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Archeognathus
''Archeognathus'' is a fossilized jaw apparatus of a large predatory conodont from the Ordovician period ( Darriwilian to Sandbian stages). Its large size has made classification difficult, and it has historically been compared to conodonts and gnathostomes (jawed fish) since its remains were first discovered in Missouri. Complete articulated jaw apparatus of ''Archeognathus primus'' are common in the Winneshiek Shale lagerstätte of Iowa, allowing its identity as a conodont to be secured. The jaw apparatus of ''Archeognathus primus'' is much more simple than that of most conodonts, with only six elements in its jaw. These include a pair of long, small-toothed, sawblade-like "coleodiform" S elements at the front of the jaw, followed by two pairs of smaller "archeognathiform" P elements with large teeth. The S elements are indistinguishable from those of many species of ''Coleodus'', a wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Winneshiek Shale
The Winneshiek Shale (originally the Winneshiek Lagerstätte) is a Middle Ordovician (Darriwilian-age) geological formation in Iowa. The formation is restricted to the Decorah crater, an impact crater near Decorah, Iowa. Despite only being discovered in 2005, the Winneshiek Shale is already renowned for the exceptional preservation of its fossils. The shale preserves a unique ecosystem, the Winneshiek biota, which is among the most remarkable Ordovician lagerstätten in the United States. Fossils include the oldest known eurypterid, ''Pentecopterus'', as well as giant conodonts such as ''Iowagnathus'' and ''Archeognathus''. Geology The Winneshiek Shale is a thin and geologically homogeneous package of dark grey to greenish-brown sandy shale. Drill core data has estimated a maximum thickness of 38 meters, though in most areas its thickness is only about 18–27 meters. The shale is replete with pyrite and organic carbon. It lies solely within the Decorah Structure, a 5.6 km ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
