Rangeroceras is an extinct nautiloid cephalopod genus that lived in what is now western North America during the latter part of the Early Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

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

Orthocone

An orthocone is a usually long straight shell of a nautiloid cephalopod. During the 18th and 19th centuries, all shells of this type were named Orthoceras, but it is now known that many groups of nautiloids developed or retained this type of shell....

s with moderately large submarginal siphuncle

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 Spirula...

s. The siphuncular rods, which lie along the lower (ventral) side of the siphuncle interiors show thin, slightly undulating, growth lamellae in vertical longitudinal section, a somewhat unique feature. Dorsal annuli only begin to form when the rod has almost filled the entire siphncle 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 (1977)originally placed Rangeroceras in the Baltoceratidae

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, existing for approximately .-Taxonomy:Baltoceratidae was...

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

Rangeroceratidae

SYSTEMATIC PALEONTOLOGY Phylum Mollusca Class Cephalopoda Subclass Nautiloidea Superorder Orthoceratoidea Order Dissidocerida Family Rangeroceratidae Evans, 2005....

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

Dissidocerida

The Dissidocerida comprise 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....

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Rangeroceras is named for one of the characters, the range ranger, in the Tajar stories by Jane Shaw Ward. For other Tajar story based genera see Tajaroceras

Tajaroceras

Tejaroceras is an extinct slender cephalopod from the uppermost Lower Ordovician of western North America, belonging to the Orthocerid family Troedssonellidae....

, Wardoceras

Wardoceras

Wardoceras is an extinct nautiloid genus from the late Early Ordovician of Western Utah, assigned to the orthocerid family, Michelinoceratidae...

, and Veneficoceras

Veneficoceras

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

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