Craigleith assemblage

[GavySwan]

Hi! 

We were at Craigleith, Ontario (Ordovician, lower Whitby formation) today for a toddler's fossil hunt birthday party, and found this neat assemblage of brachiopods, bivalves, and (I am guessing) trilobite bits.

At least, they look trilobite to me, but I was hoping someone would be able to explain them. Are they curled up? Could they be part of the larval stage? Something else entirely? 

I didn't get a scale shot but by my memory I'd say the bits I am trying to figure out are <5mm across each. 

Thanks! 

Gavy

[Rockwood]

They look like trilobite cephalons. They are somewhat crushed, and mostly expressed as molds of the ventral surface.

[Kane]

They are Triarthrus eatoni (Hall) moults methinks. The cephalon moults can be quite numerous as the way they moulted, "head first," leaving the cranidium behind in large numbers. I've attached a picture of what a full specimen would look like, via Wikipedia.

 

See Ludvigsen, R. (1979). Fossils of Ontario Part 1: The Trilobites. Royal Ontario Museum, pp. 55-6.

[Fossildude19]

As Rockwood and Kane say, these are Triarthrus trilobite cephalon molts.  Cephalons are the "Head Shields".  

When trilobites grew, they would molt their old exoskeleton, much like modern lobsters. 

The currents would then winnow away the shedded molts, and similarly weighted objects would settle in the same areas. 

Neat finds.

Regards,

[GavySwan]

Thank you! 

It always seems so obvious in hind sight. Most of the cephalons we've found are Pseudogygites latimarginatus and don't have those distinctive glabellar furrows so visible. 

[Shambala68]

Good find , bet the kids were wrapt

[GavySwan]

23 hours ago, Shambala68 said:

Good find , bet the kids were wrapt

Thanks! The older kids were pretty impressed. The little ones (toddlers) didn't quite get it, but all the kids had great finds and we're excited. My 2.5 year old is so used to trilobites that she was identifying them for the other kids, lol. 

One of the parents found a nice cephalon with eyes (I think Pseudogygites latimarginatus?) and I found a fragment of a gastropod. 

 

[Kane]

Nice Pseudogygites latimarginatus cephalon! Not as common to find whole as opposed to just the cranidium. Chapeau!

[GavySwan]

On September 27, 2016 at 10:46 AM, Kane said:

Nice Pseudogygites latimarginatus cephalon! Not as common to find whole as opposed to just the cranidium. Chapeau!

Thanks! Yes, we've really enjoyed Craigleith. We've found a few cephalons, and 2 complete specimens there. It's a fantastic place to take kids since they are pretty much guaranteed a find! Only downside is not being able to take anything home.