Geisonoceratidae is an extinct family of orthoceroid cephalopods endemic to what would be

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, and

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from the Middle Ordovician to the

Middle Devonian In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age. The Middle Devonian epoch is subdivided into two ...

Sweet, W. C. 1964. Nautiloidea- Orthocerida;

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

Part K, Teichert & Moore eds; pp K224- K242 living from about 470—380 mya, existing for approximately 90 million years. With the possible addition of an Early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

orthocerid from the western Caucasus the range of this group increases dramatically to some 350 million years, thus making it one of the longest lived families of the Nautiloidea.

Morphology

Shells of geisonoceratids are orthoconic or cyrtoconic, that is long and either straight or curved, with a subcircular cross section. The siphuncle, which varies in position from central to subventral, is composed of generally short, straight to slightly curved, orthochoanitic to subchoanitic, septal necks and thin connecting rings that may expand slightly into the chambers. Organic deposits that are formed within consist of either ring-like annuli restricted to the septal openings or which extend toward the front along the next connecting ring. In advanced species these may form a continuous lining. Cameral deposits, which are generally well developed, are formed along the front and backside of the septa, referred to as episeptal and hyposeptal. Surface modifications found in some include transverse annulations or transverse and sometimes also longitudinal striae and/or lirae.

Taxonomy

Geisonoceratidae was named by Zhuravleva (1959) and included in the Orthocerataceae in Teichert ''et al.'' (1964) and by Evans (1994 & 1996), and simply in the Orthocerida in Evans(2005). Flower in his 1962 discussion of the Michelinoceratida expressed doubt as to the usefulness of this taxon and called attention to the morphologic gradation between the Michelinoceratidae in which cameral deposits are retarded and the Geistonoceratidae in which they are more advanced.Flower, R. H. 1976. Ordovician Cephalopod Faunas and Their Role in Correlation; The Ordovician System; Paleontological Association symposium 1974.

References

{{Taxonbar, from=Q5530228 Orthocerida Ordovician cephalopods Silurian cephalopods Devonian cephalopods Carboniferous cephalopods Dapingian first appearances Early Cretaceous extinctions Middle Ordovician first appearances Middle Devonian extinctions