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Tuesday, March 27, 2012

Oldest hard-bodied creature


Erica Clites and Mary Droser from the University of California, Riverside and James Gehling from South Australian Museum describe a particularly interesting specimen from the Ediacaran Period (635 to 542 million years ago). It’s the oldest creature yet found with a hard body structure.

The very earliest multicellular organisms had soft bodies that fossilized only under the most fortuitous circumstances.  They did sometimes leave other traces of their presence, such as tracks or imprints, but these too are uncommon.  It wasn’t until the advent of hard body parts that the fossil record became as rich as it is. Those hard-bodied fossils first appeared during the Cambrian Period (from 542 to 488 million years ago).

That makes the discovery of Coronacollina acula, a small cone-shaped creature with hard radiating spindles, of great significance.  C. acula lived during the Ediacaran Period, but unlike its contemporaries, it had hard skeleton supports.  Not only that, but the creature shows similarities to Cambrian Period sponges.

Why does this matter?  Living creatures can trace their ancestry back to an organism that lived during the Cambrian Period. However, if you go further back in time to the Ediacaran Period, many of the trails disappear. So how did traits like hard skeletons arise? C. acula represents a long sought bridge between the Ediacara and Cambrian periods.

 

Caption: This is a reconstruction of how Coronacollina would have appeared in life. Coronacollina remained in place on the sea floor, and may have used its spicules as support struts. Coronacollina resembles the Cambrian fossil sponge, Choia. The three raised points on the rim are evident, with a central hollow and four spicules extending from the cone rim.
Credit: Daniel Garson for Droser lab, UC Riverside