Geisonoceratidae is an extinct family of orthoceroid

Orthocerida

Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...

 cephalopods endemic to what would be Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

, Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, and North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 from the Middle Ordovician to the Middle Devonian living from about 470—380 mya, existing for approximately 90 million years. With the possible addition of an Early Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 orthocerid from the western Caucusus 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

Orthocerataceae

The Orthocerataceae is a superfamily of orthocerid cephalopods that lived from the late Early Ordovician to the Early Cretaceous., but is no longer in general use....

 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.