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The distinctive spines of
Spinosaurus, which were
long extensions of the vertebrae, grew up to at least 1.69 meters (5.5 ft)
long and were likely to have had skin connecting them, forming a sail-like
structure, although some authors have suggested that they were covered in
muscle and formed a hump or ridge. Multiple functions have been put forward
for this structure, including thermoregulation and display. According to
recent estimates, Spinosaurus
is the largest of all known carnivorous dinosaurs, even larger than
Tyrannosaurus rex and
Giganotosaurus. These
estimates suggest that it was around 16 to 18 meters (52 to 59 ft) in length
and 7 to 9 tonnes (7.7 to 9.9 short tons) in weight.
Description
Although
Spinosaurus is well-known
to dinosaur enthusiasts due to its size, sail, and elongated skull, it is
mostly known from remains that have been destroyed, aside from a few more
recently discovered teeth and skull elements. Additionally, so far only the
skull and backbone have been described in detail, and limb bones have not
been found. Jaw and skull material published in 2005 show that it had one of
the longest skulls of any carnivorous dinosaur, estimated at about
1.75 meters long (5.75 ft). The skull had a narrow snout filled with
straight conical teeth that lacked serrations. There were six or seven teeth
on each side of the very front of the upper jaw, in the
premaxilla bones, and
another twelve in both
maxillae behind them.
The second and third teeth on each side were noticeably larger than the rest
of the teeth in the premaxilla, creating a space between them and the large
teeth in the
anterior maxilla; large
teeth in the lower jaw faced this space. The very tip of the snout holding
those few large anterior teeth was expanded, and a small crest was present
in front of the eyes.
The sail of
Spinosaurus was formed of
very tall
neural spines growing
on the back vertebrae. These spines were seven to eleven times the height of
the vertebrae from which they grew. The spines were slightly longer front to
back at the base than higher up, and were unlike the thin rods seen in the
pelycosaur finbacks
Edaphosaurus and
Dimetrodon.
Size
(Picture
Source)
Since its discovery,
Spinosaurus has been a top
contender for longest and largest theropod dinosaur, though this fact did
not reach the public consciousness until its depiction in the film
Jurassic Park III and the
description of a new specimen in 2005. Both Friedrich von Huene and Donald
F. Glut, decades apart, listed it as among the most massive theropods or the
most massive in their surveys, at upwards of 6 tons in weight and 15 meters
(49 ft) in length. In 1988, Gregory S. Paul also listed it as the longest
theropod at 15 meters (49 ft), but gave a lower mass estimate. More recent
estimates, based on new specimens, list
Spinosaurus at 16 to 18 meters (52 to 59 ft)
long and 7 to 9 tonnes (7.7 to 9.9 short tons) in weight.
François Therrien and Donald
Henderson, in a 2007 paper using scaling based on skull length, challenged
previous estimates, finding the length too great and the weight too small.
Their estimates include a length of 12.6 to 14.3 meters (41 to 47 ft) and a
mass of 12 to 20.9 tonnes (13 to 23 short tons). Their study has been
criticized for the choice of large theropods used for comparison (most of
the skeletons of large theropods used to set the initial equations are of
tyrannosaurids and
carnosaurs, which have
a different build than spinosaurids) and for issues relating to their
spinosaurid skull reconstructions. Resolution awaits more complete remains.
Sail
 |
| Illustration of
S. aegyptiacus
dorsal vertebrae by Ernst Stromer. |
Spinosaurus
sails were unusual, although other dinosaurs of the same time and area,
namely the
ornithopod
Ouranosaurus and the
sauropod
Amargasaurus,
might have developed a similar structural adaptation of their dorsal
vertebrae (however, this is not uncontroversial; see the articles about
these animals for more information). The sail is possibly
analogous (not
homologous) to that of
the Permian synapsid
Dimetrodon, which
lived before the dinosaurs even appeared; these similarities are due to
parallel evolution. The sail may also have been more hump-like than
sail-like; as noted by Jack Bowman Bailey most recently, spinosaur spines
are not thin rods but broad front to back, rather like those of some types
of buffalo, and so may have supported a thicker, fatty structure as opposed
to a skin sail.
The function of these sails is
uncertain; scientists have proposed several hypotheses including heat
regulation and display. In addition, such a prominent feature on its back
could also make it appear even larger than it was, intimidating other
animals.
If the sail contained abundant blood
vessels, the animal could have used the sail's large surface area to absorb
heat. This would imply that the animal was only partly warm-blooded at best
and lived in climates where nighttime temperatures were cool or low and the
sky usually not cloudy. It is thought that
Spinosaurus and
Ouranosaurus both lived in or at the margins of
an earlier version of the Sahara Desert, which could explain this. It is
also possible that the sail was used to radiate excess heat from the body,
rather than to collect it. Large animals, due to the relatively small ratio
of surface area of their body compared to the overall volume (Haldane's
principle), face far greater problems of
dissipating excess heat at higher temperatures than gaining it at lower.
Sails of these dinosaurs added considerably to the skin area of the body,
with minimum increase of volume. Furthermore, if the sail was turned away
from the sun, or positioned at a 90 degree angle towards a cooling wind, the
animal would quite effectively cool itself in the warm climate of Cretaceous
Africa.
Elaborate body structures of many
modern-day animals usually serve to attract members of the opposite sex
during mating. It is quite possible that the sails of these dinosaurs were
used for courtship, in a way similar to a peacock's tail. Stromer speculated
that males and females may have differed in the size of the neural spine.
If this was the case, the sails may have been brightly colored, but this is
purely speculative. Finally, it is quite possible that the sail combined
these functions, acting normally as a heat regulator, becoming a courting
aid during the mating season, being used to cool itself and, on occasions,
turning into an intimidating device when an animal was feeling threatened.
Posture
Although traditionally depicted as a
biped, it has been suggested since the mid-1970s that
Spinosaurus was at least
an occasional quadruped. This has been bolstered
by the discovery of
Baryonyx, a relative
with robust arms. This led to new restorations of Spinosaurus skeletons
depicting a quadrupedal posture. This hypothesis
has fallen out of favor, at least as a typical gait, though spinosaurids may
have crouched in a quadrupedal posture.
Classification
Spinosaurus
gives its name to a family of dinosaurs, the
Spinosauridae, of which
other members include
Baryonyx from southern
England,
Irritator and
Angaturama (which is
probably synonymous with Irritator)
from Brazil,
Suchomimus from Niger
in central Africa, and possibly
Siamosaurus, which is
known from fragmentary remains in Thailand.
Spinosaurus is closest to
Irritator, which shares
its unserrated straight teeth, and the two are included in the subfamily
Spinosaurinae.
Discovery and Species
The first described remains of
Spinosaurus were found in the
Bahariya Valley of Egypt in 1912, and were named by German
paleontologist
Ernst Stromer in 1915.
Fragmentary additional remains from Bahariya, including vertebrae and
hindlimb bones, were designated by Stromer as "Spinosaurus B" in
1934.
Stromer considered them different enough to belong to another species,
and this has been borne out; with the advantage of more expeditions and
material, it appears that they either pertain to
Carcharodontosaurus
or to
Sigilmassasaurus.
Some of the Spinosaurus fossils were damaged during transport back to
the
Deutsches Museum, in
Munich,
Germany,
and the remaining bones were completely lost due to Allied
bombing in 1944.
Two species of
Spinosaurus have been named:
Spinosaurus
aegyptiacus (meaning "Egyptian spine lizard") and
Spinosaurus
maroccanus (meaning "Moroccan spine lizard").
S. maroccanus was
originally described by
Dale Russell as a new species based on the length of its neck vertebrae.
Later authors have been split on this topic, some considering the length of
the vertebrae to be variable from individual to individual and therefore
regarding S. maroccanus as invalid or a synonym of
S. aegyptiacus,
and others retaining it as valid.
Specimens
Six partial specimens of
Spinosaurus have been
described. The probable size of these individual spinosaurs can be estimated
using comparison to known material from other
spinosaurid dinosaurs.
IPHG 1912 VIII 19,
described by Stromer in 1915 from the
Bahariya Formation, was
the
holotype. This
specimen, from a subadult individual, was destroyed in World War II.
However, detailed drawings and descriptions of the specimen remain. The
individual is estimated to have been around 14 meters (46 ft) long and to
have weighed about 6.7 tonnes (7.4 short tons). The material consisted of a
maxilla (upper jaw)
fragment, an incomplete dentary (lower jaw) measuring 75 centimeters (30 in)
long, (the skull is estimated to have been 1.45 meters (5 ft) long with a
mandible approximately 1.34 meters (4 ft) long), nineteen teeth, two
incomplete cervical vertebrae, seven back vertebrae, dorsal ribs,
gastralia, and eight
caudal centra (tail
vertebrae). The longest preserved vertebral spine was 1.69 metres (5.5 ft)
long. IPHG 1912 VIII 19 is the specimen that
Rauhut thought was chimeric.
 |
| S. maroccanus
jaw fossil, Muséum national d'Histoire
naturelle, Paris (From
Wikipedia) |
CMN 50791,
described by Russell in 1996 from the
Kem Kem Beds of
Morocco, is the
holotype of Spinosaurus maroccanus.
The material it is based on includes a mid-cervical vertebra which is
19.5 centimeters (7.7 in) long, an anterior dorsal
neural arch, an
anterior dentary, and a mid-dentary.
MNHN SAM 124,
described by Taquet and Russell in 1998 from Algeria, consists of partial
premaxillae, partial maxillae,
vomers, and a dentary
fragment. They came from an individual estimated to have been about
14 meters (46 ft) long and to have weighed about 6.7 tonnes (7.4 short
tons). The skull is estimated at approximately 1.42 meters (5 ft) long.
Office National des Mines nBM231,
described by Buffetaut and Ouaja in 2002, consists of an anterior dentary
from the
Chenini Formation of
Tunisia which is very similar to existing material of
S. aegyptiacus.
 |
| Specimen MSNM V4047 of
S. aegyptiacus in
al Museo di Storia Naturale di Milano (Picture
Source) |
MSNM V4047,
described by Cristiano Dal Sasso of the Civic Natural History Museum in
Milan and his colleagues in 2005 from the Moroccan Kem Kem Beds, consists of
premaxillae, partial maxillae, and partial
nasals, which together
measure 98.8 centimetres (38.9 in) long. The massive skull is estimated at
1.75 meters (6 ft) long, and the entire animal is estimated to have been
around 16 to 18 metres (52 to 59 ft) in length and weighed around 7 to 9
tonnes (7.7 to 9.9 short tons). UCPC-2,
also described by Dal Sasso et al.
in 2005, consists of a 'fluted crest' from the region in front of the eyes.
Other known specimens consist mainly
of very fragmentary remains and scattered teeth. For example, teeth from the
Echkar Formation of
Niger have been referred to S. aegyptiacus.
Possible material belonging to Spinosaurus
has also been reported from the
Turkana Grits of Kenya
and the Cabao Formation of Libya (which dates to
the
Hauterivian stage),
though the assignment of the later to the genus
Spinosaurus is tentative.
Paleoecology
The environment inhabited by
Spinosaurus is only
partially understood, and covers a great deal of what is now northern
Africa. Those Spinosaurus
that lived in what is now Egypt, for example, may have contended with
shoreline conditions on
tidal flats and
channels, living in
mangrove forests
alongside similarly large dinosaurian predators
Bahariasaurus and
Carcharodontosaurus,
giant
titanosaur sauropod
Paralititan, smaller
titanosaur
Aegyptosaurus,
10-meter (33-ft) long crocodilian
Stomatosuchus, and the
coelacanth Mawsonia.
A 2010 publication by Romain Amiot
and colleagues found that
oxygen isotope ratios
of spinosaurid teeth, including teeth of
Spinosaurus, indicate semiaquatic lifestyles.
Isotope ratios from tooth enamel of Spinosaurus
and the spinosaurids Baryonyx,
Irritator, and
Siamosaurus were
compared with isotopic compositions from contemporaneous theropods, turtles,
and crocodilians. The study found that
Spinosaurus teeth from five of six sampled
localities had oxygen isotope ratios closer to those of turtles and
crocodilians when compared with other theropod teeth from the same
localities, but that the differences were not as pronounced for
Spinosaurus as for other
spinosaurids. The authors noted that
Spinosaurus lived alongside both other large
theropods and large crocodilians, and postulated an opportunistic lifestyle,
switching between terrestrial and aquatic habitats.
It is unclear whether
Spinosaurus was primarily
a terrestrial predator or a fisher, as indicated by its elongated jaws,
conical teeth and raised nostrils. The hypothesis of spinosaurs as
specialized fish eaters has been suggested before by A. J. Charig and A. C.
Milner for
Baryonyx. They base
this on the anatomical similarity with crocodilians and the presence of
digestive acid-etched fish scales in the rib cage of the type specimen.
Large fish are known from the faunas containing other spinosaurids,
including the
Mawsonia, in the
mid-Cretaceous of northern Africa and Brazil. The only direct evidence for
spinosaur diet comes from related European and South American
taxa. Baryonyx
was found with both fish scales and bones from juvenile
Iguanodon in its
stomach, while a tooth embedded in a South American pterosaur bone suggests
that spinosaurs occasionally preyed on these flying archosaurs.
Spinosaurus was likely to
have been a generalized and opportunistic predator, possibly a Cretaceous
equivalent of large grizzly bears, being biased toward fishing, though it
undoubtedly scavenged and took many kinds of small or medium-sized prey.
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