Exceptionally well preserved Ancient Jellyfish

Anyone who has ever found a jellyfish washed up on the beach, knows how peculiar looking these creatures are with their soft body parts and long delicate tentacles.  Scientists know that soft-bodied jellyfish have existed for hundreds of millions of years and represent examples of the first complex multi-cellular organisms to evolve on Earth, now some amazing fossils discovered in the western USA shed more light on their evolution.

A team of American researchers from the University of Kansas have uncovered the remains of ten jellyfish in Utah, from strata dating back to the very end of the Cambrian period, making these particular animals 500 million years old.

As jellyfish have no bones, shells, beaks or other hard calcified body parts they rarely fossilise and very little is known about their origin or evolution.  Several indistinct “blobs” which may represent the remains of jellyfish and their ancestors have been found from ancient marine deposits such as the Burgess shales in Canada, but these new discoveries show the jellyfish in fantastic detail.

Two of the Fossil Jellyfish Remains (with photos of similar animals alive today)

Credits: Top Fossil Photos: B. Lieberman, Cunina photo (top right) – K Raskoff

Periphylla photo (bottom right) – Dhugal Lindsay

Copyright: JAMSTEC

The specimens remarkable state of preservation allows scientists to compare the fossils with species of jellyfish alive today.  These finds are the best preserved specimens from the Cambrian period found to date and mark a period in the evolution of life when many new body forms and types of creature appeared.  This period has been named “the Cambrian explosion”.  Scientists are still not sure why at this time in the Earth’s history that evolution began to accelerate.  Perhaps increasing levels of oxygen in the atmosphere stimulated the emergence of new life forms, or maybe the abundance of warm, shallow seas encouraged life.  There may not have been a huge increase in marine animals at all, simply that with more hard-bodied animals evolving such as Trilobites the fossil record is richer.

Such is the quality of the preserved remains that researchers from the University of Kansas were able to liken the fossils to living specimens of jellyfish alive today.  The researchers have suggested that these animals may represent early ancestors of three modern families of living jellyfish.  The picture above shows a comparison between two of the fossils and pictures of modern jellyfish genera.  If these relationships are proved, two contrasting theories as to the evolution of these animals can be put forward.

Did jellyfish evolve slowly and by the end of the Cambrian they were already complex organisms like their modern descendants?  If this is the case, then the origin of jellyfish and other soft bodied creatures would have to be pushed back into the Proterozoic era.

Alternatively, did jellyfish evolve into their current complex forms very quickly around 500 million years ago, perhaps as a reaction to the Cambrian explosion?

As with many fossils, new finds ask as many questions as they provide answers.  So very little is known about the Cambrian and Pre-Cambrian periods.  Scientists cannot even agree how best to divide up and classify these ancient times, but it was during this time that all the main animal groups alive on Earth today, including the chordates, our ancestors evolved.

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