Posts Tagged ‘ordovician’

Isotelus Molts

February 5, 2011

Working an outcrop in the Clays Ferry Formation that is in the same bed, and close to, another outcrop that I have collected extensively(see here, here, and here), I came across some curious molts of an Isotelus gigas.

The Clays Ferry Fm was deposited in a relatively shallow subtidal environment, and throughout most of the area, the formation straddles the Mohawkian/Cincinnatian boundary(early Late Ordovician). Due to deposition below wave base in typical weather, most of the fossil are complete and a diverse assemblage can be found in the column.

The Bed form which this piece comes is composed primarily of orthoconic cephalopods, Isotelus, a few bivalves, and an occasion Flexicalymene trilobite.

What I find curious about the molts is found on pygidium and thorax of the smaller dorsal specimen. I have annotated it with a white line to highlight the area.

There is a crack and indentation that runs from the anterior posterior(Jeeez, I just caught that) margin through the pygidium, and from there it appears as if it continues on through the pleurons. As there is no suture along that area of the thorax, I would assume that the distal portions of the pleurons would be adjacent to the rest of the critter, but they are not there, So that has left me wondering if the structure is pre-molt, or if it is an artifact of lithification. Any Ideals?

Advertisements

Another Ordovician Trepostomate

January 11, 2011

A while back, while working a rather new outcrop of the Millersburg member of the Lexington, I was having little luck finding anything worthy. So, on a whim, I decided to walk a few hundred meters down the road and about 10m down in the rock column to an outcrop of the Tanglewood member.

The Tanglewood was deposited near shore and above wave base, so the fossils(what few are there) are generally very abraded and of poor quality. But occasionally, I find a lens of mudstone within the Tanglewood that preserves some nice critters.

Unfortunately, this was not to be one of those days. Though, I did find a nice trepostomate bryzoan that I brought home.

I’m not much on the Bryzoa, but this one appears to be a Heterotrypa sp.

Here it is glued back together.

Micro-Bivalve

January 1, 2011

A quick post from something on the hard drive…

Often, when inspecting corals(Cnindaria) or sponges(Porifera) that I have found in the Millersburg mb. of the Lexington, I find micro-fossils at the base of the colonies. It could be coincidental, but I’m starting to think that the micros were juveniles and that their progenitor placed the off spring in a habitat that favored survival, or the ones placed there were more likely to survive… which seems more plausible.

Anyway, here is a small bivalve that was collected from just such an environment.

A little closer

Since the common bivalves from the Millersburg are modiomorphids or ambonychiids, These are probably ambonychiids… probably Bysonnychia sp. juveniles.

Enigmatic Critter

November 24, 2010

Hyolithids are a poorly understood group of critters. They first appeared in the Cambrian and became extinct during in the Great Dying(Permian-Triassic extinction) at the end of the Paleozoic. The Great Dying was the most severe crisis for the biosphere that the planet has ever experienced… about 95% of all species perished!

There are numerous hypothesis to explain the extinctions(google it), but it was probably a combination of several catastrophic changes that killed off most life.

A few hyolithids that were recovered from the Millersburg mb:

Someday, I will devote a post to the extinction event.

An Uncommon Lichid

November 8, 2010

Upon returning to Lexington, one of the first outcrops that I looked forward to collecting was a relatively small outcrop of the Millersburg member of the Lexington Limestone. I worked the outcrop for 8 years back in the 80s, and it produced some stunning fossils.

The Millersburg is a nodular unit of shales and limestones that was deposited on a shallow carbonate bank. The depositional environment was one of relatively high energy as evidenced by the broken and abraded fossils found within the member. For that reason, it is often overlooked by paleo geeks

But, I have found some spectacularly preserved inverts from the member. I pulled a well preserved example of coprophagious(poop eating) symbiosis among the gastropod Cyclonema varicosum and a crinoid from the member 25 years ago, but even better, I found an undescribed lichid trilobite from the same locality!

And, that is what bring me to this post.

That wonderful outcrop, with all of its rare fossils, is no more.

Yep, they paved paradise and put up a parking lot…

So, I moved on to an outcrop farther down the road. I found my first complete trilobite there! It too was gone- The outcrop, not the fossil( I thought that I had written a blog entry about evil civil engineers, but I guess that I didn’t; maybe in the future?)

I then moved on to the next outcrop that wasn’t destroyed, and it was a good one. Other than most of the Pychnocrinus that I have displayed on the blog, I also found a partial pygidium from a lichid trilobite.

Usually, I would pass on something as insignificant as a partial pygidium, but it was from a lichid. Too remember, I pulled an undescribed lichid up the road a bit.

The undescribed trilobite consists of 11 cephalons, two pygidia(is that the plural?), and one hypostome.

Anyway, here it is. It doesn’t look like much, but it sure got my heart racing.


The box is about 1cm

The Legend of Sleepy Lagoon

October 30, 2010

The “headless” trilobite:

An I. gigas that was found in the Clays Ferry Fm. in Anderson Co. Kentucky. When I found it, it was posterior-dorsal up. Wow, I was excited! Oh well…

Neat-none the less.

Ordovician Trepostomate

August 30, 2010

While visiting a friend’s(Herb) house, I noticed a stone that he had placed at the down spout of his gutter. Well, actually his father had placed it there many years ago in an attempt to inhibit erosion by allowing the energy from the falling water to dissipate at the surface of the stone.

The stone was placed in its location in the 50s or 60s, and the falling water, over the years, had exposed multiple “tips” of some kind of stony bryozoan. The bryozoan had been preserved as silica replacement in a bed of a muddy carbonate.

Herb knew of my enthusiasm for inverts, and when he noticed my pre-occupation with the “dissipation stone”, he ask if I wanted it!

Upon getting the rock home, I treated it with multiple baths of HCl to reveal the colony within… and a splendid colony, it was.

Trepostomate bryozoans can be particularly hard to ID without a thin section and intimate knowledge of the subject. And, I don’t have either, but the results are stunning.

It is probably some kind of calloporid.

Sorry, I don’t have a before pic and the finish is out of focus, but you get the ideal.

Since the rock was retrieved from the Kentucky River Valley near Frankfort, it is probably from the High Bridge Group; more than likely the Oregon Fm or Tyrone Fm.

EDIT:I am experiencing some kind of scripting error, so this is an off-site link.

Photobucket

EDIT: The scale is in inches(2.54cm/inch). Its a whopper!

Ouch!

August 20, 2010

Year ago while working an outcrop that has produced some stunning asasphids, I found this little Isotelus gigas. It appears that the little guy had a bite taken out of his cephalon, enrolled and died. I found it in a bed of the Clays Ferry Fm(early Late Ordovician) in Anderson Co. Kentucky. The bed is comprised of, almost entirely, I. gigas molts and orthocerid cephalopods.

EDIT: the bar at the bottom is 1 inch(2.54cm)

Sea Monsters

July 9, 2010

Usually, brachiopods don’t get me very excited(sorry lophophorate nerds), but occasionally I come across something in the field that causes me to do a double take.

Have a look at this monster. It is an orthid brachiopod that was collected from the Millersburg Mb. of the Lexington Limestone in Fayette Co. Kentucky

Hebertella sp.

anterior

Posterior

Dorsal

Apparently, I didn’t photograph the ventral… oh, well.

I have one that is even larger! Somewhere???

Trilobite Molts-Up Is Down, And Down Is Up

July 1, 2010

A while back, Chris over at Ediacaran put up a post in his “Paleoporn” series describing the environment and sedimentology of two sites, in the same formation, where the same Cambrian trilobite is found. His post is a description of the orientation of the molts in the two different environments. In the comments, we discussed the curious habit of finding inverted cephalons, ie, ventral up cephalons while the rest of the critter is found in its normal position(dorsal up).

In a thin bed of the Clays Ferry Formation in Anderson Co. Kentucky, I find numerous partial molts from the trilobite Isotelus gigas. Some of the bedding planes are almost entirely composed thoracic segments, cephalons and cranidiums, and pygidiums from this large asasphid. Occasionally, one comes across the curious preservation described above.

During ecdysis, the cephalic sutures of the trilobites rupture allowing the critter to escape from the front of its carapace. Sometimes during the egress, the critter will push the cephalon upside down. Hence, what we have here.

When I found this one, it didn’t appear that much was there.

But, I brought home anyway. While hitting it with a scribe, I noticed the ventral, but I thought that it was trash and nearly blew through it… as more became apparent, I slowed up a bit(word to the wise).

I have found several more from the same locality, but those are all that I have photographed. However, here is a nice juvenile that appears to have had a bite taken out it.

More on that later.