English: Olenellus thompsoni (Hall, 1859) - fossil trilobite from the Cambrian of Pennsylvania, USA. (YPM 6657, Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA)

This remarkable fossil trilobite is from the Kinzers Lagerstätte, a soft-bodied fossil deposit in the Lower Cambrian of Pennsylvania. About 60 species are present in the interval that contains exceptional preservation, of which 25 represent nonmineralizing organisms (principally arthropods, various "worms", algae, and bacteria).

This is the holotype specimen of Olenellus getzi Dunbar, 1925, which is a subjective junior synonym of Olenellus thompsoni (Hall, 1859). The fossil is a large, complete trilobite that is ~24.5 centimeters long total (terminal spine + body + antennae). The specimen has been tectonically elongated ~along the axial line. The anterior portion of the glabella is collapsed. A slightly circular impression of the hypostome is impressed onto the anterior part of the glabella. The third thoracic segment is macropleural. The matrix is dark to very dark gray mudrock that is heavily limonite-stained. The exoskeleton is decalcified and is now limonite. The nonmineralizing antennae are preserved; they do not display segmentation - both are broken distally. The preserved portion of the right antenna is ~4.5 centimeters long; the left is ~4.6 centimeters long. The antennae are limonite films, with a few scattered, disseminated pyrite crystals. The long pygidial spine is broken - ~8.2 centimeters are preserved. No leg appendages are present.

Three olenellid trilobite thoracic segment fragments and a partial olenellid cephalon occur around the complete specimen.

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Olenellidae

Stratigraphy: Kinzers Lagerstätte, Emigsville Member, Kinzers Formation, middle Bonnia-Olenellus Assemblage-zone, mid-Dyeran Stage (= upper Botoman Stage or lower Toyonian Stage), upper Lower Cambrian

Locality: Getz Quarry, north of the eastern end of Chestnut Ridge, north of Spring Valley Road, near the Bethel Road-Spring Valley Road intersection & ~0.65 kilometers northwest of the Rt. 741-Rt. 30 interchange, western side of the town of Lancaster, Lancaster County, southeastern Pennsylvania, USA (~~vicinity of 40° 03' 48.66" North latitude, 76° 21' 59.55" West longitude) (= United States Geological Survey locality "12x"; this locality no longer exists)

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References cited:

Hall, J. 1859. Trilobites of the shales of the Hudson River Group. Twelfth Annual Report of the Regents of the University of the State of New-York, on the Condition of the State Cabinet of Natural History: 59-62.

Dunbar, C.O. 1925. Antennae in Olenellus getzi, n. sp. American Journal of Science, Fifth Series 9: 303-308.