Spinosaurus aegyptiacus is an enigmatic species of theropod dinosaur from the Late Cretaceous of North Africa (~113-93 mya). The first specimen was discovered in 1912 by German paleontologists and fossils collectors, but these fossils were lost in the bombing of Munich during World War II. Using photographs, fragmentary remains and newly discovered partial skeletons, paleontologists are beginning to piece together the biology of this dinosaur. It had a long slender skull, like that of a crocodile, and enormous neural spines of the vertebrae on its back which would have given it a sail. Recent discoveries have shown that its leg bones were more compact than those of other theropod dinosaurs, suggesting that it spent a large part of its life in a semi-aquatic environment, probably hunting for the giant fish that lived in the North African rivers in the Cretaceous. Size estimates have suggested that it is the largest known theropod dinosaur, and at around 50 feet in length, it is longer than the longest T. rex known.
The first fossils of Spinosaurus aegyptiacus were discovered by a German fossil collector named Richard Markgraf in the autumn of 1912 (Smith et al. 2006). He was supported both financially and scientifically by the Bavarian paleontologist Ernt Freiherr Stromer von Reichenbach and the Bavarian Academy of Sciences (Smith et al. 2006). The fossils were dated to the earliest part of the late Cretaceous, an age called the Cenomanian (~97 mya) (Smith et al. 2006) and were discovered in the Bahariya Formation in the Bahariya Oasis of western Egypt (Smith et al. 2006). The holotype is a partial skeleton consisting of part of the lower right jawbone called the dentary, a fragment of the upper jaw bone, or maxilla, and a number of vertebrae with high neural spines (see morphology for description). These fossils were destroyed in World War II when a British bombing raid partially destroyed the museum where they were stored.
The first fossils of Spinosaurus aegyptiacus were discovered by a German fossil collector named Richard Markgraf in the autumn of 1912 (Smith et al. 2006). He was supported both financially and scientifically by the Bavarian paleontologist Ernt Freiherr Stromer von Reichenbach and the Bavarian Academy of Sciences (Smith et al. 2006). The fossils were dated to the earliest part of the late Cretaceous, an age called the Cenomanian (~97 mya) (Smith et al. 2006) and were discovered in the Bahariya Formation in the Bahariya Oasis of western Egypt (Smith et al. 2006).
For a long time, this was the only specimen of S. aegyptiacus known. It was, however, lost during World War 2 during the night of the 24th-25th April 1944 (Smith et al. 2006). A British bombing squadron bombed Munich, and the building that housed the Paläontologische Staatssammlung München where the specimen was exhibited was damaged (Smith et al. 2006). Much of Stromers Bahariya specimens were lost, including the fossils of Spinosaurus (Smith et al. 2006). However, in 1995, Wolfgang Stromer, Ernst Stromer’s son donated two photographs to the Paläontologische Museum which show the bones in the way they were exhibited in the Paläontologische Staatssammlung München in 1944 (Smith et al. 2006). This allowed scientists to compare the morphology from the drawings from Stromer’s 1915 paper to the actual bones, giving them a better idea of what the holotype (first specimen of an organism to be discovered) looked like.
Since then, a number of fragmentary remains of Spinosaurus aegypticus have been recovered (Buffetaut 1989, Russell 1996, Benton et al. 2000, Buffetaut and Ouaja 2002, Dal Sasso et al. 2005). For example, part of the snout of Spinosaurus was found in Southern Morocco in 1975, but was housed in a private collection till 2002 (Dal Sasso et al. 2005). This specimen was found in the Kem Kem red sandstone of Morocco near the town of Taouz (Dal Sasso et al. 2005). Since 2002, the specimen has been housed at the Museo di Storia Naturale di Milano in Milan, Italy (Dal Sasso et al. 2005). Then, in 2009, Dr. Nizar Ibrahim of the University of Chicago unearthed another partial skeleton of Spinosaurus, this time in Morocco. Dr. Ibrahim was finishing up an expedition in Morocco in 2008 when a man from the near by town of Erfoud approached him (Witze 2014). He showed him some bones he had found. Dr. Ibrahim suspected the bones to be important and sent them to the University of Hassan II in Casablanca (Witze 2014). In 2009, when Dr. Ibrahim was at the Natural History Museum in Milan, he saw the remains ofSpinosaurus from Morocco. After noticing the similarity of the bones in Milan to those the man had showed him the previous year, Dr. Ibrahim flew back to Morocco to find him (Witze 2014). He had no more than a vague recollection that the man had a mustache to go by, making the task of finding him seemingly impossible. On his second to last day in Erfoud, while he was sitting at a local café, the man walked by (Witze 2014). This seemingly perfect alignment of the stars led Dr. Ibrahim to the cave where the man had found the bones. These bones, along with other discoveries in the past have allowed scientists to get a clearer picture of the morphology of Spinosaurus aegyptiacus.
The holotype of Spinosaurus aegyptiacus was discovered in the Bahariya Formation in the Bahariya Oasis of western Egypt (Smith et al. 2006). It dates to the late Cretaceous, in an age called the Cenomanian (~97 mya) (Smith et al. 2006). Later, disarticulated remains and partial skull fragments have been recovered in the Kem Kem beds of the Cenomanian of Morocco and Albian age of the Cretaceous from Algeria (113-100 mya) (Buffetaut 1989, 1992, Russell 1996, Taquet and Russell 1998). Additionally, specimens have also been recovered from the Chenini sandstone of Tunisia, dating to the early Albian as well (~113 mya)(Benton et al. 2000, Buffetaut and Ouaja 2002). A new partial skeleton was discovered in the Kem Kem beds of Morocco in2009 (Ibrahim et al. 2014). This is, relatively, the most complete specimen recovered since the holotype was discovered in 1912.
Spinosaurus aegyptiacus belongs to the family Spinosauridae, and the sub-family Spinosaurinae (Carrano et al. 2012). The family Spinosauridae is divided into two sub-families-Baryonychinae and Spinosaurinae. The sub-family Baryonychinae consists of the European Baryonyx and the North African Suchomimus, while the sub-family Spinosaurinae consists of the North African Spinosaurus, the South American Irritator and Angaturama (Carrano et al. 2012). In North Africa, Suchomimus is found in sediments predating those in which Spinosaurus is found (Sereno et al. 1998).
Spinosaurus aegyptiacus is the name of the holotype described by Stromer in 1915. This specimen was discovered in the Bahariya Formation in Egypt. Since then, a number of Spinosaurus fossils have been recovered in Morocco. Based on the structure of a single cervical vertebra (neck vertebra), Russell classified another species, Spinosaurus maroccanus (Russel 1996). Russell and colleagues have since referred other Moroccan specimens to S. maroccanus (Taquet and Russell 1998). However, a number of scientists have suggested that the type of S. maroccanusdoes not provide adequate distinguishing features to call it a separate species, and have thus classified it as a nomen dubium of S. aegyptiacus (Sereno et al. 1998, Buffetaut and Ouaja 2002, Dal Sasso et al. 2005, Ibrahim et al. 2014). The most recent study on Spinosaurus has synonymized Stromer’s ‘Spinosaurus B’, which was once classified as Charcharodontosaurus saharaicus (Sereno et al. 1996), with S. aegyptiacus (Ibrahim et al. 2014). This study also classifies Sigilmassasaurus brevicollis as a junior synonym of S. aegyptiacus. Sigilmassasaurus brevicollis has been classified as a Charcharodontosaurus in earlier studies (Carrano et al. 2012).
No complete skeleton of Spinosaurus has been found. Since the holotype was lost during World War II, bones that have been attributed to Spinosaurus have been done so based on comparisons with the drawings and photographs of Stromer’s specimens and comparisons with other members of the family Spinosauridae, such as Suchomimus, Irritator, and Baryonyx.
A complete skull of Spinosaurus has not been found to date. What we know comes from fragmentary remains that have been referred to Spinosaurus. Stromer (1915) found a nearly complete right dentary (lower jaw bone) and described, but did not picture, a piece of the maxilla (one of the upper jaw bones) that had four alveoli, or tooth sockets (Smith et al. 2006). This dentary is about half a meter (~1.5 feet) in length. Two specimens of the snout have been recovered, one housed in Milan and the other in Paris.
The Milan specimen (MSNM V4047) was found in Southern Morocco. It is about 1m in length (about 3 feet) and consists of the premaxillae (bones of the tip of the snout), the maxillae (bones immediately behind the premaxilla) and the tips of the nasal bones (bones that usually bear the nostrils and are located adjacent to the maxillae) (Dal Sasso et al. 2005). The premaxillae have 6 alveoli (small holes) on each side, while the maxillae have 12 on either side (Dal Sasso et al. 2005). The overall shape of the snout is long and narrow, resembling that of an African Slender- Snouted Crocodile. The second and third teeth on the premaxilla are the largest, while the fourth tooth on the maxilla is the largest on this bone (Dal Sasso et al. 2005). On the maxilla, teeth increase in size till the fourth tooth and then decrease to the twelfth. The teeth are conical in shape, but the largest teeth are somewhat flattened labiolingually (from tongue side to cheek side) (Dal Sasso et al. 2005). They have no serrations, but have vertical ridges running along the length of the teeth. The tip of the snout has a number of pits (Dal Sasso et al. 2005). These likely served a sensory function.The nares or nostrils emerge laterally from the skull, but unlike other theropods, they are placed far back on the skull. The position of the nostrils on the upper lateral portions of the skull corresponds to the position of teeth 9 and 10 of the premaxilla (Dal Sasso et al. 2005). Interestingly, only the nasal bones and the maxilla form the nares (Dal Sasso et al. 2005). The premaxilla does not come in contact with the nasal bones to form the opening of the nares. This trait is unique among theropod dinosaurs. In other large theropod dinosaurs like Tyrannosaurus rex, or even members of the family Spinosauridae like Baryonyx, the nares are formed by the premaxilla, maxilla and nasals. A specimen housed at the University of Chicago (UCPC-2) that has been referred to Spinosaurus consists of the posterior portions of the nasal bones articulated with a portion of the maxilla and the lachrymal (another skull bone) (Dal Sasso et al. 2005). It has a ridge-like fluted crest on the nasal bones with a wrinkled texture (Dal Sasso et al. 2005). The wrinkling suggests vascularisation (innervation of blood vessels) of the crest (Dal Sasso et al. 2005). The height of the crest cannot be determined because it is heavily eroded.
The Paris specimen (MNHN SAM 124) was found in Albian (113-100 mya) sediments of Gara Samani from the Algerian Sahara. It is a snout from a mature individual, and consists of both premaxillae, the maxillae, vomers (another skull bone) and a fragment of the right dentary, or lower jaw bone (Taquet and Russell 1998). It is similar to the Milan specimen, except that each premaxilla has 7 teeth instead of 6 (Taquet and Russell 1998). Taquet and Russell suggest that this specimen has affinities to Spinosaurus maroccanus Russell 1996, but this species has since been synonymized with S. aegyptiacus (Taquet and Russell 1998, Dal Sasso et al. 2005).
Of the other sizeable skull specimens, a 115 mm (4 inch) long anterior fragment of the right dentary (BM 231) was found in the Albian Chenini Formation of Jebel Miteur in Southern Tunisia. This specimen has been attributed to S. aegyptiacus (Buffetaut and Ouaja 2002). Other small fragmentary remains of the upper and lower jaws, referred to S. aegyptiacus, have been found in Southern Morocco (Buffetaut 1992). Another specimen of the upper jaw housed in the collections of the Natural History Museum in London, NHMUK 16665 has been used in studies of Spinosaur feeding mechanics, but never been formally described (Cuff and Rayfield 2013).
Arguably, the most enigmatic feature of Spinosaurus aegyptiacus is its vertebral column. The specimen collected by Stromer (1915) had seven vertebrae with highly elongated neural spines (vertical extensions of bone from the upper surface of the vertebral column above the neural canal). These spines could be up to 2m (~6 feet) in length and are flattened and paddle-shaped.
While some have hypothesized that these elongated neural spines were covered by skin, forming a sail, much like that of Dimetrodon, others have suggested that the spines might have supported a hump-like structure, much like that seen in Bison or brontotheres (Bailey 1997). The exact function is still unclear, but it has been suggested that it acted as a display structure, or a thermoregulatory structure (Bailey 1997, Ibrahim et al. 2014). Since a complete vertebral column has not been found so far, the shape of the “sail” is still being debated. A recent reconstruction based on a composite of different Spinosaurid specimens, including Stromer’s holotype and new material found in Morocco has hypothesized that the spines were covered in skin and the sail thus formed would have risen sharply from the base of the neck, made a gentle curve over the back and then sharply descended to the base of the tail (Ibrahim et al. 2014). Based on this reconstruction, the sail would have looked like that of a sailfish.
Limbs and Pelvic Girdle
The first hind limbs and pelvic bones of Spinosaurus aegyptiacus were discovered by paleontologists in 2009 and described in 2014. They are part of the first moderately complete specimen of Spinosaurus discovered since Stromer’s expedition in 1912. Besides these bones, the 2009 expedition also uncovered parts of the vertebral column, fragments of the skull, and a few bones of the manus or hand (Ibrahim et al. 2014). Ontogenetic analyses suggest that this individual was a subadult, 17± 2 years of age, when it died (Ibrahim et al. 2014).
Of the pelvic bones found, the ilium was longer than the length of the femur (thigh bone). The area of the iliac blade is also reduced compared to most theropods (Ibrahim et al. 2014). The femur or upper leg bone of this specimen is shorter than the tibia, (larger of the two shin bones). The femur has a robust attachment site for the caudofemoral muscles (Ibrahim et al. 2014). These muscles allow for the posterior flexing of the leg (moving your shin backwards towards your buttocks). A more robust attachment site can imply larger muscles, which would have given the animal a formidable back kick. The last or distal bones of the toes are long, large and flattened at the bottom in contrast to the more curved bones of other theropod dinosaurs. This suggests that the claws on its feet were flattened on the bottom.
One of the more interesting findings of this study was the osteosclerotic nature of the femur. Osteosclerosis is the increase in bone density or compactness. Typically, theropods have a hollow shaft in the femur, a space called the medullary cavity. This space contains bone marrow. In the subadult specimen, the femur lacked this cavity and was very dense (Ibrahim et al. 2014). The compactness of the bone compared to that of the King Pengiun, an avian dinosaur (bird) adapted for an aquatic lifestyle (Ibrahim et al. 2014). Indeed, such adaptations are also found in mammals that are adapted for an aquatic lifestyle such as the manatee, hippopotamus and the extinct aquatic sloth Thalassocnus (Amson et al. 2014). Within the spinosaurids, this characteristic seems to be unique to Spinosaurus since other members of the family such as Suchomimus had femora with a medullary cavity (Ibrahim et al. 2014). These dense leg bones would have provided more stability to Spinosaurus in an aquatic environment.
Other skeletal elements
Large claws found in the Kem Kem have been attributed to Spinosaurus (Russell 1996, Ibrahim et al. 2014). Other spinosaurids, like Baryonyx, do have similar large claws. Thus, while it cannot be conclusively stated that these claws belong to Spinosaurus, it is a reasonable assumption to make. In their 2014 study on Spinosaurus, Ibrahim et al. suggest that the bones of ‘Spinosaurus B’, a second partial skeleton unearthed by Stromer, belonged to Spinosaurus aegyptiacus (Ibrahim et al. 2014). This based this on the similarity between the bones found by Stromer and those found by their expedition in Morocco.
Scientists have produced a number of body size estimates for Spinosaurus aegyptiacus. For example, Dal Sasso et al (2005) estimated the Milan specimen of Spinosaurus to be about 16m- 18m (50-60 feet) in length based on their reconstruction of the skull and gave it a body weight of 7-9 tonnes. However, a revision of the body size estimates predicted the Milan specimen to be about 12.57-14.34m in length (41-47 feet) and between 12-20 tonnes (Therrien and Henderson 2007). In the most recent study on Spinosaurus aegyptiacus, Ibrahim and colleagues estimate the adults would be around 15m in length (50 feet). Estimates of dinosaur size from incomplete remains are notoriously hard to determine; therefore, the true size range of Spinosaurus will only be determined when more specimens have been discovered. Most of the estimates, however, surpass the maximum length and weight estimates for Tyrannosaurus rex.
Until recently, hypotheses about the ecology of Spinosaurus aegyptiacus were based on tooth and skull morphology, isotopic analyses of the teeth, and biomechanics of the jaws (Holtz 1998, Rayfield et al. 2007, Amiot et al. 2010, Cuff and Rayfield 2013). A crocodilian analog has been proposed by many authors, given the conical shape of the teeth, the slender form of the jaws, and biomechanical similarities of Spinosaurids with extant crocodilians like the gharial (Holtz 1998, Rayfield et al. 2007). However, more recent biomechanical studies looked at the amount of side- to-side stress, up-and-down stress, and torsion stress the jaws of Spinosaurus, Baryonyx and modern crocodilians like the American alligator, gharial, and the slender snouted crocodile couldwithstand (Cuff and Rayfield 2013). The dinosaurs outperformed the crocodilians, mostly due to their size (Cuff and Rayfield 2013). When size was taken into account, Spinosaurus did not withstand the stresses on the jaws as well as a gharial or slender snouted crocodile (Cuff and Rayfield 2013). This study concludes is that the ability of a Spinosaur to hunt struggling fish developed as the animal grew in size, and it likely had a more varied diet throughout its life (Cuff and Rayfield 2013). Isotopic analyses of Spinosaurus teeth have revealed that the dinosaurs lived in a semi-aquatic habitat (Amiot et al. 2010). This supports the hypothesis that fish made up a large part of their diet. It has also been suggested that Spinosaurids used their large claws to gaff fish (reviweed in Rayfield 2011). Recent evidence of osteosclerosis in the femur of a Spinosaurus aegyptiacus specimen from Morocco adds credence to the assertion that Spinosaurs lived and hunted in a semi-aquatic habitat (Ibrahim et al. 2014). Ibrahim and colleagues also argue that the retracted nostrils (see morphology), flat feet (see morphology) and elongated neck suggest that the animal might have spent time in the water, possibly swimming (Ibrahim et al. 2014).
Spinosaurus aegyptiacus co-existed with three other large predatory theropods- Charcharodontosaurus, Deltadromeus and a ceratosaur (Sereno et al. 1996, Holtz 1998). It has been hypothesized that resource partitioning with the other large predatory dinosaurs like Charcharodontosaurus and Deltadromeus has resulted in the unique morphology and niche for Spinosaurus (Holtz 1998). Along with these predatory dinosaurs, Spinosaurus lived along side a menagerie of crocodilians, sauropods, iguanodontids, pterosaurs, and turtles. The rivers were populated with the giant coelocanth Mawsonia, the sawfish Onchopristis, sharks, actinopterygians and lungfish (Ibrahim et al. 2014).