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Orthoceras is a genus of extinct nautiloid cephalopod restricted to Middle Ordovician-aged marine limestones of the Baltic States and Sweden. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros.
The cephalopods have a long geological history, with the first nautiloids found in late Cambrian strata. [1] The class developed during the middle Cambrian, and underwent pulses of diversification during the Ordovician period [2] to become diverse and dominant in the Paleozoic and Mesozoic seas.
Belemnitida (or belemnites) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous (And possibly the Eocene [4] [5]).Unlike squid, belemnites had an internal skeleton that made up the cone.
The beak of a giant squid. All extant cephalopods have a two-part beak, or rostrum, situated in the buccal mass and surrounded by the muscular head appendages. The dorsal (upper) mandible fits into the ventral (lower) mandible and together they function in a scissor-like fashion. [1] [2] The beak may also be referred to as the mandibles or jaws ...
Nautiluses are much closer to the first cephalopods that appeared about 500 million years ago than the early modern cephalopods that appeared maybe 100 million years later (ammonoids and coleoids). They have a seemingly simple brain, not the large complex brains of octopus, cuttlefish and squid, and had long been assumed to lack intelligence ...
However, other studies have recovered it as an oegopsid squid. [3] Orthocone nautiloids range in size from less than 25 mm (1 in) to (in some giant endocerids of the Ordovician) 5.2 m (17 ft) long. Orthocone cephalopod fossils are known from all over the world, with particularly significant finds in Ontario, Canada and Morocco.
Nautiloids are often found as fossils in early Palaeozoic rocks (less so in more recent strata). The rocks of the Ordovician period in the Baltic coast and parts of the United States contain a variety of nautiloid fossils, and specimens such as Discitoceras and Rayonnoceras may be found in the limestones of the Carboniferous period in Ireland.
Belemnoids were efficient carnivores that caught small fish and other marine animals with their arms and ate them with their beak-like jaws. In turn, belemnites appear to have formed part of the diet of marine reptiles such as Ichthyosaurs, whose fossilized stomachs frequently contain phosphatic hooks from the arms of cephalopods.