Bristolia insolens Trilobite from the Latham Shale

Today I have a rather odd bug to show you. It's a partial cephalon from a Trilobite called Bristolia insolens.  It comes from the Latham shale of the Marble Mountains in California. B. insolens is odd in that it has a pair of genal spines that are attached to the front of the cephalon rather than extending from the sides or rear corners.

This particular species is well known and specific to a time period in the Cambrian and is used to designate a faunal zone. That means that if you are finding specimens of B. insolens in the rock then you should be able to find a very specific set of other fauna associated with it as well and it has a very specific age.  In this case, B. insolens is isolated to the base of the Wuliuan stage of the Miaolingian series within the Cambrian period (509 mya).

A complete specimen of this species of trilobite can be seen at the Western Trilobites webpage here.

I used the Wikipedia page on the genus Bristolia to fill out some of the details of my post.

Climacograptus typicalis graptolite from the Whitby formation

As Climacograptus typicalis is the most common graptolite found at Bowmanville, and in my experience everywhere in the upper Ordovician, I should not be surprised to find it in the Collingswood member of the Whitby formation. I have only found one specimen so far and it is super hard to get a good photo of the black carbonaceous film on black shale. But in the second photo below you can see the square shape of the thecae where the animals lived.

The Whitby formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 263 to help identify these fossils.

Plaesiomys sp. brachiopod from the Whitby formation

Another Brachiopod genus that I've found in the Collingswood member of the Whitby formation is Plaesiomys sp. This is a small round shell with the pedicle valve having a prominent beak and deeper shell than the brachial valve. I have two specimen, both of which I believe are pedicle valves.

Specimen #1

Specimen #2

William Hessin states in his book that in order to ID down to the species level you need to count the number of ribs.  Neither specimen is preserved well enough for me to say for sure which species they are. Especially as he writes "Plaesiomys subquadrata (Hall) has from fifty to seventy five ribs whereas Plaesiomys iphigenia (Billings) generally has fewer; from forty five to sixty ribs." I am not sure if those number ranges are based on the starting number of ribs near the beak, and then the end number of ribs near the margin, or just a range of the total number of ribs that are found along the margin.

The Whitby formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 122 to help identify these fossils.

Pseudogygites latimarginatus trilobite from the Whitby formation

The main reason to collect in the black shales of the Collingswood member of the Whitby formation is in the hopes of finding an articulated Pseudogygites latimarginatus. Most of the time the only parts found are the isolated pygidiums.  I have been fortunate enough to find one mostly intact example.

Specimen #1 - The large slab with a partially disarticulated example

Closer view of the specimen

This the the counterpart on a smaller flake of shale

Specimen #2 - An isolated pygidium

Specimen #3 - another pygidium

The Whitby formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 200 to help identify these fossils.

Rafinesquina alternata and Sowerbyella sericea brachiopods from the Whitby formation

This slab is a two for one in terms of species present. It has an example of Rafinesquina alternata as well as Sowerbyella sericea. It's from the Collingswood member of the Whitby formation. These are both uncommon fossils to find in the Collingswood member and could be washed in from another location by a storm as black shales generally represent anoxic, deeper water conditions.

Overview of the slab

Rafinesquina alternata

Sowerbyella sericea

The Whitby formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 125-126, 128 to help identify these fossils.