Produced by the Population Genetics and Evolution class, Furman University

The Ordovician: Graptolites
Graptolites are small organisms (17-30mm) that lived during the Paleozoic Era. They are classified in the phylum Hemichordata, having a notochord, pharyngeal gill slits, and a dorsal nerve chord like chordates but lacking a post-anal tail (Waggoner 1997). They formed both planktonic and sedentary colonies (Virtual Fossil Museum 2010), possibly held together by collagen exudate like modern colonial hemichordates. Each animal nestled in a cup-like structure ordered along the axis of the colony (Museum Victoria 2010). They have a worldwide distribution. Because they are a common, numerous, and speciose group, they are often used as "index fossils" to designate specific geological periods.

Page by Pete Calomiris
Pictures provided by: The Virtual Fossil Museum
(LEFT) Spirograptus
(RIGHT) Phyllograptus

Virtual Fossil Museum. 2010. Ordovician Grapolites Assemblage. Accessed February 2010. http://www.fossilmuseum.net/fossils /hemichordata/Phyllograptus-archaios/Phyllograptusarchaios.htm

Waggoner B. 1997. Introduction to the Hemichordata. University of California Museum of Paleontology. Accessed February 2010.

Victoria Museum Australia. 2010. Graptolites. Accessed February 2010.