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Graptolites (Subphylum Hemichordata) are extinct marine organisms.
Mode of life: Colonial mostly planktonic.
Morphology: one or more linked stipes with rows of thecae which were occupied by
simple animals called zooids.
Add a scale and the following labels to the graptolite below: Stipe
Eg Didymograptus
Graptolites first appeared in the Middle Cambrian, becoming most abundant in
Ordovician and Silurian. They declined dramatically during the Early Devonian and
finally became extinct in the Carboniferous Period
Evolutionary trends:
The first graptolites were dendroids.
Eight, four and two stiped graptolites evolved in the Ordovician.
Monograpraptids were characteristic of the Silurian.
Stipes: pendent scandent
Thecae: simple sshaped or hooked
Graptolites are good zone fossils. They were abundant in the Lower Palaeozoic and
because they were planktonic, they are widespread and independent of facies.
Many species were fast evolving and have short stratigraphical ranges. Although the
graptolite skeleton is relatively fragile, it was readily preserved in the fine sands and

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