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Triceratops sp.
Skull

• Classification:
  • Order: Ornithischia
  • Suborder: Marginocephalia
  • Infraorder: Ceratopsia
  • Family: Ceratopsidae
• Age: Late Cretaceous Period (approximately 70 mya)
• Locality: South Dakota, USA
• Formation: Hell Creek Formation

Triceratops is easily recognized by its three horns and large frill formed by a bony structure protruding upwards behind the skull. This 9-m dinosaur used these distinctive features as defensive weapons against predators. It is also believed that Triceratops relied on these features to distinguish members of its own species, as well as to win mates in head-to-head wrestling.

The front side of Triceratops’ mouth resembled a parrot’s beak and contained no teeth. Deep inside the mouth, however, numerous upper and lower teeth were packed closely together. Triceratops likely used its sharp beak to grab and pluck plants, then ground them with its teeth. Worn-out teeth were continuously replaced by new ones.

Platecarpus sp. cf. P. somenensis

• Classification:
  • Class: Reptilia
  • Subclass: Diapsida
  • Infraclass: Lepidosauromorpha
  • Order: Squamata
  • Suborder: Sauria
  • Family: Mosasauridae
• Age: Late Cretaceous Period (approx. 80 mya)
• Locality: South Dakota, USA
• Formation: Pierre Formation

Mosasaurs were a group of lizards that evolved to live in the ocean. Their legs and feet became completely modified into flippers, which it is believed they used to steer as they swam in a snake-like fashion. Mosasaurs lived near the shores of a shallow sea, where they used their powerful teeth to prey on fish.

Once a tyrant of the ocean, Mosasaurs were driven to extinction at the end of the Cretaceous Period around the same time dinosaurs disappeared from the land.

Edmontosaurus annectens
Skeletal fossils as found at the excavation site

• Locality: South Dakota, USA
• Formation: Hell Creek Formation

These are the skeletal fossils of Edmontosaurus as found at the excavation site when they were first discovered. The bones, scattered randomly, belong to at least four specimens, both fully-grown and juvenile.

In the Late Cretaceous, a shallow sea extended north to south along the eastern side of the Rocky Mountains, dividing the North American continent into eastern and western regions. It is believed that these dinosaurs died near a coastal plain, where their bones were buried in the sand and mud that was deposited by a river that changed its course each time it flooded.