Here
we have two Cambrian
Scyphozoa 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 two jellyfish fossils, 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. |