ADAM'S SILURIAN

[Tidgy's Dad]

The atrypids are mainly represented by small anazygids in the Middle to late Ordovician eg. Zygospira and Catazyga, and, lovely and numerous as these may be, it's nice to have a nice chunky atrypid in the Wenlock. Atrypa reticularis was a very successful species, lasting over 50 million years to the end of the Middle Devonian, was pretty much cosmopolitan in its distribution and thrived in a number of different habitats. It is the most common brachiopod in the Much Wenlock Limestone Formation. 

The two larger specimens shown below are from the Malvern Hills in Worcestershire while the smaller ones are from the Wren's Nest at Dudley, West Midlands. Why the size difference, I am not certain, but it may be that I've given away my smaller self-found Malvern specimens over the years while not been gifted any larger ones from Dudley.

   

One of the larger ones :

One of the smaller ones : 

 

Here's one in matrix with a rhychonellid and some bryozoa.

[Tidgy's Dad]

Although the Much Wenlock Limestone runs through much of the Welsh borders and its equivalents can be traced west to the Niagaran of North America and East to the Gotlandian of Sweden and on to the South East Baltic, different faunal communities exist with the rocks. Some species such as Atrypa reticularis and Halysites catenularius through most areas, but the regions each have different faunal communities, geographically or through different stratigraphic levels. At the Wren's Nest, Dudley, West Midlands, England, we find the Isorthis clivosa community in the lower half of the sequence and a Sphaerirhynchia wilsoni community in the upper part. Although most species of brachiopod occur in both, the percentages of different species present vary considerably. The S. wilsoni community is noted for the scarcity of molluscs and the abundance of ramose bryozoa, so I think that is where most of my collection has originated. 

Furthermore, the S. wilsoni community is split into two different sediment types; and argillaceous micrite where fossils are more spread out and a thickly fossiliferous biomicrite. The biomicrite is dominated by spire bearing brachiopods, spiriferids, atrypids and athyrids, (though Atrypa reticularis is found in large numbers in all communities) as well as rhynchonellids, presumably as they have adaptive shell morphology to be able to endure stronger water currents and a sturdy pedicle for holding on to a hard substrate in these conditions. The argillaceous micrite has a high percentage of strophomenids and orthids, more suited to calmer waters as the former could be easily flipped and the latter had comparatively weak pedicles. Most of my specimens are rhynchonellids and spiriferids and this along with the matrix being full of smashed up bits and rich in fossils suggests the high energy environment of the biomicrite. My lack of specimens of wide flat strophomenids also goes some way to explaining my failure to find many of the species of bryozoa that prefer to encrust brachiopods. 

The spiriferids were just coming into their own at this time, most of them are still comparatively small, the  larger 'winged' forms mainly appear later. The spiriferids I have from here are my oldest. The most common spiriferid in the biomicrite is Howellella elegans. A beautiful little thing, this first specimen is my best and comes from Hobbs Quarry, Longhope, Forest of Dean, Gloucestershire and is part of the May Hill inlier. 

Howellella elegans: 

 

From the same location, preserved with the Tryplasma loveni coral, not growing on it : 

Still Hobbs Quarry, this one 6 mm wide : 

Wren's Nest, 5 mm wide :

And a bit of a broken one, a lot of them are single valves and/ or broken. 4 mm wide : 

 

 

   

[Tidgy's Dad]

A much rarer spiriferid from the Wenlock Limestone is Kozlowskiellina strawi.

You can see the resemblance to Howellella elegans, and it was considered to be this species until 1957 when it was decided that the differences in shell form ( it would have wings if the specimen were complete and is clearly more rugose, among other things) were enough to give it not only its own species within the  genus Kozlowskiella but a new subfamily. The following year the genus was renamed Kozlowskiellina. Recently it has been moved into the subfamily Cyrtinopsinae which is within a different family to Howellella.

It is a small species exhibiting strong fila (concentric ornamentation) on the crenulations and I only have the one specimen from the Wren's Nest,  8 mm wide. 

 

[Tidgy's Dad]

The Sphaerirhynchia wilsoni community is so called because of the relative abundance of this species in this ecosystem though it does occur in other communities too. 

Sphaerirhynchia wilson is the most common rhynchonellid in the Much Wenlock Limestone Formation. It is very variable in its morphology but can be identified by its fine costae which are grooved toward the anterior, a weak fold, no sulcus and high tongue which often ends almost flatly. It seems to have had a comparatively thin shell as they are often found as fragments or crushed in the rock pieces, more so than the other species of rhynchonellid found here. 

These are from the Wren's Nest, Dudley. The largest specimen is 1.2 cm wide.

The biggest specimen: 

Notice the notches on the costae : 

Another specimen : 

A slightly damaged one :

And a very small one : 

 

 

 

[Tidgy's Dad]

It's nice that so many different Orders of brachiopod are represented here. You can find a huge  number of small ones in the micro matrix and in rock samples. Some of them maybe young ones of various species but most are just specimens of smaller species. 

This is the most common athyrid in the Much Wenlock Limestone formation. It is quite small and rather variable in shape. Though it looks a bit like a rhynchonellid or sometimes a spiriferid, the slightly unequally biconvex shape and hinge line rule these out.  

This is Homoeospira baylei, the largest specimen 7.5 mm long the smallest only 3 mm. This is the biggest one : 

Another specimen :

And another :

Close up of a broken beak:

A specimen with a nice pedicle area preserved : 

Tiny 3 to 4 mm ones : 

Sometimes they seem to be broader than long and look more like spiriferids : 

 

 

 

 

[Tidgy's Dad]

A larger spiriferid that occurs commonly in the Much Wenlock Limestone is Eospirifer radiatus. 

I only have one specimen, and it's only the pedicle valve with the wings broken off.

Hey ho! 

Still its sulcus and very fine striations are still very clear. 

It's from my collecting days in the South Malvern Hills, Worcestershire, England. 

 

 

[Tidgy's Dad]

Most of the strophomenids found at Dudley are large, flat species of the same families that are found in the Late Ordovician. Although these species are found in the different levels of the Much Wenlock Limestone Formation, they are less common in the biomicrite as the conditions were too turbulent to be ideal for them. 

Here is a specimen of the tiny chonetid Protochonetes minimus. It's very thin and only 3 mm wide, though the species does get up to nearly a cm wide. Though the chonetids had first appeared, probably from sowerbyellid ancestors, in the Late Ordovician, this is the earliest one I have in my collection and therefore, my oldest productid which would later emerge, along with the also recently evolved spiriferids, as the dominant brachiopod group in the later Palaeozoic. 

 

[Tidgy's Dad]

Like the strophomenids, the orthids do occur commonly in the argillaceous micrites but are rarer in the biomicrites where most of my collection comes from. 

This is Isorthis clivosa from the Wren's Nest, Dudley and has it's own community which can be found in the lower levels at Dudley and elsewhere along the Wenlock Edge, but this one is from the biomicrite as can be seen from the large number of other organic remains crammed into this interesting little rock.

After a bit of pin prepping :

This is another orthid, possibly an Isorthis brachial valve, from Hobbs Quarry, near Longhope, Gloucestershire I love the beautiful specimen of the tabulate coral Thecia expatiata in the background.:

 

 

 

[Tidgy's Dad]

Perhaps my favourite genus of brachiopod is the wedge-shaped Leptaena. Even better is that it belongs to the same family as one of my other faves, Rafinesquina. 

I have species of Leptaena from the Cincinnatian of Indiana, the Hirnantian of the English Lake District as well as some later forms, but there are three species that are fairly common in the Much Wenlock Limestone formation. 

This one is Leptaena depressa from the South Malvern Hills in Worcestershire, England. 

Parts of the shell are a bit worn showing areas of the muscle scars and median septum :

From this posterior view we can see the small pedicle foramen and the depth of the shell. 

Here is an anterior view and you can see the shell is much deeper, not just because of the wedge shape, but because the trail is partly preserved. The trail is an extension to the valves that grows out beyond where the two shells would normally meet creating a canal with a narrow gape aligned with the current for feeding purposes. It may also have been used in some species to keep the opening above soft substrates :

(diagram from https://www.hindawi.com/journals/paleontology/2014/716053/) Hoel 2014. )

Shell detail showing the pseudopunctate structure (calcite pillars that look seem like openings that don't reach the shell exterior), here seen where the outer shell layer has been worn away. In the lower half of this picture you can see the outer layer, so no pseudopunctae  : 

Trail details : 

 

 

 

 

[ClearLake]

What a great group of brachiopods!  Looking forward to what else you have to show as I have not done a lot of collecting out of the Silurian. Keep em coming!!

[Tidgy's Dad]

1 hour ago, ClearLake said:

What a great group of brachiopods!  Looking forward to what else you have to show as I have not done a lot of collecting out of the Silurian. Keep em coming!!

Thanks, mate.

Plenty more to come after a bit of pin prep.  

[Tidgy's Dad]

Another, slightly less common species of Leptaena, found in the Wenlock Limestone Formation is Leptaena rhomboidalis. 

Apart from internal detains, the main differences between this species and L. depressa are that L. rhomboidalis has much more pronounced concentric rugae and a more prominent pedicle foramen / beak. 

This one is 1.5cm wide.

 

This next one is a portion of the pedicle valve showing the prominent beak more clearly :

 

 

[FossilNerd]

Nice specimens Adam. Thanks for taking the time to show these! Those little digital microscopes are great for getting a good view of the small details. The trail detail and pseudopunctae are wonderful to see. 

[Tidgy's Dad]

22 hours ago, FossilNerd said:

Nice specimens Adam. Thanks for taking the time to show these! Those little digital microscopes are great for getting a good view of the small details. The trail detail and pseudopunctae are wonderful to see. 

Thanks again, Wayne.

I couldn't do without my digital microscope these days, it's invaluable.

Going through the micromatrix is so much easier. 

Here's some more from the Wren's Nest. 

The Rhynchotrematoidea is the most successful rhynchonellid group during the Ordovician and Silurian and contains such well known genera as, Rhynchotrema, Rostricelulla,  Hiscobeccus and.Lepidocyclus. There are a few from this superfamily in the Wenlock Limestone Formation. This photo has a few specimens, generally pretty small.

Some of them are from the family Trigonirhynchidae including Microsphaeridiorhynchus nucula (used to be Camarotoechia nucula) It never gets to more than a centimetre, on average only half of that.)

 

Can be rounded or rather flattened :

Another specimen :

 

 

[Tidgy's Dad]

From the same family, different subfamily is the very distinctive Rhynchotreta cuneata. 

Quite triangular and with a really extended beak, though this is something that is only quite so apparent in adults. Younger specimens have a shorter beak. 

Another specimen :

Another one :

And a fourth :

 

[Kane]

The long beak is quite something! On one angle, it almost appears like a victrola.  

[Tidgy's Dad]

1 hour ago, Kane said:

The long beak is quite something! On one angle, it almost appears like a victrola.  

Ha ha. 

Yes, indeed, particularly the first photo of the second specimen. 

[Tidgy's Dad]

The most common species of pentamerid in the Much Wenlock Limestone Formation is Gypidula. There are a couple of species present, but I only have fragments in bits of rock, unfortunately. 

This is an example of a bit of the ridged Gypidula galeata, 8 mm wide : 

And this bit is the smoother Gypidula dudleyensis, with a groove running down the valve. 6 mm.

 

 

[Tidgy's Dad]

The ubiquitous Atrypa reticularis is not the only atrypid found at Dudley. 

One of the others is the tiny Glassia sp. 

Scale is in mm.

 

[Ruger9a]

Thanks for posting such informative photos about your brachiopods, I love them!!!! 

[Tidgy's Dad]

10 hours ago, Ruger9a said:

Thanks for posting such informative photos about your brachiopods, I love them!!!! 

That's very kind. 

Thank you very much. 

Plenty more to come! 

[Tidgy's Dad]

One of the prettiest brachiopods found in the Much Wenlock Limestone Formation must surely be the orthid Resserella canalis. 

They may be found at the Wren's Nest but I found this specimen at Hobbs Quarry, Longhope, Forest of Dean, Gloucestershire. 

[FossilNerd]

57 minutes ago, Tidgy's Dad said:

 

One of the prettiest brachiopods found in the Much Wenlock Limestone Formation must surely be the orthid Resserella canalis. 

 

I’m not as familiar with that formation as I would like, but I have to agree that this is a real beauty! 

[Tidgy's Dad]

1 hour ago, FossilNerd said:

I’m not as familiar with that formation as I would like, but I have to agree that this is a real beauty! 

Thanks, Wayne. 

The species can be found in the Racine Formation of Wisconsin. 

[Tidgy's Dad]

I rather like boshing rocks with Harry the Hammer. It's nice, rather therapeutic. 

Sometimes I even discover something nice within. 

This piece of Much Wenlock Limestone broke nicely to reveal a specimen of a third species of Leptaena from the Wren's Nest ; Leptaena rugata. This species is much smaller than L, depressa and L.rhomboidalis. and though it has very obvious and deep rugae, it is pretty smooth in between them with little radial ornamentation. 

8 mm from ear to ear.