Cambrian Scyphozoa Jellyfish Fossils

This is an assemblage of four Cambrian Scyphozoa jellyfish fossils from the Krukowski quarry in central Wisconsin, a site that has been under intense scientific study. The Krukowski quarry yields Protichnites, Diplichnites and Climactichnites ichnofossils that may be the earliest evidence of terrestrialization of animals in the fossil record.

Two general types of jellies are found in the quarry as mass strandinds: 1) large medusoid forms of class Scyphozoa measuring up to 50 cm, far and away the largest jellyfish in the entire fossil record, and 2) smaller forms, of 25 to 75 mm Scyphozoa. The smaller jellyfish body fossils shown here are subtle with usually slight relief, and therefore this specimen has been subtly stained; the tentacles are the result of artistic license since very few of the fossils have exhibited relief that could be unequivocally attributed to tentacles. The large medusae fossil jellyfish have been described by Hagadorn (2002), but the description of the small jellyfish remains pending.

Being comprised entirely of soft tissue (living jellyfish are about 95 % water), unlike animals with exoskeletons (e.g., trilobites) or skeletons (vertebrates), jellyfish fossils are body fossils that are impressions of the jellyfish. Such fossil impressions are rare throughout the fossil record. During the Cambrian, there were no land based predators. Once washed ashore, the jellyfish likely pumped sand to form the relief seen in these fossils. Bacterial mats or rapid burial may have assisted in the preservation by mitigating erosion or bioturbation.

Phylum Cnidaria (anemones, corals, jellyfish and sea pens) are among the most ancient animals and has one of the longest fossil histories of metazoans. Though simple in body form, they remain ubiquitous and widespread in modern marine environments. The earliest forms in the fossil record appear in the Ediacarian fauna of Southern Australia, which dates to the Precambrian some 600 million years ago. Their persistence is clear testament that old and simple animals can be enormously successful, and that the clique' "climbing the evolutionary ladder" is a misnomer; rather, life either adapts to the current and changing environment, or perishes. Jellyfish may have been one of the most ferocious predators of the Cambrian marine environment.

Also see: Cambrian Shadows

Reference: Hagadorn, JW., Dott, RH., Damrow, D, Stranded on a Late Cambrian shoreline: Medusae from central Wisconsin, Geology (39) No. 2.