Spinosaurus

A Storied History and Lost Fossils

The Spinosaurus fossil was first discovered in western Egypt in 1915 by German paleontologist Ernst Stromer.
Due to its unusual appearance and size for a dinosaur of that time, its name became widely known.
However, on April 24, 1944, during World War II, most of the valuable fossils held in the Bavarian State Collection of Paleontology and Geology in Germany were destroyed in an Allied air raid.
With the destruction of the world’s only specimen, the complete picture of Spinosaurus was once again shrouded in mystery.

Although a mid-cervical vertebra believed to be from a Spinosaurus was found in Morocco around 1996, the discovery of a high-quality fossil did not happen until 2013, earning Spinosaurus the nickname “dinosaur of mystery.”
In recent years, a large number of tooth fossils have been excavated from Morocco, making Spinosaurus teeth affordable enough to be easily acquired.

From Land to Water: New Discoveries That Overturned Conventional Wisdom

Spinosaurus was once thought to be a bipedal predator on land, as depicted in the movie Jurassic Park III.
However, a series of recent discoveries has largely overturned this conventional wisdom.
It is now considered a highly adapted “aquatic pursuit predator” that primarily lived in water.

This “aquatic theory” has been one of the hottest topics in paleontology since 2014.

The Aquatic Adaptation Theory Proposed (2014)

A research team led by Dr. Nizar Ibrahim of the University of Chicago, based on new fossils discovered in Morocco, announced that Spinosaurus had remarkably short hind limbs and bone density similar to that of aquatic animals.
They proposed the revolutionary theory that it “primarily lived in water,” but this was met with some counterarguments at the time, such as the unknown shape of its tail that would have provided propulsion.

Discovery of a Paddle-Shaped Tail (2020)

The discovery of a fossilized tail in 2020 overturned those counterarguments.
Unlike the thin shape of other theropods’ tails, this tail had highly developed neural spines, giving it the shape of a massive “paddle.”
This was irrefutable evidence that it used its tail to generate propulsion and swim powerfully in the water.
It is believed that by swinging this tail from side to side, it could create great propulsive force underwater.

It could generate propulsion by swinging its tail in the water.

Penguin-like Bones (2022)

In 2022, a research team further demonstrated that Spinosaurus’s bones had a dense and heavy core, much like those of diving penguins, hippos, and crocodiles.
This suggests that the bones functioned as “weights” to suppress buoyancy and allow it to submerge in water.
These discoveries established a new image of Spinosaurus as an “aquatic pursuit predator” that not only waited for fish at the water’s edge but also actively swam and chased its prey underwater.

A Crocodile-like Head and Sensors

Its head had a shape similar to a crocodile’s and reached a size of about 2 meters.
This is the largest among theropods.
Its narrow, crocodile-like snout and conical teeth, which were perfect for catching fish, indicate that it was piscivorous.
The longest teeth at the tip of its lower jaw interlocked with the upper teeth, much like a modern crocodile’s.
It is also believed that there were many small holes at the tip of its snout, similar to those found in living crocodiles, which served as sensors to detect fish in murky water.

Its head had a shape similar to a crocodile’s.

The Mysterious Role of the “Sail”

The most distinctive feature of Spinosaurus was the sail-like structure on its back, which was supported by bones that extended from its spine and formed a ridge up to 2 meters high, covered by skin and muscle.
However, the purpose of this sail is still not fully understood today.

It was once believed that the sail functioned in thermoregulation, much like the back plates of a Stegosaurus. However, detailed examination revealed no traces of the blood vessels seen in a Stegosaurus, so this theory has been debunked.
There was also a theory that it was a hump for storing energy, but this would have made its back too heavy and difficult to balance, so that theory has also been rejected.

The most plausible current theories are that it was a display for intimidation or for attracting a mate, or that it acted as a “vertical rudder” to maintain stability in the water.
However, a fossil of a Spinosaurus’s sail with bite marks from a contemporary carnivore, Carcharodontosaurus, has also been found, which suggests that the sail may not have been very sturdy.

Ecology and Characteristics

As a terrestrial predator, Spinosaurus may have occasionally competed with Carcharodontosaurus for prey.
Its aggressive nature is also evident in fossils of its bones with bite marks from its own kind.
However, its main diet was fish, and its long, slender jaw was well-suited for catching fish in the water.
In fact, a Spinosaurus fossil was once found alongside a fossil of a 3-meter-long fish.

Additionally, Spinosaurus’s hind limbs were remarkably short compared to other large theropods, making them ill-suited for supporting its weight on land.
Its feet may have had webbing, and its three toes had long claws, which were perfect for hooking fish.
These discoveries have led to the conclusion that Spinosaurus had a unique ecology, moving between both land and water.