Monday, May 30, 2016

A silicified specimen of Douvillina inaequistriata from the Centerfield formation of New York

I've blogged before about Douvillina inaequistriata specimens from the Centerfield member of the Ludlowville formation in New York in a prior post. Today I'm showing off a silicified specimen that I found in the dissolved remains of some limestone from the same locality. It is in great condition, has both valves and  an interesting color pattern. I think the pattern is related to how much of the original shell was actually replaced with quartz. The shell also has some very nice looking "Beekite" rings

Pedicle valve
Brachial valve

As I mentioned above, this specimen has been replaced with quartz and I dissolved it from a limestone block using dilute Hydrochloric Acid. It comes from the Centerfield member of the Ludlowville formation (Devonian, Givetian stage) near East Bethany, NY.

Saturday, May 28, 2016

Phillipsastrea sp. coral from Morocco

I recently was able to purchase some really nice fossil corals from Morocco which I am tentatively identifying as Phillipsastrea sp.  This species is a colonial rugose coral that lived during the Devonian period, but instead of having depressed calices (or cups) that protected their bodies, they appear to have inverted that  model. Individual corallites are convex and poke up above the colony base. They have small dimples or cups in the center of each individual with septa radiating outward along the exterior of the mound until they met their neighbor. Since each coral colony is basically a group of clones there is little infighting between corallites. These fossils remind me of the modern coral Cycloseres sp. and it's fellow "Mushroom" corals in the Fungiidae family of Scleractinian corals.

The largest is this 8" (22cm) plate which is a complete, intact colony. This is the ventral surface

A closer view of the individual calices

The colony is somewhat squat and spread out which indicates that there was little influx of sediment that would otherwise cause it to grow upwards more that outwards.

 A view of the dorsal surface which was in contact with the substrate. The lack of an obvious hard attachment point indicates the colony grew on a semi-solid substrate rather than on top of other debris.

A closer view of the dorsal surface. The epitheca appears to have taken the brunt of the weathering as you can see some of the coral structure rather than a plain surface.

I also got a few smaller, hand sized samples like this specimen.

And this one which also features a horn coral cousin on the side.

Note that this specimen exhibits some rejuvinational growth, perhaps initiated after a storm partially covered the colony.

Here is the horn coral that decided to use the Phillipsastrea as it's hard ground. Note that the horn coral does not appear to be affecting the growth of the coral it colonized (as no evidence of subsequent growth by the Phillpsastrea can be see). The horn coral, in fact, made more stabilizing attachments to the Phillipsastrea as it grew. I interpret this as evidence that the Phillipsastrea colony had been smothered or otherwise died, and the horn coral took advantage of a hard substrate to establish itself, only later to succumb to another storm and be smothered itself.

All three specimens came from Morocco and are from the Devonian period. It comes from the Taouz region but I do not have any other locality information for it.

Thursday, May 26, 2016

Orthospirifer sp. brachiopod from the Silica Shale

Years ago I purchased some brachiopods that came from the middle Devonian aged Silica Shale in Ohio. These were fossils that had been collected in the 80's and 90's and came from older collections. Among the various species were these two articulated shells. The label that came with them called them Orthospirifer sp. but they look very similar to Mediospirifer audaculus which is a somewhat common brachiopod species from the middle Devonian. I've done a little research and it seems to me that the most visual difference between Orthospirifer and Mediospirifer is that the brachial valve on Orthospirifer is a little more convex and the interarea is slightly recurved. On Mediospirifer the brachial valve is nearly flat and the interarea is straight. This is just based on my collecting experience and visual inspection of fossils in my collection.

Specimen #1 - brachial valve
Pedicle valve

Specimen #2 - brachial valve
Pedicle valve

Both specimens side by side.

Tuesday, May 24, 2016

Results from a short visit to the Florissant Fossil Quarry

As part of my vacation last fall I had an hour or so to kill in my schedule and happened to be passing near Florissant, Co. The town is well known for the Florissant Fossil Beds National Monument which preserves an ancient lake bed from the Eocene that was near a field of volcanoes. The volcanoes would erupt with lots of ash and this would rain onto the lake and the surrounding environment. As the ash settled it would cover anything that happened to be floating on or above the lake surface. The ash layers deposited as thin films and millions of years later have been compressed into "paper" shale (so called because each layer is as thin as a sheet of paper). Splitting the shale is easy but also hard. You have to use a very thin, sharp blade (a razor blade is perfect) to split the fine layers. If you are lucky you will find an insect or plant trace from long ago.

Outside of the park boundaries is a fee quarry, on private land, that allows you to split some of the paper thin shale and keep the fossils you find. It's called the Florissant Fossil Quarry and I've been to this site several times over the years. You can see some of the other fossils I've collected  by clicking here, here, here, or here. This trip only allowed me a hour but I found a few interesting specimens.

This is a small snail with a partial leaf. The shell has been crushed but you can still see some of the shiny nacre.

A beech or elm type leaf

A seed of some sort, although it looks like the seed itself is missing and only the surrounding "wings" are left. This looks similar to slippery elm seeds.

Lastly, a fly or bee (wasp?) of some sort. The preservation is not the best and it looks better from a distance than up close.

The Florissant fossil beds are called the Florissant formation and are dated to the latest Eocene epoch (Priabonian stage) of the Paleogene.

Sunday, May 22, 2016

Peilinia quadriplicata pelecypod from Texas

Another pretty cool looking oyster that I found in the Texas creek I was exploring is Peilinia quadriplicata (also called Ostrea quadriplicata). This species is very easy to ID based on the look of the shell. I only found a left valve but it has the typical splayed look to it, kind of like a duck foot. While the shell started out with a relatively smooth margin, as the animal grew older it started to have some distinct "points" with flat, straight areas of margin between them. Overall the shell is subpentagonal in shape with some obvious, widely spaced growth lines. There is also some gentle undulations on parts of the shell. The interior of the valve is smooth with a scallop shaped indentation where muscles once attached.

Left valve, top view
Ventral view
Interior view
Dorsal view
Right profile
Left profile

I found the above specimen in a creek that cuts through the Duck Creek formation but P. quadriplicata is not found in those rocks. Likely this washed downstream from a higher, younger formation such as the Denton Clay or Paw Paw formation which are Cretaceous (Albian and Cenomanian stages respectively) in age.

Friday, May 20, 2016

Texigryphaea corrugata pelecypod from the Duck Creek formation of Texas

Here is a fossil oyster shell from the Duck Creek formation that I found as float in the creek gravels. It belongs to the Genera Gryphaea Texigryphaea and is somewhat narrow with two undulations on the left valve (all Gryphaea Texigryphaea type oysters have a convex left valve and flat to concave right valve). As is often typical for oysters there are a number of seemingly overlapping growth lines that are hardly ever regular or flat. In profile the left valve is strongly recurved to nearly coiled over the right valve and angles off to one side a little. The interior of the valve is smooth and I don't see any obvious muscle attachment scars. The specimen I show below is missing it's right valve.

I am not familiar enough with the Gryphaea Texigryphea to ID this down to the species level. The excellent website North Texas Fossils lists two possible species for the Duck Creek formation: Gryphea corrugata (Say) and Gryphea washitaensis (Hill). I found another reference on Google Books in "The Lower Cretaceous Gryphaeas of the Texas Region" by Hill and Vaughan, USGS 1898. Even using the illustrations in that book I have a hard time deciding what I found as both species appear to be very similar looking to me. Indeed, the Authors have the same problem with specimens found in the Duck Creek formation (pg. 62) and postulate that the two species interbred with each other. So at this point I am going to call it Gryphaea Texigryphaea corrugata as that seems to be the most common species and also the "parent" species from which G. T. washitaensis developed.

Update 6/6/16: A vigilant reader pointed out that the genera Gryphaea is restricted to Europe and that the equivalent in the Cretaceous of Texas/Oklahoma is Texigryphea. He also recommended an old issue of "Oklahoma Geology Notes", Vol 35, No. 2 which has an paper by Robert Fay titled "The Type Species of Mortoniceras and the Holotype Specimens of the Lower Cretaceous Texigryphaea of the Southwestern United States". It has some helpful information and a key that may be used to ID specimens of Texigryphaea. The link above takes you directly to the paper but if you click here you can go to the Oklahoma Geological Survey site and look through all 74 volumes (up to winter of 2014). There are a lot of good publications and information on their website.

Left valve top
Left profile
Right profile
Interior of left valve
Ventral view
Dorsal view

The above specimen comes from the Duck Creek formation which is Cretaceous (Albian stage) in age.

Compare G. T. corrugata to a few other species from the lower Cretaceous of Texas: Texigryphaea navia, Texigryphaea marcoui and Ilymatogyra arietina