Glossary :: D

Devonian

The fourth period of the Palaeozoic. Spans 409-353Ma. The rocks of this period are referred to as Old Red Sandstone (ORS) as they are often red coloured sandstone. The name originates from the county of Devon in South West England. The colonisation of lan...More

Directional selection

Fitness increases/decreases with trait magnitude. E.g. selection on bill size in Darwin�s medium ground finch � Geospiza fortis. Population crashes in 1977, 1980 and 1982, due to droughts, selected for increased bill depth due to abundance of hard seeds o...More

Disruptive selection

Individuals with extreme trait values have greatest fitness. E.g. selection on bill size in the black-bellied seedcracker � Pyrenestes o. ostrinus. This species of African finch exhibits non-sex related polymorphism in bill size. Members of the species ha...More

Dunham Classification

A classification of limestone based on depositional textures. The classification consists of mudstone (90% mud), wackestone (>10% grains, mud supported), packstone (grain supported, but contains mud), grainstone (grain supported, no mud) and boundstone (g...More

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