is an assemblage of six 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,
ichnofossils that may be the earliest evidence of terrestrialization
of animals in the fossil record.
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.
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
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.
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
Hagadorn, JW., Dott, RH., Damrow, D, Stranded on a Late Cambrian
shoreline: Medusae from central Wisconsin, Geology (39) No. 2.