Echinosphaerite?

[Tethys]

Spring fever has me rock hunting in odd places. I found these in landscape gravel. Judging by the bryozoa I found, they are mid to late Ordovician. The echino is 3 cm across, 2.5 cm tall, and is coated in whiskey colored calcite crystals. It is not a perfect sphere, it looks somewhat like a bulb of garlic. There appear to be some brachiole fragments on one side. There is a void underneath, visible in photo 3. I can't get a pic of the inside, but it looks like the echino surface is whole, though completely covered in crystals. Thanks for looking!

Edited March 3, 2015 by Tethys

[Tethys]

Here is a close-up of what I think are the remains of brachioles, and three tiny plates that have the calcite broken away. They are just under 1 mm. I tried to capture the edge of the white body plate, to show how thin and delicate they are. It is visible on the right side of the photo.

[Tethys]

Top and bottom of bryozoa.

[dragonsfly]

Tethys, The first couple have the general appearance of crinoid crown and anchor to my eye, no expert though. John

[FossilDAWG]

I don't think this is an Echinosphaerites. I have collected this cystoid in Virginia, and have seen specimens from Scandanavia. They are sometimes called "crystal apples" because they are quite spherical and are completely filled with radiating calcite crystals. Your specimen is partially filled with matrix, leaving an irregularly shaped hollow that is partly filled with crystals of some mineral, a configuration quite unlike any Echinosphaerites I have seen. Also, I don't see the "brachioles" you mention, but at any rate as far as I know (and also based on a review of Echinosphaerites that was published a few years ago) neither brachioles nor the stem is known for this cystoid. The stem must have been very slender and fragile, judging from the attachment site.

I do not know what your specimen may be, as I cannot see any features beyond a vague shape. In particular, I cannot see any indication of the original surface. I think the crystals look quite attractive, personally I'd keep it just for that reason.

Don

[Tethys]

Thank you Don, and Dragonfly. I agree that it could be a crinoid face down in the sediment after seeing some of Calebs fantastic specimens. I was hesitant to posit a rare species, but Carabocrinus is known from here, and has thin rhomboidal plates. The Cotylacrinna also looks like it has thin plates and is consistent with the overall shape of my find. I then found this photo of a Carabocrinus that has identical tiny plates visible on its arm. Did Ordovician crinoids have multiple layers of arm plating? I don't see anything like those tiny cover plates on the arms of Caleb's specimen. The sediment itself is unusually coarse grained sandy limestone, but matches the orange color of some layers in the Platteville. I'm currently poking about in archives trying to find any mention of fossils coated in amber brown calcite.