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Clymeniida

Clymeniida is an order of ammonoid cephalopods from the Upper Devonian characterized by having an unusual dorsal siphuncle. They measured about in diameter and are most common in Europe, North Africa, and South China but are known from North America (New York, Ohio, Oklahoma, and Utah) and Australia (New South Wales) as well.

Morphologic characteristics

Clymeniids produced a variety of shells ranging from smooth to ribbed and spinose, from evolute with all whorls exposed to strongly involute with the last whorl covering the previous. Some were even triangular in lateral view. With the exception of the first few chambers, all have a siphuncle that runs along the dorsal margin, i.e., along the inner edge of each whorl, rather than the outer edge as in most ammonoids.

Developmentally, the siphuncle in clymeniids starts off ventrally, like that in other ammonoids, but after the first few septa it migrates to a dorsal position indefinitely. Septal necks are retrosiphonate, characteristic of their nautiloid ancestors, and are commonly very long, forming an almost continuous siphuncular tube. The septa, unusually simplified in shape, are convex toward the front as is characteristic of ammonoids.

Classification

Miller, Furnish, and Schindewolf, 1957, in Part L of the Treatise on Invertebrate Paleontology included three superfamilies in Clymeniida: Gonioclymeniaceae, Clymeniaceae, and Parawocklumeriaceae. Gonoclymeniaceae unites five families, Clymeniaceae three. Parawocklumeraceae was established for the single family Parawocklumeriidae.

In 1999, Saunders, Work, and Nikolaeva divided Clymeniida into two suborders, Gonioclymeniina and Clymeniina. Gonioclymeniina includes Sellaclymeniaceae, with 7 families and 20 genera; Gonioclyemniaceae, containing a single family with six genera; and Parawocklumeraceae, also containing a single family but with only three genera. Clymeniina contains a single superfamily, Clymeniaceae, which unites five families with a total of 36 genera.

Per the GONIAT website, two suborders fall into Clymeniida. They are Clymeniina with four superfamilies and Gonioclymeniina, established for a single superfamily. In contrast, Dieter Korn in 2006 divided Clymeniida into Clymeniina and Cyrtoclymeniina, named by him in 2002. Shevyrev, on the other hand, in 2006 divided Clymeniida into Clymeniina and Gonioclymeniina, in line with GONIAT and with the work of Saunders, Work, and Nikolaeva. The Taxonomy section below presents Korn's (2006) classification.

Taxonomy

Clymeniida

References