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

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

, and North America from the

Middle Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

to the

Middle Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...

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

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

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 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

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 Orthoceratidae is an extinct family of actively mobile carnivorous cephalopods, subclass Nautiloidea, that lived in what would be North America, Europe, Asia, Africa, and Australia from the Ordovician through Triassic from 490—203.7 mya, exis ...

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