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A Pair of Shelled Eggs Inside A Female Dinosaur

Authors:
Tamaki Sato at Kanagawa University
Tamaki Sato
Yen-nien Cheng
Yen-nien Cheng
Yen-nien Cheng
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Xiao-Chun Wu at Canadian Museum of Nature / Musée canadien de la nature
Xiao-Chun Wu
Darla Karen Zelenitsky at The University of Calgary
Darla Karen Zelenitsky
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Abstract

An oviraptosaurian specimen (Dinosauria, Theropoda) from an Upper Cretaceous formation in China retains a pair of shelled eggs in the pelvis, providing direct evidence that oviraptorosaurian dinosaurs laid paired elongatoolithid eggs. The presence of the paired eggs suggests that theropod dinosaurs had two functional oviducts (like crocodiles) but that each oviduct produced only one egg at a time and that an entire egg clutch was laid through multiple ovipositions (like birds). The orientations of the eggs inside the skeleton and in clutches indicate that the mother came to the center of the nest to lay eggs.
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A Pair of Shelled Eggs Inside
A Female Dinosaur
Tamaki Sato,
1
*
Yen-nien Cheng,
2
Xiao-chun Wu,
1
*
Darla K. Zelenitsky,
3
Yu-fu Hsiao
4
Reproductive biology is now an important topic
in the study of dinosaur-bird relationships (1).
Two immature eggs in Sinosauropteryx (2)and
discoveries of paired eggs in maniraptoran nests
(3–5) have been used to suggest that theropod
dinosaurs had paired functional oviducts. Oc-
currences of paired eggs in the nests may also
indicate a lack of egg rotation by the adults (5).
Maniraptoran specimens found atop egg
clutches might imply that entire egg clutches
were laid in a single
sitting (like crocodiles)
or laid in multiple sit-
tings (like birds) of the
adult female (4–6). We
present here a fossil
that tests these ideas.
The specimen is a
three-dimensional pel-
vis that contains a
single pair of shelled
eggs within its body
cavity (Fig. 1). It was
identified as an ovir-
aptorosaurian on the
basis of the pelvis
morphology and a
preliminary phyloge-
netic analysis (sup-
porting online text).
Aside from a shift to
the left side during
fossilization, we be-
lieve that the eggs
retain their approxi-
mate original orienta-
tion and position
within the oviducts.
Compared with the
immature eggs of
Sinosauropteryx (2),
these eggs are located
more caudally in the
body cavity and, on
the basis of their po-
sition relative to the
cloacal region, were
likely in the uteri at
death. The caudal end
of the right egg is
more pointed than
the cranial end of the
left egg (Fig. 1D),
suggesting a slightly asymmetrical profile
of the eggs in life. The left egg has mea-
surable diameters of 175 mm by 78 to 80
mm by 55 mm. The egg shape and surficial
ornamentations indicate an affinity to elon-
gatoolithids, and their microscopic structures
resemble those of Macroolithus yaotunensis
(supporting online text).
Two adult oviraptorid specimens have been
found atop ring-shaped clutches that contain at
least 15 eggs (6). Given the relatively large egg
size of our specimen, the position of the cloaca
(estimated as ventral to the anteriormost caudal
vertebra), and the inferred location for shell
deposition in the uterus as in modern birds and
crocodiles, it is unlikely that this specimen
could have had multiple pairs of shelled eggs
inside the body at one time. Unless sequential
eggformationandshellingwasveryrapidand/
or there was an extremely prolonged period of
egg laying, the preservation of only two tightly
juxtaposed eggs in the specimen strongly in-
dicates that each of the paired oviducts simul-
taneously produced a single egg. This supports
the theory that maniraptoran dinosaurs retained
two functional oviducts like crocodiles but had
reduced the number of eggs ovulated to one per
oviduct, as in birds.
The pairedness of eggs in some oviraptoro-
saurian nests was therefore likely due to the
oviposition of two eggs nearly simultaneously,
rather than the result of egg manipulation by the
parent(s). It is also evident that, as in birds,
multiple ovipositions would have been required
to lay an entire clutch. Furthermore, the slightly
pointed end of each egg directing caudally
inside the body and toward the periphery in the
nests (4) suggests that the females came to the
centers of the nests to lay neat, multilayered,
ring-shaped clutches.
References and Notes
1. D. J. Varricchio, F. D. Jackson, in Feathered Dragons,P.J.
Currie, E. B. Koppelhus, M. A. Shugar, J. L. Wright, Eds.
(Indiana Univ. Press, Bloomington, IN, 2004), pp. 215–233.
2. P.-J. Chen, Z.-M. Dong, S.-N. Zhen, Nature 391, 147 (1998).
3. M. A. Norell, J. M. Clark, L. M. Chiappe, D. Dashzeveg,
Nature 378, 774 (1995).
4. Z.-M.Dong,P.J.Currie,Can. J. Earth Sci. 33, 631 (1996).
5. D. J. Varricchio, F. Jackson, J. J. Borkowski, J. R. Horner,
Nature 385, 247 (1997).
6. J. M. Clark, M. A. Norell, L. M. Chiappe, Am. Mus.
Novit. 3265, 1 (1999).
7. We thank M. Norell and C. Mehling of the American
Museum of Natural History, New York, for access to the
oviraptorid egg nests and R. Holmes of the CMN for
reading earlier drafts. T.S., D.K.Z., and X.-C.W. were
supported by the Japan Society for the Promotion of
Science, Alberta Ingenuity Fund, and the CMN, respectively.
Supporting Online Material
www.sciencemag.org/cgi/content/full/308/5720/375/
DC1
SOM Text
Fig. S1
References and Notes
2 February 2005; accepted 4 March 2005
10.1126/science.1110578
BREVIA
1
Canadian Museum of Nature (CMN), Post Office Box
3443, STN D, Ottawa, Ontario K1P 6P4, Canada.
2
National
Museum of Natural Science, 1 Kuan Chien Road, Taichung,
Taiwan (ROC).
3
The University of Calgary, Department of
Geology and Geophysics, 2500 University Drive North-
west, Calgary, AB T2N 1N4, Canada.
4
Paleowonders Fossil
and Mineral Museum, 442 Section 2, Wen-Hwa Road,
Banchiao, Taipei, Taiwan (ROC).
*To whom correspondence should be addressed.
E-mail: tsato@mus-nature.ca (T.S.); xcwu@mus-nature.ca
(X.-c.W.)
Fig. 1. The oviraptorosaurian specimen at the National Museum of Natural
Science in Taiwan (specimen no. NMNS-VPDINO-2002-0901) was
excavated from the Upper Cretaceous Nanxiong Formation of the
Hongcheng Basin near the city of Ganzhou, in the southern Jiangxi Province,
China. It consists of six sacral vertebrae; the first two caudal vertebrae; the
ilia, pubes, ischia, and femora; the lower part of the left leg; and a pair of
eggs inside the pelvis. The pubes and ischia are slightly disarticulated, but
otherwise these bones retain their original anatomical relationships. The
eggs are located dorsal to the pubic symphysis, about one egg length
anterior to the cloacal region. They are side by side and closely apposed,
although the right egg was slightly more ventrally positioned than the left
egg. Y.-n.C. and Y.-f.H. supervised the preparation of NMNS-VPDINO-2002-
0901, confirming that it is not a composite. (A and B) Right lateral view. (C)
Left lateral view. (D) A right close-up view of the two eggs. Caud, caudal
vertebrae; e, egg; lfib, left fibula; lpu, left pubis; ltib, left tibia; rfem, right
femur; ril, right ilium; ris, right ischium; rpu, right pubis; sac, sacral.
www.sciencemag.org SCIENCE VOL 308 15 APRIL 2005
375
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  • NATURE
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  • Jan 1998
  • NATURE
  • 147
  • P.-J Chen
  • Z.-M Dong
  • S.-N Zhen
P.-J. Chen, Z.-M. Dong, S.-N. Zhen, Nature 391, 147 (1998).
for access to the oviraptorid egg nests and R. Holmes of the CMN for reading earlier drafts
  • M We
  • C Norell
We thank M. Norell and C. Mehling of the American Museum of Natural History, New York, for access to the oviraptorid egg nests and R. Holmes of the CMN for reading earlier drafts. T.S., D.K.Z., and X.-C.W. were supported by the Japan Society for the Promotion of Science, Alberta Ingenuity Fund, and the CMN, respectively.
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Z.-M. Dong, P. J. Currie, Can. J. Earth Sci. 33, 631 (1996).
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  • J M Clark
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  • L M Chiappe
J. M. Clark, M. A. Norell, L. M. Chiappe, Am. Mus. Novit. 3265, 1 (1999).
  • Jan 1995
  • 774
  • M A Norell
  • J M Clark
  • L M Chiappe
  • D Dashzeveg
M. A. Norell, J. M. Clark, L. M. Chiappe, D. Dashzeveg, Nature 378, 774 (1995).
3 The University of Calgary, Department of Geology and Geophysics, 2500 University Drive Northwest, Calgary, AB T2N 1N4, Canada. 4 Paleowonders Fossil and Mineral Museum, 442 Section 2, Wen-Hwa Road
  • Kuan Chien Road
Kuan Chien Road, Taichung, Taiwan (ROC). 3 The University of Calgary, Department of Geology and Geophysics, 2500 University Drive Northwest, Calgary, AB T2N 1N4, Canada. 4 Paleowonders Fossil and Mineral Museum, 442 Section 2, Wen-Hwa Road, Banchiao, Taipei, Taiwan (ROC).