Late Ordovician-Late Devonian
Fast-moving, low-level epifaunal carnivore.
Characteristics of the Order
- Typically spiny with densely granulate or tuberculate exoskeletons.
- Typically 8-13 , spine-tipped, thoracic segments.
- Glabella broad, large, extending to anterior border.
- Eyes typically present, holochroal, usually smaller.
Treatise on Invertebrate Paleontology (1959):
- Medium sized to exceptionally large trilobites chiefly characterized by distinctive cephalic and pygidial features. Glabella broad, extending to anterior border, which may be ill-defined; with pair of lateral glabellar furrows longitudinally elongated; lateral glabellar and occipital lobes tend to fuse with one another and with other parts of the cranidium; facial sutures opisthoparian. Pygidium large, pleural regions usually flattened and composed of 3 pairs of pleurae that commonly exhibit leaf-like or strongly spinose form. Dorsal surface almost invariably tuberculate.