Protcycloceratidae is an extinct family of slender, commonly annulate, members of the
cephalopod
A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...
order
Ellesmerocerida
The Ellesmerocerida is an extinct order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician.
Morphology
The Ellesmerocerida are characterized by shell ...
that lived during 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 ...
.
Protocycloceratidae, named by Kobayashi (1935), are characterized by transversely ribbed, elongate shells that may be straight or slightly curved, as to be either
endogastric or
exogastric.
[Flower 1964, Furnish & Glenister 1964] Although not universally accepted, Kröger and Mutvie (2005) revised the Protocycloceratidae to include only those ellesmerocerids that have straight transverse sutures and
siphuncles with concave segments and thick connecting rings.
Protocycloceratidae (''sensu'' Flower, 1964) includes the follow
genera
Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
, given with brief descriptions.
*''
Protocycloceras''. Strongly annulate
orthocones; cross section circular; annulations and sutures transverse and essentially straight; siphuncle tubular, ventral but not marginal, about 0.3 corresponding shell diameter.
Lower Ordovician
The Early Ordovician is the first epoch of the Ordovician period, corresponding to the Lower Ordovician series of the Ordovician system. It began after the Age 10 of the Furongian epoch of the Cambrian and lasted from to million years ago, unt ...
, cosmopolitan.
*''
Catoraphiceras''. Annulate orthoconic shells with a circular to slightly depressed cross section, marginal siphuncle, and sutures characterized by a deep ventral lobe. Upper Lower Ordocician, widespread.
*''
Diastoloceras''. Lngicones with a slight exogastric curvature and circular cross section, surface with close spaced prominent
flanges; siphuncle submarginal, relatively narrow, segments expanded, necks very short, connecting rings thin. Lower/Upper Ordocian, Australia.
*''
Ectocycloceras''. Compressed exogastric annulated cyrtocones with straight transevse sutures and a small marginal siphuncle composed of concave segments. Lower/Middle Ordovician, Eastern North America.
*''
Endocycloceras''. Rapidly expanding endogastric forms with well-developed surface annulations and a marginal siphuncle composed of concave segments. Sutures straight and transverse. Early Lower Ordovician (
Gasconadian Stage
{{Infobox geologic timespan
, name = Gascondian
, color =
, manual_color =
, top_bar =
, time_start = 488
, time_start_prefix =
...
) of North America.
*''
Kyminoceras''. Generally small, straight annulated shells with straight transverse sutures, circular cross section, and a small ventral siphuncle. However connecting rings in the type appear to be thin, putting its inclusion in question.
*''
Notocycloceras''. Straight shells with transverse annuli, apparently straight transverse sutures, and a comparatively large ventro-marginal siphuncle composed of faintly concave segments. Upper Lower Ordovician, Australia.
*''
Rudolfoceras''. A genus of moderately expanding, annulated slender exogastruc shells with generally straight sutures and tubular siphuncle that may be in contact with the ventral margin. May include species in which sutures are faintly sinuous. Upper Lower Ordovician,
Champlain Valley
The Champlain Valley is a region of the United States around Lake Champlain in Vermont and New York extending north slightly into Quebec, Canada. It is part of the St. Lawrence River drainage basin, drained northward by the Richelieu River into ...
, North America.
*''
Apocrinoceras'', in which siphuncle segments are expanded and septal necks weakly
cyrtochoanitic, included in the Protocycloceratidae in the
Treatise
A treatise is a Formality, formal and systematic written discourse on some subject concerned with investigating or exposing the main principles of the subject and its conclusions."mwod:treatise, Treatise." Merriam-Webster Online Dictionary. Acc ...
(Furnish & Glenister 1964), is included in the
Apocrinoceratidae (Flower, 1964).
References
*Flower, R.H. 1964, The Nautiloid Order Ellesmeroceratida (Cephalopoda)
Memoir 12; New Mexico Bureau of Mines and Mineral Resources, Socorro, NM
*Furnish & Glenister 1964. Nautiloidea -Ellesmerocerida. Treatise on Invertebrate Paleontology Part K, Geological Society of America and University of Kansas Press.
* Kröger and Mutvie 2005; Nautiloids with multiple paired muscle scars from Early-Middle Ordovician of Baltoscandia. - Its bearing for taxonomic and phylogenetic reconstructions; Palaeontology, 48:1-11.
{{Taxonbar, from=Q7251961
Cephalopod families
Ellesmerocerida
Early Ordovician first appearances
Early Ordovician extinctions