Bipedal Walking on two legs only. Some types of dinosaur were bipedal. Others could only walk on two legs for short periods of time, perhaps to reach treetops or to run away. Bipedal dinosaurs were generally much faster than their quadrupedal relatives.

Carnivores Meat-eating animals. All carnivorous dinosaurs were theropods.

Cretaceous Period The period of Earth’s history from 143 to 66 million years ago. During the Cretaceous Period, much of the Earth was covered by shallow seas and temperatures were very warm. Flowering plants, which had evolved during the Jurassic, replaced more ancient plants, and grasses appeared.

Dinosaurs A group of reptiles that lived on the land during the Mesozoic Era (252–66 million years ago). Unlike other reptiles, they walked upright on legs held beneath their bodies. The word dinosaur means “terrible lizard”. It refers to the terrifying appearance of the first dinosaur finds, which were very large, but in fact dinosaurs came in all shapes and sizes. The dinosaurs spread out across the world and ruled the land for about 175 million years until 66 million years ago, when they suddenly died out.

Extinction The dying out of a species.

Gondwanaland A huge southern continent. It was once part of the “supercontinent” Pangaea, but drifted away during the Jurassic Period. It included the modern continents of Australia, Africa, southern Europe, Antarctica and South America.

Herbivores Plant-eating animals. The sauropodomorphs and ornithischians were all herbivores.

Iridium A metal that is believed to be present only in the core of the Earth and in asteroids (rocky objects from space). A layer of iridium discovered by scientists is used as evidence that the K-Pg extinction was brought about by an asteroid impact.

Jurassic Period The period of Earth’s history from 201 to 143 million years ago. During the Jurassic Period, the climate became wetter. Plants became abundant and dinosaurs began to grow much larger.

K-Pg extinction The mass extinction that took place 66 million years ago, between the Cretaceous and Palaeogene periods. (The letter K stands for the German word Kreidezeit, meaning “Cretaceous”.) The extinction wiped out all dinosaurs, pterosaurs and marine reptiles. Most scientists now agree that the extinction was caused by the impact from an asteroid (a rocky object from space). The atmosphere would have been filled with dust, blotting out the Sun and lowering temperatures for many years. Other ideas have been suggested over the years, such as the theory that a massive volcanic eruption could have caused the extinction, but these have been rejected by most scientists.

Laurasia A huge northern continent. It was once part of the “supercontinent” Pangaea, but broke away during the Jurassic Period. It included the modern continents of Asia, North America and Europe.

Mesozoic Era The span of time in Earth’s history from 252 to 66 million years ago. It is divided into the Triassic, Jurassic and Cretaceous periods. During the Mesozoic Era, dinosaurs ruled the land. For this reason, it is often known as the Age of Dinosaurs.

Ornithischians The “bird-hipped” dinosaurs, one of two major types of dinosaur (the other were the saurischians). Ornithischians had backward-slanting pubic bones—the lower part of the hip bone.

Quadrupedal Walking on four legs. Most quadrupedal dinosaurs were large animals that needed all four legs to support the weight of their bodies. They were slower than their bipedal relatives, and had to rely on tough hides and sheer size as defence against meat-eating predators. Some species also developed protective body armour.

Saurischians The “lizard-hipped” dinosaurs, one of two major types of dinosaur (the others were the ornithischians). They had forward-jutting pubic bones—the lower part of the hip bone. Saurischians included the theropods and the sauropodomorphs.

Sauropodomorphs A group of large, plant-eating saurischian dinosaurs. They had very long necks and tails. This group includes the prosauropods and the sauropods.

Theropods A group of mostly meat-eating dinosaurs. They all had three toes.

Triassic Period The period of Earth’s history from 252 to 201 million years ago. This is the period when the dinosaurs first appeared.

Consultant: Chris Jarvis