An orthocone is an unusually long straight shell of a nautiloid

cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

.; During the 18th and 19th centuries, all shells of this type were named '' Orthoceras'', creating a wastebasket taxon, but it is now known that many groups of nautiloids developed or retained this type of shell. An orthocone can be thought of as like a '' nautilus'', but with the shell straight and uncoiled. It was previously believed that these represented the most primitive form of nautiloid, but it is now known that the earliest nautiloids had shells that were slightly curved. An orthoconic form evolved several times among cephalopods, and among nautiloid cephalopods is prevalent among the ellesmerocerids, endocerids, actinocerids, orthoceratoids, and

bactritid The Bactritida are a small order of more or less straight-shelled (orthoconic) cephalopods that first appeared during the Emsian stage of the Devonian period (407 million years ago) with questionable origins in Pragian stage before 409 million ye ...

s. Orthocones existed from the Late

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

to the Late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

, but they were most common in the early

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ...

. Revivals of the orthocone design later occurred in other cephalopod groups, notably baculitid ammonites in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Period. Orthocone nautiloids range in size from less than to (in some giant endocerids of the Ordovician) long. Orthocone

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

are known from all over the world, with particularly significant finds in

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

, and

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to A ...

References

{{Cephalopod anatomy Cephalopod zootomy