; ec, ectopterygoid; eo, exoccipital; f, frontal; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pm,

premaxilla; po, postorbital; q, quadrate; qj, quadratojugal; sa, surangular; sq, squamosal; sr, sclerotic ring. Scale bar 10 cm. Illustration by Marco

Auditore.

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100/2112), Citipati sp. (MPC-D 100/42) and Rinchenia mongoliensis

(MPC-D 100/32-1). The specimen is not well enough preserved to

determine whether or not the nasal was pneumatic, as it clearly

was in Rinchenia and other mature oviraptorid individuals. The

presence of a crest is generally associated with oviraptorines rather

than ingeniines, but may in fact be correlated with size and

maturity; most ingeniines are in fact smaller than most

oviraptorines [2]. The anteroventral margin of the premaxilla is

almost perpendicular to the ventral margin of the jugal (Figure 5).

The height of the premaxilla below the external naris is 44.8 mm.

The premaxillary-maxillary suture is nicely preserved on the right

side of the skull (Figure 5). If a line is drawn through the ventral

margins of the quadratojugal and maxilla (Fig. 5A), then the

tomial margin of the premaxilla clearly projects well below the

maxilla. This may ultimately turn out to be a size correlated

character of little taxonomic utility. The lacrimal is platelike and

projects lateral to the orbit in both MPC-D 107/15 and the

holotype. Although the skull roof cannot be seen as well as in the

holotype, the nasal of MPC-D 107/15 appears to have been no

longer than the frontal. It appears unlikely that the frontals and

parietals were pneumatized like the nasals, because the small

sections of preserved surfaces of these bones are flat in MPC-D

107/15. There is no evidence for a separate prefrontal in either

this specimen or the holotype. The postorbital process of the jugal

extends posterodorsally from the suborbital process of the jugal

(Figure 5). The basal tubera cannot be seen in MPC-D 107/15,

but appear to be well developed in the holotype [14]. As in other

oviraptorids, the jaw is deep (the maximum height of the dentary is

a third of the jaw length), and the external mandibular fenestra is

large, making up more than a quarter of the jaw length (Figure 5).

A prominent process of the surangular invades the back margin of

the external mandibular fenestra as in all oviraptorids.

Postcranially, the ends of most bones were destroyed,

presumably by insect scavengers (Figures 3, 4). Most of the

scapula (180 mm) is present, and the total length appears to have

been about 185 mm. The minimum shaft width is 15 mm, and the

distal end expands to 27 mm. Although the full length of the

humerus is not preserved, the minimum shaft width (transverse)

has a diameter of 19 mm. Amongst sixteen oviraptorosaurs (Table

S4), there is a strong correlation (r2 =0.95) between humerus

length and transverse shaft width, which suggests that the humerus

would have been 152 mm long in MPC-D 107/15. The ratio of

the lengths of the scapula to the humerus can therefore be

calculated as 1.2, which is typical of the majority of oviraptorids.

The distal end of the deltoid process is preserved, but little can be

said other than it was well developed and extended far down the

shaft as in other oviraptorids. Only small sections of the shafts of

the radius (the diameter of the shaft width is 12 mm) and ulna

(SW=14 mm) are preserved, but show that the diameter of the

shaft of the radius was 0.86 that of the ulna. The length of the

radius was estimated as 144 mm using 10 pairs of measurements

of oviraptorid radii, plus the measurements of radii from seven

individuals of the oviraptorosaurs Avimimus and Caudipteryx

(b = 1.35, k = 0.75, r2 = 0.89). The estimates based on shaft widths

suggest that the ratio of radius length to humerus length is 0.95,

which is close to the same ratios in Citipati osmolskae (MPC-D 100/

979), and Conchoraptor gracilis (MPC-D 110/21). In contrast, the

ratio is less than 0.80 in Ingenia (MPC-D 100/32, 100/33, 110/03)

and Rinchenia (MPC-D 100/32-1). The ratio is intermediate

between the two extremes in all other oviraptorid taxa. The

hands were also badly damaged, but it is clear that the phalanges

(I-1, I-2) of the first digit were more massive than those of the

second digit (II-2, II-3) (Fig. 6A), that the distal end of the second

digit does not extend far beyond the distal end of the first digit, and

that the third metatarsal is slender. These are all characters that

are diagnostic for Ingeniinae.

The pubic shaft is preserved in MPC-D 107/15, and was clearly

curved anteroventrally (is anteriorly concave in lateral view) as in

other oviraptorids.

Most of the femur is preserved, although the distal end is in poor

condition (Fig. 4B). Its length can be estimated from the transverse

diameter of the shaft (31 mm) and is approximately 286 mm when

compared with 26 oviraptorids and dromaeosaurids (b=1.22,

Figure 6. Hands of Nemegtomaia barsboldi. 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. lr, left

radius; lu, left ulna. Scale bar 5 cm. Illustration by Marco Auditore.

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k=0.83, r2 =0.95). The length of the femur is 10% longer

(305 mm) in MPC-D 100/42 (Citipati sp.), which has similar

dimensions in other parts of the skeleton to MPC-D 107/15. This

suggests that the humerus was roughly half the length of the femur.

The shaft width of the tibia, when compared with 23 other

oviraptorids and dromaeosaurids (selected because they are not

arctometatarsalian; b=1.55, k=0.64, r2 =0.87), produces an

estimated length of 317 mm for the tibia. This makes sense

because it suggests that the tibia in the folded legs of MPC-D 107/

15 (Fig. 4B) is about 5–10% longer than the femur as in other

oviraptorids.

Posture

MPC-D 107/15 shows no evidence of post-mortem transpor-

tation. It is preserved in a facies hypothesized to have been

deposited in a single sandstorm or dune-shifting event. The body

had shifted slightly to the right of center, rather than being exactly

symmetrical across the midline of the skeleton; the right forearm

and part of the right foot are obscured in dorsal view (Figure 3).

This shift of the body suggests that the sediment deposited upon

the skeleton may have come toward the animal from its left side. A

similar assumption was made by Clark et al. [6] for another

nesting oviraptorid (Citipati osmolskae, MPC-D 100/979) from

Ukhaa Tolgod. Overall, MPC-D 107/15 shares several similarities

with the brooding Citipati (MPC-D 100/1004) of Erickson et al.

[8]. The neck curves toward the left and downward, and the skull

is facing the outside of the nest in a position lower than much of its

body (Fig. 3A,B). The humeri are oriented down and back, the

radius and ulna of the left side are oriented forward and down (the

right side is partially obscured by matrix), and the left hand is

folded backwards. The forelimbs do not extend laterally as much

as observed in other known nesting oviraptorid dinosaurs [4–6,8].

The legs are folded up into a crouching position. The feet are

upright and are medial to the position of preserved broken eggs.

The tail, ischia, and presumably a large portion of the nest have

been eroded away (Fig. 3C,D,E). In addition, the vertebral column

and the neck, parts of the pelvic bones, ribs, and the vast majority

of articular surfaces were scavenged before fossilization by

saprophagus insects and/or other small scavengers such as small

theropods or mammals. However, considering the overall

preservation of the skeleton, the absence of all cervical, dorsal

and sacral vertebrae is puzzling.

Taphonomy

Specimen MPC-D 107/15 is a terrific source of information on

taphonomic processes in the semi-arid environments of the

Baruungoyot Formation. In fact, a combination of different

factors resulted in the final preservation of the body: 1. lateral shift

of the body due to mono-oriented sediment accumulation; 2.

partial burial and subsequent deterioration (and possibly predation

by scavengers) of vertebral column, neck, and hips; 3. gradual

decomposition under xeric conditions; 4. intense scavenging by

insect colonies and; 5. final burial. In addition to minor

deformation caused by vertical compression during and after

burial, much of the damage observed in the skeleton and nest were

caused by intense activity of invertebrates. A number of studies

have dealt with insect traces on fossil bone and their implication in

constraining the reconstruction of the taphonomic history of a

specimen [42–48]. Such studies also document bone modification

during early stages of fossilization and indicate a common pattern

in areas where damage is more extensive, and in particular in the

cranial and dorsal vertebrae [49,50]. Traces of dermestid beetles

and possibly other saprophagus insect activity are documented by

bone borings, bone-chip-lined burrows, and reworked sediment in

specimen MPC-D 107/15 (Figure 4), some of which may have

been caused by the construction of pupal chambers. Nearly

circular borings passing completely through thin bones are

preserved in the left side of the skull and range between 3 and

6 mm in diameter (Fig. 4D,E,F,G). Similar borings have been

previously reported from the Baruungoyot Formation and coeval

Djadokhta Formation [30,49] on Bagaceratops, Pinacosaurus, Proto-

ceratops, Velociraptor, and other ankylosaurid skeletons [6,51–54].

Feeding traces are also abundant in the joints of the skeleton and

nearly obliterate all articular surfaces (Fig. 4A,B,C). Bone-chip-

lined burrows have been found around the skeleton, and the

largest of these are approximately 35 mm in diameter and contain

fragments of bone up to 7 mm wide (Fig. 4G). Furthermore, a

large section of the nest revealed reworked sediment in the form of

a light colored, elongate tunnel under the neck and the skull:

interestingly, such larger traces are found only in the part of the

nest where neither eggs nor egg fragments have been recovered

(Fig. 4H). Similar to several specimens collected in the Gobi desert

of Mongolia and China [48,55], no pupal chambers or similar

structures have been observed. As pointed out by Hasiotis et al.

[44], dermestid beetle activity implies specific environmental

conditions. Present day dermestids, for instance, feed primarily on

dried muscle tissue and they do not eat moist materials;

furthermore, rapid burial prevents any activity [56]. The presence

of such intense damage to bones supports the hypothesis that the

carcass was partially buried with the upper part of the body

exposed and subject to rapid exsiccation and deterioration for long

enough to allow a dermestid colony to develop. If skeletons are

kept in dermestid colonies for long enough, depending on

environmental and seasonal conditions, articular surfaces and

thinner bones (such as skull, ribs, scapulae, etc.) are totally

destroyed by the beetles [44,57]. Recently, Saneyoshi et al. [49]

suggested that some of the largest borings found on a Protoceratops

skeleton collected from the aeolian beds of the Djadokhta

Formation at Tugrikin Shire can be referred to scavenging

activities of small mammals. Similarly, remains of small mammals

have been found in the Baruungoyot and Nemegt formations of

the Trans-Altai Gobi [35,58]. Thus, it is possible to consider small

mammals as responsible for bone damage observed in MPC-D

107/15, and in particular for the damage observed in the vertebral

column.

Description and taphonomy of specimen MPC-D 107/16

MPC-D 107/16 is a partial skeleton of another oviraptorid from

the Baruungoyot Formation. Most of the skeleton had eroded

away before it was discovered, but half a dozen ribs, the anterior

edge of the right ilium, the distal ends of the left radius and ulna,

both hands, and most of both femora (Figs. 6, 7) were recovered.

The specimen can be identified as Nemegtomaia on the basis of its

hands, which have all the same ingeniine characteristics as MPC-

D 107/15. The diagnostic features of the hand that these two

specimens share include the relatively large first digit with a strong

ungual, and a third digit that is so small that the third metacarpal

is reduced to a splint. The specimen is significant in that it provides

information on the anatomy of Nemegtomaia that is not available

with either the holotype or MPC-D 107/15. It is also

approximately 35% smaller than either of the other two

specimens.

The rib fragments all appear to be from the right side, and the

spacing suggests that they were buried during the Cretaceous as

part of a fully articulated skeleton. The positions of the

anteroventral edge of the right ilium, and the right femur also

suggest that this is true. However, in the same block of sandstone is

the articulated right hand, but it is far enough behind the right leg

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to suggest that either it has been separated from the specimen, or

that it represents a second individual of the same size. The

orientation of the forearm and hand suggests the latter may be

true. The articulated left hand was found in another block of

sandstone, and therefore does not help to establish whether there

are one or two individuals. Both hands are the same size, and are

from an individual that was the same approximate size as the hind

limbs. The most parsimonious interpretation would be that all

elements represent a single individual because dinosaur skeletons

recovered from the Baruungoyot Formation tend to be articulated

but are not normally associated with each other. However,

multiple oviraptorid skeletons have been found in single quarries

in nearby parts of Mongolia (including a pair of Ingenia collected at

Khermeen Tsav [MPC-D 102/02, MPC-D 102/03] by an earlier

‘‘Dinosaurs of the Gobi’’ expedition, and a pair of Khaan excavated

by the American Museum of Natural History at Ukaa Tolgod

[39]. For the purposes of this paper, we are assuming that MPC-D

107/16 represents a single, somewhat disarticulated individual.

The shafts and distal ends of the left ulna and radius are

preserved in articulation with the hand, which is folded

perpendicular to the forelimb (Fig. 6C). The ulna has a straight

shaft like those of Heyuannia and Ingenia but is distinctive from the

bowed shafts found in most oviraptorids. The diameter of the shaft

of the radius is 78% that of the ulna. Using the same formula that

was used to estimate the length of the radius of MPC-D 107/15,

we can estimate the length of the radius as 99 mm in MPC-D

107/16.

The length of the hand (mc II+phalanges II-1, II-2, II-3) of

Nemegtomaia (MPC-D 107/16) is relatively short for an oviraptorid,

and is 36% the length of the femur, which is comparable with

Ingenia yanshini (40% in MPC-D 100/33). This suggests that the

hand overall is shorter than in Khaan mckennai (MPC-D 100/1002,

74%) and Citipati n.sp. (MPC-D 100/42, 97%).

MPC-D 107/16 shows that Nemegtomaia had at least three carpal

bones. The semilunate carpal of the right hand is still in position

capping the first and second metacarpals (Fig. 6B,C). Like

Figure 7. Skeletons of Nemegtomaia barsboldi specimens (known elements in grey). A, the holotype (MPC-D 100/2112); B, MPC-D 107/15

(the left side of the skull, left forelimb, pubis and toes are reversed and superimposed to the right side). C, MPC-D 107/16 (the left forelimb is reversed

and superimposed to the right side). In D, the preserved elements of MPC-D 107/15 and 16 are scaled to and superimposed on the holotype (the skull

depicted is that of the better preserved MPC-D 100/2112). Scale bar 20 cm. Illustration by Marco Auditore.

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Machairasaurus [11], the semilunate carpal protrudes between the

proximal ends of metacarpals I and II, and the distal articular facets

are angled away from each other. Three carpals are visible in the left

hand. One is presumably the semilunate carpal but it is partially

obscured by matrix. It has drifted a few millimeters away from the

metacarpus, and therefore was clearly not fused to it. The semilunate

carpal often fuses with the first two metacarpals in oviraptorids,

including specimens of Heyuannia [19] and Ingenia (MPC-D 100/30).

This is clearly an age related phenomenon, and fusion may have

occurred in larger specimens of Nemegtomaia. The second carpal is a

small, round bone positioned between the distal ends of the ulna and

radius. The identity of the third carpal is uncertain because it is

small, round and featureless, and has drifted out of position to lie on

the proximodorsal surface of the first metacarpal.

The metacarpus is well preserved in both hands. The first

metacarpal is slightly more than half the length (52%) of the

second metacarpal, which is comparable with Conchoraptor (58% in

MPC-D 100/38), Heyuannia [19], Ingenia (69% in MPC-D 100/30),

and Machairasaurus (63% in IVPP 15979). The percentage is less

than fifty in other oviraptorids. Even though it is shorter than the

other metacarpals, the shaft of metacarpal I is 50% thicker than

that of metacarpal II, and is four times thicker than the shaft of

metacarpal III. The same shaft thickness ratios are slightly less in

Ingenia (1.38 for McII and 2.93 for McIII in MPC-D 100/33) and

Heyuannia [19]. The proximal end of the first metacarpal is divided

into a large proximolaterally oriented facet for contact with the

semilunate carpal and a smaller proximomedially facing surface.

Metacarpal III is about 90% the length of McII. However, its

proximal end is more distal in position than that of McII;

consequently, the distal end of McIII almost reaches the distal end

of McII. The proximal end of metacarpal III is also separated from

the carpus in Heyuannia [19], Khaan [39], and Machairasaurus [11].

The shafts of metacarpals II and III are closely appressed as in

other oviraptorids. As in MPC-D 107/15, the shaft of the third

metacarpal is reduced to a splint.

The first digit is almost as long as the second digit, with the tip

of the first ungual reaching mid-length the second ungual, as it

does in the articulated hand of MPC-D 107/15. In comparison,

Citipati, Khaan and Machairasaurus each have a first ungual that

extends to the end of the penultimate phalanx of digit II, whereas

in Ingenia the tip of the first ungual reaches the same level as the tip

of the second one. The first phalanx of the first manual digit is

robust, and is about 40% thicker than the first phalanx of the

second digit. In Heyuannia and Ingenia, manual phalanx I-1 is

double the diameter of phalanx II-1. In the second digit of MPC-D

107/15, the combined lengths of phalanges II-1 and II-2 equal

29.5 mm, which is shorter than the length (34 mm) of the second

metacarpal (87%). This is also true for Ingenia (MPC-D 100/30,

78%; MPC-D 100/31, 76%; MPC-D 100/33, 77%) and Heyuannia

[figure 13.4 in 19], in which the sum of the lengths of these two

phalanges is about the same as the length of the associated second

metacarpal; in all other oviraptorosaurids, the sum is greater.

Phalanx II-2 is shorter than phalanx II-1, which is similar to the

situations in Heyuannia, Ingenia and Machairasaurus; in most of the

other oviraptorids, phalanx II-2 is longer than phalanx II-1. The

third digit of the right hand, except for the base of the first

phalanx, was destroyed by erosion. There are at least two small

phalanges on the third digit of the left hand, but the distal end of

the second one is incomplete. In the left hand of MPC-D 107/15,

and both hands of MPC-D 107/16, III-1 is less than two thirds the

length of II-1 and almost half its diameter.

Only the anteroventral corner of the preacetabular process of

the ilium is preserved, but it is similar to the shape of those parts of

the ilia of the holotypes of Nemegtomaia and Ingenia.

The femora are almost complete and as preserved are up to

21 cm long. Using the transverse shaft width and the same

regression that was used for MPC-D 107/15, the calculated length

of the femur is 222 mm.

Phylogenetic analysis

Phylogenetic analysis was performed by adapting the matrix of

Longrich et al. [11] and using the exhaustive search algorithm of

PAUP* 4.0b10 [59] (Figure 8) (Tables S1, S2, and S3). Velociraptor

was used as the outgroup for the Oviraptorosauria, Avimimus was

used as the outgroup for the Oviraptoridae, and taxa (Chirostenotes,

Gigantoraptor, Incisivosaurus and Nomingia) were excluded if fewer

than 50% of the 183 characters (Table S2) were coded. Heyuannia,

Machairasaurus and Oviraptor, also had fewer than 50% of the

characters coded, but were left in because they are part of the

ingroup being analyzed. The subset included twelve taxa (Avimimus

portentosus, Citipati osmolskae, Citipati n.sp. (MPC-D 100/42, also

referred to in other analyses as ‘‘Oviraptor philoceratops’’ or the

Zamyn Khondt [=Dzamyn Khond] oviraptorid), Conchoraptor

gracilis, Heyuannia huangi, Ingenia yanshini, Khaan mckennai, Machair-

asaurus leptonychus, Nemegtomaia barsboldi, Oviraptor philoceratops,

Rinchenia mongoliensis and Velociraptor mongoliensis). Three characters

are ordered, and the remaining ones are unordered. All characters

have equal weight. A total of 654,729,075 trees were evaluated to

produce two most parsimonious trees of length 210 (consistency

index of 0.867, a retention index of 0.731 and a rescaled

consistency index of 0.633). The only difference between the two

trees is that Oviraptor clustered in one tree with Rinchenia mongoliensis,

Citipati osmolskae and Citipati n.sp. in a monophyletic Oviraptorinae,

whereas in the other tree Oviraptor was the sister to all other

oviraptorids. The Ingeniinae includes (Khaan+(Conchoraptor+

(Machairasaurus+(Ingenia+(Heyuannia+Nemegtomaia))))).

Robustness was determined using bootstrap (1000 replicates)

and decay indices (Fig. 8). All ingroup nodes have decay values

greater than 1, and are still present in the strict consensus of all

trees either one or two steps beyond the Most Parsimonious Tree.

With the exception of Oviraptor, all bootstrap values within the

Oviraptoridae have high bootstrap values (greater than 75%).

In all runs of the phylogenetic analysis, Nemegtomaia is shown to

be one of the most derived ingeniine oviraptorids, and is most

closely related to Ingenia and Heyuannia. The original analysis by Lu

et al. [14] recovered Nemegtomaia as an oviraptorine oviraptorid

closely related to Citipati osmolskae, thereby demonstrating that the

additional anatomical information from the new specimens

significantly improves our understanding of oviraptorid systemat-

ics (Figure 8).

Some of the characters in the Longrich et al. [11] matrix rely

on ratios of bones that are incomplete in MPC-D 107/15, and to

code the characters, missing dimensions were calculated from

the parts of the bones that are preserved. Five of these characters

(130, 134, 136, 138, 139) were coded, and may have unduly

influenced the results. Because this is a potential source of error,

the five characters were rescored as unknown for Nemegtomaia,

and the analysis was rerun. This time the phylogenetic analysis

was performed using the heuristic search algorithm of PAUP*

4.0b10 [59] using 1000 replicates, and once again the analysis

produced two most parsimonious trees with tree lengths of 210.

The consensus tree topology is identical to that of the previous

analysis, the CI remained the same at 0.867, and the RI is

slightly less at 0.728. With the exception of Oviraptor, all

bootstrap values (1000 replicates) within the Oviraptoridae still

have high bootstrap values, although each dropped in value by 2

to 4%.

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The Nest

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.

Figure 8. Phylogeny of Oviraptoridae. 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.

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Eggs

None of the eggs is preserved in its entirety, and therefore all of

the dimensions of an egg cannot be measured accurately (Fig. 9A).

Available data on oviraptorid eggs in the literature [5–

7,20,21,60,63,64] indicate an average length of 17 cm

(min = 11.5 cm, max = 25 cm), and a width of 7 cm (min = 5 cm,

max=8.5 cm). By comparison, the most complete eggs found in

specimen MPC-D 107/15 are estimate to be 5 to 6 cm wide and

14 to 16 cm long. Preserved eggshells are macroscopically nearly

identical to those described by Norell et al. [20,21] and can be

referred to the elongatoolithid oofamily [60,65,66], originally

considered to be the ornithoid basic type (Figure 10). Eggshells are

relatively thin, ranging between 1 and 1.2 mm. The outer surfaces

of the eggs are ornamented with linearituberculate ridges and

nodes that rise approximately 0.3 mm above the shell (Fig. 10F).

Such longitudinal ornamentations do not show any specific trend

Figure 9. 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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or variation from the equatorial to apical region. Eggshell

microstructure from a total of eight fragments collected from the

nest were studied in tangential and radial thin sections, using

optical and polarizing light microscopy, and scanning electron

microscopy. Unfortunately, all analyzed fragments were heavily

altered and re-crystallized calcite, and all histostructures, including

pore canals, were obliterated. Furthermore, no pores were

observed on the external surfaces of the eggshells.

Discussion

The Nemegt locality provides excellent exposures of the

transitional interval between the Baruungoyot and Nemegt

formations, and in particular the gradual southeastward prograda-

tion of the Nemegt Formation depositional system (characterized

by channel-fill and sheet-flood deposits) on top of the Baruungoyot

Formation (dominated by semi-arid or arid environments with

recurrent aeolian beds) [33]. This interval is also the most fossil-

rich vertebrate stratigraphic section in the area, hosting most of

the vertebrates observed in the Nemegt beds [33]. This

assumption draws attention to the palaeobiology of faunal

assemblages recovered from this interval. In particular, oviraptor-

ids of Mongolia and China have been collected primarily from

deposits representing semi-arid or xeric environments [1,4–7,10–

12,20,39,67–70]. The sole exception was represented by the type

specimen of Nemegtomaia, which was collected from the fluvially-

dominated Nemegt Formation. Insufficient data are available at

present for the type specimen of Heyuannia huangi [68,71],

recovered from the? Maastrichtian Zhutian Formation in southern

China. However, this study suggests that Nemegtomaia is found in

the typical upper Baruungoyot Formation facies, in the Baruun-

goyot-Nemegt interfingering interval, and also in the Nemegt

Formation. Therefore, this study provides additional evidence that

both environments co-existed laterally, and that the generally

distinctive faunas from the two units do overlap as in the case of

Avimimus, Ingenia, Nemegtomaia, and Tarchia [30,33,36,72,73]. The

occurrence of a Nemegtomaia nest in this stratigraphic interval may

indicate that oviraptorid nesting grounds were chosen near

permanent or seasonal streams that provided soft and sandy

substrate as well as a source of food within an otherwise xeric

environment. The large number of adult oviraptorids found in

brooding positions may indicate that they brooded their clutches

for relatively long periods of time. This is similar to some present

day birds from arid regions of Africa and Australia (such as the

ostrich [Struthio camelus], the emu [Dromaius novahollandiae], and the

black-breasted buzzard [Hamirostra melanosternon]), which incubate

Figure 10. Eggs of Nemegtomaia barsboldi. Details of eggs preserved in the upper layer of eggs in specimen MPC-D 107/15. Scale bar A–E 5 cm.

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their brood for more than 40 days with limited food and water

supplies. In desert environments, thermal stress may be most

critical during reproduction, as the adult is restricted to the nest for

large portions of the day. Furthermore, eggs and nestlings are

particularly susceptible to thermal damage. Mechanisms allowing

successful incubation in extreme heat, such as a specific choice of

the nesting area, must have existed in the Late Cretaceous Gobi.

One suggestion for the appearance and evolution of rectrices in

oviraptorosaurs is as an adaptation to shade and protect eggs in

the nest [74,75].

The new specimens demonstrate that Nemegtomaia is similar to

derived ingeniine oviraptorids like Heyuannia, Ingenia and Machair-

asaurus in having a robust, relatively short manus with a robust

metacarpal I that had a powerful ungual. There are relatively few

oviraptorid specimens (eight) that have both femora and hands

preserved. Nevertheless, regression analysis of a suite of theropods

shows that the lengths of the second metacarpals in Citipati and

Khaan are close to what would be expected in a velociraptorine

dromaeosaurid, whereas the lengths of the metacarpi are reduced

in Ingenia and Nemegtomaia. The relative lengths of different

elements of the hand of ingeniines should be thought of in terms

of the relative shortening of the second digit rather than the

lengthening of the third metacarpal. During theropod evolution,

the first metacarpal becomes relatively shorter in relation to the

length of the second metacarpal. An ingeniine seems to have a

relatively long first metacarpal compared with the second

metacarpal, but this is not a reversal in the theropod trend

because it is accomplished in a different manner (through the

shortening of the second metacarpal rather than by increasing the

length of the first metacarpal). Nevertheless, there are changes in

the ingeniine metacarpal I in that it becomes relatively thicker to

support a more robust finger, and it expands to cover the

posteroventral surface of the second metacarpal at the proximal

end. This presumably immobilizes the metacarpus, and in the

holotype of Ingenia (MPC-D 100/30), this is taken a step further

through coossification of the semilunate carpal with the three

metacarpals. The phalanges in digit II also become relatively

shorter in comparison with the second metacarpal so that the

finger overall is also shortened. This presumably is associated with

a change in function, and may have something to do with the

presence of long remiges behind the forelimb that also attach to

the second manual digit. A similar trend of digital reduction

(especially in the ungual) can be found in Confuciusornis [76]. As the

second digit assumed the function of feather support, it reduced its

capability for using it as a grasping appendage. This function

seems to have been largely taken over by the first digit, which is

probably why it became more robust in the Ingeniinae. The size

reduction of the third finger is a logical consequence of the

feathered hand because it would be positioned above and behind

the feathers where it could not be used effectively for grasping.

Nemegtomaia barsboldi is the only member of the subfamily

Ingeniinae that is known to have a crest. Crestless skulls of other

ingeniines (Conchoraptor, Heyuannia and Khaan) are smaller than

either of the two skulls of Nemegtomaia, which makes it possible that

crest development is controlled by ontogeny or by absolute size.

The crests tend to be highly pneumatic, and the presence of

pneumatic nasals and frontals in at least Conchoraptor suggests that

they had the potential for inflating these bones into crests in larger,

more mature individuals. This taxon is known from the

Baruungoyot Formation, from which at least two specimens of

Nemegtomaia have been recovered. However, many skulls and

skeletons of Conchoraptor have been collected in recent years and

they are all of the same uniform small size. Their numbers, and the

fact that at least one of the Ingenia specimens (MPC-D 100/30) has

a coossified carpometacarpus, suggest that these animals probably

never became as large as Nemegtomaia.

Ingeniinae are characterized by having seven or eight vertebrae

incorporated into the synsacrum, whereas other oviraptorids have

only six vertebrae incorporated into the sacrum. Irrespective of

size, ingeniines have longer deltopectoral crests, more bowed ulnar

shafts, and shorter hands with more powerful first manual digits.

Conclusions

Nemegtomaia is the fourth genus of an oviraptorid dinosaur that has

been found on top of a nest, but is the first within the Ingeniinae

clade. Although the name means ‘‘good mother of Nemegt’’, it

received that name before there was any association between adults

and eggs. Although the phylogenetic analysis of Lu et al. [19] found

that Nemegtomaia was most closely related to the oviraptorine Citipati,

the recovery of additional specimens clearly shows it to be an

ingeniine oviraptorid. The hands of Ingeniinae genera are shorter

than those of oviraptorines, but have more robust first digits. The

more powerful claw on the first manual digit, the reduction in the

length of the second manual digit, and reduction in size of the third

finger are probably characters correlated with the presence of

rectrices on the forelimb of these oviraptorids that were possibly

used to protect the eggs in nests. Oviraptorid dinosaurs were one of

the most common types of animals in arid environments during

Late Cretaceous times of central Asia; nesting areas may have been

selected with respect to nearby channel systems.

Supporting Information

Table S1 Characters modified from, or added to, the

character list of Longrich et al. [11]. Additional data on for

caenagnathids as in [77] and for Heyuannia as in [78].

(DOC)

Table S2 Character description. Characters for phyloge-

netic analysis of the relationships among oviraptorosauria

(modified after Longrich et al. [11]).

(DOC)

Table S3 Character-taxon matrix.

(DOC)

Table S4 Selected measurements of oviraptorids. Se-

lected measurements of oviraptorids used for calculating the

lengths of missing elements in MPC-D 107/15 and MPC-D 107/

16. Measures in millimeters (PJC). Abbreviations: SL, skull length

(preferably from the edge of paraoccipital process to the tip of the

premaxilla, but in most cases taken from the quadrate to the

premaxilla); Pm1, premaxilla height (below naris); Pm2,

premaxilla height; Ao sl, antorbital skull length; o l, orbital

length; d, dentary length; d 2, dentary maximum height; j l, jaw

length; sc l, scapula blade length; sc sw, scapula shaft width; h l,

humerus length; h sw, humerus shaft width; r l, radius length; r

sw, radius shaft width; u l, ulna length; u sw, ulna shaft width;

mc I, metacarpal 1; mc II, metacarpal 2; mc III, metacarpal 3;

I-1, first digit, first phalanx; I-2, first digit, second phalanx; II-1,

second digit, first phalanx; II-2, second digit, second phalanx; II-

3, second digit, third phalanx; III-1, third digit, first phalanx; il l,

ilium length; f l, femur length; f sw, femur shaft width; f c, femur

shaft circumference; t l, tibia length; t sw, tibia shaft width; III-3,

digit three, third phalanx; IV-2, digit four, second phalanx; IV-3,

digit four, third phalanx; IV-4, digit four, fourth phalanx; IV-5,

digit four, fifth phalanx. Additional data on oviraptorid specimens:

Gigantoraptor erlianensis [79]; Hagryphus giganteus [80]; Heyuannia huangi

[81]; Oviraptor philoceratops [1]; Oviraptor incertae sedis [82].

(XLS)

New Specimens of Nemegtomaia from Mongolia

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Acknowledgments

MPC-D 107/15 was found on August 22, 2007 by Federico Fanti, and

excavated by the authors of this paper and a team from ‘‘Dinosaurs of the

Gobi’’ under what were at times difficult circumstances. The specimen was

prepared by Clive Coy (currently at the University of Alberta, Edmonton).

MPC-D 107/16 was found and collected on the following day (August 23)

by Nick Longrich. Specimens described in this paper were illustrated by

Marco Auditore, who also provided enlightening discussions on oviraptorid

anatomy. All necessary permits were obtained for the described field

studies from the Mongolian Government by the Paleontological Center of

the Mongolian Academy of Sciences, where the specimens are housed. No

additional specific permissions were required for locations or activities

related to this study. In particular, the location described is neither

privately-owned nor protected. This study did not involve endangered or

protected species.

Author Contributions

Analyzed the data: FF PJC DB. Wrote the paper: FF PJC DB.

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