The Biserial Graptolites

The term Axonophora describes graptolites with an axis and is based on a translation from the Greek language. The distal development of the nema in graptolite colonies has often been identified as the virgula, especially in the Monograptidae. The axonophoran sicula is very similar in its construction to the sicula of the earlier graptoloids. The virgellar spine, or in short the virgella, is one of the most prominent features of all axonophorans, but is not restricted to this clade. In the literature, thecal shapes are often described by referring to typical genera. The Climacograptidae Frech, 1897 is one of the difficult groups of biserial graptolites, and its evolutionary relationships are controversial. In terms of colony shape, the family Dicranograptidae is one of the most diverse families of the Ordovician axonophorans. The Neograptina were a group of relatively inconspicuous biserial graptolites in the Middle Ordovician and may easily be overlooked