Atrypa fossil

[blackmoth]

who could explain the subtle differences between Atrypa reticularis　and Ａ.devoniana?

I just bought a wonderful piece labeled atrypa (from Guangxi China). The seller does not know anything about it.

[blackmoth]

sorry about the quality of the images. my smartphone costed me $45.

[Fossildude19]

Not sure about your question, but there appears to be plenty of information available online about the area, including some interesting PDFs.

Here, ... and Here.

Interesting page HERE as well.

Regards,

[FossilDAWG]

Atrypid brachiopods are one of the more difficult groups to work with. Externally they are very conservative, meaning there is little evolutionary change, which leads to a lot of homeomorphy (different species with similar external appearance). Accurate discrimination of genera and species requires detailed views of the internal structures, and sometimes shell microstructure. Researchers will accomplish this by grinding and photographing polished sections at closely spaced intervals from well preserved specimens. Ultimately this destroys the specimen, but the sections can be stacked up to recreate a detailed view of the interior, exterior, and the microstructure.

Obviously collectors are unlikely to have the equipment or the desire to do this with their specimens. The alternative, for us, is to refer to published research dealing with brachiopods from the specific formation and area that was the source of our specimens. Although there are dozens of genera, and many hundreds of described species of atrypids, a particular geological formation will contain a far smaller number. In that case, a collector may be able to match the external appearance of their specimen to a species known to occur at the same place and formation. Such an ID is a hypothesis (unless you can actually see the interior and exterior and the specimen is exceptionally well preserved), but it can be a high confidence hypothesis if you have detailed locality data and you can reference relatively recent published work that deals with your locality or specific geological origin of the specimen. If you do not know the exact geological formation for your specimen, or you do not have good literature to refer to, you may be matching your specimen to a larger number of possible species. Another problem is that the older literature mainly uses very general form species concepts, often based only on external features; these old species concepts have been split up into many species based on more modern studies. If this is your situation, your hypothetical ID will be less strong.

"Atrypa reticularis" is a great example of a form species generally identified based on external characteristics that actually apply to many species. The name often appears in lists of fossils presented in publications that deal with the geology of particular areas or formations; such publications are generally authored by people concerned with geology and the species ID is not the main focus, so it is done without the detailed studies I described above. You will see the name applied to fossils from a wide range of Silurian and Devonian localities around the world. A detailed study of atrypid brachiopods from the Silurian of Gotland and the Welsh Borderlands area of Britain, published by Paul Copper in 2003, showed that true Atrypa reticularis is common only at one horizon on Gotland (where the original specimens were collected), and it is less common in Britain. Atrypids are abundant at many levels in both places, but almost all belong to different genera and species, though they resemble Atrypa reticularis externally and were previously identified with that species. Similarly, atrypids from elsewhere in the world, and all the Devonian species, are highly likely to be something different from true Atrypa reticularis.

Despite the fuzzy photos, it is obvious that your specimen is very different from Atrypa reticularis. At least superficially it resembles a Desquamatia or Iowatrypa. If you know the source geological formation or have more specific locality data maybe we can find some relevant papers.

Don

[Ridgehiker]

I have about 40 species of Atrypa (Spinatrypa, etc) brachiopods. There is no way of telling most apart from the exterior. One needs to do a serial grind. Even though then, ID is based mostly on the locale, formation, etc.

Just a note...brachs, like all fossils have no value without specific collecting info. It is just another ornament.

[blackmoth]

thank you all for so all the information provided. Before posting this question I actually did quiet some digging with bing, as google is blocked here. little luck.

this site is just so valuable with all your expertise.