The enigmatic theropod Spinosaurus aegyptiacus (“Egyptian spine reptile”) stands among the commonly recognisable dinosaurs to the general public with its distinctive dorsal spines. Hailing from coastal biomes from the Middle Cretaceous of North Africa, it was first discovered during the spring of 1912 by the German fossil collector Richard Markgraf, uncovering a partial skeleton which then became the holotype of the species by Ernst Stromer’s 1915 description. The specimen, catalogued as IPHG 1912 VIII 19, was mounted in the Palaeontological Museum of Munich where it remained until its destruction in World War II, during a British bombing raid at April 1944. While the loss of the holotypic specimen was unfortunate, the detailed drawings and descriptions of the specimen remained, as well as photographs. Additional remains soon came to light during the later part of the 20th century and afterwards, mostly in the form of isolated, fragmentary specimens.
A partial skeleton of a subadult (est. ~17 years at death) from Morocco was collected in 2008 and described in 2014, showing that Spinosaurus, and by extension other spinosaurines, possessed shorter hindlimbs and a smaller pelvic girdle than previously though. This specimen was catalogued FSAC-KK 11888 and erected as the neotype of S. aegyptiacus. A few years later the nearly-complete tail of the neotype individual was discovered after further expeditions and described in 2020, showing that the tail was shaped like a paddle.
While still incomplete, enough of Spinosaurus and its relatives are now known to make reasonable inferences about the animal’s morphology and habits. The animal would have possessed a long, slender skull, adorned with a fluted crest, a long neck, a ribcage approximating the shape of a sausage, and, again, the proportionally diminutive hindlimbs and paddle-shaped tail. The tall neural spines forming its distinctive dorsal ridge would have stretched across its back and hips. Isotope studies and bone density indicate a semiaquatic lifestyle for Spinosaurus. Swimming would have been propelled mainly by the paddle-shaped tail.
The reconstruction of the holotype takes cues from the neural spine arrangement proposed by Andrea Cau, based on the angle of the spines, although the first three neural spines have been moved back three positions from Cau’s proposal to accommodate a transition between the cervical and dorsal spines, and the posteriormost tall neural spine in a sacral rather than caudal position as the nearly complete tail from the neotype precluded a caudal placement.
The sacral centra of the holotype and neotype specimens appear to be similar in size, and furthermore their dorsal centra appear to be similar in diameter, thus they were reconstructed here as having similar-sized appendicular and caudal elements. The known cervical centra also appear to indicate a similar size between the necks of the two type specimens. Using the colour-coded reconstruction from Ibrahim et al. (2014) as a guide, their estimated skull lengths also end up similar. However, the dorsal centra of the neotype are greater in length, and thus, while the two specimens seem to scale to similar sizes in several aspects, the neotype ends up somewhat larger than the holotype due to a longer dorsal series. Both specimens end up at around ~11-11.5 metres.
Certain isolated specimens assigned to S. aegyptiacus suggest that adults possibly reached massive sizes and may have been among the largest known theropods. MSNM v4047, a 98.8 cm long rostrum described in 2005, is here scaled as an animal 132% the dimensions of the neotype, as per Ibrahim et al. (2014). This results in an animal about 15 metres long. Furthermore, a dentary, NHMUK R 16421, also suggests a very large theropod, perhaps as large or larger than MSNM v4047. The length of the element as preserved is 69 cm, broken off through the 17th dentary alveolus. If the dentary had a total of 17 alveoli when complete, scaling via the total toothrow lengths between NHMUK R 16421 and the holotype dentary (51 cm from the dentary tip to the midsection of the posteriormost dentary alveolus) yields an animal around ~135.3% the scale of the holotype. Anterior depth and width give scale factors of around ~127.5% and 153.3% respectively. The mean scaling factor obtained here, around ~138.7%, was used to scale NHMUK R 16421 here. This results in an animal nearly 16 metres long, longer than estimated for MSNM v4047 here despite the shorter dorsal column of the holotype specimen as compared to the neotype.
Missing portions not covered by any documented Spinosaurus material were filled in using Irritator, Sigilmassasaurus, Suchomimus and Baryonyx.
Reconstructed dimensions
- IPHG 1912 VIII 19
- Hip height: ~1.94 metres
- Back height: ~3.45 metres
- Shoulder height: ~2.35 metres
- Total height: ~3.73 metres
- Standing length: ~10 metres
- Axial length: ~11.16 metres
- FSAC-KK 11888
- Hip height: ~1.94 metres
- Back height: ~3.61 metres
- Shoulder height: ~2.43 metres
- Total height: ~3.8 metres
- Standing length: ~10.2 metres
- Axial length: ~11.4 metres
- MSNM v4047
- Hip height: ~2.56 metres
- Back height: ~4.77 metres
- Shoulder height: ~3.21 metres
- Total height: ~5.02 metres
- Standing length: ~13.44 metres
- Axial length: ~15 metres
- NHMUK (BMNH) R 16421
- Hip height: ~2.69 metres
- Back height: ~4.78 metres
- Shoulder height: ~3.26 metres
- Total height: ~5.17 metres
- Standing length: ~13.87 metres
- Axial length: ~15.5 metres
Note that back height includes the dorsal spines.
References
- Stromer, 1915, “Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens. II. Wirbeltier-Reste der Baharîje-Stufe (unterstes Cenoman). 3. Das Original des Theropoden Spinosaurus aegyptiacus nov. gen., nov. spec.“
- Charig & Milner, 1997, “Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey”
- Milner, 2003, “Fish-eating theropods: A short review of the systematics, biology, and paleobiogeography of spinosaurs”
- Dal Sasso et al., 2005, “New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its size and affinities”
- Ibrahim et al., 2014, “Semiaquatic adaptations in a giant predatory dinosaur”
- Ibrahim et al., 2020, “Tail-propelled aquatic locomotion in a theropod dinosaur”
- Cau, 2015, Theropoda blog – Spinosaurus geometricus
Published: January 16, 2020
Last update: August 23, 2020
The Sauropodomorph's Lair 