Hylaeosaurus

MEANING: Forest lizard

PERIOD: Early Cretaceous

CONTINENT: Europe

Hylaeosaurus is a nodosaurid ankylosaur covered in osteoderms. It carried at least three long spines on each shoulder, but only limited remains have been found and much of its anatomy is unknown. It was about 5 m long, and weighed around 2 t. Hylaeosaurus was one of the first dinosaurs to be discovered, in 1832 by Gideon Mantell.

Hylaeosaurus is from the Early Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Early Cretaceous making up roughly the first half, lasting from about 143 to 100 million years ago. The poles were ice-free, due to the relatively warm climate, and forests extended into high latitudes. The continued breakup of the continents created new coastlines and isolated landmasses, influencing the evolution of distinct dinosaur faunas.

It was a time of transition, as many groups of animals and plants began to take on more modern forms while others declined or disappeared. Pterosaurs continued to thrive, though early birds were becoming more diverse and widespread. Mammals remained small but adapted to a variety of ecological niches. In the oceans, ichthyosaurs and plesiosaurs were common, and early mosasaurs began to appear.

Dinosaurs remained the dominant land animals, with groups like iguanodontians, spinosaurids, and carcharodontosaurids rising to prominence. While sauropods declined in some regions, they remained abundant in the Southern Hemisphere. The first true ceratopsians appeared, and ankylosaurs replaced stegosaurs in their niche. Dromaeosaurs and other small theropods diversified. During this time, the first flowering plants evolved, gradually changing global ecosystems by providing new food sources for herbivores.

Hylaeosaurus is a nodosaurid. Nodosaurids are a family of armored dinosaurs within Ankylosauria, distinct from their ankylosaurid relatives most notably by the absence of a tail club. Like all ankylosaurs, they were herbivorous, quadrupedal, and covered in bony osteoderms for protection. However, nodosaurids generally had narrower skulls, longer limbs, and more pronounced shoulder spikes compared to ankylosaurids.

They first appeared in the Late Jurassic and thrived until the end of the Cretaceous Period. Nodosaurids are primarily known from North America and Europe, with some fossils also found in South America and Asia, indicating a wider distribution than previously thought.

Nodosauridae and ankylosauridae make up the larger group ankylosauria, which, along with the stegosaurs, form the group Thyreophora, known for their various combinations of armor and spikes.