MEANING: Thick nosed lizard
PERIOD: Late Cretaceous
CONTINENT: North America
Pachyrhinosaurus is a centrosaurine ceratopsid dinosaur from the Late Cretaceous period of North America. Instead of horns, its skull bore massive, flattened bosses - a large boss over the nose and a smaller one over the eyes. A prominent pair of horns grew from the frill and extended upwards. The skull also bore several smaller horns or ornaments that varied between individuals. Size estimates for the largest Pachyrhinosaurus species indicate lengths of 6–8 m and a weight of 3–4 t. Pachyrhinosaurus was herbivorous and possessed strong cheek teeth to help them chew tough, fibrous plants.
Pachyrhinosaurus 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.
Pachyrhinosaurus is a ceratopsian. Ceratopsia is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia. They primarily flourished during the Cretaceous Period, although ancestral forms lived earlier, in the Late Jurassic. Ceratopsians lived until the Cretaceous–Paleogene extinction event, 66 million years ago, when they went extinct along with the other non-avian dinosaurs.
Early members of the ceratopsian group were small bipedal animals. Later members became very large quadrupeds and developed elaborate facial horns and frills extending over the neck. While these frills might have served to protect the vulnerable neck from predators, they may also have been used for display or thermoregulation. Ceratopsians ranged in size from 1 meter and 23 kilograms to over 9 meters and 9,100 kilograms.
Ceratopsians are easily recognized by features of the skull. Though less pronounced in basal ceratopsians, more derived species, like the ceratopsids are characterized by beaks, rows of shearing teeth in the back of the jaw, elaborate nasal horns, and a shelf that extends back and up into a frill. Various shapes and arrangements of well-developed brow horns and elaborate spines on the frill are also characteristic of many species.
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