''Michelinoceras'' is the oldest known genus of the Michelinocerida, more commonly known as the

Orthocerida Orthocerida, from Ancient Greek ὀρθός (''orthós''), meaning "straight", and κέρας (''kéras''), meaning "horn", also known as the Michelinocerida, is an order of extinct Orthoceratoidea, orthoceratoid cephalopods that lived from the ...

, characterized by long, slender, nearly cylindrical

orthocone An orthocone is the long, cone-shaped Exoskeleton, shell belonging to several species of ancient nautiloid cephalopod—the prehistoric ancestors of today's marine cephalopod Mollusca, mollusks, including the cuttlefishes, nautiluses, octopuses an ...

s with a circular cross section, long camerae, very long body chambers, and a central or near central tubular siphuncle free of organic deposits. Septal necks are straight; connecting rings cylindrical and thin. Cameral deposits are well developed. A radula has been found in one species, with seven teeth per row. It had ten arms, two of which formed longer tentacles.

Range

''Michelinoceras'' ranges from late in the Early

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

to the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

with more poorly known species from the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

to the Late

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

included in the genus. The earliest known unequivocal species is ''Michelinoceras primum'' found in Cassinian age strata near the top of the Lower Ordovician El Paso Group in southern New Mexico and west Texas. A less well known species of ''Michelinoceras'', ''M. primum?'', comes from further down in the same formation, near the beginning of the Cassinian.

Taxonomy and derivation

''Michelinoceras'' named by Foeste in 1932 is the ancestral and characteristic genus of the Michelinoceratidae, established and described by Flower in 1946; derived from empty siphuncle

Baltoceratidae Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, exist ...

References

* Flower, R.H. 1976; Ordovician Cephalopod Faunas and Their Role in Correlation, pp 538–541; proceedings pub. Paleontological Association, Gr Br. * Hook, J.C. and Flower, R.H. 1976; ''Tajaroceras'' and the Origin of the Troedsonnellidae. Jour Paleontology v 50, no 2, pp 293–300, March 1976 * Sweet, W.C, 1964; ''Michelinoceras'', pp 225–226 in Orthoceratidae, pp 224–231 in the ''

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 ...

'' Vol K. GSA and Univ Kansas Press. Excellent descriptions in: * RISTEDT, H. 1971. Zum Bau der orthoceriden Cephalopoden. Palaeontographica A, 137:155-195 * KISELEV, G. N. 1971. Embryonalnye rakoviny silurskich michelinoceratin. Voprosy Paleontologii, 6:41-5 * SERPAGLI, E., AND M. GNOLI. 1977. Upper Silurian cephalopods from southwestern Sardinia. Bollettino della Societh Paleontologica Italiana, 16:153-196 {{Taxonbar, from=Q3856857 Orthocerida Ordovician cephalopods Silurian cephalopods Devonian cephalopods Early Ordovician first appearances Devonian extinctions Prehistoric cephalopods of North America Fossils of Georgia (U.S. state) Paleozoic life of Ontario Paleozoic life of Quebec

Range

Taxonomy and derivation

See also

References

Further reading