MEANING: Many thorns
PERIOD: Early Cretaceous
CONTINENT: Europe
Polacanthus is a medium-sized nodasaurid ankylosaur. It was a sturdy quadrupedal herbivore, estimated at around 4-5 m in length, and 1-2 t in body mass. Like many basal nodosaurids, Polacanthus had a large fused pelvic shield over its hips, as well as the typical ankylosaurian osteoderm armor running down its back and the length of its tail.
Polacanthus is from the Cretaceous. The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct flora and fauna, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.
Polacanthus 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.