Graptolite

Taxonomy

Phylum: Hemichordata

Class: Graptolithina

Diagnostic features

Stick-shape (often branched)

One or both edges may appear serrated

Thecae

Rhabdosome

Stipes

Stratigraphic range

Cambrian to Carboniferous (Dendroids)

Ordovician to Middle Devonian (Graptoloids)

Way of life

Colonial

Planktonic (mostly, although some dendroids were sessile benthonic)

Suspension feeders

Typical preservation

Flattened along bedding planes, normally in shales

Carbonization or pyritization of the animal

Advanced notes

Graptolites, because of their abundance and variation in morphology are very good index fossils. At a very basic level the angle between the stipes and number of stipes can be used to give a rough age for the fossil, with Early Ordovician graptolites having two stipes with the 'sawtooth' facing each other (pendent), later Ordovician graptolites having a more open oblique or reflex angle between the 'sawtooth' faces, and Siluran graptolites having the 'sawtooth' faces back to back (scandent) or having lost one stipe altogether (for example monograptids).

Specimens

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