A subclass of graptolites, specifically the more advanced forms that lived during the Paleozoic era.
From graptolite + -oidea suffix; refers to a specific division within the graptolite group based on evolutionary features.
Graptoloideans were the 'success story' of the graptolite world—they dominated oceans for over 100 million years before mysteriously vanishing, and their abundance makes them invaluable for dating rocks.
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