Early Ordovician – Late Triassic
Orthocerida is an extinct order of nektonic carnivores
Characteristics of the Order
- Nautoloid with straight to curved shells; never coiled
- Shells smooth or elaborately ornamented
- Siphuncles with orthochoanitic, or secondarily cyrtochoanitic septal necks and thin connecting rings
Treatise on Invertebrate Paleontology, Part K (1964)
- Straight-to-curved but never coiled nautiloids with smooth or elaborately ornamented shells, typically well-developed cameral deposits, and siphuncles with orthochoanitic, or secondarily cyrtochoanitic septal necks and thin connecting rings, either empty or occupied by parietal or annulosiphonate deposits. The Orthocerida almost certainly developed from the Baltoceratidae of the Ellesmerocerida.