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Aachenosaurus is a fossil that was initially consideration to be jaw fragments from a duckbilled dinosaur (a hadrosaur), but the fossil turned out to be petrified wood.

Aardonyx an early phase in the growth of sauropods.

Abavornis was a ancient bird that lived throughout the late Cretaceous era, about 85 million years ago.

Abelisaurus "Abel's lizard" that has been reconstructed from a single skull.

Abrictosaurus was a heterodontosaurid (an ornithischian), a bipedal, plant-eating, long-tailed dinosaur that was around 4.6 feet (1.2 m) long and weighed about 43 kg.

Abrosaurus it is a sauropod, a long necked, plant eating dinosaur. It had a large body, column-like legs, and a small head with a nasal crest; the nostrils were nearly above the eyes.

Acanthopholis was an unbreakable, quadrupedal, plant-eating Ankylosaur dinosaur from the early Cretaceous era
Aepycamelus is alias of Alticamelus, a prehistoric camel that lived from the middle during late Miocene.

Afrovenator bakensis was a dinosaur about 27-30 feet (8-9 m) elongated. It was a theropod, a bipedal, meat-eating, three-fingered, stiff-tailed marauder from Niger, Africa throughout the Cretaceous era, about 130 million years back.

Age an element of geological time. Example: Ice Age.

Allosaurus large carnivorous theropod dinosaur (Jurassic).

Amber a translucent or solid yellow, fossil resin from coniferous trees.

Ankylosaurs a cluster of dinosaurs that lived from the mid-Jurassic to the late Cretaceous periods and were herbivorous, ornithischian and had unbreakable plates on their bodies for protection.

Apatosaurus large herbivore from the infraorder sauropoda (Jurassic).

Asteroid a small stony body that orbits a star. Over 100,000 asteroids orbit the sun.

Atmosphere Gaseous coating surrounding the Earth.

Atom the smallest particle of an element. Everything is made up of minute atoms.