SPATIAL AND TEMPORAL PATTERNS OF TRILOBITE SIZE ACROSS THE LOWER PALEOZOIC

Trilobites have one of the richest fossil records of all invertebrate groups, reaching a peak in their diversity in the late Cambrian – early Ordovician. Families such as the Paradoxididae (Cambrian), Asaphidae (Ordovician) and Lichidae (Ordovician-Silurian) are notable for their larger size range, with the largest trilobite (Isotelus rex) reaching over 70 cm. The aim of this work is to compare the dimensions of trilobite specimens across the Cambrian – Devonian, and between high and low paleolatitude terranes.

Measurements of holaspid trilobites were taken from museum collections in Europe, Morocco and from various literature sources of type specimens. Ages of specimens were averaged across their known stratigraphic ranges. The distributions of sizes were compared across low paleolatitude terranes (i.e Laurentia) and high latitude terranes (i.e Gondwana).

Preliminary results indicate that: (1) mean size is highest in the early Paleozoic, followed by a decreasing trend towards the Devonian; (2) there is no significant difference between terranes at higher and lower paleolatitudes; (3) all terranes show a peak in size in the Llanvirn, possibly representing a greater extrinsic control and (4) trilobite size was affected by the end Ordovician mass extinction, with the average size of recovery faunas generally smaller.