''Tajaroceras'' is an extinct slender

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 ...

from the uppermost

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 ...

of western North America, belonging to the

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

family Troedssonellidae.

Background

The shell of ''Tajaroceras'' is smooth and straight. The

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

which is at least 0.35 the shell diameter is subcentral. Septal necks are short and the connecting rings are thin and homogeneous. The distinguishing feature of Tajaroceras lies within its siphuncle. Along the ventral side, within the

, is a continuous rod, much like that found in a group known as rod-bearing

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 ...

. On the dorsal side, overlying within, are annular deposits that grow forward to form a continuous lining that ultimately rests against the ventral rod, leaving a small opening slightly above the center. The camerae contain deposits of organic calcite. ''Tajaroceras'', first described by Hook and Flower (1976), has been found in the Upper Cassinian Wahwah

Limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

in Western Utah and in the equivalent Florida Mountains Formation in Southern New Mexico and is the probable ancestor of the Troedssonellidae, being followed in overlapping sequence by '' Buttsoceras''. The type, ''Tajaroceras wardae'', was found 55–65 ft above the base of the Wahwah Ls in the Ibex area of western Utah. ''Tajaroceras'' is named for Jane Shaw Ward's character, the Tejar.

''References''

*Hook,S.C.and Flower,R.H. 1976. ''Tajaroceras'' and the origin of the Troedssonellidae:

Journal of Paleontology The ''Journal of Paleontology'' is a peer-reviewed scientific journal covering the field of paleontology. It is managed and published by Cambridge University Press on behalf of the Paleontological Society. Indexing The ''Journal of Paleontology ...

v.50, p. 293-300 *Hook,S.C.and Flower,R.H. 1977. Late Canadian (Zones J,K) Cephalopod Faunas from

Southwestern United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural list of regions of the United States, region of the United States that includes Arizona and New Mexico, along with adjacen ...

: Memoir 32, New Mexico Bureau of Mines and Mineral Resources. {{Taxonbar, from=Q7676791 Orthoceratoidea