North American biogeography and taxonomy of Cryptolithus (Trilobita, Ordovician)

Abstract

Museum and field restudy of Cryptolithus from all known geographic and stratigraphic occurrences in eastern North America shows that the principal variable character in this genus is the number of fringe pit arcs. Because this character varies within populations and even single individuals, it cannot be used to distinguish the earlier, typologically defined species of the genus. Instead, a neotype is designated here for the type species, Cryptolithus tessellatus Green, 1832, and morph designations are used for all pit arc variants. Over the time span considered, the species increased the number of pit arcs, but the ecological and evolutionary mechanisms responsible cannot be identified with certainty.