Page 426 - Introduction to Paleobiology and The Fossil Record

DEUTEROSTOMES: ECHINODERMS AND HEMICHORDATES 413

Box 15.8 Graptolite classifi cation

A complete classification of the group is presented here although in practice it is only the dendroids
and graptoloids that have good fossil records. (The stolonoids, an encrusting or sessile group,
restricted to Poland, may be Pterobranchia.)

Class GRAPTOLITHINA
Order DENDROIDEA
• Multibranched colonies; stipes, commonly supported by dissepiments, have autothecae, bithecae
and a stolotheca. Anisograptids, intermediate between the dendroids and graptoloids, are retained
here
• Cambrian (Middle) to Carboniferous (Namurian)

Order TUBOIDEA
• Similar to dendroids but characterized by irregular branching and reduced stolothecae. Autothe-
cae and bithecae commonly form clusters
• Ordovician (Tremadocian) to Silurian (Wenlock)

Order CAMAROIDEA
• Encrusting life mode; endemic to Poland. Autothecae with expanded, sack-like bases. Bithecae
small and irregularly spaced. Stolotheca black and hard
• Ordovician (Tremadocian-Darriwilian)

Order CRUSTOIDEA
• Encrusting life mode; endemic to Poland. Autothecae with complex apertures
• Ordovician (Floian-Darriwilian)

Order DITHECOIDEA
• Sister group to the dendroids and graptoloids; central axis with a holdfast
• Cambrian (Middle) to Silurian (Lower)

Order GRAPTOLOIDEA
• The jury is still out on the detailed classification of this group. The position of the anisograptids

(included here with the dendroids) is uncertain, as is the status of the dichograptids; the retiolitids
are aberrant diplograptids. Colonies with few stipes (one to eight), a nema and sicula and a single
type of theca
• Ordovician (Tremadocian) to Devonian (Pragian)

Suborder DICHOGRAPTINA
• Basal graptoloids lacking both bithecae and virgellae
• Ordovician (Tremadocian-Katian)

Suborder VIRGELLINA
• Virgella always present
• Ordovician (Floian) to Devonian (Pragian)