Spinosaurus

MEANING: Spine lizard

PERIOD: Late Cretaceous

CONTINENT: Africa

Spinosaurus is the longest known carnivorous dinosaur, at about 15 m in body length and weighing 8 t. It is generally thought to have been semi-aquatic to some degree, the long slender snout well adapted for a piscivorous diet. Spinosaurus is named for the neural spines protruding from its back, which may have been used for sexual display or thermoregulation.

Spinosaurus is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.

The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.

On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.

The Cretaceous (along with the Mesozoic) ended with the Cretaceous-Paleogene (K-Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K-Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.

Spinosaurus is a spinosaurid. Spinosauridae is a unique group of large theropod dinosaurs known for their elongated skulls, conical teeth, and semi-aquatic adaptations. While the group includes both Baryonychinae and Spinosaurinae, the latter subfamily contains the most iconic and specialized forms. Members of Spinosauridae exhibit traits that suggest a lifestyle closely tied to water. These include long, narrow jaws suited for catching fish, retracted nostrils positioned farther back on the skull, and in some cases, dense limb bones that may have helped with buoyancy control. Fossil evidence even points to reduced hindlimbs and broad tail structures in some taxa, features not seen in any other known theropod dinosaurs.

Spinosaurids are best known from the Cretaceous Period and have been found primarily in Africa, South America, and Europe. Their fossils are often discovered in fluvial or deltaic sedimentary environments, further supporting the idea that they spent much of their time in aquatic or semi-aquatic habitats. Unlike other large theropods that dominated dry terrestrial ecosystems, spinosaurids likely occupied ecological niches similar to those of modern crocodilians—predators of rivers, lakes, and coastal zones.