Trilobita (Order: Corynexochida)
Trilobites are extinct euarthropods, probably stem lineage representatives of the Mandibulata, which includes crustaceans, myriapods, and hexapods (Scholtz and Edgecombe, 2006).
Ogygopsis – from Ogygia, in Greek mythology, the 7th daughter of Amphion and Niobe; Ogygia was first used as a trilobite genus name in 1817.
klotzi – after Otto Klotz, the Dominion topographical surveyor who provided the fossils for Rominger's study and description.
Holotype (K. burgessensis) – USNM65511 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA (Resser, 1942); Type status under review – (K. dawsoni), University of Michigan Museum of Paleontology, Ann Arbor, Michigan, USA.
Burgess Shale and vicinity: Ogygopsis spinulosa Rasetti, 1951, from the slightly older Cathedral Formation on Mount Stephen.
Other deposits: species of Ogygopsis have now been described from elsewhere in the Cambrian of North America, as well as in Greenland and Siberia.
Middle Cambrian, Bathyuriscus–Elrathina Zone (approximately 505 million years ago).
The Trilobite Beds and smaller localities on Mount Stephen.
Brief history of research:
Ogygopsis klotzi was first described in the same 1887 publication as several other important Mount Stephen trilobites. Rominger named the largest and most abundant species after Klotz, placing it in the genus Ogygia. The following year, Charles Walcott questioned this assignment, and in 1889 proposed the new genus name Ogygopsis. For decades afterwards, Ogygopsis was thought to be unique to the Mount Stephen Trilobite Beds, where it is the most conspicuous fossil on the mountain slope. In fact, Walcott designated the occurrence as the “Ogygopsis shale” in 1908, and subsequently named the Burgess Shale as its geographic equivalent (although Ogygopsis itself has never been found on Fossil Ridge!)
Hard parts: adult dorsal exoskeletons may be up to 13 cm long and are elongate oval in outline, with a large crescentic cephalon, a thorax of eight segments ending pointed blade-like tips, and a large semi-circular pygidium without spines. The glabella is long and barrel-shaped, smoothly rounded in front, reaching almost to the anterior border. Thin eye ridges angle back from near the front of the glabella to long narrow eyes located opposite glabellar mid-length. Free cheeks extend back into straight, short genal spines. The large pygidium has 9 axial rings decreasing in size backwards, followed by a terminal piece; 8 or 9 pairs of pygidial ribs become progressively shorter and more backwardly directed. The whole exoskeleton is mostly smooth externally, with fine ridges parallel to the margins; free cheeks and posterior fixed cheeks may show a distinctive pattern of fine anastomosing (interlinking) ridges.
Unmineralized anatomy: only a very few specimens of Ogygopsis klotzi are known with preserved evidence of limbs, but these show that there was a pair of flexible, multi-jointed antennae on the cephalon (Hofmann and Parsley, 1966).
Ogygopsis klotzi is extraordinarily abundant at the Mount Stephen Trilobite Beds, where it is the most common fossil encountered (Rudkin, 1996; 2009), but it does not occur on Fossil Ridge. The vast majority of more-or-less complete specimens lack free cheeks, and many paleontologists have interpreted these as moulted individuals.
The shape and size of Ogygopsis klotzi adults suggest that they walked along the sea bed. Because Ogygopsis occurs in such enormous numbers, it is hard to imagine it as a predator/scavenger, like Olenoides. It may instead have consumed much smaller organic particles in unusual environments. Obvious healed injuries have been described on a number of Ogygopsis specimens; some of these may be evidence of predation on freshly moulted “soft-shell” trilobites by larger arthropods such as Anomalocaris (Rudkin, 1979; 2009). The tiny larval stages and early juveniles of Ogygopsis probably swam and drifted in the water column above the sea bed.