File:Crinoid stem (Fort Payne Formation, Lower Mississippian; Rt. 61 roadcut, north of Burkesville, Kentucky, USA) 5 (27549539307).jpg
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Crinoid stem in the Mississippian of Kentucky, USA. The Fort Payne Formation of southern Kentucky & Tennessee is a shale and limestone succession of Early Mississippian age. Fossils are common to abundant in many intervals. The unit is dominated by crinoids, which are sessile, benthic, filter-feeding, stalked echinoderms. Crinoids are relatively common in the marine fossil record. They are also alive today, but are generally uncommon in modern oceans. A crinoid is essentially a starfish-on-a-stick. The stick, or stem, is composed of numerous stacked columnals, like small poker chips. Stems and individual columnals are the most commonly encountered crinoid fossils in the field. Intact, fossilized crinoid heads (crowns, calices, cups) are unusual. Why? Upon death, the crinoid body starts disintegrating very rapidly. The soft tissues holding the skeletal pieces together decay and the skeleton falls apart. The crinoid stem shown here consists of columnals having two sizes. The larger-sized columnals are called nodals. The smaller ones are called internodals. Nodals may have cirri (root-like structures extending laterally from the stem) and internodals lack cirri. Internodals can vary in size in shape, usually in cycles. Crinoids having a stem with nodals and internodals are said to have a heteromorphic column. This is a common condition in many camerate crinoids. Nearly all cladid crinoids have nodals and internodals, but in the mature portion of the stem, the columnals all look alike - the stem appears homeomorphic. Classification: Animalia, Echinodermata, Crinoidea Stratigraphy: Fort Payne Formation, Osagean Stage/Series, upper Lower Mississippian Locality: Burkesville North Outcrop - Route 61 roadcut at milepost 23, way north of Burkesville, Kentucky, USA. (36° 54’ 08.08” North latitude, 85° 25’ 56.19” West longitude) |
| Date | |
| Source | Crinoid stem (Fort Payne Formation, Lower Mississippian; Rt. 61 roadcut, north of Burkesville, Kentucky, USA) 5 |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/27549539307 (archive). It was reviewed on 12 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 04:07, 12 October 2019 | | 2,820 × 2,299 (3.67 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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