EXQUISITE EROSION: TIME & TIDE

OUR CAMBRIAN PAST

Wanneria dunnae / Eager Formation

There is so much more to Canada than meets the eye. Deep in the ground beneath our feet is window into our past. It speaks of ancient oceans, continents on the move, powerful forces upthrusting whole coastlines and creating mountains.

And through that window, on the west side of the Kootenay River at its confluence with the St. Mary's, we find some of the oldest fossils in Canada.

This specimen of Wanneria dunnae is from the Lower Cambrian Eager Formation 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. Trilobites were amongst the earliest fossils with hard skeletons. While they are extinct today, they were the dominant life form at the beginning of the Cambrian.

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.

What is missing in this photograph is any detail around the specimen's eyes. 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.

FUSED RIBS: TURTLES

Turtle ribs fuse together with some of their vertebrae so they have to pump air in and out of the lungs with their leg muscles instead?

Another unusual feature in turtles is their limb girdles (pectoral and pelvic) have come to lie 'within' their rib cage, a feature that allows some turtles to pull its limbs inside the shell for protection. Sea turtles didn't develop this behaviour (or ability) and do not retract into their shells like other turtles.

Turtle shells are different from the armoured “shells” we see on dinosaurs like the ankylosaurs. Turtles are covered by a special bony or cartilaginous shell developed from their ribs that acts as a shield. It is fundamentally different from the armour seen on our other vertebrate pals. Turtle armour is made of dermal bone and endochondral bones of the vertebrae and rib cage.

Armadillos have armour formed by plates of dermal bone covered in relatively small, overlapping epidermal scales called "scutes," composed of bone with a covering of horn. In crocodiles, their exoskeletons form their armour. It is made of protective dermal and epidermal components that begin as rete Malpighii: a single layer of short, cylindrical cells that lose their nuclei over time as they transform into a horny layer.

Depending on the species and age of the turtle, turtles eat all kinds of food including seagrass, seaweed, crabs, jellyfish, and shrimp,. That tasty diet shows up in the composition of their armour as they have oodles of great nutrients to work with. The lovely example you see here is from the Oxford Museum collections.

MAMMOTH HOT SPRINGS

Mammoth Hot Springs Yellowstone National Park