Sunday, 25 July 2010

Dickinsonia and Spinther: A Frustrating Comparison

The Ediacaran genus Dickinsonia is an iconic form which still eludes identification. In its time it has been identified as a Vendobiont, a placozoan, a cnidarian polyp, a coral, a sea anemone,  a polychaete worm, a turbellarian, a mushroom, a xenophyophoran protist, a lichen and even a close relative of chordates.

When viewed as a polychaete worm, an interpretation which is now seen as lacking support (merely being an attempt to shoehorn), it was compared to the genus Spinther. Clarkson, in Invertebrate Palaeontology and Evolution (4th ed.) writes:

A close resemblance to the modern segmented worm Spinther, which lives on and eats sponges, has been noted, so Dickinsonia  has been considered to be an annelid. It differs from Spinther  only in that the distal claws (parapodia) situated on the ends of the segments and used for crawling are lacking. 

My frustration came when I tried to search for an image of Spinther purely out of curiosity. Below is the only image I could find:

I can see why it is compared to Spinther, but the resemblance is superficial even without a proper image. Below is a good quality image of Dickinsonia for comparison:
I would love to some day go through all the different interpretations of Dickinsonia, especially as there are so many, but when it was so difficult to find an image of Spinther  I am not sure it will be worthwhile. For the record, I go with Vendobiont. 

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