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Showing results for tags 'birdsong formation'.
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The Devonian period is known as "The Age of Fish", but could also be known as "The Age of Brachiopods." In the Early / Lower Devonian, brachiopods reached the height of their diversity towards its end in the Emsian. We see the ancestral groups occurring, lingulids, craniids, orthids, protorthids, pentamerids, rhynchonellids and strophomenids, as well as the later successful groups we have seen before such as atrypids, athyrids and orthotetids, plus the rise of spiriferids, spiriferinids and productids and the beginning of the terebratulids. By the end of the Devonian , several of these groups are extinct or severely reduced in importance and brachiopods never quite recover. Also, the Devonian is the last time we see trilobites with such variation, large sizes and numbers and orthocerids too are much more uncommon after the rise of the goniatites. The massive tabulate coral reefs also disappear after the Devonian. Fascinating period and I hope to share some of its wonders with you. Equally, a lot of this is rather new to me, so I would be very grateful for any assistance, corrections or further information on my specimens. Thank you. The Early Devonian epoch is split into three stages, so let's start with the first of those, the Lochkovian, that began about 419 mya and finished roughly 411 mya. I have been sent a nice selection of brachiopods from the Kalkberg Formation, Helderberg Group by the Mighty @Misha, mostly. But the kind gentleperson also sent me this fascinating little bryozoan hash : It is dominated by fenestellids, which is usually the case in the Devonian, but other orders sill occur. These ones, I think, are Fenestella, but there are so many species in the formation that I wont take a guess as to species : Not sure what this one is ;
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I have 11 specimens of this, and all of them are incomplete. I am posting an example that shows the salient features that apply to all. This is from the lower Devonian Birdsong Shale member of the Ross formation in Parsons, Tennessee. All specimens are 30~50 mm ovals consisting of growth rings only, and any hinge area is missing from all. The rings have no radial features or ornamentation. They are very shallowly concave and seemingly have no prominent apex The growth rings center from what appears to be a muscle scar, and the outer ring is always slightly thicker and wider. The shell is quite thin at about 1 mm. I can post other photos, but this one has all the key features that are perplexing me.
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- birdsong formation
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