With the long weekend in full swing, I decided to get up early and have a look at the pit/pond just beyond my backyard. Much of it is Bois Blanc and Dundee Fm fill. I've made a lot of posts about the area in the last five years. This time around, I found something new.
I spent some time in a 10 m x 10 m area by the pond, breaking whatever looked promising. I've found some interesting gastropod steinkerns in the past, and this one was no exception.
Trilobite partials to the left, a brachiopod on the right. Typical fare for these lower to mid Devonian rocks.
A nice split with a little bit of everything - mostly brachiopods and one horn coral calyx (the round item).
A high-spired gastropod steinkern (partially buried in matrix) with its impression.
Closeup of a bryozoan.
More trilobite partials (two pygidia impressions and one cephalon impression fragment)
Eldredgeops sp. cephalon fragment.
Believe it or not, this was the major find of the trip. Although it is only about 2.5 cm wide and kind of looks like it could be a fragment of coral, it is indeed a trilobite fragment... but which one?
I also ensured to collect the negative as well. It is a good idea, when in doubt about a specimen, to collect it - and all the other pieces it is associated with!
So to which trilobite does this "toothy" fragment belong? Courtesy of our resident trilobite expert Scott, on The Fossil Forum, the answer can be found here:
Stauffer, C.R. 1915
The Devonian of Southwestern Ontario.
Geological Survey of Canada Memoir, 34:1-341
It is Odontocephalus sp. and as Scott tells me, in the last century or more, this trilobite has only been reported in a few papers from Ontario, thus making this a far from common find! Pictured below is a simplified line illustration of what it looks like complete.
So... that's quite exciting! This site has now yielded up the following trilobites in the last few years:
Odontocephalus sp. (?selenurus)
This figure from Lesperance and Bourque (1971) shows the evolutionary branching from the genus Roncellia. My recent find means that I have representatives of each of the three major synphoriinae branches (Odontocephalus branch, Anchiopsis branch, and Trypaulites branch). What distinguishes them significantly is both the anterior glabellar process/border, but also the pygidial "spike" (or lack thereof). Note here the bifid spine that appears in both Odontocephalus and Coronura.
At this point, I am a bit more confident in assigning this one to the species of O. selenurus given the presence of 9 rather than 11 glabellar denticles as would be found on O. aegeria (which is also not reported to be found outside New York).
According to Stumm (1954), only three fragments of O. selenurus have ever been found in Ontario; the first, by Carl Rominger in 1888, and two by Stauffer in 1915. Assuming no further fragments have since been found, my find would be the first in 103 years, and the fourth in Ontario's paleontological history. This makes this find quite exceptional and rare!
This particular species is cited only a few times, including in Stauffer (1915), Stumm (1954), Lesperance and Bourque (1971), Lesperance (1975), Sanford and Norris (1975), and Ludvigsen (1979).
1. Lesperance, P. (1975) Stratigraphy and Paleopntology of the Syphoriidae (Lower and Middle Devonian Dalmanitacean Trilobites). Journal of Paleontology 49.1: 91-137
2. Lesperance, P. and P.A. Bourque (1971). The Syphoriinae: An Evolutionary Pattern of Lower and Middle Devonian Trilobites. Journal of Paleontology 45.2: 182-208.
3. Ludvigsen, R. Fossils of Ontario: The Trilobites. ROM.
4. Sanford, R.V. and A.W. Norris. (1975). Devonian stratigraphy of the Hudson Platform. Geological Survey of Canada, Memoir 379 I. 1-124; II. 1-248
5. Stumm, E.C. (1954). Lower Middle Devonian Phacopid Trilobites from Michigan, Southwestern Ontario, and the Ohio Valley. Contributions from the Museum of Paleontology, University of Michigan XI.11: 201-21.
6. Stauffer, C.R. (1915). The Devonian of Southwestern Ontario. Geological Survey of Canada Memoir, 34:1-341