Triarthrus sp. with Nautiloid shell on top

[Alexthefossilfinder]

Hey everyone,

I wanted to show this fossil I found back in November as I think it's pretty cool. On my first trip that involved splitting shale, I found this Triarthrus cephalon, which is cool on it's own but it was only later that I looked back to it and realized the particular shape that resides on top of and below the cephalon. This trilobite appears to have been buried with the shell of a nautiloid!

Please excuse if it's hard to see, the first few pictures were really difficult to get and my phone isn't the best at taking close up shots as it is. The 1st and second pictures represent the two halves of the piece, while the 3rd and 4th pictures are the same thing with a rough tracing of where the shell is. The 5th picture is an older picture I came across while making this post that while blurry shows the shaping somewhat decently.

So yeah, there's a pretty cool find in my collection, I don't know how rare this kind of thing is or how they ended up together but I think it's really fascinating anyway!

[Kane]

I can see it. 

These won't be rare; in fact, in some of the shales (particularly in Ottawa), there are massively profuse hash beds that contain numerous Triarthrus cranidia and nautiloids (in addition to moulted pieces of the asaphid, Pseudogygites latimarginatus). Both trilobites and nautiloids were present in that deep, anoxic environment (nautiloids did, after all, predate upon trilobites), and so upon death they would sink to the silty bottom ocean depths. One may find similar in Whitby and Collingwood. As one proceeds east beyond Montreal, there are dense beach shales that have only three dominant faunal associations of numerous complete Triarthrus, nautiloids, and graptolite beds.