Orthocone
Encyclopedia
An orthocone is a usually long straight shell of a nautiloid
cephalopod
. During the 18th and 19th centuries, all shells of this type were named Orthoceras
, 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
shell, 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, orthocerids, and bactritids.
Orthocones existed from the Late Cambrian
to the Late Triassic
, but they were most common in the early Paleozoic
. Revivals of the orthocone design later occurred in other cephalopod groups, notably baculitid ammonite
s in the Cretaceous
Period. Orthocone nautiloids range in size from less than an inch to (in some giant endocerids of the Ordovician
) seventeen feet (or five meters) long.
Nautiloid
Nautiloids are a large and diverse group of marine cephalopods belonging to the subclass Nautiloidea that began in the Late Cambrian and are represented today by the living Nautilus. Nautiloids flourished during the early Paleozoic era, where they constituted the main predatory animals, and...
cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
. During the 18th and 19th centuries, all shells of this type were named Orthoceras
Orthoceras
Orthoceras is a genus of extinct nautiloid cephalopod. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros ....
, 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
Nautilus
Nautilus is the common name of marine creatures of cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in two genera, the type of which is the genus Nautilus...
shell, 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, orthocerids, and bactritids.
Orthocones existed from the Late Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
to the Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
, but they were most common in the early Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
. Revivals of the orthocone design later occurred in other cephalopod groups, notably baculitid ammonite
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
s in the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period. Orthocone nautiloids range in size from less than an inch to (in some giant endocerids of the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
) seventeen feet (or five meters) long.