Here
we have a mass mortality plate of Cambrian
Scyphozoan jellyfish, from the Krukowski quarry in Central
Wisconsin that has been under currently intense scientific study
since 2000. The Krukowski quarry yields ichnofossils that are the
earliest evidence of terrestrialization of animals in the fossil
record
The
plate contains four tentacled jellyfish, which are rare
in the quarry. The fossils are actually body cavity infillings
that formed as the animal's ingested sand while pumping their
bodies in a futile attempt to escape their stranding on the
intertidal zone of a Cambrian shoreline. Because these jellyfish
body fossils are incredibly subtle in vertical relief, the specimen
has been subtly stained. Some Blackberry Hill jellyfish fossils
approach two feet in diameter.
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. Appearing during the Ediacaran, jellyfish were
some of the most ferocious predators of the Cambrian marine environment.
The Blackberry Hill scyphozoan fossils are almost surely the
result of a mass stranding on an ancient Cambrian beach, possibly
caused by a storm surge.
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 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.
Reference: Hagadorn, JW., Dott, RH., Damrow, D, Stranded on a
Late Cambrian shoreline: Medusae from central Wisconsin, Geology
(39)
No. 2. |