| Discosorida Fossil range: Middle Ordovician - Devonian |
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Discosorida is a unique order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Devonian is a geologic period and system of the Paleozoic era spanning from to million years ago. Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Nautiloids are a group of marine Mollusks in the subclass Nautiloidea, which all possess an external shell the best-known example being the modern Nautiluses The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 The Devonian is a geologic period and system of the Paleozoic era spanning from to million years ago. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the chambers in cephalopods, which unlike those in other orders is zoned longitudinally along the segments rather than laterally. The siphuncle is a strand of tissue passing longitudinally through the shell of a Cephalopod Mollusk. Siphuncle structure indicated that the Discosorida evolved directly from the Plectronoceratida rather than thru the more developed Ellesmerocerida, as did the other orders. The Ellesmerocerida comprise early Nautiloid cephalopods from the late Upper Cambrian (Trempealeauan and Ordovician that are typically rather small with close Finally and most diagnostic, discosorids developed a reenforcing, grommet-like structure in the septal opening of the siphuncle known as the bullette, formed by a thickening of the connecting ring as it draped around the folded back septal neck.
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Evolution
Discosorida evolved from the primitive Ruedemannoceratidae, which are known from the early Middle Ordovician, into a number of families. Some were endogastrically curved, with the lower, siphuncle side concave, others were exogastrically curved with the same side convex. The siphuncle is a strand of tissue passing longitudinally through the shell of a Cephalopod Mollusk. In some the aperture was a simple opening. In others it became contracted into a pattern of slits. In earlier, Ordovician forms the bullette became quite large and readily noticeable. In later forms the bullette became reduced, in some to the point of being vestigial. A bulette or Landshark is a large Fictional carnivorous magical beast from the Dungeons & Dragons Fantasy Role-playing
The Discosoridae, one of the last families to evolve, found in Silurian and questionably in Devonian rocks, are characterized by a rapidly expanding siphuncle with segments that extend into the adjacent chambers, and overlapping connecting rings that form endocones.
Ecology
Discosorids were probably benthic forms that crawled over the bottom in search of food or safety, or hovered close to. The benthic zone is the ecological region at the lowest level of a Body of water such as an Ocean or a Lake, including the sediment surface and some sub-surface The general orientation during life was most likely head down, with the aperture of the shell facing the general direction of the sea floor and shell carried above. Nothing is known of what the animal itself may have looked like; how many tentacles they had and relative length or how well they may have seen.
Related taxa
In general form the Discosorida resembled the Oncocerida, which lived about the same time, but evolved from a completely different stock. The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous) united by The two convergent groups differ in their internal details.
References
- Rousseau H. Flower. 1964. The Nautiloid Order Ellesmerocerida (Cephalopods); relevant pages. Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.
- Rousseau H. Flower and Curt Teicher. 1957. The Cephalopod Order Discosorida; University of Kansas Paleontological Contributions, Mollusca, Article 6.
- Curt Teichert. 1964. Nautiloidea -Discosorida; Treatise on Invertebrate Paleontology, Vol. K, pp. K320.
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