Spinosaurus

Life reconstruction of Spinosaurus aegyptiacus

Size comparison of various specimens of Spinosaurus to a human

Size comparison of Spinosaurus (red) to several other theropod dinosaurs. Click to enlarge.

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Spinosaurus was a large carnivorous theropod dinosaur that lived during the Late Cretaceous period, around 99–94 million years ago, in what is now North Africa. Its name means "spine lizard."

Currently, there is one confirmed species - S. aegypticus - found primarily in Egypt and Morocco. A second possible species, S. maroccanus, has been suggested, but the consensus among paleontologists is that these fossils likely belong to S. aegypticus.

In terms of length, Spinosaurus appears to have been the largest known carnivorous dinosaur (theropod), exceeding even the famous T. rex, although T. rex was heavier. Size estimates vary, but it likely reached lengths of at least 14 m - possibly more - and stood around 2.3 m tall at the hips. Its estimated weight is around 7.4 tonnes, though some estimates place it higher. Its long, narrow skull was around 1.6–1.7 m in length.

Spinosaurus has become one of the most debated dinosaurs in recent years, especially regarding its swimming ability and semi-aquatic lifestyle. While some scientists argue it was a true aquatic predator, others believe it was more of a wading shoreline hunter. In this article, we'll try to explore what is known - and what is still uncertain - about this fascinating dinosaur's adaptations, habitat, and way of life.

Anatomy and Adaptations

Diagram of a Spinosaurus skull

Spinosaurus had a distinctive, crocodile-like snout designed for catching slippery prey like fish. It had approximately 64 straight, cone-shaped teeth - about 12 in each side of the upper jaw, and more in the lower jaw. These teeth were smooth, sturdy, and ideal for gripping rather than tearing. The bulge at the front of its snout housed larger teeth that worked like a trap, quickly gripping fish before they could escape.

Many semi-aquatic predators, including Spinosaurus, have jaws adapted more for speed than strength. In water, it's important to snap quickly to catch fast, slippery prey like fish - before it gets away. Crushing bites take longer and are better for breaking hard shells or tough skin. While animals like crocodiles and sharks do have powerful bites, their feeding styles differ: crocodiles often ambush larger land prey or crush turtles, while sharks use strong jaws to tear chunks from their food. In contrast, animals that mainly eat fish - like gharials (a crocodile relative), herons, and alligator snapping turtles - tend to rely on fast-snapping jaws to grab and swallow prey quickly. Spinosaurus likely fed in a similar way, using speed over strength to catch fish in rivers and swamps.

Its nostrils were located far back on its snout, allowing it to breathe even when the tip of its mouth was underwater, though they are not positioned on top of the snout like those of crocodiles or hippos. This means that, despite earlier suggestions, Spinosaurus would still need to lift much of its head above the water to breathe. The placement of the nostrils is clear in the fossils, but how much this feature aided in aquatic hunting is still debated among paleontologists. It also had nerve sensors in its snout, similar to modern crocodiles, possibly used to detect movement in water.

Unlike most carnivorous dinosaurs, Spinosaurus had relatively short hind legs, only about a quarter of its total body length, and unusually small hips for its size. Its strong arms, large claws, and wide feet - with long toes and flat claws - suggest adaptations for walking on soft, muddy terrain. One toe that typically stayed elevated in other dinosaurs touched the ground in Spinosaurus, possibly indicating webbing between toes. Dense leg bones may have further helped it stay submerged, similar to modern diving birds or crocodiles.

A tall sail composed of spines extended along its back, possibly covered in tight skin rather than a fatty hump. Its tail was long, tall, and paddle-like, assisting with swimming like a crocodile or newt.

Diet and Hunting Strategies

Direct fossil evidence from close relatives, like Baryonyx, shows fish scales in their stomachs, confirming that spinosaurs ate fish. Baryonyx also occasionally fed on small dinosaurs, and spinosaur teeth embedded in pterosaur bones indicate these dinosaurs could catch flying reptiles. Based on this, Spinosaurus probably had a similar diet.

The anatomy of Spinosaurus, including its conical teeth and specialized snout, suggests it primarily hunted fish like the large Mawsonia, common in its aquatic environment. It likely also preyed on turtles and small crocodile-like creatures abundant in its habitat. Pressure-sensitive openings in its snout would have helped detect prey underwater.

Although specialized in aquatic hunting, Spinosaurus was likely opportunistic, scavenging or hunting smaller terrestrial animals when fish were scarce. Its relatively weak bite force compared to other large theropods suggests it did not regularly hunt large, tough land animals, instead filling a niche similar to modern semi-aquatic predators.

Aquatic Lifestyle: Evidence and Debate

Spinosaurus is widely regarded as one of the most aquatic dinosaurs. Fossil evidence, such as its crocodile-like snout, dense bones, short hind limbs, and fin-like tail, strongly supports its adaptation to aquatic life. Oxygen isotope ratios in its tooth enamel closely match those of modern aquatic animals like crocodiles and turtles, rather than land-dwelling dinosaurs. This suggests that Spinosaurus spent a significant amount of time in water. Recent discoveries, including a tail found in 2020, suggest it could propel itself through water using side-to-side tail movements.

However, there remains debate about how aquatic it truly was. Researchers like Nizar Ibrahim argue it was capable of swimming and possibly diving. Others, including David Hone, Thomas Holtz, and Paul Sereno, disagree, highlighting the absence of true aquatic features like flippers and expressing doubts about its diving capabilities due to buoyancy and drag from its large sail. These scientists envision Spinosaurus as a wading ambush predator that hunted in shallow waters rather than actively swimming underwater. The current consensus positions Spinosaurus as a highly specialized shoreline predator, though its exact swimming abilities remain contentious.

Habitat and Ecology

Spinosaurus lived in North Africa around 100 million years ago, in an environment filled with rivers, lakes, wetlands, tidal flats, mangrove forests, and abundant aquatic life including fish, turtles, and crocodile-like animals. It shared its habitat with various other dinosaurs, suggesting competition for resources in a rich ecosystem resembling modern African savannas but significantly wetter. As a specialized semi-aquatic predator, Spinosaurus likely occupied a unique ecological niche, focusing on aquatic prey and reducing direct competition with other large theropods such as Carcharodontosaurus and Deltadromeus, which hunted more traditional land-based prey.