Oesia disjuncta Cambrian Explosion Fossil

Part and counterpart of an enignatic metazoan from Utah's Marjum Formation

Oesia disjuncta

Walcott (1911), who originally described it from the Burgess Shale as an Annelid worm

Kingdom Animalia, Phylum Hemichordata (?) recently supported by newer data, otherwise, incertae sedis

There are a number of enigmatic metazoans from the great cambrian radiation - this is one of the more mysterious; Walcott (1911) wrote first description

Geological Time: Upper Early Cambrian, (~525 million years ago)

Size (25.4 mm = 1 inch): Fossil is 32 mm (curve measure) on a 70 mm by 60 mm and 80 mm by 60 mm matrix pair

Fossil Site: Marjum Formation, Millard County, Utah

Fossil Code: STF15

Price: $995.00

Oesia disjunctaDescription: The time popularly known as the “Cambrian Explosion” was one in which many body plans were explored, subsequently being winnowed down to the phyla we know at present Sometimes enigmatic animals were shoehorned by early researchers into known phyla while others were placed in new ones. Work continues even now, and all researchers are not in universal agreement. This unusual specimen was named Oesia disjuncta by C. D Walcott when he found it in the famous Burgess Shale deposits of Canada, and was thought by him to be a polychaete worm (he had many, many “worms”). Later, it was thought to be a tunicate, then a chaetognath, and most recently a hemichordate. Whatever its affinities, it is most unusual. To my knowledge this is the first example found outside the Burgess, and displays all the features of the taxon. The downward-pointing feature in the main photograph is interpreted as the anterior; the structure at the end may be jawlike in nature. I have included one photo taken with high-angle polarized light to help with the interpretation. For a collector of early life this would be a centerpiece specimen.

Reference: Acta Palaeontologica Polonica, 54 (1), 2009, pp 175=179.

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