AMERICAN PERMIAN NAUTILOIDS

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Abstract
Nautiloids are widely distributed in the marine Permian of western United States, and a few specimens are known from southwestern Canada, northeastern Mexico, and northern Colombia (and probably adjacent portions of Venezuela). Stratigraphically they range throughout the system and locally they are abundant in the Lower Permian of north-central Texas and southeastern Wyoming and the Middle Permian of the Southwest. All of them have either orthoceraconic or nautiliconic conchs, but that of one genus (Pseudorthoceras) is slightly cyrtoceraconic. Ribs, nodes, and even spines are present on many of the coiled forms. Most of the straight (and the slightly curved) ones have cyrtochoanitic siphuncles, but a few of these and all of the coiled ones are orthochoanites. Altogether about a hundred species of nautiloids are known from the Permian of the Americas. On the basis of the structure of the siphuncle, the form of the conch, the shape of the sutures, and the nature of the surface “ornamentation” of the test, these can be grouped into nine families: (1) the Pseudorthoceratidae, which includes Pseudorthoceras and Mooreoceras; (2) the Orthocerotidae, which includes Michelinoceras and Bitaunioceras; (3) the Bactritidae, which includes Bactrites; (4) the Koninckioceratidae, which includes Koninckioceras, Knightoceras, and Endolobus; (5) the Domatoceratidae, which includes Domatoceras, Stearoceras, Titanoceras, and Stenopoceras; (6) the Tainoceratidae, which includes Tainoceras, Aulametacoceras, Temnocheilus, Foordiceras, Metacoceras, and Cooperoceras; (7) the Liroceratidae, which includes Liroceras and Coelogasteroceras; (8) the Ephippioceratidae, which includes Ephippioceras; and (9) the Solenochilidae, which includes Solenochilus. The first of these families contains all of the cyrtochoanites known from the Permian; the first three contain all of the orthoceracones (and cyrtoceracones); and the last six consist exclusively of nautilicones.

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