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Data discussed in this paper can be found in the supplementary
materials. All artifacts are stored at the Institute of Archeology
and Ethnography, Yerevan, Armenia. We thank the following
organizations for their financial support: the University of
Connecticut [2008–2014: Norian Armenian Programs Committee,
College of Liberal Arts and Sciences (CLAS), Office of Global
Affairs, Study Abroad; and CLAS Book Committee]; the UK
Natural Environment Research Council (grant IP-1186-0510), the
L. S. B. Leakey Foundation (2010 and 2011), the Irish Research
Council (2008 and 2009), and the University of Winchester.
We also thank P. Avetisyan and B. Yeritsyan, Institute of Archeology
and Ethnography, Republic of Armenia, for their collaboration.
Materials and Methods
Figs. S1 to S16
Tables S1 to S7
Databases S1 and S2
27 May 2014; accepted 19 August 2014
Semiaquatic adaptations in a giant
Nizar Ibrahim,1 Paul C. Sereno,1 Cristiano Dal Sasso,2 Simone Maganuco,2
Matteo Fabbri,3 David M. Martill,4 Samir Zouhri,5 Nathan Myhrvold,6 Dawid A. Iurino7
We describe adaptations for a semiaquatic lifestyle in the dinosaur Spinosaurus
aegyptiacus. These adaptations include retraction of the fleshy nostrils to a position
near the mid-region of the skull and an elongate neck and trunk that shift the center of
body mass anterior to the knee joint. Unlike terrestrial theropods, the pelvic girdle is
downsized, the hindlimbs are short, and all of the limb bones are solid without an open
medullary cavity, for buoyancy control in water. The short, robust femur with hypertrophied
flexor attachment and the low, flat-bottomed pedal claws are consistent with aquatic
foot-propelled locomotion. Surface striations and bone microstructure suggest that
the dorsal “sail” may have been enveloped in skin that functioned primarily for display
on land and in water.
Bones of the predatory dinosaur Spinosaurus aegyptiacus first came to light over a cen- tury ago from Upper Cretaceous rocks in Egypt (1–3) but were destroyed in World War II (4). More recently, isolated teeth
and bones (5) and the anterior half of an adult
skull (6) have been discovered in the Kem Kem
beds of eastern Morocco (Fig. 1A) and equiv-
alent horizons in Algeria, but are insufficiently
complete to estimate the size, proportions, and
functional adaptations of this species. Here
we report the discovery of a partial skeleton of
S. aegyptiacus from the middle of the Kem Kem
sequence (Fig. 1B), which is probably Cenomanian
in age (~97 million years ago) (7).
The subadult skeleton, here designated the neotype of S. aegyptiacus (8), preserves portions of the
skull, axial column, pelvic girdle, and limbs. It was
discovered in fluvial sandstone that has yielded remains of the sauropod Rebbachisaurus (9) and three
other medium-to-large theropods (an abelisaurid,
Deltadromeus, and Carcharodontosaurus) (7, 10).
We regard two additional Kem Kem theropods,
Sigilmassasaurus brevicollis and S. maroccanus
(11, 12), to be referable to S. aegyptiacus (8).
The neotype skeleton and isolated bones refer-
able to S. aegyptiacus were scanned with com-
puted tomography, size-adjusted, and combined
with a digital recreation of the original Egyptian
fossils (Fig. 2A, red). Missing bones were extrap-
olated between known bones or estimated from
those of other spinosaurids (6, 13, 14). The digi-
tal model of the adult skeleton of Spinosaurus
(Fig. 2A), when printed and mounted, measures
over 15 m in length, longer than Tyrannosaurus
specimens (~12.5 m) (15).
A concentrated array of neurovascular foramina
open on the anterior end of the snout and appear similar to foramina in crocodilians that
house pressure receptors that detect water movement (8, 16) (Fig. 2B and fig. S6). The enlarged,
procumbent, interlocking anterior teeth are well
adapted for snaring fish (5, 6) (Fig. 2B and fig. S4).
The fossa for the fleshy nostril is small and, unlike
any other nonavian dinosaur, is retracted to a
posterior position to inhibit the intake of water
(Fig. 2C and figs. S4 and S6) (8).
Most cervical and dorsal centra are elongate
compared to the sacral centra, resulting in a proportionately long neck and trunk (Figs. 2A and 3
and tables S1 and S2). The anteriormost dorsal
centra, however, are proportionately short, exceptionally broad, and concavoconvex (Fig. 2D).
These characteristic vertebrae, the affinity of which
has been controversial (7, 11, 12), are referred
here to S. aegyptiacus, based on their association
with spinosaurid skeletons in Niger (8) and Egypt
(2). The horizontal cervicodorsal hinge created
by these broad centra would facilitate dorsoventral excursion of the neck and skull in the pursuit of prey underwater.
The distal two-thirds of the tail comprises vertebrae with relatively short centra, diminutive
zygapophyses, and anteroposteriorly compressed
neural spines (Fig. 2G). The affinity of these
caudal elements has been uncertain (17), but
comparisons with associated remains from Egypt
(2) and more proximal caudals in the neotype
(Fig. 2A) allow referral to Spinosaurus. Short
centra and reduced neural arch articulations
enhance lateral bending during tail propulsion
in bony fish (18).
The forelimb has hypertrophied deltopectoral
and olecranon processes for powerful flexion and
extension (Fig. 2A). Elongate manual phalanges
(Fig. 2H) and less recurved, manual unguals that
1Department of Organismal Biology and Anatomy, University
of Chicago, Chicago, IL 60637, USA. 2Museo di Storia
Naturale di Milano, Corso Venezia 55, 20121 Milan, Italy.
3School of Earth Sciences, University of Bristol, Queen’s
Road, Bristol, BS8 1RJ, UK. 4School of Earth and
Environmental Sciences, University of Portsmouth, Burnaby
Road, Portsmouth, PO1 3QL, UK. 5Laboratoire de
Géosciences, Faculté des Sciences Aïn Chock, Université
Hassan II, Casablanca, Morocco. 6Intellectual Ventures, 3150
139th Avenue Southeast, Bellevue, WA 98005, USA.
7Dipartimento di Scienze della Terra, Sapienza Università di
Roma, Piazzale Aldo Moro 5, 00185 Rome, Italy.
*Corresponding author. E-mail: email@example.com