An Embryonic Enantiornithine Bird and Associated Eggs from the Cretaceous of Mongolia

Abstract

Enantiornithes is the most speciose clade of Cretaceous birds, but many taxa are known from isolated postcranial skeletons. Two embryonic enantiornithine bird skeletons of Gobipipus reshetovi gen. et sp. nov. from the Upper Cretaceous (Campanian) Barun Goyot Formation of the Gobi Desert in Mongolia provide new insights into the anatomy, radiation, and mode of development of early avialans. In recent times, both enantiornithine and ornithuromorph birds are known from the Barun Goyot Formation as well as from the Djadokhta and Nemegt Formations. The 80-million-year-old Gobipipus skeletons encased within eggshells shows several features characteristic of enantiornithine birds. The wing skeleton and shoulder girdle show morphological features indicating that Gobipipus achieved sophisticated powered flight. Gobipipus reshetovi gen. et sp. nov. is quite distinct from the sympatric enantiornithine species Gobipteryx minuta from the same strata in many anatomical features. Phylogenetic analysis of 26 avialan ingroup taxa based on distribution of 202 characters indicate that Gobipipus is a basal member of enantiornithine birds along with Confuciusornis and shares more characters with ornithuromorphs than previously recognized. The embryonic nature of Gobipipus specimens sheds new light on the developmental history of enantiornithine birds. The well-ossified bones of the fore- and hind limbs, and fusion of many skeletal elements indicate a precocial mode of development in Gobipipus. Apparently Gobipipus hatchlings could walk away from the ground nests as soon as they emerged from their eggs. The asymmetry of egg poles are unique features of Gobipipus eggs (oogenus Gobioolithus) among Cretaceous avialans. The microstructure of the shell in Gobioolithus eggs with the embryos of Gobipipus is typical avian (of ornithoid basic type) and less ratite-like in morphology of the spongy layer than is that in the other possible egg-remains of enantiornitine birds (oofamily Laevisoolithidae).

Full text

ISSN 00310301, Paleontological Journal, 2013, Vol. 47, No. 11, pp. 1252–1269. © Pleiades Publishing, Ltd., 2013.
1252
1
INTRODUCTION
The Late Cretaceous continental sediments of the
Gobi Desert of Mongolia are famous for the spectacu
lar dinosaur and mammal fossils, but in recent times
small but interesting bird fossils—both enantiorni
thines and ornithuromorphs—have been discovered
from three stratigraphic levels: Barun Goyot and Dja
dokhta formations of Campanian age and Nemegt
Formation of Maastrichtian age (Elzanowski, 1981;
Kurochkin, 1996; Clarke and Norell, 2002; Chiappe
et al., 2001). These formations have been considered
to represent at least two distinct Late Cretaceous envi
ronments and vertebrate faunal horizons. The spec
tacular orangered sediments of the Djadokhta/Barun
Goyot were deposited in arid environment and have
yielded protoceratopsids, armoured ankylosaurs, liz
ards, and mammals, but the overlying Nemegt beds
1
The article is published in the original.
were laid down under more humid conditions and
have produced massive dinosaurs such as hadrosaurs,
sauropods, and tyrannosaurs (Novacek, 1996). Simi
lar to dinosaur distributions, these two horizons tend
to show two distinct avialan assemblages; the lower
two formations, Djadokhta and Barun Goyot are
dominated by enantiornithines, whereas ornithuro
morphs birds are more common in the overlying Nem
egt Formation, represented by various taxa of Hesper
ornithes, a derived bird
Teviornis
, and several
unnamed taxa (Clarke and Norell, 2004). Fragmen
tary and isolated remains represent many of the avi
alan taxa that make it difficult to ascertain their affin
ities. So far,
Apsaravis
is the only known ornithuro
morph bird from the Djadokhta Formation
represented by excellent postcranial material (Clark
and Norell, 2002).
Fossils of Mesozoic birds are extremely rare from
the Gobi Desert, and embryonic skeletal remains are
even more so. The fossil record of avian embryos is
An Embryonic Enantiornithine Bird and Associated Eggs
from the Cretaceous of Mongolia
1
E. N. Kurochkin
a
, S. Chatterjee
b
, and K. E. Mikhailov
a
a
Borissiak Paleontological Institute, Russian Academy of Sciences,
123 Profsojuznaya Street, Moscow GSP7, 117868 Russia
b
Museum of Texas Tech University, Lubbock, Texas 794093191, USA
email: sankar.chatterjee@ttu.edu
Received May 27, 2012
Abstract
—Enantiornithes is the most speciose clade of Cretaceous birds, but many taxa are known from iso
lated postcranial skeletons. Two embryonic enantiornithine bird skeletons of
Gobipipus reshetovi
gen. et sp. nov.
from the Upper Cretaceous (Campanian) Barun Goyot Formation of the Gobi Desert in Mongolia provide
new insights into the anatomy, radiation, and mode of development of early avialans. In recent times, both
enantiornithine and ornithuromorph birds are known from the Barun Goyot Formation as well as from the
Djadokhta and Nemegt Formations. The 80millionyearold
Gobipipus
skeletons encased within eggshells
shows several features characteristic of enantiornithine birds. The wing skeleton and shoulder girdle show
morphological features indicating that
Gobipipus
achieved sophisticated powered flight.
Gobipipus reshetovi
gen. et sp. nov. is quite distinct from the sympatric enantiornithine species
Gobipteryx minuta
from the same
strata in many anatomical features. Phylogenetic analysis of 26 avialan ingroup taxa based on distribution of
202 characters indicate that
Gobipipus
is a basal member of enantiornithine birds along with
Confuciusornis
and shares more characters with ornithuromorphs than previously recognized. The embryonic nature of
Gobipipus
specimens sheds new light on the developmental history of enantiornithine birds. The wellossified
bones of the fore and hind limbs, and fusion of many skeletal elements indicate a precocial mode of devel
opment in
Gobipipus.
Apparently
Gobipipus
hatchlings could walk away from the ground nests as soon as they
emerged from their eggs. The asymmetry of egg poles are unique features of
Gobipipus
eggs (oogenus
Gobioolithus
) among Cretaceous avialans. The microstructure of the shell in
Gobioolithus
eggs with the
embryos of
Gobipipus
is typical avian (of ornithoid basic type) and less ratitelike in morphology of the spongy
layer than is that in the other possible eggremains of enantiornitine birds (oofamily Laevisoolithidae).
Keywords
: embryos and eggs, enantiornithine bird,
Gobipipus
,
Gobioolithus
, Upper Cretaceous, Barun Goyot
Formation, Gobi Desert
DOI: 10.1134/S0031030113110087

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1253
much poorer than for eggs for various reasons. First,
the skeleton is not well developed for a considerable
portion of embryo’s growth, especially for altricial
birds. The embryonic skeleton undergoes considerable
change as the cartilage skeleton is calcified. Second,
embryo may be present but hidden within the fossil
ized eggs. Third, embryonic skeleton is very small,
because it has to fit inside an egg, and is often unrec
ognized in the field. If eggshell is not present, it may be
difficult to separate bones of a late term embryo from
those of a hatchling (Carpenter, 1999). This is why
Gobipipus
embryos (Chatterjee, 1997) are crucial in
understanding the early radiation of Mesozoic avi
alans and their developmental history. Like
Gobipteryx
,
the association of
Gobipipus
embryo within an egg
clearly suggests that these specimens are truly
embryos, not hatchlings.
In 1971, the Joint SovietMongolian Paleontologi
cal Expedition discovered a Khermeen Tsav site rich
by dinosaurs and mammals of the Middle Campanian
age (Barun Goyot Formation) in the southern Gobi
Desert. At the same year, the PolishMongolian Pale
ontological Expedition found for the first time the
small, elongated eggs in Khermeen Tsav (Kielan
Jaworowska and Barsbold, 1972). From the beginning,
these eggs considered as the turtle or crocodilian eggs.
However, later, Polish paleontologists discovered in
some of these fragmented eggs the partial and delicate
embryonic skeletons that were subsequently described
by Elzanowski (1981) based on seven specimens. Elza
nowski concluded that these embryonic specimens
probably belong to a primitive palaeognathous bird
Gobipteryx minuta
, which he described earlier from the
Barun Goyot Formation of the Khulsan site, about
120 km east of Khermeen Tsav (Elzanowski, 1974,
1976, 1977, 1995). However, Elzanowski’s proposal of
the affinity of
Gobipteryx
was challenged. Later, Mar
tin (1983) endorsed the affiliation of
Gobipteryx
with
enatiornithine bird, and has been accepted by other
workers (Chiappe, 2007).
The Joint RussianMongolian Paleontological
Expedition explored the Khermeen Tsav site in later
years and discovered several new nesting sites of birds.
From this nesting site, three avian eggs containing
partial embryonic skeletons were discovered (Plate 1,
Figs. 1, 2). One of us (Mikhailov, 1991, 1992, 1996,
1997a) described in details the microstructure and
variation of the eggshells from these eggs, using the
scanning electron microscope (SEM). These eggs
have been described in terms of parataxonomy as
oogenus
Gobioolithus
(oofamily Gobioolithidae) and
oospecies
G. minor
(Mikhailov, 1996). In this paper, we
provide a comparative embryological study of the two
embryonic specimens from Khermeen Tsav, their
morphological difference, mode of development,
affinity, and phylogeny, as well as the microstructural
architecture of their eggshells. The embryonic bird
skeletons of
Gobipipus reshetovi
were found scrunched
in ovalshaped eggs, which make the identification of
these eggs certain. An abbreviated description of
Gobi
pipus reshetovi
was made at its identification of a new
species (Chatterjee, 1997). Here, we detail morphol
ogy of
Gobipipus
and compare it with other Cretaceous
birds from Mongolia such as
Gobipteryx minuta
(Elza
nowski, 1977, 1981) and
Apsaravis ukhaana
(Clarke
and Norell, 2002) and offer its phylogenetic place
ment within Enantiornithes, a major radiation of Cre
taceous birds traditionally referred to as “opposite
birds.” Because of its embryonic nature, we have com
pared
Gobipipus
with a large number of precocial
embryos of modern birds (Starck, 1993) to understand
the developmental strategy.
The material described here consists of two embry
onic skeletons of birds, both were found within the
similar eggs (
G. minor
) in one local spot. These fossils
were recovered from the eastern side of the northern
mouth of Khermeen Tsav Sayr, probably from the
same site that was described by KielanJaworowska
and Barsbold (1972) and Elzanowski (1981). This
locality lies at the eastern outpost of the Transaltai
Gobi, about 50 km west of the famous spring Naran
Bulak. Because of the abundance of avian eggs the
SovietMongolian Expedition dubbed this Bulak site
“Bird’s Hill” (Plate 1, Figs. 3, 4). V. Reshetov and his
field party collected both embryonic specimens in
1977 expedition. In addition, one more embryonic
skeleton and a large number of differently preserved
eggs were collected by the RussianMongolian Expe
dition teams from the same general locality and from
the other site on the opposite slope of the Khermeen
Tsav Sayr mouth. Both embryonic specimens and
associated eggshells are housed at the Borissiak Pale
ontological Institute of the Russian Academy of Sci
ences, Moscow (PIN).
SYSTEMATIC PALEONTOLOGY
A V A I LA E GAUTHIER, 1986
PYGOSTYLIA CHATTERJEE, 1997
ENANTIORNITHES WALKER, 1981
Genus
Gobipipus
Kurochkin,
Chatterjee et Mikhailov, gen. nov.
Etymology. After
Pipos
(Greek); a young bird
or chick, alluding to the embryonic nature of the fossil
from the Gobi Desert.
Type s p e cies.
Gobipipus reshetovi
Kurochkin,
Chatterjee et Mikhailov, sp. nov.
D i a g n o s i s. Toothless enantiornithine bird with
upturned rostrum showing the following autapomor
phies: maxilla forms an inner and lower flange of the
external naris; anterior part of mesethmoid has a ven
tral flange within the antorbital fenestra; lateral sur
face of dentary shows a deep horizontal groove poste
riorly and two rows of vascular pits anteriorly; pre
served manual phalangeal formula is 110, with digit
1 much longer than digit 2; mandibular symphysis;
acromial process of scapula has a medioventral projec
tion for the procoracoid process.

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PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
Plate 1
1 3
24
5 6
Explanation of Plate 1
Figs. 1 and 2.
Embryonic skeleton of
Gobipipus reshetovi
gen. et sp. nov. from the “Bird’s Hill”, KhermeenTsav locality; holotype;
PIN, no. 4492/3: (1) left lateral view; (2), dorsal view.
Fig. 3.
General view of the “Bird’s Hill” in Khermeen Tsav locality of the Gobi Desert, showing the horizontally bedded sand
stone of the Late Cretaceous Barun Goyot Formation.
Fig. 4.
A clutch of
Gobipipus
eggs in situ in “Bird’s Hill”.
Fig. 5.
Photomicrograph of arkosic sandstone matrix enclosing the bird embryo (PIN, no. 4492/4) within the small egg shell,
Barun Goyot Formation. Photo (under crossed polarized light) shows general texture of poorly sorted arkosic sandstone and
diverse feldspar grain types. The dominant minerals are quartz, feldspar, biotite and rock fragments with calcite cement; long
dimension of photo is 1 mm (Courtesy, T. Lehman).
Fig. 6.
Photomicrograph of arkosic sandstone matrix enclosing the bird embryo (PIN, no. 4492/4) within the small egg shell,
Barun Goyot Formation. Photo (under plane polarized light) shows clay/iron coatings (likely a result of soil forming processes)
and altered, angular feldspar grains; long dimension of photo indicates 0.25 mm (Courtesy, T. Lehman).

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1255
R e m a r k s. Chatterjee (1997) used the generic
name
Gobipipus
without any description or diagnosis.
The name
Gobipipus
Chatterjee, 1997 is thus nomen
nudum.
Gobipipus reshetovi
Kurochkin, Chatterjee et Mikhailov, sp. nov.
E t y m o l o g y. The specific name is given in mem
ory of Dr. Valery Reshetov—former leader of the
MongolianRussian expedition team, who discovered
the specimens.
H o l o t y p e. PIN, no. 4492/3, partial skeleton
(skull, part of the vertebral column, shoulder girdle,
forelimb) of an embryo; locality Khermeen Tsav site,
South Gobi Desert, Mongolia; Barun Goyot Forma
tion, Middle Campanian, Upper Cretaceous (Jerzyk
iewicz and Russell, 1991).
D e s c r i p t i o n (Plate 1, Figs. 1, 2; Figs. 1–5).
The description of
Gobipipus
is based on two speci
mens: PIN, nos. 4492/3 and 4, both are virtually
undistorted and complementary to each other. The
former represents the skull, shoulder girdle, wings,
and vertebrae, while the latter shows the pelvis and
hindlimb. These specimens provide a rare opportunity
for the reconstruction of individual skeletal elements
of an embryonic avian fossil for the first time. Because
of its prenatal condition, the overall morphology of the
embryo is probably distinct from an adult individual,
as allometry and ontogenetic changes can result large
morphological differences and degree of fusion during
growth. The degree of ossification of skeletons in these
specimens is remarkably advanced, indicating preco
cial mode of development comparable to the condi
tion of some modern birds just prior to hatching. Lin
ear measurements of skeletal elements of
Gobipipus
are
shown in Table 1.
Skull.
The bones of avian skull are extensively fused
in few months after hatching, but embryos retain some
individual sutures. The skull of
Gobipipus
preserves
most the sutures so the shape and relationships of each
bone can be determined. The skull is 16 mm long,
7 mm wide, and 5 mm deep and (Fig. 2a) and has a
pronounced beak. Many of the skull bones show a
beginning of fusion. Both the upper and lower jaws are
entirely edentulous, and the beaks were probably
encased in a horny rhamphotheca. The premaxillae
are broad terminally, somewhat upturned at the tip,
and are fused medially. Posteriorly, the premaxilla
extends to meet the maxilla. The external naris is large
and extends considerably anteriorly. The lacrimal is a
Tshaped bone, where the dorsal end is wide antero
posteriorly but the ventral end is narrow and contacts
the jugal bar. The mesethmoid has a forward projec
tion within the antorbital fenestra and is exposed dor
sally on the skull roof. The jugal is a narrow, rodlike
bone. The quadrate has a broad, flattened pterygoid
condyle, a large otic condyle, and a wide mandibular
process. The morphology of the articular head is
unclear, but appears to be doubleheaded. In the
braincase, the basisphenoid complex shows a broad
basitemporal plate with a large ventral sinus. The lower
jaw (Figs. 2a, 2b) has a suture in the symphyseal area
between the right and left mandibular rami. A mandib
ular fenestra is present at the posterior region of the
jaw ramus. The anterior part of the jaw is broad and
spatulate. The dentary is marked laterally by a longitu
dinal groove and a row of nutrient foramina.
Vertebral column.
Ossification of the vertebral col
umn in living birds takes place at a later stage of
embryonic development and proceeds progressively
from the cervical to the caudal region (Starck, 1993).
In
Gobipipus
skeleton, PIN, no. 4492/3, an associated
series of 7 cervicals and 4 anterior thoracic vertebrae
are preserved between the two shoulder girdles
(Fig. 1e). The vertebrae are exposed in dorsal aspect.
The anterior seven cervicals lack neural spines and
show widely spaced zygapophyses; it seems that one of
them shows the centrum with flat articulated surfaces
as in embryonic birds. Hetercoely develops later in life
as birds grow in size (Bellairs and Jenkin, 1960). Two
of the caudal cervicals bear bases of the flat, back
wardly directed ribs. The thoracic vertebrae show a
Table 1.
Estimated linear measurements (in mm) of
Gobipipus
PIN
44923 PIN
44924
1. skull length 16
2. skull width 7
3. skull height 5
4. scapula length 9
5. scapula,
greatest width across glenoid rim 1.3
6. coracoid length 6
7. coracoid, greatest proximal width 2.4
8. coracoid, greatest ventral width 1.6
9. furcula length 5
10. humerus length 13
11. humerus,
length of the deltopectoral crest 3.6
12. humerus, greatest proximal width 3.3
13. humerus, least diameter of the shaft 1
14. radius length 14
15. radius, least diameter of the shaft 0.4
16. ulna length 15
17. ulna, least diameter of the shaft 0.9
18. metacarpal II length 7.2
19. manus length 11.2
20. ilium length 7
21. ilium height 6
22. pubis length 6
23. femur length 9
24. femur, least diameter of the shaft 0.9
25. tibiotarsus length 13
26. tibiotarsus, least diameter of the shaft 0.8
27. fibula length 12
28. fibula, least diameter of the shaft 0.8

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PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
narrow span of the zygapophyses and low neural
spines. The posterior aspect of a last preserved thoracic
vertebra is exposed, where the centrum is concave and
slightly heterocoelous with a large neural canal; the
neural arch appears to be fused with the centrum
(Fig. 3c).
Shoulder girdle.
The shoulder girdle and wing ele
ments are well ossified, indicating that
Gobipipus
may
have had flight capability soon after hatching, as in
some modern galliforms (Figs. 3c, 3c). The highly
elongated wings, welldeveloped carpometatacarpus,
flexible coracoscapular joint at an acute angle, and
the strutlike coracoid with a procoracoid process indi
cate that
Gobipipus
possessed sophisticated flight skill
(Fig. 4). The components of the shoulder girdle are the
long, narrow scapulae, running parallel to the verte
bral column, the dorsal end of the right coracoid, the
slender clavicle, and a flat sternum. In PIN,
no. 4492/3, both sides of the shoulder girdles are pre
served, articulating with the wings. Seen from above,
(a)
(b)
(c)
(d)
(e)
pm
m
ph me
pop q soc
mcII
ul
hu ra sc mcIII
bs
bo
co
ve
uln
popr
trc
rad
5 mm
pm
m
mcII
ve
hura
q
me
m mcIII
mcIII
bs
bo
sc
co
co
ve
sc
hu
ul
ra co
bo
pop
mcIImcIII
popr
d
sq
lfu
st
p
ph
soc
mcI
fe
as + ca
ti
fi
il
pu
fm
mcIII
d
ra
hu
ul
sc
ve
eggshell
mcIImcI
l
Fig. 1.
Gobipipus reshetovi
gen. et sp. nov.: (a–c, e) holotype PI N, no . 4492 /3; ( d), sp ecim en PIN , no. 4492/ 4: (a ), lef t lat eral v iew
of partial skull and wing elements; (b), dorsal view of partial skull, shoulder girdles, and wing elements; (c), ventral view showing
braincase, a series of dorsal vertebrae, shoulder girdles and wing elements; (d), lateral view of right ilium, femur, tibiotarsus and
fibula; (e), left lateral view of wing elements and vertebral column; Upper Cretaceous of Gobi Desert, Mongolia. Designations:
a, angular; acr, acrocoracoid process; as+ca, astragalus and calcaneum; ar, articular; bo, basioccipital; bs, basisphenoid; co, cora
coid; d, dentary, dpc, deltopectoral crest; f. frontal; fe, fermur; fi, fibula; fm, foramen magnum; fu, furcula; hu, humerus; il, ilium;
it, internal tuberosity; j, jugal; l, lacrimal; ld, ligamental depression;
m
, maxilla;
mcI
–
mcIII
, metacarpal I–III; me, mesethmoid;
mf
, mandibular fenestra;
n
, nasal;
p
, parietal;
ph
, phalanx,
pm
, premaxilla;
pop
, postorbital process;
popr
, paroccipital process;
pra
, prearticular;
prc
, procoracoid;
q
, quadrate,
qj
, quadratojugal;
ra
, radius;
rad
, radiale;
sa
, surangular;
sc
, scapula;
soc
,supraoccipital;
sq
, squamosal;
st
, sternum;
ti
, tibia;
trc
, triosseal canal;
ul
, ulna;
uln
, ulnare;
ve
, vertebra; I–III, manual digits.

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1257
the scapulae are long, straight, and narrow bones,
tapering posteriorly and running parallel to the verte
bral column. Anteriorly each scapula is expanded with
a large acromial process as in
Gobipipus
, directing
medially for articulating with furcula. Below of this
proc ess, a fl ange of b one is pr ojected cr anioventrall y to
articulate with the procoracoid process. Laterally the
scapula shows a large glenoid cavity, which faces
directly laterally and somewhat dorsally. On the right
side of the girdle, the dorsal end of the coracoid forms
the triosseal canal in conjunction with the scapula and
furcula. The coracoid is elongated and strutlike as in
other enantiornithine birds. However, its dorsal sur
face is flat rather than concave. A thin bar of bone,
perhaps the furcula is preserved on the left side
between the jugal bar and a pterygoid.
Forelimbs.
The forelimbs are preserved in a tightly
folded position in a compact Zfashion so that the
anterior (palmar) surface of the humerus is strongly
appressed with the corresponding surface of the radius
and ulna. The wing is significantly longer than the
hindlimb where the ratio of forelimb (humerus + ulna)
to hindlimb (femur + tibiotarsus) is about 1.3. Both
the ulna and radius are slightly longer than the
humerus. The relative proportions of wing elements in
Gobipipus
reflect the extensive upgrading of the flight
system, where the forearm is longer than the humerus,
and the elongated hand forms a strong platform for the
attachment of primary feathers. The humerus is
robust, about 13 mm long, with expanded proximal
and distal ends and with a proximal head. Proximally,
there is no sign of a pneumatic fossa or external tuber
osity, most likely because of its embryonic nature.
Proximally, the humerus shows concave cranial and
convex caudal surface, a feature of enantiornithine
bird (Chiappe and Walker, 2002). The deltopectoral
crest in the right humerus and the internal tuberosity
in the left one are represented in its infancy. Unlike
Gobipteryx
and other enantiornithine birds, the del
toptectoral crest is subdued and more proximally
placed and the proximal expansion is not deflected
ventrally. However, the bicipital crest in the opposite
5 mm
(a)
(b)
(c)
(d)
(e)
pm q
me
m
co
II
III
d
l
ld
p
soc
I
me
m
d
d
l
gl
dpc
hu
prc
acr
uln
rad
ar
a
pra
ld
dpc
hu
uln
pm
d
ar
II
III
I
a
5 mm
(h) (i)
(f)
(g)
Gobipteryx
minuta
Gobipipus reshetovi
po
qj
sa
j
it
Fig. 2.
Comparison between embryonic skeleton of
Gobipipus reshetovi
gen. et sp. nov., holotype PIN, no. 4492/3 (a–e) and
Gobi
pteryx minuta
(f–i): (a), composite restoration of skull and lower jaw of
Gobipipus
, lateral view; (b), restoration of lower jaw, ventral
view; (c), left coracoid, dorsal view; (d), anterior (palmar) view of right humerus; (e), dorsal view of left manus; (f), lateral view
of the snout of
Gobipteryx
; (g), ventral view of the lower jaw showing lack of symphysis; (h), anterior (palmar) view of right
humerus; (i), dorsal view of left manus. (f–i), simplified from Elzanowski (1981). For abbreviations, see Fig. 1.

1258
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
5 mm
5 mm
5 mm
5 mm
hu
sc
ve
ul
gl
acr
prc
co
st
fu
(b)
(e)
(g) (h)
(d)
gl
acr
co
hu
sc
co
sc
sc
sc
gl
acr
acp acp
gl gl
gl
co
sc
fu ve
ve
ce
na
nc
trc
(a)
(c)
(f)
Fig. 3.
Gobipipus reshetovi
gen. et sp. nov.: (a–c, e, g), composite restoration of shoulder girdle and presacral vertebrae of
Gobipi
pus
, based on holotype PIN, no. 4492/3: (a), dorsal view of the shoulder girdles and a series of dorsal vertebrae of
Gobipipus
;
(b), left lateral view of the shoulder girdle of
Gobipipus
; (c), posterior view of a dorsal vertebra of
Gobipipus
; (e), right scapula of
Gobipipus
, dorsal view; (g), left coracoid of
Gobipipus
, dorsal view. (d, f, h), corresponding bones of
Gobipteryx
and Enantiornithes
for comparison (after Elzanowski, 1981, Walker, 1981): (d), dorsal view of the embryonic skeleton of
Gobipteryx minuta
for com
parison (after Elzanowski, 1981); (f), right scapula of
Gobipteryx
(af ter Elzanowski, 1981); ( h), le ft cor acoid of an enantiornithine
bird, dorsal view, showing narrow proximal end and absence of procoracoid process (modified from Walker, 1981).

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1259
corner is prominent as in other enantiornithine birds
(Chiappe and Walker, 2002). The shaft is long, cylin
drical and slightly sigmoidal. The distal end is tilted
anteriorly but the internal and external condyles are
flattened and compressed craniocaudally as in enan
tiornithine birds.
The radius is shorter and slimmer than the ulna.
The ulna is stoutly built and displays a slight outward
curvature. The olecranon process and quill nodes are
not expressed. Most of the features of these two epipo
dial bones remain concealed. The manus is intact and
preserved in both sides (Fig. 4e). It is about 11.2 mm
long, slightly shorter than the humerus. Two proximal
carpal bones, the radiale and ulnare are represented in
the right manus. The radiale is larger and lies on the
exterior surface of the carpal joint. The three metacar
pals are fused proximally with the distal (semilunate)
carpals, but separated distally. They are very long and
have a similar thickness. The alular metacarpal (Mc I)
is short and slender, about 35% as long as major metac
arpal (Mc II). The major metacarpal (Mc II) is stout
and straight, wider in crosssection than the minor
metacarpal (Mc III). The minor metacarpal is slightly
curved and longer than the metacarpal II, and its distal
end is curved to contact major metacarpal as in other
enantiornithines. The alular digit has a long proximal
phalanx, longer than the metacarpal I; there is one pha
lanx in the major digit; the metacarpal III lacks any
phalanx. The manual digits are extremely reduced in
Gobipipus
, where the phalangeal formula is 110.
Pelvic girdle.
The specimen PIN, no. 4492/4 shows
the articulated right side of the ilium, femur, tibia and
fibula, but the ischium and the pubis are absent
(Fig. 5). The ilium has a shallow iliac blade with a very
long, tapering posterior process, but the short
rounded, anterior process appears to be incomplete.
The anteroposterior length of the preserved portion
of the ilium is 4.7 mm. The acetabulum is perforated
and receives the femoral head. A robust ischiadic
peduncle is visible. On the opposite side of the pre
served portion of the pelvis a narrow, rodlike bone
about 5 mm long, may represent the left pubis.
Hindlimb.
The preserved hind limb bones are fully
ossified. The distal end of the femur is missing, but its
proximal end shows an inturned head directed medi
ally and a welldeveloped posterior trochanter later
ally. The femur is stout and shorter than the tibiotar
sus. The proximal shaft is flattened craniocaudally
with a narrow lateral side and a wide medial side. The
estimated length of the femur is about 8 mm. The tibia
would be about 12 mm long. Its proximal end is miss
ing and the distal end is slightly swollen and shows a
fused astragalocalcaneum to form the tibiotarsus. The
ossification of astragalocalcaneum in
Gobipipus
is con
sistent with other enantiornithine birds. Embryonic
ossification of astragalocalcaneum is known in two
precocial birds, the buttonquail (
Turnix
) and maleo
(
Macrocephalon
) (Starck, 1993). The fibula of
Gobipi
pus
is slimmer in two and half times than the tibia and
reaches its distal end, terminating above the level of
the tarsus.
Material. Holotype; specimen PIN,
no. 4492/4, pelvis and hindlimb elements of an
embryo (Fig. 1d).
* * *
Affinity of
Gobipipus
.
Phylogenetic analysis indi
cates that there are five major hierarchical radiations
of Mesozoic birds—Avialae, Pygostylia, Enantiorni
thes, Ornithuromorpha, and Ornithurae, which are
successively closer to the crown group Aves (Clarke
and Norell, 2002; Chiappe, 2002, 2007). Phylogenetic
analysis of 24 ingroup terminal taxa and two outgroups
(dromaeosaurids and
Archaeopteryx
) were scored for
202 characters (listed in appendix 1, based on Clarke
and Norell, 2002 and Zhou and Zhang, 2006) to assess
the phylogenetic position of
Gobipipus
among Meso
zoic birds (Fig. 6). With the dethroning of
Archaeop
teryx
from its urvogel status,
Jeholornis
became the
most basal avialan (Xu et al., 2011). Analysis produced
two most parsimonious trees and identifies
Gobipipus
as a basal member of Enantiornithes (Fig. 6).
Most phylogenetic studies identify Enantiornithes
as a monophyletic group, but their systematics and
ingroup relationships are highly controversial.
27 characters have been proposed earlier as derived
morphologies of Enantiornithes (Walker, 1981; Kuro
chkin, 1996: Chiappe, 1996), but Clarke and Norell
(2002) reduced the number of autapomorphies to just
four, none of which is preserved in
Gobipipus.
Chiappe
and Walker (2002) recognized 16 valid characters,
some of which are used here to establish the enantior
nithine affiliation of
Gobipipus.
Because the diagnostic
features are not fully expressed in the embryonic stage
of
Gobipipus
, its precise relationships with other enan
tiornithine birds is tentative at best.
Gobipipus
shares
the following synapomorphies with Enantiornithes
listed by Chiappe and Walker (2002): (1) dorsal margin
of the humeral head concave in its central portion, ris
ing dorsally, and ventrally; (2) prominent bicipital
crest of the humerus; (3) distal end of the humerus
very compressed craniocaudally; (4) minor metacar
pal distally projecting farther than major metacarpal.
It is generally believed that enantiornithines were
the dominant land birds of the Cretaceous, but repre
sent an evolutionary experiment that diverged entirely
separately into opposite direction from the lineage
leading to modern birds (Walker, 1981; Martin, 1983).
Recent study contradicts the basal dichotomy and
suggests that enantiornithines represent sistergroup
of the Ornithuromorpha lineage leading to modern
birds (Clark and Norell, 2002; Chiappe, 2007).
However,
Gobipipus
alters the topology of the cla
dogram of the early radiation of Mesozoic birds, as it
strengthens the ties of
Confuciusornis
with Enantiorni
thes (Fig. 6).
Confuciusornis
was first interpreted as an
enantiornithine bird and allied with
Gobipteryx
(Hou
et al, 1995). Later, Hou et al. (1996) removed
Con

1260
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
fuciusornis
from Enantiornithes and regarded as its sis
ter taxon, a view supported by recent analysis in this
paper. In contrast, Chiappe (1997) suggested an alter
native hypothesis that
Confuciusornis
is a member of
Ornithothoraces that split into two clades, Enantior
nithes and Ornithuromorpha. With the inclusion of
Confuciusornis
as a basal member of enantiornithines,
the clade Ornithothoraces disappears. In our phylog
eny (Fig. 6), Pygostylia splits into two lineages, Enan
tiornithes and Ornithuromorpha, the former incorpo
rates
Confuciusornis
as the most basal member as sug
gested by Hou et al. (1995). These two groups of
5 mm
5 mm
(c)
dpc ld
hu ra ul
rad
uln
I
II
III
(e)
hu
(a) (b) (d)
(h)
ld
dpc it
(f)
(g)
II III
I
uln
GOBIPIPUS
GOBIPTERYX
Fig. 4.
Gobipipus reshetovi
gen. et sp. nov. compared with
Gobipteryx minuta
: (a–e),
Gobipipus reshetovi
gen. et sp. nov., composite
restoration of forelimbs: (a), dorsal view of right humerus of
Gobipipus
; (b), anterior (palmar) view of right humerus of
Gobipipus
;
(c), proximal view of right humerus of
Gobipipus
; (d), dorsal view of left radius and ulna of
Gobipipus
; (e ) dorsal view o f left manus
of
Gobipipus
; note intermetacarpal space between metacarpals II and III. (f, g, h), corresponding elements of
Gobipteryx minuta
for comparison (after Elzanowski, 1981): (f), anterior (palmar view) of right humeus of
Gobipteryx
; note robust deltopectoral
crest, capital groove and internal tuberosity; (g), proximal view of right humerus; (h), dorsal view of left manus, here metacarpals II
and III are cylindrical and lack an intermetacarpal space.

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1261
Cretaceous avialans, Enantiornithes and Ornithu
morpha, differ significantly in morphology, flight
style, habitat, and physiology.
Enantiornithines became globally distributed dur
ing the Cretaceous period but they died out at the KT
extinction event (Chiappe and Walker, 2002). Among
seven embryos described by Elzanowski (1981) from
the Late Cretaceous Barun Goyot Formation of Khul
san locality, in the Nemegt Valley of the Mongolian
Gobi Desert, only three specimens (ZPAL MgR 1/33,
1/34, and 1/88) show diagnostic features. Elzanowski
considered all embryos as
Gobipteryx minuta.
Chiappe
et al. (2001) described a new adult skull of
Gobipteryx
minuta
from the Late Cretaceous Sandstone of Ukhaa
Tolgod of Mongolia that amplified the cranial anat
omy of this enantiornithine bird. They suggested that
Nanantius valifanovi
described by Kurochkin (1996)
from the Barun Goyot Formation of Khermeen Tsav
locality of the Southern Gobi, about 100 km west of
Khulsan area, may actually belong to
Gobipteryx.
Since
Gobipipus
is also known from the Khermeen
Tsav site, it is crucial to document the similarities and
difference between
Gobipteryx
and
Gobipipus.
A majority of enantiornithine taxa, for which cra
nial material is known, possess teeth except
Gobip
teryx. Gobipipus
is also edentulous. The morphological
differences between
Gobipipus
and
Gobipteryx
embryos
can be seen in the beak curvature, size and position of
the external naris, premaxilla/maxilla suture pattern,
presence or absence of a mandibular fenestra, relative
5 mm
(a)
(b)
(c)
as + ca
fi
ti
fe
pu
ve
il
eggshell
as
+
ca
fi
ve
ti
il
fe
ve
pu
eggshell
Fig. 5.
Gobipipus reshetovi
gen. et sp. nov., Pelvic girdle and hindlimb, based on the specimen PIN, no. 4492/4: (a) lateral view of
the right ilium, femur, tibiotarsus and fibula; (b) anterior view of right ilium and femur, left pubis, and few caudal vertebrae;
(c) anterolateral view of right tibiotarsus and fibula; note the distal capping of astragalocalcaneum.

1262
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
size of the cervical neural spine, nature of coraco
scapular joint, morphology of the coracoid, relative
size of the deltopectoral crest and the ventral tilt of the
proximal expansion, presence or absence of internal
tuberosity and capital groove, relative length of the
third metacarpal, and the nature of intermetacarpal
space (Fig. 2).
Gobipipus
shows the following derived
features that are lacking in
Gobipteryx
: absence of lac
rimal/jugal contact; posterior bifurcation of dentary;
presence of procoracoid process; and development of
tibiotarsus (Cracraft, 1986; Chiappe, 2002). All these
features indicate that
Gobipipus
and
Gobipteryx
are
fundamentally different taxa and occur in different
lineages of enantiornithine birds (Fig. 6). Moreover,
the morphology of the egg and the microstructure of
their shells, as discussed later, are different between
Gobipipus
and
Gobipteryx.
Clark and Norell (2002) showed that many previ
ously proposed unique enantiornithine morphologies
(Walker, 1991; Chiappe and Walker, 2002; Kurochkin,
1996) appear to have a broader distribution within avi
alans.
Gobipipus
shares the following synapomorphies
with Ornithuromorpha (Chiappe, 2002; Clarke et al.,
2006): (1) dentary forked posteriorly; (2) quadrate
with doubleheaded cranial articulation (3) loss of
coronoid bone; (4) scapular shaft sagitally curved;
(5) procoracoid process on the coracoid; (6) inter
metacarpal space present; (7) ungual phalanx of the
major digit absent; (8) distal ends of metacarpals par
tially fused.
Mode of development.
The phylogeny of the preco
cialaltricial mode of development has been a subject
of great interest in recent years both from a paleonto
logical and neontological standpoint. Elzanowski
(1981, 1985, 1995) noticed heterochrony in the devel
opmental pattern in early birds. He argued that the
welldeveloped wings and high degree of ossification
pattern in the skeletons of embryos indicate its super
precociality, and its hatchlings were probably able to
fly. On the other hand, he pointed out that the pelvis
and hindlimbs of
Gobipteryx
show retarded develop
ment compared to wing elements. He thus argued that
the superprecocial development of powered flight was
accompanied by the slowing down of the development
of hindlimb, a tradeoff between aerial and terrestrial
modes of locomotion.
Starck (1989, 1993) studied in detail the patterns
and sequence of ossification of a wide range of extant
birds by means of staining bone and cartilage. He plot
ted these ontogenetic data over the phylogenetic cla
dogram of birds (Cracraft, 1988), and found that pre
cociality is an ancient developmental mode, whereas
altriciality is derived. Thus precociality associated with
lack of parental care, as exhibited by megapodes, is
specialized and not a primitive trait and might have
evolved from Galliformes precociality (Starck and
Sutter, 1994). Similarly, altriciality evolved indepen
dently in several avian lineages as well as in nonavian
dinosaurs (Horner and Weishampel, 1989).
Dromaeosauridae
Jeholornis
Sapeornis
Confuciusornis
Gobipipus
Cathayornis
Concornis
Neuquenornis
Gobipteryx
Patagopteryx
Archaeorhynchus
Liaoningornis
Yanornis
Apsaravis
Hesperornis
Baptornis
Lithornis
Ichthyornis
Crax
Gallus
Chauna
Anas
Crypturellus
Yixianorrnis
Hongshanornis
Archaeopteryx
AVIALA E
ENANTIORNITHES
PYCOSTYLIA
ORNITHUROMORPHA
ORNITHURAE
AVES
Fig. 6.
Phylogenetic relationship of
Gobipipus reshetovi
and other Mesozoic birds (strict consensus cladogram of two most parsimo
nious trees). Phylogenetic analysis was conducted using PAUP Version 4.0b10. A total of 202 morphological characters were used in
Appendix 1, following Clarke and Norell (2002) and Zhou and Zhang (2006). Heuristic search method was employed for character
optimization. Tree length = 1123; consistency index (CI) = 0.57; homoplasy index (HI) = 0.93; CI excluding uninformative char
acters = 0.57; retention index (RI) = 0.62; rescaled consistency index (RC) = 0.42. Two equally parsimonious trees were found.

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1263
The large extent of ossified area in the skeleton of
Gobipipus
, especially the ossification of the cervical
vertebrae, forelimbs, and hind limbs indicates a near
term embryonic stage of a precocial bird. When the
ossification pattern of
Gobipipus
is compared with the
embryological data of Starck, it becomes clear that the
skeleton of
Gobipipus
corresponds well with stage 39 of
a typical precocial 2 bird such as the European quail
(
Coturnix coturnix
). In contrast, the skeleton of a typi
cal altricial bird, such as the Java sparrow (
Lonchura
orzivora
), remains largely cartilaginous at this stage. In
fact, the ossification pattern of
Gobipipus
confirms
Starck’s assessment that precociality is the most prim
itive stage in the evolution of avian ontogeny. It is
likely that with their fully developed limbs and girdles,
Gobipipus
hatchlings were probably capable of both
terrestrial and aerial locomotion as soon as they
emerged from their eggs (Fig. 7).
* * *
Two types of the avian eggs in the Cretaceous Gobi.
Two types of avian egg were found at the Cretaceous
sediments of the Gobi Desert: (1) slightly asymmetric
(ovoid) eggs with rare embryo remains, preliminary
attributed to “eggs of
Gobipteryx
” and parataxonomi
cally described as Gobioolithid remains (Mikhailov,
1996); (2) symmetrical (ellipsoid) eggs described as
Laevisoolithid remains (Sabath, 1991; Mikhailov,
1991, 1996). The association of eggshell with embry
onic and hatchling remains allows us to correlate these
two distinct types of egg structure with specific avian
taxa: the eggs
Gobioolithus minor
belong to
Gobipipus
reshetovi
and the eggs
Subtiliolithus multituberculatus
to
Nanantius valifanovi
Kurochkin, 1996 (=
Gobipteryx
minuta
sensu Chiappe et al., 2001). Other Laevi
soolithid remains may belong to other enantiornithine
birds.
Eggs of
Gobipipus.
Numerous
Gobipipus
eggs
(oofamily Gobioolithidae, oogenus
Gobioolithus
Mikhailov, 1996) were collected from three eggbear
ing localities of the southern Mongolian Gobi by the
PolishMongolian and SovietMongolian expeditions
(Fig. 8). Besides smaller eggs,
Gobioolithus minor
Mikhailov, 1996, (30–46
×
20–24 mm) some of which
contain the welldeveloped embryos of
Gobipipus
,
larger eggs,
Gobioolithus major
Mikhailov, 1996, (53–
70
×
26–30 mm), of the same shape and shell structure
were found in the same ancient breeding sites
(Mikhailov, 1996). Apparently they belong to another
representative of the same group of birds. Both vari
ants of these eggs are found in the same localities,
though smaller eggs (G. minor) are relatively abun
dant in Khermeen Tsav locality, whereas the large type
(
G. major
) is more common in Khulsan site. The
abundance of
G. minor
eggs (some with embryos of
Gobipipus
) from different stratigraphic levels at Kher
meen Tsav demonstrates the site fidelity of the
Gobipi
pus
birds (Sabath, 1991).
In the shell of
Gobipipus
eggs the recrystallization of
the uppermost layer obliterates the external zone and
macroorganization (expressiveness of the columns
and prisms) in the spongy layer. However, clear subdi
vision of mammilla on secondary spherite and wedges,
as well as squamatic ultrastructural pattern in the inner
(nonrecrystallised) zone of the spongy layer suggests
that the shell in
Gobipipus
eggs is well comparable to
the thin paleognathe eggshells, for example that of
tinamou and kiwi, but its overall shape and size are dis
tinctive.
Despite the general similarity of eggshell structure,
combination of the small size and asymmetry of egg
poles are unique features of
Gobipipus
eggs among the
Cretaceous finds. The outer surface is smooth and
shell thickness ranges from 0.1–0.2 mm in the smaller
eegs (
G. minor
) to 0.2–0.4 in the larger one (
G. major
).
Fig. 7.
Reconstruction of
Gobipipus
embryo curled in a
fetal position in its 4 cmlong egg. Artist, Michael
W. Nickell.

1264
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
Other enantiornithine egg.
The solitary complete
egg with particular ornithoid shell structure (specimen
PIN, no. 2970/5) was found from the Upper Creta
ceous Nemegt Formation at the Bugeen Tsav locality
and was initially described by Sochava (1969). Later
Mikhailov (1991) named this egg as
Laevisoolithus
sochavi.
The egg is about twice the size of the smaller
Gobipipus
egg (=
Gobioolithus minor
). As the external
surface of the egg is secondarily recrystallized, actual
thickness of its shell may not exceed 0.7 mm. Numer
ous eggshell fragments with same ultra and micro
structure were collected from the redbeds of Khai
chinUla locality (Campanian or early Maastrichtian)
and were described as oogenus
Subtiliolithus
(Mikhailov, 1991). Now, it is clear that oogenera
Lae
visoolithus
and
Subtiliolithus
share similar shell struc
ture and should be assigned to a single oofamily Laevi
soolithidae (Mikhailov, 1996, 1997a). Meanwhile, in
Fig. 8.
A large collection of small elongated eggs from
Gobipipus
at Khermeen Tsav locality, Gobi Desert, natural size (above); egg
of
Laevisoolithes sochavi
, specimen PIN, no. 2970/5, Bugeen Tsav, Upper Cretaceous Nemegt Formation, natural size (below).
The egg probably belonged to an enantiornithine bird.

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1265
1991, a complete skeleton of an enantiornithine
Nan
antius valifanovi
Kurochkin, 1996 (=
Gobipteryx
minuta
sensu Chiappe et al., 2001) was found associ
ated with
Subtiliolithus
eggshell fragments, thus offer
ing a direct correlation between eggshells and the pro
ducer of the egg. The eggshell is very thin (0.3–
0.4 mm), with particular microtuberculation on the
surface, very characteristic of
Subtiliolithus
eggshell.
Unfortunately, no complete egg in association with an
adult bird has been found.
The ultra and microstructure of the
Nanantius

enantiomithine eggs is of ornithoid basic type and well
expressed ratite morphotype (shared with Ratitae and
Galloanserae birds), but it lacks the external zone
(Fig. 8b). In this character state it resembles theropod
eggshell of the oofamily Elongatoolithidae, but the
ratio of spongy (=continuous) to mammillary layer,
ranging from 1 : 1 to 1 : 2, is unique within the recent
and fossil eggshells of ornithoid type (Mikhailov,
1997a,b), and may be a distinctive feature of this line
of enantiornithine birds. Among recent birds such a
strong development of the mammillary layer (but not
higher than 1:1) is characteristic only for eggshells of
geese (i.e. genera
Anser
and
Branta
), which, however
display an explicit external zone.
Thus, two types of Cretaceous avian eggs from the
Upper Cretaceous of Gobi Desert, namely those of
Gobipipus
(=oogenus
Gobioolithus
) and some other
enantiornithine birds (=oogenus
Subtiliolithus
), can
easily be distinguished by the following criteria:
(1) Laevisoolithids’ eggs are of ovoid shape and with
shell ratio 3 : 2–2 : 1 of spongy layer to mammillary
layer and (2) Laevisoolithids’ eggs (oogenera
Subtili
olithus
and
Laevisoolithus
) of ellipsoid shape with shell
ratio 1 : 1–1 : 2 of spongy to mammillary layer. Smaller
egg size, thinner eggshell, and expressiveness of the
boundaries of the vertical shell units in spongy (=con
tinuous) layer in
Gobipipus
provide additional evidence
for its identification.
PALEOECOLOGY
The Upper Cretaceous Barun Goyot Svita of the
Gobi Desert is regarded as originating from aeolian
and wateraccumulated sands (Gradzinski and
Jerzykiewicz, 1974). Sedimentological studies indi
cate that it is predominantly dune deposits, but inter
mittent fluvial and lacustrine sediments occur in the
interdune areas. These mixed sediments indicate the
presence of periodic streams frequently changing
channels, which from time to time flooded the inter
dune areas. Most of the Barun Goyot Svita was depos
ited under a semiarid, seasonal climate. On the other
point of view, the sediments of the Barun Goyot Svita
were formed in alluvial and humid conditions that
supported by lithological analysis of these sands (Shu
valov, 1985).
The sediment inside the eggs with
Gobipipus
embryos, which has been studied microscopically, is
moderate to poorly sorted arkosic sandstone similar in
composition to the surrounding rock. Apparently the
sediment infiltrated into the egg through cracks and
breaks. The dominant minerals are feldspars (ortho
clase, microcline and plagioclase in decreasing abun
dance) and quartz. Some reworked sedimentary rock
fragments are present, as are a few grains of biotite,
muscovite, chlorite and epidote. The grains are coated
with a thin film of iron oxide and clay, and the pore
space is filled with blocky equant calcite cement.
Several features of the sediment matrix in these
eggs suggest that they were buried in a noneolian
environment. The poorly sorted texture of sediment
and the angularity of grains, as well as arkosic miner
alogy (Plate 1, Figs. 5, 6), are features not typical of
modern eolian dune sands. The thin coating of iron
oxides and clay on the grains suggest that the sediment
was deposited in an environment subject to soilform
ing processes. Such conditions may have existed in
alluvial fan or braidplain environments marginal to
the dune field or within interdunal corridors.
The eggs of the Barun Goyot Formation were prob
ably laid on the banks of ephemeral rivers and lakes
(Mikhailov et al., 1994). It is likely that these birds
abounded in Cretaceous terrestrial ecosystem of the
Gobi and lived in colonies, as evident from the distri
bution of eggs. The abundance of
Gobipipus
eggs
(=oogenus
Gobioolithus major
), occurring at different
levels in the weathered slope of “Bird’s Hill” at Kher
meenTsav locality, indicates that this area was a
repetitive nesting site for this species.
The taphonomic setting of the nesting site is inter
esting. Mikhailov (1991) interpreted these sites as
longterm colonial nesting areas along the margins of
lakes and estuaries. The egg shape of
Gobipipus
is
always well preserved without any distortion, though
thin shell in some cases may be completely dissolved or
destroyed. Separate eggs always exhibit subvertical
position and evenly distributed within a layer of sandy
matrix, close to each other; yet, these arrangements of
eggs are random without any hint of forming a definite
clutch. There are two interpretations for this unusual
distribution of eggs. Like modern megapods,
Gobipi
pus
might have laid separate eggs buried underground.
Alternatively, the eggs could be primarily arranged in
clutches, but as a result of frequent flooding of the
nesting colonies, some of them were washed out from
the nests and floated in a subvertical to vertical posi
tion (which is usual for avian eggs after some days of
incubation). As the water level dropped, the eggs
would slowly sink to the soft bottom substrate in the
same subvertical position with random distribution.
Strong recrystallization of the outer half of the shell in
almost all eggs, filling of pore canals with secondary
calcite, and fusion of eggshell surface all collectively
favour the second scenario of recurrent flooding of
nesting sites, a feature common among modern shore
birds (gulls, sterns, some waders, and ducks). Most of
the eggs found indicate that nests were open, laid on
grounds, and often flooded as a result of fluctuating
water levels.

1266
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
APPENDIX 1
DATA MATRIX (\=ambiguiti; & = polymorphism; matrix based on Clarke, Norell, 2002; Zhou, Zhang, 2006)
10 20 30 40 50 60 70 80 90 100
Anas
2111?21021 2111111101 1221102111 2111111101 1000111101 1212101010 6211011121 31131011 0110110100 ?10\11110111
Chauna
1111?10211 2111\2111101 0221101111 2111111101 1000111101 1212101210 6211011111 3111140010\1 0110110101 1111010111
Gallus
1111?10211 2112111101 1221101111 111111111 1000110101 1212101011 621001111\21 3111121012 0012110101 1111110111
Crax
2111?10211 2112111101 1221101111 1111111101 1000110101 1212101011 6211011121 3111121012 0012110101 1111110111
Crypturellus
2111?11211 2110\1010100 10111110101 1001101111 1131100101 0212101011 6210110221 311112?010 0012110101 10101110111
Lithornis
2111?11211 21100?0100 0111110101 10?110\11101 ?1111?01?1 02121012?0 5&611?1?11\21
\21 3111221010 0?10110101 0111100111
Ichthyornis
1\21010?11? ???????0?? ????100\11?1 1101110100 102????101 ?0\11200111? 4&51100211\2
?? 31102200?0 0?10110100 ?111100111
Hesperornis
110010?111 1112001?1? 0?1010??11 10011100?? 00?????101 0212101100 501001121? 1?0002020? 001??0?100 ?0???00000
Baptornis
l\2???????? ?????????? ?????????1 100??0??1? 1????????? ?212101100 401001121? 1\2\3??012???
? ??1010?100 ?0???0000?
Patagopteryx
????????? ????????0? 0?1??????0 0??1111100 00???????? ?201000000 30???????? ????0????? ??10010??? ??0101??1?
Calhayornis
0\100010?01? ??1??????? ?????????? ?????????? ?0??????0? ????0111?? 201?0?10?? 30??1\2??012 1?11011??? ??010?1011
Concornis
?????????? ?????????? ?????????? ?????????? ?????????? ????01111? ??????10?? 30??1?0012 1011011??0 ?001001012
Neuquenornis
?????????? ?????????? ?????????? ?????????? ?????????? ????0110?? ?????????? 31?????011 1?1?011010 ?001?01012
Gobipteryx
1111?10010 000?001?1? 0?10????00 ?????0???0 0??0???1?? ?????????? 3\4?????10?? ????????12 1?11010010 ?0?1001011
Gobipipus
11111110?? ?0?????1?? ????1???1? ???10????? ???1????11 ?????????? ?????????? ?1????1100 1?11111000 ?0010???11
Apsaravis
???1?10??? ?????????? ?????????? ??0?10\1????? ?1?0?????? ?2?20010?0\1 4010011??? 31??1????? ??10010010 ?0?1001011
Yanomis
10010??010 ?1???????? ?????????? ?????????? ?1001?1?01 0001001100 30????1110 31??1?1010 0010110100 ?1?1100?11
Yixianornis
10?011?01? ????????? ????????? ?????????? ?1001?1?01 0001001100 3?10??1110 31?01?1010 0110110100 ?1?1101?11
Hongshanornis
?111???010 ?1???????? ?????????? ?????????? ?00?????01 ?0????0??? ??1???1110 1\2\3??????01
1?01?111??? ?0?10????1
Archaeorhy
chus
1111???010 00???????? ?????????? ?????????? ?????????? ?????????? 10???1\2??1\20 2\31??l?0010 011?110??? ?1?10????1
Liaoningomis
?????????? ?????????? ?????????? ?????????? ?????????? ?????????? ?????????? 21?01?0??? ???????0??? ?0????????
Confuciusornis
1111?0&10010 010??????? ????10??00 ??011200?? ?11\2?111110 01000?00&10
0101000100&10 2000120001 ?00?010010 ?0??0???00
Sapeomis
0011110000 00???????? ?????????? ??0????000 01?00???0? 01000?00&10
010100?1000 ???????001 0000000000 ?0?1000?11
Jeholornis
?110110010 00???????? ?????????? ??0????000 000?0???1? 0000000200 0000000?00 0?001?0000 0010010000 ?1?1001011
Archaeopteryx
000010?000 0000000??00 0110??00?0 ??000?00?? ?00????00? 0000000000\1 0000000?00 0\1??????000 000?000000 ?000000000
Dromaeosau
ridae 000000?000 0000000000 000000?000 0?000??? 000????000 0000000000 0000000?10 0?00000001 000?000000 ?000000000

PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
AN EMBRYONIC ENANTIORNITHINE BIRD AND ASSOCIATED EGGS 1267
APENDIX (Contd.)
110 120 130 140 150 160 170 180 190 200
Anas
1000011100 1100120110 0001011101 1111111231 1301101011 1021??1111 1101111111 1110112102 1100210311 12\322100001 02
Chauna
1010211100 1100120110 0001011101 1011111231 1302202222 1021??1111 1111111112 1110212102 1200211311 1222221001 00
Gallus
1100111110 1100120110 0001011101 1011111131 1303101121 1021??1121 1111111112 1110212102 1100211311 1322221001 11
Crax
1100111110 1100120110 0001011101 1011111131 1301101121 1021??1111 1111111112 1110212102 1100211311 1322221001 10
Crypturellus
1100111110 1100120110 0001110101 1011111031 1301101111 10201?1120 1101111112 1110212102 1100211311 1222210\1001 01
Lithornis
1?01111100 110011\21110 0001010101 1011111131 12011100\111 1020&100112
0 1101111112 111021201 1000211311 1222211001 00&1
Ichthyornis
1110111100 1011111010 0001010&1101 1121111?31 1101110011 ?12000110\10 0101?11?12 1110212111 1100211311 11\22?210000 02
Hesperornis
10??0????? ???????0?? ??0??????? ?????????? ?????????? ??201?1110 0001111112 1110212111 1100211311 1122210220 02
Baptornis
????0????? ???????0?? ???????01 ??0\110\1????? ?????????? ??201?1110 0001111112 1110212111 1100211211 1122212020 ?2
Patagopteryx
1100\100???0\l ?10????010 00000?0\1001 ??1\200???3? 0????????0 0?20001000 0?011011?2 ?0????20?0 ?001\2111310 0110000000 ?0\1
Cathayornis
0000100101 100\0?102011 111?0\1?1?? 1???210121 001?1?01?0 1010011??0 ?000?000?1 1???111\20?0 ?0?10\11?0\1
?0 ??????0??? ??
Concornis
0???0\ 1001?1 10??102?1? ??10???10\11 ??1\2??????? ?????????0 1????????? ?????00?1? ??????20?0 ?00??111?0 0??1???0\11? ?0
Neuquenornis
0???l\2??l?? ?01????0?? ???0/1???1?1 1???2???21 001???01?? ?????????? ?????????1 10?1?1?0?? ?????1?0\1 ?0 ???1?0111? ??
Cobipteryx
0?001\2001?1 ?011???0?? ?????????? 11?121??0\1\2? 0??????1?0 ??1??????? ???0???1?? ?0????1?10 ?001111110 00?11?111? 0?
Gobipipus
1000100001 ?011000111 111?0?0011 ???0010?01 00?10?1000 ??10?????? ?0????1?10? ??????1?1? ??01?00??? ?????????? ??
Apsaravis
11011111?0 1011101\2011 1110000101 1021110?2\31 1101100?? ??201?110\10 010111111? 111??2?10 1211211131 011?201000 ?1
Yanornis
100111110? 11100?2011 0011000001 1???211131 10010??001 00201?1100 10?10000?2 1?????2?10 0111?11311 0201001000 00
Yixianornis
110011110? 1110???01? ?01??00001 1020211131 1100100001 00201?1100 10010001?2 10???1211? 01??211311 0201001000 02
Hongshanomis
10000111?? ?110??2??? ?0???????? 1????1??21 0000??0001 00?01?1??0 ?0??000??? ??????2??? ?1???112\310 0??0\1??100? ??
Archaeorhyn
chus
10001111?? 0110????1? ?0??????01 1??011??1\2\31 10000??001 001\201?1?00 00?10000?? ??????0\1\21?0 0?0??1?210 0?00\100100? 00
Liaoningornis
?????????? ?????????? ??0?????01 ????2????? ?????????? ?????????? ??????0011 1?1?0121?? 0011111211 020100100? 00
Confuciusornis
00?00000?0 0021??0010 0000000101 0021010111 1\20\1100?0000 0010011000 0000000011 1010112000 1000111 100 001110100? 00
Sapeornis
00?01000?0 0100??1010 0000100001 0000010011 10000??000 0000001100 00?000010? ?0????2010 ?000010100 000100100? 00
Jeholornis
00000000?0 0100??000? ?000?00001 0000011111 00000?0000 0000001100 ?00000000? 10100?0000 0000010100 000100100? 01
Archaeoptervx
00?00000?0 01100?000? ?000?00001 000000??00 00000?0000 0000000000 ?0??0000?0 00000000?0 0?0?0\110100 00000?100? ??
Dromaeosau
ridae 00?00000?0 01000?000? ?000?00001 000000??00 00000?0000 00000000&10 00000&10000&
10 0000000000 0000000000 00000\10000? 00

1268
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
KUROCHKIN et al.
ACKNOWLEDGMENTS
We thank the late Halszka Osmolska and Karel
Sabath for allowing studying embryos of
Gobipteryx
at
the Institute of Paleobiology of the Polish Academy of
Sciences. We also thank Andrzej Elzanowski, Tom
Lehman, J. Mathias Starck, Lawrence M. Witmer,
and David B. Weishampel for review of the manu
script, Ben Creisler for suggesting the generic name,
and Richard Porter for photography. This research was
supported by the RussianMongolian Paleontological
Expedition, the Frank M. Chapman Memorial Fund
of the American Museum of Natural History, and
Texas Tech University, and the Russian Fund for Basic
Research, grants 960450822, 100400575 and
961598069.
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