File:Marrella splendens (Burgess Shale Formation, Middle Cambrian; Walcott Quarry, above Field, British Columbia, Canada).jpg

English: Marrella splendens Walcott, 1912 (~2 centimeters long, including antennae), preserved as a carbonized film in slightly metamorphosed shale from the Burgess Shale (Middle Cambrian) of southwestern Canada (YPM 5861, Yale University’s Peabody Museum, New Haven, Connecticut, USA). Note that the body fluids have been squeezed out from the posterior end of the animal by compaction in the original muddy sediments.

---

The Middle Cambrian-aged Burgess Shale is the most famous fossil deposit on Earth. It is located near the town of Field in Yoho National Park, southeastern British Columbia, western Canada. The deposit is famous for its spectacular soft-bodied preservation - the organisms have had their appendages & internal organs preserved. Many tens of thousands of fossils have been collected from the Burgess Shale Formation over the last century. Including known, but unnamed species, and excluding known or demonstrable junior synonyms, the Burgess Shale biota totals at least ~280 species.

Many claim that Charles Walcott discovered the Burgess Shale Lagerstätte (as soft-bodied fossil deposits are called by paleontologists) in 1909. However, it was actually discovered in 1886 or 1888 by Richard McConnell, based on anomalocarid appendage material from Mt. Stephen, in the Campsite Cliff Member of the Burgess Shale Formation. The main collecting localities have been two quarries (Walcott Quarry & Raymond Quarry) on the western side of the ridge connecting Mt. Field and Wapta Mountain a little north-northeast of Field. Numerous other smaller localities have been identified in the same area & for many, many kilometers to the south. Collecting at the Burgess Shale was most intense in 1910-1917 (Charles Walcott), 1925-1930 (Harvard’s Museum of Comparative Zoology), 1966-1967 (Geological Survey of Canada), and 1975-2000s (Royal Ontario Museum).

The most common soft-bodied species in the Walcott Quarry Member of the Burgess Shale Formation is an odd, small arthropod called Marrella splendens Walcott, 1912. It cannot be classified with any traditional arthropod group, and several new high-level taxa have been created to accomodate it and other soft-bodied arthropods (e.g., see Hou & Bergström, 1997 - Fossils & Strata 45).

Classification: Arthropoda, Lamellipedia, Marrellomorpha, Marrellida, Marrellidae

Marrella is quite distinctive - it has two large, curved lateral cephalic spines and a pair of large, posteriorly-directed cephalic spines. Many Marrella specimens have squeezed-out gut contents (as in this example).

Stratigraphy: Walcott Quarry Member, Burgess Shale Formation, Ptychagnostus praecurrens Interval-zone, lower Marjuman Stage, middle Middle Cambrian.

Locality: Walcott Quarry, western side of ridge between Mt. Field & Wapta Mountain, north-northeast of the town of Field, southeastern British Columbia, southwestern Canada.