''Rangeroceras'' is an extinct orthoceratoid

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

that lived in what is now western North America during the latter part of the Early

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

Background

Shells of ''Rangeroceras'' are smooth, slightly depressed, rod-bearing

orthocone An orthocone is an unusually long straight shell of a nautiloid cephalopod.; During the 18th and 19th centuries, all shells of this type were named ''Orthoceras'', creating a wastebasket taxon, but it is now known that many groups of nautiloids d ...

s with moderately large submarginal

siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...

s. The siphuncular rods, which lie along the lower (ventral) side of the siphuncle interiors show thin, slightly undulating, growth

lamella Lamella (plural lamellae) means a small plate or flake in Latin, and in English may refer to: Biology * Lamella (mycology), a papery rib beneath a mushroom cap * Lamella (botany) * Lamella (surface anatomy), a plate-like structure in an animal * ...

e in vertical longitudinal section, a somewhat unusual feature. Dorsal annuli only begin to form when the rod has almost filled the entire siphuncle toward to apical end. Connecting rings are thin, but layered. Cameral deposits are known from the dorsal side, the ventral side of the type specimen lost from erosion. Hook and

Flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

(1977) originally placed ''Rangeroceras'' in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

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 ...

because of the siphunclular rod and thin connecting rings. Evans (2005) proposed the family

Rangeroceratidae Rangeroceratidae is a family of orthoceroid cephalopods known from the late Early Ordovician in eastern North America (New York and Quebec) and Great Britain, included in the order Dissidocerida. The family was named by Evans, 2005, and contains ...

for ''Rangeroceras'' and a somewhat similar genus '' Cyclorangeroceras'' from Great Britain and included them in the

Dissidocerida Dissidocerida is an order of Early Ordovician to the Early Silurian orthoceratoid cephalopods in which the siphuncle has a continuous lining or a longitudinal rod-like structure within. The order Dissidocerida was proposed by Zhuravleva (1994) ...

. ''Rangeroceras'' is named for one of the characters, the range ranger, in the Tajar stories by Jane Shaw Ward. Other Tajar story based genera include ''

Tajaroceras ''Tajaroceras'' is an extinct slender cephalopod from the uppermost Lower Ordovician of western North America, belonging to the Orthocerid family Troedssonellidae. Background The shell of ''Tajaroceras'' is smooth and straight. The siphuncle whi ...

'', '' Wardoceras'', and ''

Veneficoceras ''Veneficoceras'' is a genus of the rod-bearing Baltoceratidae, an extinct cephalopod family with characteristics of the orthoceratoid Dissidocerida, found in Cassinianage, Lower Ordovician, limestone in western Utah Utah ( , ) is a stat ...

'' The type, ''Rangeroceras hintzei'' came from the Wahwah Limestone in the Ibex area in Western Utah.

References

* Stephen C. Hook and Rousseau H. Flower 1977. Late Canadian (Zones J,K) Cephalopod Faunas from Southwestern United States. Memoir 32, New Mexico Bureau of Mines and Mineral Resources. {{Taxonbar, from=Q7292788 Orthoceratoidea Taxa named by Rousseau H. Flower