Climacograptus

Climacograptus, genus of graptolites, extinct colonial animals related to the primitive chordates, found as fossils in marine rocks of the Middle and Late Ordovician Period (about 472 million to 444 million years ago). Climacograptus is characterized by a single, serrated branch suspended from a thin stem below an irregular float; its outline is distinctively angular. Several species are recognized, and the genus is useful for correlating smaller time divisions within the Ordovician.