Artists and advertisers appreciate the power of a distinctive silhouette: a shape that cannot be mistaken for anything else, even when it’s only partly visible. The power of these outlines is reflected in the fact that our most popular and iconic dinosaur species are recognisable from their profiles alone. Who among us does not instantly associate a three-horned face with Triceratops, long necks and tails with Brontosaurus and Diplodocus, or the marrying of a giant head with ferocious teeth and tiny, two-fingered hands with Tyrannosaurus?



Fig. 1. Spinosaurus aegyptiacus, one of the strangest and most enigmatic of all predatory dinosaurs. Although Spinosaurus is the most famous of the spinosaurid dinosaurs and a popular research subject among modern palaeontologists, much about this species remains mysterious and controversial, from their lifestyles and taxonomy to such basics as their body proportions and size.

A relatively recent addition to this list is the enormous predatory dinosaur Spinosaurus aegyptiacus, which had a body unlike any other dinosaur. The crocodile-like head was long and narrow, with a series of enormous conical teeth and a bony crest in the middle of the forehead. A long and flexible neck led to a body equipped with large, muscular arms, massive hand claws, and remarkably short legs. Most distinctive of all was the huge sail running along the back, approaching 2m tall and supported by giant extensions of the backbone. Recent discoveries have shown that the tail was also modified into a sail-like structure, recalling the elaborate tails of some newts. Combine this with the fact that Spinosaurus was among the largest of all predatory dinosaurs, likely topping 12m in length and weighing in at more than 5 tonnes, plus the multiple signals that it was primarily a predator of aquatic animals, and we have a genuinely peculiar dinosaur. Every species is unique by definition, but it is probably fair to say that Spinosaurus was more unique than many. Words like ‘bizarre’, ‘odd’ and ‘strange’ get thrown around a lot when discussing prehistoric animals, but those descriptors are genuinely appropriate for Spinosaurus fossils. They are, well, weird.

Spinosaurus was not only unusual in its anatomy. Among the popular dinosaurs with a distinctive ‘look’, it stands out for its almost continual modification and reinvention by researchers. The forms of Tyrannosaurus, Triceratops, Diplodocus and so on have not escaped some revision at the hands of palaeontologists, but they have received minor tweaks and adjustments compared to the whole-body reinventions that have occurred repeatedly throughout the research history of Spinosaurus. Discovered in Egyptian rocks during the early twentieth century, the first fossils of S. aegyptiacus were too fragmentary to hint at their strange body plan, and they were initially interpreted as a somewhat short-legged but essentially Tyrannosaurus-like dinosaur, characterised primarily by a long body and a sail. It was also obvious at this early stage that Spinosaurus was enormous, the size of Tyrannosaurus rex or bigger, although little fanfare was made of this fact until much later.



Fig. 2. The changing shape of Spinosaurus. Few dinosaurs have been subjected to such dramatic revisions in form and predicted ecology as this peculiar dinosaur, and discussions about these topics continue today.

A deficit of new Spinosaurus fossils, as well as the destruction of the original specimens by an Allied bomb during World War II, meant that this ‘generic’ interpretation became the longest-lived iteration of Spinosaurus. It is the version that anyone with memories of the last century will be familiar with from dinosaur books, in which it received token mentions as an unusual, sail-backed predatory species, as well as one of the few notable African dinosaurs known at that time. Older artwork of Spinosaurus shows few features to distinguish them from other large dinosaur carnivores other than their sails, the function of which was often ascribed to temperature regulation. On account of their long bodies, some artists and authors presented Spinosaurus as a quadruped, contrasting it with all other predatory dinosaurs, which were bipeds. 

For all its suspected strangeness and grand size, Spinosaurus remained relatively obscure until the approach of the new millennium when, finally, new discoveries of Spinosaurus and its close relatives revealed more elements of their anatomy. Spinosaurus became part of a lineage of similarly adapted, high-spined, long-snouted dinosaurs: the Spinosauridae (both ‘spinosaur’ and ‘spinosaurid’ are widely used anglicised synonyms for this term). These dinosaurs, it seemed, were all large animals, with even the smallest species probably being around 8m long and close to a ton in weight as adults. Along with long, low jaws and slender, flexible necks, they all had tall extensions of their torso vertebrae that, although not developed into sails in most species, clearly recall the exaggerated spines of Spinosaurus. Most intriguing, however, were their three-fingered hands, the thumb of which ended in a powerful, talon-like claw. These traits were best demonstrated by the British Baryonyx walkeri and the Nigerien Suchomimus tenerensis, both of which remain key species for understanding spinosaurid biology.

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