An oviraptorosaur adult-egg association 
from the Cretaceous of Jiangxi Province, 
China
Authors: Xingsheng Jin, David J. Varricchio, Ashley 
W. Poust, & Tao He
This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of 
Vertebrate Paleontology on 2019-11-01, available online: https://
www.tandfonline.com/10.1080/02724634.2019.1739060.
Jin, Xingsheng, David J. Varricchio, Ashley W. Poust, and Tao He. “An Oviraptorosaur Adult-Egg 
Association from the Cretaceous of Jiangxi Province, China.” Journal of Vertebrate Paleontology 
39, no. 6 (November 2, 2019): e1739060. doi:10.1080/02724634.2019.1739060. 
Made available through Montana State University’s ScholarWorks 
scholarworks.montana.edu 
An oviraptorosaur adult-egg association from the
Cretaceous of Jiangxi Province, China
Xingsheng Jin , David J. Varricchio , Ashley W. Poust & Tao He
To cite this article: Xingsheng Jin , David J. Varricchio , Ashley W. Poust & Tao He (2019) An
oviraptorosaur adult-egg association from the Cretaceous of Jiangxi Province, China, Journal of
Vertebrate Paleontology, 39:6, e1739060, DOI: 10.1080/02724634.2019.1739060
To link to this article:  https://doi.org/10.1080/02724634.2019.1739060
ABSTRACT—With abundant well-preserved clutches and several adult-clutch associations, oviraptorids provide some of the 
most detailed information on reproduction for dinosaurs. Here, we describe an oviraptorosaur closely associated with two eggs 
from the Upper Cretaceous Nanxiong Formation of Jiangxi Province, China, and discuss its implications for various 
reproductive hypotheses. The specimen consists of a partial skeleton (gastralia, pelvis, portions of both hind limbs, and tail), 
with one egg within the pelvic canal and the other just posterior to it, ventral to the anterior caudal vertebrae. Several 
geopetal features indicate that the individual came to rest on its left side, with the eggs likely extruded during buildup of 
abdominal gases during decomposition. Similarity of pubis, caudal vertebrae, and pes dimensions to recently described 
material from the formation, e.g., Tongtianlong and Jiangxisaurus, suggests oviraptorid affinities. The specimen provides 
additional association of elongatoolithid eggs and the oogenus Macroolithus with oviraptorosaurs and further evidence for 
monoautochronic ovulation, i.e., iterative laying of two eggs at daily or greater intervals. With each egg 36–48% the size 
predicted for a modern bird of the same adult mass, total egg production would be slightly lower to similar between this 
non-avian maniraptoran and Neornithes. Histological tissues and open neurocentral sutures indicate that this reproductively 
active individual was several years old but still growing at the time of death, a pattern observed in other non-avian 
maniraptorans. The complete absence of medullary bone in this egg-bearing individual may challenge the identification of 
this tissue in other dinosaurs more distantly related to birds.
INTRODUCTION
The unusual occurrences of embryonic remains or eggs within adult skeletons provide important information about the repro-ductive 
mode (e.g., oviparity, viviparity) for extinct taxa (e.g., Caldwell and Lee, 2001; Zelenitsky et al., 2008; O’Keefe and Chiappe, 2011; Liu et 
al., 2017). They also can potentially furnish information on clutch size, neonate size relative to adult, reproductive output, sexual maturity, 
dimorphism, and female-specific histological tissues (e.g., Knell et al., 2011; Lü  et al., 2011; Cadena et al., 2018; Bailleul et al., 2019). A 
number of marine reptiles occur in association with embryonic remains within or adjacent to the adult skeleton. For example, ichthyo-
saurs described over a hundred years ago contain embryonic remains, demonstrating viviparity in this clade of fully marine rep-tiles 
(Pearce, 1846; Woodward, 1906; Liepmann, 1926). Speci-mens show embryos within the rib cage, partially extruded through 
the pelvic canal and outside the adult body cavity. Early interpretations suggested that death occurred during parturition 
 (Pearce, 1846), an interpretation also proposed by Motani et al. (2014) for a specimen of an early ichthyopterygian Chaohusaurus and 
suggested as a possibility for the mosasaur Carsosaurus (Caldwell and Lee, 2001). Caldwell and Lee (2001) based this conclusion on 
one perinate occurring outside the mother and two others posteriorly located within the abdomen. However, Liepmann (1926) and 
more recently Böttcher (1990) and McGowan (1991) suggested that the extrusion of embryos could have occurred postmortem due 
to either the internal buildup of gasses associated with decay within the adult or com-paction by overlying sediments.
Viviparity has been inferred for a variety of other marine rep-tiles based on similar specimens. A skeleton of the aquatic mosa-sauroid 
Carsosaurus preserves the remains of four embryos positioned with their skulls facing anteriorly (Caldwell and Lee, 2001). Their large size 
and fully formed bones indicate that they were born alive and tail first, as in modern cetaceans (Caldwell and Lee, 2001). The large, 
singular embryo associated with the plesiosaur Polycotylus is evidence of viviparity and a K-selected strategy similar to that of modern 
cetaceans (O’Keefe and Chiappe, 2011). Further, a specimen of the Triassic marine reptile Dinocephalosaurus with an enclosed embryo 
represents the first evidence of live birth in an archosauromorph (Liu et al., 2017). The occurrence of well-developed young associated 
with adults in other aquatic clades such as mesosaurs (Piñeiro
et al., 2012), choristoderes (Ji et al., 2010), and basal sauroptery-gians (Cheng et al., 2004) may support the frequent 
independent evolution of viviparity in aquatic forms. But see Motani et al.(2014) for a contrary view.
In contrast to these aquatic forms, preservation of terrestrial vertebrates with embryos or eggs within adults is much more 
uncommon. Two specimens of the turtle Adocus preserve eggs within the carapace, providing a definitive link between this taxon 
and specific egg forms or ootaxa (Zelenitsky et al., 2008; Knell et al., 2011). The occurrence of two eggs, one within and the other 
just posterior to the pelvis, in the pterosaur Kunpengop-terus permits the recognition of both cranial and pelvic dimorph-ism 
within the taxon and monoautochronic ovulation (Lü et al., 2011; Wang et al., 2015). Monoautochronic ovulation describes the 
condition in which each ovary ovulates a single egg simul-taneously, followed by a period of inactivity; this produces clutches 
consisting of an egg pair in a variety of extant lizards (Smith et al., 1973).
Despite occasional suggestions of viviparity in dinosaurs (Bakker, 1986; Mikhailov, 1997), no embryonic remains have ever 
been found associated with an adult that would support this speculation. However, three non-avian dinosaur specimens have been 
described with internal eggs. A scattering of some 13 small (6–10 mm diameter) spherical objects occur within and outside of the 
type specimen of Compsognathus from the Jurassic of Germany. Although lacking eggshell, Griffiths (1993) inter-preted these as 
eggs based on the presence of phosphorus and sulfur and their ventral occurrence along the skeleton. However, they may 
represent a product of decay and gas for-mation (Reisdorf and Wuttke, 2012) or mature ovarian follicles (O’Connor et al., 2013). 
Chen et al. (1998) describe a specimen of the closely related Sinosauropteryx as having two larger (37 × 26 mm) eggs preserved 
internally, potentially casting further doubt on the identification of the Compsognathus eggs. Neverthe-less, the largely two-
dimensional preservation in Sinosauropteryx and the absence of eggshell may challenge the identification of these features as eggs 
as well.
A pair of well-preserved eggs within the lower rib cage of a dinosaur from the Upper Cretaceous Nanxiong Formation of 
Jiangxi Province, China, permitted the association of the ootaxon Macroolithus yaotunensis with oviraptorosaurs (Sato et al., 
2005). As implied by Chen et al. (1998) for Sinosauropteryx, Sato et al. (2005) interpret the presence of two relatively large eggs as 
indicative of monoautochronic ovulation, as first hypoth-esized for oviraptorosaurs and troodontids based on within-clutch egg 
pairing (Varricchio et al., 1997). Based on their orientation within the pelvic region, Sato et al. (2005) consider the oviraptor-osaur 
eggs as laid pointed end first.
Recently, Zheng et al. (2013) described three basal birds from the Lower Cretaceous of China with aggregations of mature 
or nearly mature ovarian follicles. Each individual bird retains a single mass, suggesting the presence of only one 
functional ovary. Bailleul et al. (2019) described a Cretaceous enantior-nithine with an internal mass of eggshell 
interpreted as a crushed pathological egg. These specimens indicate that basal birds reached sexual maturity before 
skeletal maturity (Zheng et al., 2013; Bailleul et al., 2019).
Here, we describe a new specimen from the Cretaceous of Jiangxi Province, China, consisting of a partial 
oviraptorosaur skeleton closely associated with two elongatoolithid eggs. This specimen provides relevant information 
about the taphonomy of adults with associated eggs or embryos, monoautochronic ovu-lation and the rate of reproductive 
output in theropod dinosaurs, and taxon-ootaxon associations. Additionally, the specimen affords the opportunity to 
compare sexual versus somatic matur-ity and to examine a reproductively active (i.e., adult) dinosaur for the presence of 
medullary bone. Establishing osteological fea-tures such as bone texture or skeletal fusion that can be used
independently from histology to gauge somatic and/or sexual maturity remains an important research goal in better under-
standing taxonomy (Irmis, 2007; Bailleul et al., 2016; Hone et al., 2016).
Further, many modern birds produce medullary bone in antici-pation of egg laying. Females deposit this complex tissue within the 
cavities or medullary spaces associated with red bone marrow within their long bones as a mineral reserve utilized during egg formation 
(Werning, 2018; Canoville et al., 2019). Recently, this tissue has been reported from the dinosaurs Tyran-nosaurus rex, Allosaurus, 
Tenontosaurus, and Dysalotosaurus (Schweitzer et al., 2005; Lee and Werning, 2008; Hübner, 2012), enantiornithine birds (O’Connor et 
al., 2018;  Bailleul et al.,  2019), and possibly two pterosaurs (Chinsamy et al., 2009; Prond-vai and Stein, 2014). Schweitzer et al. 
(2016) also recently provide biochemical support for their earlier identification of medullary bone in the same T. rex individual. However, 
the purported medul-lary tissue in these archosaur examples remains problematic (Prondvai, 2017; O’Connor et al., 2018), because 
medullary-bone-like endosteal tissues can develop pathologically (Chinsamy and Tumarkin-Deratzian, 2009). We address maturity and 
medul-lary bone in this new egg-associated oviraptorosaur specimen through both gross examination and histological sampling.
Institutional Abbreviations—ES, Department of Earth Sciences, Montana State University, Bozeman, Montana, U.S.A.; 
IGM, Mongolian Institute for Geology, Ulaanbaatar, Mongolia; IVPP, Institute of Vertebrate Paleontology and Paleoanthropol-
ogy; MPC, Paleontological Center of the Mongolian Academy of Sciences, Ulaanbaatar, Mongolia; NMNS, National Museum of 
Natural Science, Taipei, Taiwan; ZMNH, Zhejiang Museum of Natural History, Hangzhou, Zhejiang, China.
MATERIALS AND METHODS
Geological Setting
The Zhejiang Museum of Natural History collected ZMNH M8829 in 2011 after its discovery during blasting by a construction 
crew in the western industrial area of Longling Town, Nankang City, Jiangxi Province, China. This specimen comes from the 
Upper Cretaceous Nanxiong Formation of the Ganzhou Basin near the city of Nankang, in the southern part of the Jiangxi Pro-
vince. This same formation has produced a wealth of oviraptorid material, including Shixinggia (Lü and Zhang, 2005), Banji (Xu and 
Han, 2010), Ganzhosaurus (Wang et al., 2013), Nankangia (Lü et al., 2013), Jiangxisaurus (Wei et al., 2013), Huanansaurus (Lü et 
al., 2015), and Tongtianlong (Lü et al., 2016) and Corythor-aptor (Lü et al., 2017), eggs with embryos (Wang et al., 2016), and a specimen 
with two internal eggs described by Sato et al. (2005).
The Cretaceous series of Jiangxi Province consists of widely distributed, red continental clastic material (Bureau of Geology and 
Mineral Resources of Zhejiang Province, 1989). The varie-gated sedimentary rocks of the stratigraphically lower Huoba-shan 
Group range from 1,500 to 2,700 m in thickness and contain lamellibranch bivalves and conchostracans. The overlying Ganzhou 
and uppermost Nanxiong formations are mainly brick-red clastic rocks, 2,400 to 8,900 m thick, that contain vertebrate fossils 
(Bureau of Geology and Mineral Resources of Zhejiang Province, 1989).
Although the stratigraphic orientation of ZMNH M8829 was not recorded in the field, the specimen includes several geopetal 
structures that indicate stratigraphic up and allow proper orien-tation. Further, preparation of the specimen at the museum assured the 
veracity of the skeleton-egg association. The speci-men consists of eggs and skeletal material preserved primarily within three blocks of 
red, very fine muddy sandstone (Fig. 1). All authors observed the specimen during preparation at the ZMNH.
FIGURE 1. ZMNH M8829, an oviraptorosaur preserved in association with two eggs preserved in three blocks. A, major block in right lateral view
containing portions of the pelvis and hind limb, tail, and two eggs. B, left pes in dorsal medial view with portions of the distal tibia and portion of the
gastral basket. Presence of portion of the distal pubis allows positioning of this block relative to the major block. C, major block as in A, but in left
lateral view. A portion of the internal egg is visible ventral to the ilium and anterior-most caudal vertebrae. Part of the external egg is visible more
posteriorly. D, block containing articulated right pes and distal tibia and fibula in posterior view. E, reconstruction of the skeleton in its hypothesized
original orientation in map view with right side up. Gray shading and stippling represents visible bone and eggs, respectively. Scale bars equal 10 cm.
Histology
Thin sections were prepared using standard paleohistological methods (e.g., Werning, 2012; Lamm, 2013). Samples 
were taken from the diaphysis of the right femur. Preservation precluded sampling at the exact midpoint of the diaphysis.
Approximately the distal half of the diaphysis is absent, and the specimen retains only a negative mold of this portion of 
the femur. The sample was removed from the section of preserved
bone closest to the midshaft, 13.5 cm from the proximal end. Although slightly proximal to the ideal sampling location, this area 
nonetheless lies outside the metaphyseal region.
The sample was embedded in Silmar-41 clear polyester resin (U.S. Composites). Slices were removed from the embedded block using a 
thin diamond blade Isomet low-speed saw (Buehler). Penetrant stabilizer (PaleoBond PB002) was added before premount grinding. 
Specimens were mounted using 2-ton epoxy (Devcon) and allowed to cure for 24 hours. Mounted slides were ground to optical clarity using 
increasingly fine paper from 120- to 1200-grit on the grinder/polisher.
Slides were examined and imaged using a D300 DSLR camera (Nikon) tethered to an Optophot2-Pol light transmission micro-scope. 
Filters permitted visualization of histological structures through enhanced birefringence. These included regular trans-mitted light 
(single polarizer), cross-polarized light, and ellipti-cally polarized light.
Bone tissue of ZMNH M8829 was further examined by inspect-ing postfossilization fracture surfaces of hind limb elements using a 20× 
hand lens and a low-angled light source. Magnification per-mitted observation of the medullary cavity, endosteal lamellar bone, secondary 
osteons, and vascular canals. Observations were made at 10.5, 13.5, and 25 cm from the proximal end of the 31 cm long right femur and 
sections 9 cm from the distal end of both tibiae.
Eggshell Analysis
Eggshell samples were removed from the two eggs, and half of each sample was prepared as a standard thin section (30 µm thick) using 
Epotek-301 as an embedding resin and Loctite Impruv 362 as the mounting adhesive and studied with a Nikon Eclipse polar-ized light 
microscope. Samples were taken from the middle sec-tions of both eggs, where lineartuberculate ornamentation predominates. 
Eggshell thin sections include ES 19, ES 474, and ES 475 from the internal egg and ES 369 and ES 528 from the external egg. The 
remaining half of each eggshell was coated with gold (10 nm), mounted on an aluminum stub, and imaged at 10–15 kV with a 
JEOL 6100 scanning electron microscope (SEM) or a J. R. Lee Instrument personal SEM. The same pro-cedures were followed for 
eggshell from an oviraptorosaur associ-ated with eggs (IGM 100/979), used for comparison.
Phylogenetic Analysis
We conducted an analysis to assess the phylogenetic position of ZMNH M8829 following the analysis of Lamanna et al. (2014). With 
the addition of ZMNH M8829, this matrix contains 42 oper-ational taxonomic units (OTUs) and 230 characters. It was ana-lyzed using 
TNT (Tree Analysis Using New Technology) version 1.1 Willi Hennig Society edition using the gui interface (Goloboff, 2008). A 
traditional search (tree bisection-reconnec-tion swapping algorithm, 1,000 replicates, a random seed of 1,000, and 10 trees saved per 
replication) yielded 2,320 most par-simonious trees of 511 steps each. The addition of ZMNH M8829 did not alter the fundamental 
relationships recovered by Lamanna et al. (2014).
To test whether the addition of postcranial characters would improve our confidence in the position of ZMNH M8829, we ran a separate 
analysis using the matrix of Funston and Currie (2016). This matrix is based on that of Lamanna et al. (2014), to which they added a 
number of new characters and removed the ordered condition of several more.
DESCRIPTION
Taphonomic Aspects
ZMNH M8829 consists of a partial oviraptorosaur skeleton that is closely associated with two elongatoolithid eggs preserved within 
three blocks of fine sandstone (Fig. 1). Preserved portions of the skeleton include an incomplete pelvis, a sacrum, a nearly complete caudal 
series, and portions of both hind limbs. These elements remain in articulation except for displacement of the proximal tail away from the 
sacrum and portions of bones lost to modern erosion or during collection. A small number of articu-lated gastralia are the only other 
skeletal elements representing the adult.
Several geopetal features (discussed below) indicate that the carcass originally rested on its left side (Fig. 2). The tail is strongly 
arched, curling up and over the pelvis such that the last caudal vertebra lies well forward of the ilia. The right femur is retracted 
relative to the right pubis (Fig. 1). The knee bends at a right angle so that the right crus extends posteriorly with the foot lying 
plantar side up (Fig. 1D, E). In contrast, the left leg remains more folded, with its femur slightly protracted and the foot pro-jecting 
anteriorly, plantar side down (Fig. 1B, E).
The remnants of the gastral basket lie distal to the left foot (Fig. 1B). These include a series of arched elements lying with their concave 
aspect facing dorsally, i.e., toward the body cavity. The more posterior elements lie close to the distal termination of the pubes, in an 
anatomically consistent position. However, more anteriorly, the gastralia flare away from where the body cavity would have lain (Fig. 1).
One of the two eggs remains within the pelvic canal as formed by the sacrum, remnants of left and right ilia and ischia, and the right 
pubis, the missing portions having been lost to erosion and during collection. The long axis of the egg parallels the sacrum, with the blunt 
end of the egg extending to the first chevron between the second and third caudal vertebrae. One small (6 mm wide by ca. 50 mm long), 
unidentified, elongate, and arched bone lies anatomically dorsal to this egg (Fig. 2C). The second egg is posteroventrally positioned relative 
to the pelvis, with its long axis perpendicular to the internal egg. The blunt end of the external egg lies just beneath caudal 7, with the 
remain-der extending below the chevrons associated with caudals 6 and 5.
Four geopetal features corroborate that the oviraptorosaur came to rest with its left side down (Fig. 2): (1) the right femur angles down 
(or toward the anatomical left) distally from its articulation with the acetabulum, and the remaining portions of the right limb all lie on a 
single horizontal plane (Fig. 2A); (2) the disarticulated proximal end of the tail lies below and to the left of the last sacral vertebrae, and the 
articulated caudal series extends slightly up and then down over the external egg before coming to rest on the same plane as the lower 
right leg; other elements, including the left tibia, fibula, and foot, and the gastra-lia, also lie on this same plane; (3) the egg within the pelvic 
region lies atop the left elements and away from those of the right side (Fig. 2C); and (4) the external egg exhibits asymmetric crushing, 
likely due to sediment loading, with a largely undamaged lower half and a more compressed and fractured upper half (Fig. 2B), an 
orientation pattern documented with other Cretaceous Chinese eggs (Wilson et al., 2014). Further, the distortion of the internal egg, as 
visible in its exposed cross-section, parallels the bedding plane interpreted for the specimen (Fig. 2C).
All bones are either in good condition with no evidence of weathering and scavenging or exhibit damage attributable to 
modern erosion and collection. The eggs, but not the bones, exhibit both internal and external blue-gray halos adjacent to the 
inner and outer surfaces of the eggshell. Inspection of the exposed broken portions of long bones with a 20× hand lens reveals 
simple hollow cross-sections, with no indication of medul-lary bone.
lacks a midline groove, giving the centrum an overall bean-
shaped cross-section (Fig. 2C). Two sacral ribs extend laterally
from the sides of the exposed vertebra, widening toward their
lateral contact with the ilia. An open line of suture, emphasized
by damage to the cortical bone, occurs where they join with the
sacral vertebra (Fig. 2C). The break, which lies anterior to the
attachments of these ribs, may have followed the growth plate
of the anterior face of the centrum. The last, largely obscured
sacral vertebra provides few morphological details, but its shape
conforms to that of the more anterior one in possessing a
convex ventral face, lacking a groove. The line of fusion
between the two vertebrae remains apparent.
A small, unidentified, boomerang-shaped bone about 65 mm
long lies against the ventral surface of the sacrum (Fig. 2C).
The bone curves at an oblique angle and maintains a fairly con-
sistent width of 7.5–10 mm throughout its length. An oval hole
in the upper side of this element appears taphonomic in origin.
Identification of this bone remains problematic; it may represent
a piece of rib, although the curve seems too abrupt to be the angle
of the rib. A gastralium also seems unlikely because the gastralia
in this specimen are much thinner and strut-like.
The tail is disarticulated from the sacrum, with the first caudal
vertebrae displaced dorsally by about 4 or 5 cm from the last
sacral. The well-preserved caudal series includes 26 vertebrae,
with perhaps the last few posterior vertebrae missing. This is con-
sistent with typical oviraptorid tails, which typically possess ca. 30
or fewer vertebrae (Barsbold et al., 2000; Persons et al., 2014).
Unfortunately, we cannot say with certainty whether the tip of
the tail possessed modified pygostyle-convergent vertebrae like
those of oviraptorosauroids such as Nomingia (Barsbold et al.,
2000), Anzu (Lamanna et al., 2014), Conchoraptor (Persons
et al., 2014), and Citipati (Persons et al., 2014). The high vertebral
count precludes a close resemblance to Nomingia, which has only
24 caudal vertebrae including the modified distal caudals (Bars-
bold et al., 2000). Pleurocoels are present on the lateral sides
until at least the 23rd vertebra. This is a much higher proportion
of pleuroceol-bearing caudals than the 11–18 reported for most
Oviraptorosauria (Osmólska et al., 2004). The position of the
pleurocoels in ZMNH M8829 resembles that of Jiangxisaurus
(Wei et al., 2013), although only the anterior nine caudals are pre-
served in the latter specimen. In contrast, only anterior caudals of
FIGURE 2. Features in ZMNHM8829 that provide geopetal information. Anzu possess pneumatic foramina.
A, posterior view of the major specimen block that shows the animal on its The centra of the caudal vertebrae range from large and rather
left side, with the right femur angling down from its articulation with the anteriorly square to slightly more rounded but of similar pro-
right iliac blade to ground level where the caudal vertebrae lie. The exter- portions in the smaller posterior vertebrae (Table S1 in Sup-
nal egg is visible ventral to the anterior caudal vertebrae and chevrons. B,
similar view as in A showing external egg ventral to the anterior caudal plemental Data). Transverse processes are present on at least
vertebrae and chevrons, which lie on their left side. Plane of compaction the first 20 caudal vertebrae. The lines of fusion between the
of egg (marked by the white arrowheads) parallels plane defined by the centra and the neural arches remain visible in all vertebrae.
tail. As typical for fossil eggs (Wilson et al., 2014), the stratigraphically This suture zigzags and arches over ca. 3 mm above the large
upper portion has been flattened in comparison with the more naturally central pleurocoel. All centra possess large pleurocoels posi-
curved down side. The angled femur is seen in the background, with the tioned laterally above the midline and below the line of suture
missing shaft marked by dotted lines. C, anterior view of pelvic canal with the neural arches (Fig. 3A, B). The pleurocoels of the first
showing the internal egg sitting along the left interior margin. The distor- and second caudal vertebrae show a rounder outline than those
tion to the normal circular cross-section of the egg also concurs with the of more distal caudals. The lateral pleurocoel of the first caudal
animal coming to rest left side down. A small, unidentified bone sits just
anatomically dorsal to the egg. Abbreviations: ee, external egg; f, femur; forms a nearly perfect circle nestled within a deeper excavation.
ib, iliac blade (right); ip, iliac peduncle; p, pubis (right); sv, sacral vertebra; The second caudal has a shorter, squared-off foramen with a
uid, unidentified bone. Scale bars equal 10 cm (A), 5 cm (B), and 3 cm (C). slightly longer ventral reach to its anterior edge. The first
caudal uniquely bears a second slit-like pleurocoel on the
lamina several millimeters in length, with the long axis oriented
dorsoventrally (Fig. 3A). The second caudal exhibits a shallow
Skeletal Anatomy depression in this same location.
The spinopostzygapophyseal laminae of the anterior caudals
Vertebral Column—The specimen preserves no vertebrae are stout and extend far posteriorly, thereby creating a deep
anterior to the sacrum, which consists only of the last two sacral central depression. The spinoprezygapophyseal laminae are simi-
vertebrae. The penultimate is broken anteriorly and revealed in larly stout, although they do not sweep quite as far forward as
transverse cross-section. The vertebral body is dorsoventrally their counterparts do posteriorly. However, they extend far
short, with a concave depression in the center of the dorsal enough forward to shelter a series of three to four small foramina
surface within the neural canal. The convex ventral surface on the neural spines. The thick, pyramidal neural spines are
FIGURE 3. Morphological features of oviraptorosaur ZMNH M8829. A, anterior caudal vertebrae in lateral view. Note the persistent neurocentral
sutures. B, mid-caudal vertebrae. C, right pubis in lateral view still articulated with peduncle of ilium. D, left pes in dorsomedial view. Abbreviations:
cv, caudal vertebra; ip, iliac peduncle; ns, neural spine; p, pubis; pf, pneumatic foramina; pre, prezygapophysis; post, postzygapophysis; sl, spinoprezy-
gapophyseal laminae; sut, suture. Scale bars equal 3 cm (A, B, D) and 5 cm (C).
highly pneumatized and largely reduced to a network of struts with a very thin cortical cover that is worn or absent in many 
cases. The anterior blade of the neural spine comes to a point and the zygapophyseal laminae rise dorsally nearly to the 
dorsal extent of the vertebrae, resulting in a pyramidal-shaped neural spine with a wide triangular lateral face. There appear to be 
several additional, pleurocoelous foramina in the vertebrae, variably expressed. Some of these may not fully penetrate the cor-tical 
layer and thus represent concavities.
The transverse processes of the anterior caudals are robust and triangular in anterior view, but rectangular and backward swept in 
ventral view. Two small openings along the backward sweep of the transverse process of the first caudal appear natural. The second 
and third caudals each preserve two small natural open-ings close to one another on the mid-ventral portion of the tri-angular face 
anterior to the transverse process.
The facets of the robust prezygapophyses are heart-shaped, with the point of the heart facing the neural canal. The larger 
upper lobe of the facet extends dorsally from the prezygapophy-sis, whereas the smaller lower lobe does not extend very far ven-
trally and only slightly anteriorly. The bottoms are slightly inclined medially. The postzygapophyses are only about half the 
length of the prezygapophyses, and their facets are more inclined.
ZMNH M8829 shares with all other oviraptorosaurs a tail that gradually transitions between proximal and distal caudals, lacking a 
distinct morphological demarcation (Osmólska et al., 2004). Where preserved, the sequentially smaller vertebrae have nor-mally 
positioned transverse processes projecting off of the central region of the neural arch directly above the single lateral pneumatic 
foramen.
Chevrons—The first caudal lacks a chevron, whereas chevrons in several other proximal vertebrae remain articulated. It remains 
unclear whether the absence of a chevron after the first caudal is anatomically or preservational. The fourth caudal also lacks a visible 
chevron. Those chevrons positioned behind the second and third caudals are visible on the animal’s left side. The chevron following 
the third caudal has been prepared so that it is also visible on the right side of the specimen, where chevrons following the fifth and 
sixth caudals are also present. The last of these are broken distally, but adequately preserved to demon-strate the contact between the 
external egg and the skeleton. Importantly, the most anterior chevrons differ in shape from those more posterior. The visible anterior 
chevrons are flattened mediolaterally, elongate, and possess a ventral head with two articular facets that contact the two centra (Figs. 
1A, 3A). In con-trast to the first chevron that is strongly concave anteriorly, chev-rons 2–5 display mild asymmetry that produces a 
slightly concave posterior aspect in lateral view (Fig. 1C). Additionally, in chevron 1, the angle between the proximal articular facets 
and the des-cending hemal spine is offset posteriorly, whereas in the following chevrons it rotates forward to be essentially straight 
(Fig. 1A). Another distinct difference is in the distal width of the ventral projection of the hemal spines. Unlike the finger-like 
projections found in most oviraptorosaurs (e.g., Balanoff and Norell, 2012), the distal ends of the proximal chevrons in ZMNH M8829 
expand to form an anteroposteriorly oriented blade. This blade
is widest in the fourth and fifth chevrons, which are damaged but nonetheless preserve a distal hemal spine twice the width of the narrowest 
portion. As in other oviraptorids (Osmólska et al., 2004), the posterior chevrons are dorsoventrally short and possess boot-shaped 
triangular profiles.
Gastralia—Several small bones lie among the left pedal pha-langes and to the medial side of the foot (Fig. 1B). We interpret these as 
posterior gastralia, only slightly removed from their expected position. They are all thin (∼3 mm diameter) and frac-tured at both ends at 
lengths ranging from 25 to >45 mm. They lack articular ends but exhibit a curvature consistent with gastra-lia. They are disarticulated, their 
long axes broadly aligned with their concave edges toward the belly of the animal and parallel to the orientation of the phalanges.
Pelvic Girdle—Both ilia and ischia are partially preserved and embedded in the matrix supporting the skeleton; the pubes lack most of 
their distal ends. The short remaining portions of the ilia exhibit fairly straight dorsal margins until the posterior-most ca. 5 cm where 
there is a sharp downward turn. The postacetabular blade appears quite robust and has a maximum mediolateral thick-ness of nearly 2 cm. 
The left side, however, preserves a strongly robust posterior edge that turns down sharply at almost 120°. The pubic peduncle of the 
right ilium remains in articulation with the proximal pubis. The peduncle is fairly narrow, although broken posteriorly, and only slightly 
thicker mediolaterally than the proximal pubis. The anterior ilium, including the cuppedicus fossa and the rest of the preacetabular 
process, is missing forward of the pubic peduncle. A small proximal portion of the pubic process of the right ischium remains in 
articulation with the pubis at the acetabulum. This does not include the shaft and does not extend far enough to preserve any portion of 
the obtura-tor foramen. The shaft of the right ischium, visible only in trans-verse cross-section, is slightly smaller than that of the pubis 
and strongly mediolaterally compressed.
Both pubes are preserved in articulation and surround the internal egg. The pubic shaft is strongly curved proximally as in some 
oviraptorids such as Nankangia (Lü et al., 2013) and Cor-ythoraptor (Lü et al., 2017) but straightens for the last three-quar-ters of its 
preserved length (Fig. 3C). The pubic shaft begins to flatten in its distal third, becoming laterally compressed and ante-roposteriorly broad 
toward the boot. If this represents the end of the shaft, then this condition is similar to that of Nomingia (Bars-bold et al., 2000). The overall 
shape of the pubis compares favor-ably with Khaan (Balanoff and Norell, 2012), but the distal curvature in Khaan is much greater than in 
ZMNH M8229.
Femur—The articulated right femur retains the proximal head and shaft and distal end separated by an impression of the distal 
diaphysis. The femur measures 31 cm in length and curves slightly posteriorly. The proximal end articulates with portions of the 
proximal pubis, pubic peduncle of the ilium, and a small part of the anterior curvature of the proximal ischium. A 2.8-cm section 
of the diaphysis remained in situ until sampled for his-tology (Fig. 4), and a 12-cm section is missing between this and the complete 
distal end (Figs. 1, 2A). The medial portion of this missing segment is preserved as a mold, allowing reliable measurements of 
total length and diameter and assessment of cur-vature. The diaphyseal diameter is 30.0 mm near the midshaft and remains constant along 
the length of the femur until widening in the last 40 mm to about 35 mm at the distal end. Although missing some cortical bone 
anterolaterally, the diameter of the epiphysis conforms to the end of the impression. Neither the bone nor impression shows evidence 
of a fourth trochanter.
The well-preserved proximal femur bears a distinct femoral head separated from the body of the femur by a clear neck. The 
anteroposteriorly compressed head appears less spherical than that of some other oviraptorosaurs, such as Gigantoraptor (Xu et al., 
2007) or  Khaan (Balanoff and Norell, 2012). In poster-olateral view, the broad greater trochanter has a smoothly curved
ventral extent. It is positioned lower than the femoral head and lacks any foramina. The lesser trochanter does not appear to extend above 
the line of the neck of the femur as in more basal coelurosaurs, e.g., Tyrannosaurus rex (Brochu, 2002). A very narrow fissure separates the 
greater trochanter from the medio-laterally thin and anteriorly strongly convex lesser trochanter. The ridge extending from the lesser 
trochanter down the anterior side of the femur is blade-like and recurved medially, forming a ‘J’ shape in proximal view.
The distal femur has a distinct though relatively shallow patellar groove, medial compared with its position in Gigantoraptor (Xu et al., 
2007). The strongly pronounced lateral epicondyle extends both distally and laterally beyond the body of the tibia. The smaller medial 
epicondyle projects mostly anteriorly, with a clear ridge running up the anteromedial surface of the distal femur. The medial surface of the 
distal femur is very flat and smooth. The inter-condylar groove is deep posteriorly, with an oval outline. Both the fibular and tibial condyles 
are slightly damaged; however, the incomplete cristatibiofibularis is prominent. A robust, blade-like crest extends proximally from the 
medial condyle.
Tibia, Fibula, and Tarsals—The proximal portions of both tibiae are missing, but the preserved distal portions remain in articulation 
with the feet. The medial malleolus extends distally ca. 0.5 cm farther than the lateral malleolus and appears medially flattened.
The fibula, where preserved distally, is reduced to a thin splint, only 1–1.5 mm thick, representing perhaps 1/15 to 1/20 of the 
anteroposterior width of the tibia. The fibula appears to extend fully to the base of the tibia to contact the tarsals, based on obser-vation of 
the right hind limb (Fig. 1D).
Both sets of proximal tarsals are articulated. The right and left astragali are visible in posterior view and in medial view, respect-ively. 
The tall ascending process of the left astragalus extends at least 80 mm above the articular surface of the ankle. The proximal tarsals of 
the right foot appear unfused and slightly separated by a thin layer of matrix, but further details of the calcaneum are obscured by 
matrix.
Metatarsals and Phalanges—Both left and right pes are well preserved, although some elements of the right pes are eroded. The more 
complete left pes preserves metatarsals I–IV with all phalanges of the four digits articulated and visible along their complete lengths. The 
right metatarsal I (MT I) is medially expanded to a scalloped edge, a feature more irregular than in other known oviraptorosaur feet, 
including those of Ganzhosaurus (Wang et al., 2013) and Khaan (Balanoff and Norell, 2012). The left MT I also has a pronounced 
anterodistal expansion but is incompletely preserved. The distal articular surface of MT I is large, triangular in dorsal view, and extends far 
back on the shaft, implying a great degree of poss-ible extension at the phalangeal joint. Metatarsals II–IV (MTs II–IV) appear relatively 
shorter than in other oviraptorids (Table S2), although an accurate comparison with the complete tibia length remains impossible. MTs II 
and IV are robust and broad in comparison with that of the narrower MT III, which is only 5 mm wide at its proximal end, as opposed to 
MT II, which measures 18 mm wide at its proximal end. Metatarsals II–IV exhibit similar lengths, with MT III marginally the longest and 
MT IV only a few millimeters longer than MT II. The distal heads of MTs II and IV are hemispherical in lateral and medial views, 
respectively. The articular surfaces of the distal condyles extend onto the medial portion of MT II and the lateral portion of MT IV. In 
contrast, the fairly flat articular surface of MT III is nearly twice as mediolaterally wide as those of the other two metatarsals and is 
confined to the distal end of the bone, with only a minor medial depression. Although the plantar surface remains partially obscured by 
matrix, the distal articulation of MT III appears weakly ginglymoid. The lateral ligament fovea at the distal end of MT III exhibits a 
diameter more than twice that of MT II.
FIGURE 4. Osteohistology of oviraptorosaur ZMNH M8829. A, cross-section of mid-diaphysis of femur. Boxes indicate positions of detailed photo-
graphs in B–E. B, detail of A showing bone degradation at medial apex; note remnants of secondary osteons (circled). C, anterolateral detail of A
showing primary cortical tissue; exterior to upper left; note three LAGs (arrows); second LAG is diffuse, indicated by bracket. D, same as C but
taken through first order retardation plate (¼ lambda tint plate). E, posterior detail of A under elliptically polarized light. Note differing birefringence
of lamellar endosteal bone on interior of cortex (thick arrow). Scale bars equal 5 mm (A) and 1 mm (B–E).
MT V is fractured and retains few discernible details. The break exposes cancellous bone proximal to a small, open medullary 
cavity. The gracile element is only 4 mm wide, and its length is less than one-third that of MT IV.
The phalangeal formula of 2-3-4-5 corresponds to the typical theropod condition. The relatively long phalanges are more 
gracile than in other taxa, such as Wulatelong (Xu et al., 2013). The large pedal unguals are only slightly curved, but more so 
than in Heyuannia (Lü, 2002), Khaan (Balanoff and Norell, 2012), and Anzu (Lamanna et al., 2014). 
The dorsoventrally shallow unguals also differ from Anzu, which has a deep, short ungual morphology similar to that in 
Gigantoraptor (Xu et al., 2007). In contrast to the distinct dorsal and ventral blood grooves of Gigantoraptor, the unguals 
of ZMNH M8829 possess a single groove with a broader surface, deepening distally. The second ungual slightly exceeds the 
others in size but is not sub-stantially larger as in Deinonychosauria. This mild enlargement of the second digit may help 
distinguish this taxon from Khaan,
for which Balanoff and Norell (2012) found no evidence of ungual over most of its length that becomes more nodose at the pole. A
size difference. fracture exposes the egg in transverse cross-sectional view where
Histology—The uncrushed right femur retains the original it measures 90 mm in diameter in a horizontal plane and 47.7 mm
dimensions of the shaft with a rounded, triangular cross-section. vertically. This suggests a significant amount of compaction. The
Calcite-filled cracks are present around the circumference of eggshell thickness varies from 595 to 1245 µm depending on
the bone and predominately extend radially, with the exception height of the ornamentation and the individual sample. Radial
of one large fracture that breaks through the cortex on the thin sections and SEM imaging of ES 319 reveal two structural
lateral side to run circumferentially along the endosteal surface layers of calcite, a 519-µm-thick mammillary layer (ML) and a
(Fig. 4A). Oxidized sediment indistinguishable from the country 670-µm-thick continuous layer (CL), with a ML:CL ratio of
rock fills the medullary cavity. Clasts of up to a 2 mm are inter- 1:1.3 (Fig. 5A–C). A relatively straight (rather than undulating)
mixed with the infilling matrix. No clear sedimentary structures contact separates the two layers. The inner mammillary layer con-
are visible, although there does appear to be a preferential orien- sists of narrow, closely packed, elongate mammillary cones that
tation of linear clasts in a band extending from the anteromedial average about 127–225 µm in diameter (Fig. 5D). The radiating
to the posterolateral side of the medullary cavity. In a few places, crystallites that constitute the cones originate from nucleation
especially medially, the calcite-filled cracks appear to continue sites at the inner surface of the eggshell. These calcite nuclei
into the matrix. No cancellous bone is present (Fig. 4A). Through- are typically intact and well preserved (Fig. 5D), although some
out the cortex, sections of bone show evidence of taphonomic eggshells show pressure dissolution that likely results from
alteration. In these areas, the bone appears darker in color, is contact with quartz grains in the surrounding matrix. Approxi-
largely opaque, and lacks birefringence and details of osteocyte mately 250 µm above the nucleation sites, the radiating spheru-
lacunae, canaliculi, and even osteons (Fig. 4B). Other authors lites of the mammillae are no longer apparent and the
have attributed similar patterns of alteration to the activity of bac- crystalline structure displays a blocky appearance (sensu Jin
teria or fungi (e.g., Werning, 2012). This renders parts of the bone et al., 2007) (Fig. 1A, B, D). The overlying continuous layer exhi-
difficult to interpret. Intriguingly, the degradation appears more bits horizontal or gently undulating accretion lines that weakly
prevalent in the areas with the most secondary osteons (Fig. 4B). follow the ornamentation. Some eggshell samples (ES 475 2A)
Bone deposition appears uniform, with little secular change show greater calcite recrystallization, as well as delamination of
radially from the endosteal to the periosteal surface. The pattern the surface ornamentation (Fig. 5E). Thin sections viewed
of vascularization is laminar/subplexiform throughout, with most under crossed Nicols exhibit sweeping extinction in less altered
of the primary osteons longitudinally oriented and confined to cir- areas of the eggshell. A tangential section shows round to sub-
cumferentially arrangedbands (Fig. 4C–E). Themajority of visible rounded pores that measure 12–26 µm in diameter. Alteration
Volkmann’s canals extend circumferentially between these of the eggshell prohibits confident identification of all pores and
primary osteons, rather than anastomosing radially. The highly therefore prevents accurate assessment of pore density.
laminar organization of the cortical vascularization suggests rela- External Egg—The asymmetric external egg measures 190 mm
tively high growth rates (Castanet et al., 1996). The cortex consists long. Crushing created an irregular plane of fractures paralleling
predominantly offibrolamellar tissue,withminimalwoven-fibered the plane containing the series of caudal vertebrae. As with the
bone. Secondary osteons are concentrated mostly in the medial, internal egg, linear ridges of the ornamentation align with the long
posterior, and anterior regions, consistent with muscles attaching axis of the egg. The 1,091-µm-thick eggshell (ES 369) exhibits two
in these directions (Currey, 2002). These same areas are the structural layers: a 456-µm-thick mammillary and a 635-µm-thick
most altered, possibly from bacterial or fungal invasion, and there- continuous layer (Fig. 6A). The mammillary cones are ca. 120–215
fore difficult to characterize. Nevertheless, the circular outlines of µm wide, and the calcite nuclei are typically absent. The contact
the secondary Haversian systems remain visible in some areas. between themammillaryand thecontinuous layer appears relatively
Three lines of arrested growth (LAGs) occur within the exist- distinct and straight to slightly undulating. In scanning electron
ing cortical bone. The middle LAG is composed of two to three photomicrographs, prominent radiating crystals are visible in the
closely spaced annuli and an additional annulus slightly offset basal part of the mammillary cones and the contact with the over-
endosteally to the others (Fig. 4C, D). The innermost LAG is a lying continuous layer is less apparent than in standard thin sections
double LAG, with two lines distinguishable in parts of the (Fig. 6B). In someareas, ‘lenses’of blocky crystals occur in the upper
bone’s circumference. The fibrolamellar bone continues evenly portionof themammillary layer, and these features exhibit relatively
to the periosteal surface where there is no evidence of an external distinct boundaries, similar to that of the ML-CL contact (Fig. 6A).
fundamental system or other signals of cessation of radial growth. Eggshell thickness and proportions of the mammillary and continu-
The inner surface of the cortex of M8229 does not preserve ous layers differ among eggshell samples, likely due to differences in
continuous, finished, lamellar endosteal bone. Small amounts of sample location on the egg, eggshell alteration, and greater weather-
endosteal bone occur in isolated packets, some of which (e.g., ing of some fragments.
on the posterior lateral side of the medullary cavity) show moder- Comparisons—The internal and external eggs in ZMNH
ate thickness and extent. Under elliptically polarized light, the M8829 exhibit similar eggshell thickness and microstructure,
remnant endosteal bone is visibly parallel-fibered, with a lamellar with a ML:CL ratio of 1:1.3 to 1:1.4. The eggs are referable to
organization of the collagen fibers (Fig. 4E). Where preserved, the Elongatoolithidae on the basis of their elongate shape, two-
the inner surface of this tissue is rough, irregular, and cuts layered eggshell structure, narrow and closely spaced mammillae,
across the lamellae. Distinguishing between the possible origins lack of visible prisms in the continuous layer, and lineartubercu-
of this eroded inner surface remains problematic, but it may late, nodose, and dispersituberculate ornamentation (Zhao,
simply be a product of medullary cavity drift. Few, if any, 1975; Mikhailov, 1991, 1997).
erosion rooms are present in the inner cortex, and in at least The Elongatoolithidae includes the oogeneraMacroelongatoo-
one place the endosteal edge cuts across some secondary Haver- lithus, Elongatoolithus, Trachoolithus, Macroolithus, and Nanh-
sian systems. There is no medullary bone present. siungoolithus (Mikhailov, 1997). Eggs of the last oogenus are
rare and the eggshell structure inadequately illustrated (Mikhai-
Eggs and Eggshell Microstructure lov, 1997). Egg size largely distinguishes the remaining fouroogenera from each other. Macroelongatoolithus vary from
Internal Egg—Neither egg is adequately exposed to provide a about 25 to over 50 cm in length, thus excluding the eggs of
complete set of measurements nor a full examination of ornamen- ZMNH M8829 from this oogenus. Elongatoolithus and Trachoo-
tation. The internal egg exhibits lineartuberculate ornamentation lithus are less than 17 cm, whereas the diagnosis forMacroolithus
FIGURE 5. Structure of internal egg from ZMNH M8829. A, eggshell in radial thin section under plane-polarized light. B, same as A under crossed
Nicols. C, SEM of eggshell from same egg. D, enlargement of mammillary cones in A; arrow indicates intact nuclei. E, eggshell (ES 475) showing dela-
mination of the surface ornamentation; fracture extends across entire eggshell thickness. Outer eggshell surface is at the top of each image.White bars in
A, B, and E indicate contact between the mammillary and continuous layers; gray bar in C indicates same. Scale bars equal 1 mm (A–C, E) and 500 µm
(D).
indicates that they range from 16.5 to 21 cm in length (Zhao, 1975; Elongatoolithid eggs directly associated with oviraptorosaur
Carpenter, 1999). The 19 cm length of the external egg of adults and embryos represent several ootaxa, including Elonga-
ZMNH M8829, together with the typical elongatoolithid micro- toolithus, Macroolithus, and Macroelongatoolithus (e.g., Dong
structure, suggests that the eggs likely belong to the oogenus and Currie, 1996; Clark et al., 1999; Sato et al., 2005; Grellet-
Macroolithus. Tinner et al., 2006; Weishampel et al., 2008; Wang et al., 2016;
FIGURE 6. Structure of external egg from ZMNHM8829.A, eggshell in radial thin section under plane-polarized light. Arrow points to blocky crystal
lens in the upper mammillary layer. White bar indicates contact between the mammillary and continuous layers.B, SEM image of same. Note prominent
calcite spherulites of the lower mammillary layer, compared with more altered structure in the upper portion of the same layer. Scale bars equal 1 mm.
Pu et al., 2017), See Simon et al. (2019) for a review of these eggs preservation. The pes provides the best comparisons: ZMNH
associated with embryonic or adult skeletal material. The eggs M8829 shares a proximally compressed MT III with Wulatelong,
preserved in ZMNH M8829 compare most favorably with those a feature also present in Khaan (Balanoff and Norell, 2012) and
associated with IGM 100/979, an adult Citipati osmolskae that purportedly shared with stem oviraptorosaurs (Xu et al., 2013).
overlies an unhatched egg clutch (Clark et al., 1999), and However, the feet of ZMNH M8829 have an MT II and an MT
others, both from the Nanxiong Formation, potentially assigned IV equal in size, unlike in Wulatelong where MT II is smaller.
to Macroolithus yaotunensis (Sato et al., 2005; Wang et al., ZMNH M8829 shares a straight pubic shaft with caenagnathids
2016). Sato et al. (2005) described an adult oviraptorosaur with such as Anzu (Lamanna et al., 2014). Although incomplete, the
two elongatoolithid eggs within the body region and noted simi- remaining portions of the pubis distinguish the specimen some-
larities between their specimen and M. yaotunensis. Similarly, what from a previous oviraptorosaur discovered with eggs
Wang et al. (2016) more recently described eggs with embryos (NMNS VPDINO-2002-0901; Sato et al., 2005) from the Nan-
and also considered them to be similar to M. yaotunensis. All of xiong Formation, which has an anteriorly curving pubic shaft
these eggs, including those of ZMNH M8829, are 17–19 cm with a more distal inflection point and a relatively larger diameter
long and have eggshell thicknesses of ca. 1.0–1.2 mm (Table 1). than ZMNH M8829.
The possible M. yaotunensis eggs (Sato et al., 2005) also have Themorphology of the pubis, the caudal vertebrae, and the rela-
the closest ML:CL ratio, 1:2, to the 1:1.4 ratio of ZMNH tive dimensions of the pes compare well with material from the
M8829. Our measurements of eggshell from Citipati eggshell, recently identified cloud of oviraptorids from the Nanxiong For-
IGM 100/979, yield mammillary and continuous layer thicknesses mation of Jiangxi and Guangdong provinces. These similarities
of 357 and 613 µm, respectively, with total shell thickness of 970 suggest oviraptorid affinities, consistent with the abundance of
µm. The ML:Cl of 1:1.7 of this eggshell is somewhat higher than the clade in the Upper Cretaceous of southern China. The
in ZMNH M8829. However, Grellet-Tinner et al. (2006) discuss absence of cranial features prohibits a more definitive assessment.
several eggs associated with adult oviraptorosaurs (IGM 100/ Phylogenetic analysis recovered ZMNH M8829 as the sister
979, IGM 100/1004, and IGM 100/1125), including the Citipati taxon to the Caenagnathoidea, a group composed of Caenag-
specimen. They report thinner eggshell ranging from 500 to 641 nathidae and Oviraptoridae. However, the incompleteness of
µm, with a 169-µm-thick mammillary and a 402-µm-thick continu- the specimen and the distribution of the missing data (i.e.,
ous layer. The thicknesses of these oviraptorosaur eggshells are absence of cranial or forelimb material) likely contribute to the
less, whereas the ML:CL ratio (1:2.4) exceeds that of eggs from placement of this specimen in an earlier-diverging position. In
ZMNH M8829. Other eggs containing oviraptorosaur embryonic the Lamanna et al. (2014) matrix, 60% of the characters
remains are more difficult to compare with ZMNH M8829 concern cranial and mandibular elements. Fewer than one-
because of the incomplete nature of the specimens and therefore quarter correspond to elements present in ZMNH M8829 and
the absence of original egg length (Norell et al., 1994; Weisham- not all of these are visible for scoring. If the condition of hind
pel et al., 2008). Overall, the eggs most similar to those of ZMNH limb and caudal characters in ZMNHM8829 are relatively plesio-
M8829 also come from the Upper Cretaceous Nanxiong For- morphic, this may generate a suspect basal position in the phylo-
mation of Jiangxi, China, and are likely assignable to geny. Refinement of the oviraptorosaurian phylogeny may test
M. yaotunensis. this possibility, especially with the inclusion of more postcranial
characters. Using the matrix of Funston and Currie (2016) did
not result in a clearer position for the specimen. Rather, a strict
DISCUSSION consensus resulted in a collapse of Caenagnathidae into a poly-
Taxonomic Placement tomy that includes ZMNH M8829. As to why this tree resultedin the collapse of the clade, we do not speculate but note that
Preservation of only the posterior half of ZMNH M8829 com- many of the characters record autapomorphies in Elmisaurus or
plicates taxonomic identification. The newly named Tongtianlong a small number of allied Caenagnathids.
is poorly preserved behind the pectoral girdle due to damage
during collection (Lü et al., 2016). The holotype includes a pes
similar to ZMNH M8829 in almost all respects and shares the Taphonomy
concave shape of the distal astragalus. Only a few elements The posture of the skeleton and the close position of the eggs in
overlap with the recently named Jiangxisaurus (Wei et al., ZMNHM8829 suggest that the eggs belong to the associated indi-
2013), including proximal caudals in ventral view and unde- vidual. The skeleton retains a pose common to many Mesozoic
scribed fragmentary pelvic remains. Both taxa share short, wide theropods, lying on its side with recurved tail over the back and
proximal caudal vertebrae with dorsally located pleurocoels, fea- splayed hind limbs. This specimen may fit the opisthotonic
tures common to oviraptorosauria and not diagnostic. Conse- posture of Faux and Padian (2007). This posture, combined with
quently, the overlapping elements do not preclude the two the high degree of articulation, suggests an absence of hydraulic
specimens from being the same taxon. Other Nanxiong oviraptor- modification. The position of the two complete eggs, one within
ids, including Huanansaurus (Lü et al., 2015) and Banji (Xu and the pelvic canal and the other just posterior to it near the presumed
Han, 2010), share little to no overlapping material with ZMNH cloaca and draped in part by the proximal chevrons, argues
M8829. More comprehensive comparisons, therefore, must strongly that they belong to the adult and were neither consumed
await the fuller description of these elements or new discoveries nor washed in. A specimen of the pterosaur Kunpengopterus
of oviraptorids from Jiangxi Province. retains two eggs in nearly the same arrangement (Wang et al.,
Other described oviraptorosaurs share more overlapping 2015). Further, the arrangement of the eggs relative to the skeleton
material, facilitating better comparisons. Femoral and caudal parallels the occurrence of young that lie partially exiting and
anatomy is similar to that of Nankangia (Lü et al., 2013), but external to adult ichthyosaurs and othermarine reptiles (Böttcher,
ZMNH M8829 lacks the distinctive infraprezygapophyseal fossa 1990; McGowan, 1991; Motani et al., 2014). The adult may have
present on the lateral surface of the anterior caudals of this perished just after laying one egg, but more likely the eggs were
taxon. The large process of the lesser trochanter has a more partially to fully extruded by postmortem gases associated with
blade-like shape than the ‘finger-like’ trochanter of Nankangia. internal decay built up inside the coelom. We have observed
Only cranial features provide diagnostic characters for Wulate- similar extrusion of young in a drowned, pregnant cow (Fig. 7).
long (Xu et al., 2013), and comparison with the postcrania of This same process has been hypothesized as the cause of the full
this skeleton is difficult due to its generally poor state of and partial expulsion of ichthyosaur young from Holzmaden
TABLE 1. Comparison of some eggs and eggshell associated with adult or embryonic oviraptorosaurs.
Egg Eggshell
Specimen length thickness Mammillary Continuous ML:
Taxon or ootaxon Specimen number (cm) (µm) layer (ML) (µm) layer (CL) (µm) CL Source and reference
Oviraptorosaur Adult; ZMNH M8829- — 1245 1193– 506 739 1:1.3 This paper
internal egg A (ES 475) 1245
Oviraptorosaur Adult; ZMNH M8829- 19 1022 209 813 1:1.4 This paper
external B (ES 369,
egg 528)
Citipati osmolskae Adult with IGM 100/979 18–19 970 357 613 1:1.7 Measured from thin
eggs sections, Clark et al.
(1999), Barta (2014)
Oviraptorosaur Adult with NMNS 17.5 988–1270 190–250 798–1020 1.2 Sato et al. (2005)
(Macroolithus eggs VPDINO-
yaotunensis)* 2002-0901
Oviraptor Adult with IVPP V9608 15 737 204 533 1:2.6 Dong and Currie (1996)
philoceratops* eggs
Oviraptorid Egg with IGM 100/971 — 920 198 724 1:3.7 Norell et al. (1994);
embryo measured from thin
sections, Barta (2014)
Oviraptorid Misc. Unspecified — 500–641 169 402 1:2.4 Grellet-Tinner et al.
specimens IGM (2006)
specimens
Oviraptorid Eggs with MPC-D100/1017 — 730–1000 190–330 540–670 1:2 to Weishampel et al.
embryo 1:3 (2008)
Cf. M. yaotunensis Eggs with IVPP V20184 16.4–18 1200–1760 240–440 960–1320 1:3 to Wang et al. (2016)
embryo 1:4
*Measurements from published figure.
adult specimens (Böttcher, 1990; McGowen, 1991). The displaced Reproductive Implications
anterior portion of the gastral basket likely also reflects the disten-
sion and rupture of the abdominal cavity, consistent with decay- Monoautochronic ovulation, the production of one egg from
associated carcass bloat. Alternative interpretations, e.g., that each ovary and oviduct simultaneously at daily or greater inter-
the external egg is associated merely by chance with the adult, vals (Smith et al., 1973), was hypothesized to represent an inter-
seem unlikely. Nor does it appear that the external egg belongs mediate step between more primitive en masse laying from two
to a previously existing clutch, because it lacks a close neighbor reproductive tracts and the iterative laying of a single egg from
as typically found in the elaborate tight rings of oviraptorosaur a single functional ovary and oviduct in birds (Varricchio et al.,
clutches (Clark et al., 1999) and there are no signs of any additional 1997). Non-avian maniraptorans would iteratively produce two
eggs in the three blocks. eggs from two avian-like reproductive tracts (Varricchio et al.,
One small isolated bone exists within the pelvic canal in a pos- 1997). First hypothesized for oviraptorosaurs and troodontids
ition anatomically dorsal to the egg. This element may simply rep- by Varricchio et al. (1997) based on within-clutch egg pairing,
resent a displaced sacral or posterior dorsal rib. However, the monoautochronic ovulation was later supported by the presence
overall shape seems inconsistent with both. Potentially, this of two eggs within the rib cage of an oviraptorosaur (Sato et al.,
bone may represent a digested element that, like the egg, was 2005). The presence of two eggs with a similar level of develop-
being forced out of the body by the buildup of internal gases, ment in ZMNH M8829 provides further support for monoauto-
because the large intestine would lie just dorsal to the reproduc- chronic ovulation. The narrow fit of the egg in the pelvic canal
tive tract before converging in the cloaca. argues against the hypothesis that theropods laid eggs in boundpairs (Li et al., 1995; Larson, 1998).
The iterative style of laying resulting from monoautochronic
ovulation may have allowed production of larger eggs relative
to adult body mass, because birds produce far larger eggs relative
to adult mass than reptiles (Blueweiss et al., 1978). The overall
size of the eggs in this oviraptorosaur, relative to the adult
mass, is consistent with hypothesis. Using the egg dimensions
(190 mm long with cross-section 47.7 × 90 mm) and the equation
of Hoyt (1979), the estimated egg mass is 500 g. Based upon the
femur circumference with diameters of 31.2 mm and 33.4 mm and
the equations of Anderson et al. (1985) and Campione et al.
(2014), adult weight is estimated at 47.4 kg or 69.7 kg, respect-
ively. By the equation of Blueweiss et al. (1978), birds of these
adult masses are predicted to produce a single egg weighing
1,040 or 1,390 g. Thus, as noted by Varricchio and Jackson
(2004), the iterative production of two eggs by these Mesozoic
maniraptorans is on par with the reproductive output of extant
birds as measured by net weight.
FIGURE 7. Extrusion of calf out of drowned cow along Yellowstone The two internal eggs described by Sato et al. (2005) in another
River, Montana. Jiangxi oviraptorosaur are oriented with their narrow end
pointing toward the pelvic canal. This orientation concurs with Regardless of the reason for its absence in this specimen, 
egg formation in modern birds, where the pointed end is caudad caution is required in using ‘medullary bone’ or its absence as a 
(Olsen and Byerly, 1932; Gill, 1989; Salamon and Kent, 2014). gender indicator in dinosaurs (Chinsamy and Barrett, 1997; Chin-
Although some evidence suggests that there is a 180°rotation an samy and Tumarkin-Deratzian, 2009). [Note: Isles (2009) and 
hour prior to laying to reorient the egg into a blunt-end-first Werner and Griebeler (2013) erroneously cite Varricchio et al.
position (Bradfield, 1951), most birds appear to lay their eggs (2008) as using the absence of medullary bone as indicator of 
pointed end first (Olsen and Byerly, 1932; Wood-Gush and sex.] Because oviraptorosaurs are more closely related to birds 
Gilbert, 1969; Salamon and Kent, 2014). In contrast, the two eggs than the three dinosaurs with supposed medullary bone, the 
associated with ZMNH M8829 sit having exited or about to exit absence of this tissue in a clearly reproductively active individual 
the cloaca blunt end first. This blunt-end-out arrangement may may challenge the avian homology of medullary tissue in these 
simply reflect the postmortem extrusion of the oviraptorosaur more distantly related specimens unassociated with eggs or 
eggs prior to their rotation into a pointed-end-posterior position young and supports the more cautious approach to the interpret-
and would therefore lack biological rel-evance. Alternatively, it ation of medullary-like bone as advocated by both Prondvai 
may represent either egg rotation or for-mation of the egg blunt (2017) and O’Connor et al. (2018). An adult pterosaur, also 
end posterior, both of which have been observed in some modern associated with two eggs, similarly lacks medullary bone (Wang 
domestic fowl (Olsen and Byerly, 1932; Bradfield, 1951). If et al., 2015).
biologically significant, the orientation in ZMNH M8829 would 
require greater manipulation of the eggs in order to form a typical 
oviraptorosaur clutch in which the narrow end of the egg points Sexual Dimorphism
down and away from the clutch center. The preservation of caudal chevrons in a known female dino-
saur sheds light on the possibility of sexual dimorphism in these 
Medullary Bone elements. Past authors have occasionally sought to distinguish the 
Medullary bone in modern birds serves as a calcium store sexes of archosaurs on the basis of the size of the first chevron, 
during eggshell formation, and this bone tissue may persist days although Erickson et al. (2005) were subsequently unable to find 
to weeks after oviposition (Simkiss, 1967; Chinsamy and Tumar- support for this method in Alligator. The specimen, ZMNH 
kin-Deratzian, 2009; Werning, 2018; Canoville et al., 2019). The M8829, represents the first known female with articulated 
thickness and fully formed nature of the oviraptorosaur eggshell chevrons, but it possesses a first chevron fully as long as the 
suggests that death occurred just prior to egg laying. The ZMNH second, indicating that reduced chevron size is not necessary for 
M8829 adult was clearly reproductively active at the time of its egg laying in oviraptorosaurs. The posteriorly inclined hemal spine 
death and consequently would represent a likely candidate to seen in the first chevron of ZMNH M8829 is intriguing, but with 
exhibit medullary bone, as proposed to exist in several other only one specimen we cannot rule out the presence of this 
dino-saurs (Schweitzer et al., 2005, 2016; Lee and Werning, 2008; character in all individuals.
Hübner, 2012). However, we observed no trabeculae or other A different example of possible sexual dimorphism in ovirap-
medullary bone during the visual inspection of the available torids was recently reported in specimens of Khaan mckennai 
cross-sections of the right femur and tibiae. Thin sections of the (Persons et al., 2015). The case rests on the difference in hemal 
right femur also show an absence of such large-scale features (Fig. spine morphology between two otherwise very similar specimens. 
4A). Where preserved, intact, poorly vascularized, lamellar Whereas one (MPC-D 100/1127) has simple, finger-like hemal 
endosteal tissues or fibrolamellar bone marks the interior of the spines for anterior chevrons, the other (MPC-D 100/1002) pos-
femoral cortex, with the outline of the medullary cavity cross- sesses prominent posterior projections to the second through 
cutting these tissues. This geometry suggests normal secondary fourth chevrons and was identified as most likely male.
absorption along the endosteal surface, as would be expected in a Although wider distally and less rugose than in the specimen of 
growing element. Given the absence of significant taphonomic Khaan, the anterior chevrons of ZMNH M8829 show a similar 
erosion of the femoral cortex and lack of trabeculae in any ventral posterior projection resulting in an increasingly antero-
femoral or tibial cross-section, we interpret ZMNH M8829 as posteriorly extended hemal spine in the second through fifth 
  . They also share a smaller, more dorsal anterior projec-lacking medullary bone, as developed in reproductively active chevrons
 tion of the hemal spine. Presence of this morphology in ZMNH female birds.
     M8829 indicates that either this feature characterizes females Several plausible explanations may explain the absence of instead or may have limited utility as a sexually dimorphic feature.
medullary bone in this oviraptorosaur: (1) as in most extant rep-
tiles (Simkiss, 1967; Schweitzer et al., 2005; Dacke et al., 2015), 
this taxon simply may have not required medullary bone as a 
  Sexual versus Somatic Agecalcium store during eggshell deposition, instead obtaining 
mineral from the structural bone of the skeleton; given that this Several features of this specimen indicate that although sexu-
individual appears to be still growing somatically, nutrients for ally mature, this individual was still growing somatically at the time 
egg laying may have simply been acquired as the medullary of death. The perimeter of the femoral cortex lacks an exter-nal 
cavity was expanded during normal growth; (2) alternatively, it fundamental system and instead consists of fibrolamellar bone 
may not have required medullary bone due to a high-calcium with laminar/subplexiform vascularization. Additionally, neuro-
and -phosphorus diet, which might be expected if oviraptoro- central sutures remain visible (‘open,’ sensu Brochu, 1996) on 
saurs were predominantly carnivorous; currently, it remains the anterior caudals and between the two preserved sacrals. This 
unclear whether diet can account for the absence of medullary concurs with the findings of Erickson et al. (2007) that non-avian 
bone observation in some extant birds (Werning, 2018); further, maniraptoran theropods achieved sexual maturity prior to somatic 
the lack of modern carnivorous birds of similar body mass maturity and a marked slowing of growth. The femoral cortex 
prohibits comparison; (3) finally, this individual may have preserves three LAGs; however, the cortex appears rather thin 
suffered from a pathological absence of this tissue or (4) all relative to the large medullary cavity, and bone remodeling during 
medullary bone may have been resorbed with completion of ontogeny likely eliminated multiple earlier-formed LAGs.
these eggs.
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