Spinosaurus

What is Spinosaurus?

Characteristics: The Ever-Changing Largest Carnivorous Dinosaur

Spinosaurus is one of the largest carnivorous dinosaurs in history, surpassing even Tyrannosaurus. Its length exceeded 13 meters. The defining features of Spinosaurus are its long dorsal sail and a slender, crocodile-like snout. The sail on its back reached 2 meters at its highest point. Its appearance has continued to change more dramatically than any other dinosaur due to a series of recent discoveries. Once thought to be a typical terrestrial predator, features akin to aquatic animals have been discovered one after another. Today, it is almost certain that it was a dinosaur highly adapted to hunting in or near water and shallows.

Its slender, crocodile-like snout equipped with sensors at the tip, along with conical teeth suited for catching fish, indicate that they were piscivorous.

Forefront of the Debate: Swimming Dinosaur or Shallow-Water Ambush Hunter?

The debate over whether Spinosaurus was aquatic has been one of the hottest topics in paleontology since 2014.

2014: Proposal of the Aquatic Adaptation Theory

In 2014, a research team led by Dr. Nizar Ibrahim published findings based on new fossils discovered in Morocco, revealing that Spinosaurus had remarkably short hind legs and bone density similar to aquatic animals. They proposed the revolutionary theory that it "lived primarily in water." However, there were counterarguments, such as "the shape of the tail that would generate propulsion is unknown."

2020: Discovery of a Paddle-Like Tail

Overturning that counterargument was the discovery of tail fossils from the same specimen, announced in 2020. The tail did not have the slender shape of other theropods, but rather a massive "paddle" shape with highly developed neural spines. This was evidence that it generated propulsion to powerfully swim through the water by swinging its tail from side to side.

2022: Decisive Evidence? Penguin-like Bones

Furthermore, in 2022, the research team showed that the bone density of Spinosaurus was very similar to that of diving penguins, hippos, and crocodiles, featuring dense and heavy bone all the way through. This means it functioned as a "weight" to reduce buoyancy and allow diving underwater. These discoveries established a new image of the dinosaur: not just waiting for fish by the water's edge, but an "underwater pursuit predator" that actively swam and chased prey.
However, this theory would also be shaken by new findings in 2026.

It has also become clear that the hind legs of Spinosaurus were significantly shorter compared to other large theropods. Normally, theropods had their center of gravity in the back and supported most of their weight on their hind legs, but Spinosaurus seemed ill-suited to support its weight solely on its hind legs.

2026: New Species Spinosaurus mirabilis and the "Hell Heron" Model

Adding further fuel to the debate over the aquatic adaptation theory was the discovery of a new species, Spinosaurus mirabilis, announced in February 2026. It was discovered in the central Sahara Desert of the Republic of Niger by an international research team led by Professor Paul Sereno of the University of Chicago.

Spinosaurus mirabilis possessed a massive "scimitar" shaped cranial crest reaching about 50 cm in height. It also had a jaw structure called a "fish trap," where the upper and lower teeth interlocked closely, showing ultimate evolution for efficiently catching slippery aquatic prey.

Furthermore, Professor Sereno and his team overturned the previous "swimming underwater predator" model and proposed the "Hell Heron" model. The 2m-tall sail on its back would have created massive drag underwater, and recent simulations showed it was highly prone to capsizing while swimming. Therefore, rather than diving deep to swim, it is thought to have hunted by standing firmly in shallow water like a massive modern heron, striking down at prey beneath the surface with lightning speed.
Also, based on the analysis of preserved tibiae, the hind limbs of Spinosaurus mirabilis might have been relatively longer than those of Spinosaurus aegyptiacus.

Role of the Sail (Neural Spines)

The role of the back sail has also been cast in a new light following the aquatic theories. The previously considered thermoregulation function has been discredited, and for a time, its role as a "vertical stabilizer" to maintain balance underwater was favored. However, currently, the theory that it functioned as a "billboard" for display to assert presence to peers or attract mates, alongside the massive cranial crest, is gaining the most traction.

Numerous holes remaining at the tip of Spinosaurus's snout

Isotope measurements of tooth fossils conducted in 2009 showed that Spinosaurus teeth had oxygen isotope ratios similar to those of turtles and crocodiles, suggesting the possibility that it was semi-aquatic (living in both aquatic and terrestrial environments). In 2014, a research team from the University of Chicago and others summarized their findings, proposing the theory that "Spinosaurus was adapted to life in water."
By digitizing fossil specimens and examining their skeletal structure, they found that it was equipped with "bone density suitable for gaining buoyancy" and a "snout suited for preying on aquatic animals."

The tip of Spinosaurus's snout had many holes. This is a feature also seen in modern crocodiles.
The nervous system at the tip of the snout was highly developed, and it is thought to have functioned as a sensor to detect fish for food even in murky water.

Role of the Sail (Neural Spines) - "Thermoregulation" theory denied

Regarding the role played by the back sail (neural spines), the following theories were once proposed:

• Thermoregulation
• Display (for intimidation or attracting mates, etc.)
• Posture control in water

When Spinosaurus was first reconstructed, the sail was thought to function for thermoregulation, similar to the plates of the thyreophoran Stegosaurus. However, detailed examination of the surface and cross-section of the sail (neural spines) revealed no blood vessel traces like those seen in Stegosaurus, so the "thermoregulation" theory is now denied.

Later, theories such as a "display for intimidation or attracting mates" and a "function to stabilize posture in buoyant water" were debated. However, in the "Hell Heron" model proposed in 2026, it was pointed out that the back sail would be a source of drag underwater, hindering swimming and diving. Therefore, the theory that it served as a visual display, a "billboard" to assert presence to peers in complex river environments, is now considered much more plausible.

Spinosaurus hit by air raid

In 1912, German paleontologist Ernst Stromer discovered a massive dinosaur in the Bahariya Formation of western Egypt. A lower jaw, teeth, cervical vertebrae, dorsal vertebrae, tail bones, and more were excavated, and in 1915, it was published under the name "Spinosaurus (spine lizard)." This is the type species "Spinosaurus aegyptiacus" based on specimen number BSP 1912 VIII 19.

Due to its unusual appearance and size for a dinosaur known at the time, the name Spinosaurus became widely known, and Stromer published a reconstruction of the full skeleton in 1936.

In 1944, the ravages of war were spreading across Germany. Stromer suggested moving the Spinosaurus fossils brought from Egypt to a safe location to evacuate them, but this was not accepted. The specimen housed in the Bavarian State Collection of Paleontology and Geology in Germany was destroyed on April 24, 1944, by an Allied air raid.

In 1996, a mid-cervical vertebra believed to belong to Spinosaurus was found in the Kem Kem Beds of Morocco. This mid-cervical vertebra, specimen number NMC 50791, is the holotype specimen of "Spinosaurus maroccanus" and measures 19.5 cm in length. After that, it was called a "mystery dinosaur" until well-preserved Spinosaurus fossils were found in 2013.

In recent years, large quantities of tooth fossils have been excavated from Morocco, and Spinosaurus teeth can be obtained relatively cheaply.