Copy of `Sedgwick Museum of Earth Sciences - Geological glossary`

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Sedgwick Museum of Earth Sciences - Geological glossary Category: Earth and Environment > Geology Date & country: 15/12/2007, UK Words: 108

Burgess Shale
a layer of Cambrian rocks in British Columbia, Canada, which contains fossils of a variety of strange soft-bodied animals. The fossils are the centre of a debate amongst palaeontologists about whether they are the ancestors of animals alive today, or whether they are evolutionary oddities with no living descendants

Bivalve
a group of molluscs with flattened bodies enclosed by a pair shells (valves) made of hard calcite

Belemnoid
A group of extinct cephalopod molluscs with an elongate, tapering body and an internal shell. They probably looked rather like squid or cuttle fish. The rear part of the bullet-shaped, cylindrical shell is known as the rostrum and has a conical cavity in the wide end into which fits a small conical structure called the phragmacone. This is divided by septa and cut by a siphuncle.

Basalt
a dark coloured igneous rock erupted from volcanoes and fissures on the Earth's surface. Flows of basalt cover 70% of the Earth's surface, and large areas of the surfaces of the other terrestrial planets, so it is a very important crustal rock. It is produced by the partial melting of rocks deep inside the Earth's mantle

Bacteria
Tiny, single-celled, prokaryotic organisms that reproduce by cell division and usually have rigid cell walls. Bacteria are very diverse. They can be shaped like spheres, rods or spirals and can be found in virtually any environment. The earliest fossils found on Earth are bacteria, almost 3.3 billion years old

Arthropod
An arthropod is a member of a group of invertebrate animals that includes insects, spiders and crustaceans. An extinct group of fossil arthropods is the trilobites. The arthropods first appear in the fossil record in the early Cambrian, and account for 75% of all animal species ever described. Arthropods are characterized by having exoskeletons, and paired jointed limbs. This word comes from the Greek words arthron (joint) and podos (foot)

Amphibians
a group of vertebrate animals that spend part of their time on land and part in the water; so they are considered an intermediate form between fishes and reptiles. Amphibians must return to the water to breed and they have distinct larval and adult forms. Members of this group include frogs, toads, and salamanders.The name is derived from the Greek word amphibios which means 'living a double life'

Ammonoid
A group of extinct cephalopod molluscs with coiled shells. They lived in the seas during the Mesozoic Era. Their shells are divided into chambers. The final chamber of the shell was relatively large and long and held the soft body of the animal, which was probably rather like a squid or octopus with tentacles and a beak. The chambers are separated by walls of shell known as septa, often with highly folded margins where they connect with the outer shell layers (sutures). Each septum was perforated by a tube (the siphuncle) which joins together all of the chambers of the shell from its earliest growth stage (the tiny, egg-like protoconch) to the final septum. This tube has a special surface which allowed the animal to regulate the quantity of gas (mainly nitrogen) and water in each chamber and therefore move up or down in the sea, rather like a submarine. We interpret the characteristics of ammonoids by comparing them with nautiloids which are still alive today