Hunting for Middle Ordovician Echinoderms

[historianmichael]

For the Columbus Day weekend my girlfriend planned a three-day trip down to Southwestern Virginia as a birthday present to me. The plan was to do a little sightseeing, go on some hikes, enjoy the fall foliage, and, most importantly, collect some fossils. Unfortunately Hurricane Delta had other plans for us. As the weekend approached it looked like the entire weekend would be soaked with rain. We tried to change our reservations, but we were not allowed to postpone. Not knowing what to expect for the weekend, we made our trip. Sunday was to be my big day of fossil collecting. It was also the day that Hurricane Delta was expected to pass through Southwestern Virginia... Lucky for me, luck turned out to be on my side (at least in part). I had an all-day fossil trip planned, but due to the weather, I had to cut the trip in half. After a later start to the day than I had hoped for, we headed towards two sites that I had identified for the day. Both were exposures of the Middle Ordovician Benbolt Formation. A few showers on the drive but for the most part the rain held off while we collected.

 

Our first stop was a large, open road cut. The limestone there is just covered with brachiopods, trilobite pieces and bryozoa

 

 

I thought the number and orientation of all of the bryozoa in this hash plate were very cool

 

There were a lot of bryozoa at this site. Some small and some large, like these pieces of Mesotrypa sp. and Batostoma sevieri

 

My favorite bryozoan found here though was Ceramoporella sp.

 

This piece of Corynotrypa inflata comes in a close second. This bryozoan is encrusting and was often found on the inside of loose valves of Strophomena sp.

 

I am still trying to identify all of the brachiopods. I believe the left and bottom center ones in the second photo are Rafinesquina champlainensis while the right most one is Multicostella platys

  

 

Another really interesting fossil was this undetermined sponge

 

One of the unfortunate things about this site is that because it is so exposed, the fossils there weather very quickly. This is most apparent on all of the trilobite pieces. Here are two cephalons and a pygidium of Illaenus fieldi

    

 

I think this is a right cheek and eye of Eoharpes sp.

 

Here is an additional mystery trilobite piece

  

 

 

 

 

 

[Tidgy's Dad]

Very nice finds. 

Love the brachiopods, but some of those bryozoa are very pretty.  

 

[historianmichael]

However, the real reason I had for making this stop was to add to my growing collection of echinoderm fossils. The treasure of this site are the dozens of Echinosphaerites aurantium cystoids that can be chiseled out of the exposure or found loose among the talus. Here are a few of the ones I found

 

It is hard to imagine what these looked like in real life. Here is one rendering

 

The cool thing about this cystoid is that it is covered by a very thin calcareous "skin" that shines in the light

  

 

Some of them even have crystals inside

 

My favorite though is this one that has a well-preserved anal plate. I drew an arrow pointing to what I am referring to

 

This plate was also interesting as it displays both two complete cystoids and the inside skin of a third. It is hard to see, but, as seen in the second photo, the skin is covered in tiny pores that were its respiratory structures

  

[historianmichael]

In contrast to our first stop, the collecting at our second stop was mostly done on our hands and knees. This is because the fossils here are much smaller and weather out of the surrounding rock to be picked up loose by hand.

 

The fossils here are similar to the first. There were lots of bryozoa to be found. My girlfriend gets credit for finding the largest, which is the one on the left that measures 4.5cm

 

Here is a tiny Graptodictya sp. bryozoan

 

We also found some more pieces of Illaenus fieldi. The left piece is a ventral thorax piece while the ones on the right are pieces of the pygidium

 

Bumastus sp. pygidium

 

Most of the brachiopods were small. Here are some Sowerbyella sp.

 

Glyptorthis bellarugosa

 

I did find one larger one though, which was this pedicle valve of Strophomena medialis

 

Some of my favorite fossils were the sponges we found. Here is one of the undetermined sponges

 

This is the other

 

One of the described sponges found in the Benbolt Formation is Receptaculites sp. We found these three pieces

 

[historianmichael]

However, some of the most impressive fossils of the Benbolt Formation are the calyxes or calyx plates of the various echinoderms that can be found here.

 

We found some very interesting crinoid elements, including these crinoid columnals with tiny spines radiating out

 

Many of the loose rocks have larger stems on them. My girlfriend found the loose stem on the bottom that has a piece of cirrus still attached

 

The prizes of the site though are the loose echinoderm plates. Here are some plates of the crinoid Acolocrinus hydraulicus

 

This is a plate diagram for Acolocrinus hydraulicus. The top two plates would have been near the stem while the bottom two plates would have been near the arms on the calyx

 

My favorite plates were these deltoid and radial plates from the parablastoid Meristoschisma hudsoni

 

This is a plate diagram for Meristoschisma sp. identifying where the deltoid and radial plates were located on the calyx

 

This is what it would have looked like all together

 

 

All in all, it was another successful fossil trip. We have talked about doing it again soon so that I can visit the sites that I had to cut from the trip. Fingers crossed! At the very least we need to make another trip to make up for the views we had on our hike...

 

At least we saw some beautiful fall foliage

[TqB]

Mouthwatering collection, and fascinating, detailed report.  I love everything, but especially the sponges!

[Fossildude19]

Great report and finds, Michael!

Thanks for posting this.   

[minnbuckeye]

Nice report. Those cystoids are great!!! Wish my local Ordovician contained them.

 

 Mike 

[piranha]

15 hours ago, historianmichael said:

Here are two cephalons and a pygidium of Illaenus fieldi

    

 

I think this is a right cheek and eye of Eoharpes sp.

 

Here is an additional mystery trilobite piece

 

 

Congrats on all the great fossils!

 

'Illaenus' fieldi was reclassified as Thaleops.  The Harpetidae should have small circular eyes.  The mystery specimens appear to be isoteline forms.

 

Amati, L., Westrop, S.R. 2004

A Systematic Revision of Thaleops (Trilobita: Illaenidae) with New Species form the Middle and late Ordovician of Oklahoma and New York.

Journal of Systematic Palaeontology, 2(3):207-256  PDF LINK

[historianmichael]

@piranha Thank you so much for that information. I was using Butts' 1940 Geology of the Appalachian Valley in Virginia to help with my identifications, so clearly my information is dated. I agree that the eye on the second trilobite might be too large for Eoharpes. Could it be something larger in that order? Perhaps Hibbertia?

[piranha]

1 hour ago, historianmichael said:

Could it be something larger in that order? Perhaps Hibbertia?

 

 

I don't see any matching features for the Harpetidae.  Perhaps some better photos might prove otherwise?

 

 

Isotalo, P.A. 2015. Ordovician Trilobites of Southern Ontario, Canada and the Surrounding Region: An Illustrated Guide. Siri Scientific Press, 224 pp.

[FossilDAWG]

I have collected Dolichoharpes at that site, but I don't see anything in the photo that suggests a harpid to me.

 

Don

[historianmichael]

@piranha @FossilDAWG Thank you for that further information. Perhaps I am just thrown off by the eye and the amount of head around the eye. When I think about it, the eye does look a lot like the eye of Isotelus.

 

  

 

  

 

[Monica]

The cystoids and sponges are fantastic!  My favourite sponge is this one:

The detail on this piece is amazing!!!