Yorgia
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Yorgia waggoneri is a fossil from the Ediacaran period. It can be up to 25 cm across. It is bilateral in symmetry and segmented. The shape is roughly egg shaped.
Yorgia is classified in family Dickinsoniidae-(Dickinsonia), class Dipleurozoa, phylum Proarticulata. It shares features of both Dickinsonia and Spriggina.
Trails made by Yorgia have been found. The trail consists of repeated oval shapes of the fine details of the segmented pattern of the ventral side. The longest recorded trail is 4.3 meters long. It is positive on the lower bed surface. Each oval impression is called a platform. The platforms make a chain, and can overlap each other.
The interpretation is that Yorgia produced abundant mucus whilst gliding. The mucus sealed the mud bed surface and cemented it so that it was not eroded by subsequent currents. Yorgia would have fed using cilia in its grooves. This would sweep bacteria towards the central groove, where more cilia would have swept the microorganisms to its mouth.
Another interpretation is that the marks are due to a death roll.
Other Yorgia fossils show internal structure in the original organism, showing two symmetrical rows of nodules, a central tube, rib like tubes, and a semicircular shape with a hole in the circle centre positioned towards the head end. This structure probably is the impression of gonads, intestine and mouth.
Yorgia has been found in the Zimnie Gory in the White sea region of Russia, dated around 555.5 Ma.
