Tuesday, 24 January 2017

WANNERIA DUNNAE. EAGER FORMATION.

Wanneria dunnae




















Trilobites were amongst the earliest fossils with hard skeletons. They were the dominant life form at the beginning of the Cambrian.

This specimen of Wanneria dunnae is from the Lower Cambrian Eager Formation in the East Kootnays of British Columbia and is typical of the group.

He's from the Rifle Range outcrop near Cranbrook. The site is just a shade older than the Burgess Shale, Middle Cambrian deposits though the species found here are much less varied.

Back in the late 1990's and early 2000's, it was a glorious place for fossil collecting. I have many beautifully preserved Wanneria and abundant Olellenus from here along with a few rare and treasured Tuzoia.

The shale matrix lends itself to amazing preservation. This specimen of Wanneria is a big fellow. Five inches long and four inches wide. Wanneria are slightly less common here than Olenellus. Olenellus are slightly smaller in size with a large, semi-circular head, a body of 15 segments and a long spine on the 15th segment with a wee tail. You find a mixture of complete specimens and head impressions from years of perfectly preserved molts.

The Wanneria are their bruising cousins by comparison with their large heads lacking conspicuous furrows and a robust body without an expanded third segment.

As luck would have it, the plate he is in split him right down the centre. Bless the hardness of shale for preservation and it's sheer irony for willfully cracking exactly where you least desire it.

Trilobite eyes were compound like those found in modern crustaceans and insects. The eyes of these earliest trilobites are not well known. They were built in such a way that the visual surface dropped away and was lost during molting or after death throwing a wrench in studying them. We may learn more from the Burgess Shale and the lovely soft mud that was the foundation of their preservation.