DK Science: Glossary

the response of a living organism to changes in its environment.

a unit of geological time, which is characterized by some feature (like an Ice Age).

a yellowish, fossilized tree resin that sometimes contains trapped matter.

an early marine creature. It was protected by a spiral-coiled shell, which contained many air-filled chambers.

animals that live in the water during their early life (breathing through gills), but usually live on land as adults (and breathe with lungs), for example frogs and salamanders.

animals that walk on two legs are bipeds. Many carnivorous dinosaurs were bipedal, including T. rex.

fossilized body parts, such as bones, teeth, claws, skin, and embryos.

carnivores are animals that eat meat. They usually have sharp teeth and powerful jaws. All the theropods were carnivores, and some were hunters, while others scavenged.

animals that rely upon the temperature and their behaviour (like sunning themselves) to regulate their body temperature are cold-blooded.

(“dung stone”) fossilized faeces. Coprolites record the diet and habitat of prehistoric animals.

the last period in the Mesozoic Era, from 145 to 65 million years ago. Flowering plants flourished and dinosaurs were at their height during the Cretaceous Period. There was a mass extinction at the end of the Cretaceous, marking the end of the dinosaurs and many other species of animals and plants.

primitive seed plants that dominated the Jurassic landscape. They have palm-like leaves and produce large cones.

(“terrible lizard”) extinct land reptiles that walked with an erect stance during the Mesozoic Era. Their hip structure caused their legs to stick out from under their bodies, and not sprawl out from the side like other reptiles.

the ratio of the brain weight of the animal to the brain weight of a similar animal of the same body weight.

a process in which the gene pool of a population gradually (over millions of years) changes in response to environmental pressures, natural selection, and genetic mutations. All forms of life came into being by this process.

the process in which groups of organisms (species) die out. Species go extinct when they are unable to adapt to changes in the environment or compete effectively with other organisms.

mineralized impressions or casts of ancient plants and animals (or their traces, like footprints).

stones that some animals swallow and use to help grind up tough plant matter in their digestive system are called gastroliths. They are also called gizzard rocks.

a primitive seed-bearing tree that was common during the Mesozoic Era. A deciduous tree, it has fan-shaped leaves.

the southern continent formed after Pangaea broke up during the Jurassic Period. It included what are now the continents South America, Africa, India, Australia, and Antarctica.

Animals that eat plants. Most dinosaurs were herbivores.

a primitive, spore-bearing plant that was common during the Mesozoic Era. Its side branches are arranged in rings along the hollow stem. Horsetails date from the Devonian Period 408-360 million years ago, but are still around today and are invasive weeds.

index fossils are commonly found fossils that existed during a limited time span. They help in dating other fossils.

this is a heavy metal element that is rare on the Earth's surface, but abundant on meteors and in the Earth's core.

the second period of the Mesozoic Era, from 200 to 145 million years ago. Birds and flowering plants evolved, and many dinosaurs flourished during the Jurassic Period.

boundary between the Cretaceous and Tertiary periods, about 65 million years ago. This was a time of the huge mass extinction of the dinosaurs.

this was the northern supercontinent formed after Pangaea broke up during the Jurassic Period. Laurasia included what are now North America, Europe, Asia, Greenland, and Iceland.

these are hairy, warm-blooded animals that nourish their young with milk. Mammals evolved during the Triassic Period. People are mammals.

this is was a major geological time span, from 250 to 65 million years ago. It is informally known as the Age of the Dinosaurs. The Mesozoic is sub-divided into the Triassic, Jurassic, and Cretaceous periods.

(“bird-hipped”) dinosaurs that had a hip structure similar to that of birds. The two lower bones on each side lie parallel and point backwards. They were also herbivores.

mainly bipedal ornithischian dinosaurs that developed special teeth to grind up tough plant food.

a scientist who studies the forms of life that existed in former geological periods, mainly by studying fossils.

a supercontinent consisting of all of Earth's landmasses. It existed during the Permian Period through the Jurassic Period. It began breaking up during the Jurassic, forming the continents Gondwana and Laurasia.

plant-eating saurischians with long necks and thumb claws.

animals that walk on four legs are quadrupeds. Most of the horned, armoured, and plated dinosaurs were quadrupeds.

a group of animals that have scales, breathe air, and, usually, lay eggs.

(“lizard-hipped”) the ancestors of birds, these dinosaurs had a hip structure similar to that of lizards – the two lower bones on each side point in opposite directions.

large, quadrupedal plant-eating saurischians. They had long necks and tails.

animals that eat dead animals that they did not kill themselves. Hyenas are modern-day scavengers.

a method of dating fossils by observing how deeply a fossil is buried. Generally, deeper rocks and fossils are older than those found above them.

a group of saurischian dinosaurs that includes all the carnivores. Almost all the theropods were bipedal.

a series of footprints left behind as an animal walks over soft ground. They can indicate the animal's speed, weight, and herding behaviour.

the first period in the Mesozoic Era, from 250 to 200 million years ago. Dinosaurs and mammals evolved during the Triassic Period.