This article is about the marine animal. For the novel see Ammonite (novel), for the Biblical people, see Ammon (nation), and for the ancient Egyptian god see Ammon. Nicola Griffiths first novel, Ammonite was published in 1993, with ISBN 0-345-37891. ... For the extinct mollusc see Ammonite. ... For the people in the Bible, see Ammon (nation). ...

Ammonites are an extinct group of marine animals (subclass Ammonoidea) in the phylum Mollusca and class Cephalopoda. Their closest living relative is probably the modern nautilus, whom they resemble. Their fossil shells have the form of flat spirals (though there are some rarer non-spiraled forms, called heteromorphs) and are responsible for the animals' name as they somewhat resemble a tightly coiled ram's horn (the god Ammon was commonly depicted as a man with ram's horns). Plinius the Elder (died 79 AD near Pompeii) called fossils of these animals ammonis cornua, "horn of Ammon." Often the name of ammonite species ends in ceras, Greek (κέρας) for "horn" (e.g. Pleuroceras). The conservation status of a species is an indicator of the likelihood of that species continuing to survive. ... Download high resolution version (600x682, 99 KB)A large ammonite, 0. ... Scientific classification - Wikipedia /**/ @import /skins/monobook/IE50Fixes. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria Acoelomorpha Orthonectida Rhombozoa ?Myxozoa Superphylum Deuterostomia    Chordata (vertebrates, etc. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Orders Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida Nautilida The Cephalopods (head-foot) are the mollusc class Cephalopoda characterized by bilateral body symmetry, a prominent head, and a modification of the mollusc foot into the form of arms or tentacles. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... ... Families all extinct Goniatites are an extinct group of ammonite, which are related to the nautiloids. ... In biology and ecology, extinction is the ceasing of existence of a species or group of species. ... In object-oriented programming, subclass is a class that is derived from another class or classes. ... Phylum is one of the levels of scientific classification of organisms; see the Phylum (biology) article. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... The term class, when used by itself, has several meanings in English. ... Orders Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida Nautilida The Cephalopods (head-foot) are the mollusc class Cephalopoda characterized by bilateral body symmetry, a prominent head, and a modification of the mollusc foot into the form of arms or tentacles. ... Species Allonautilus perforatus Allonautilus scrobiculatus Nautilus belauensis Nautilus macromphalus Nautilus pompilius pompilius Nautilus pompilius suluensis Nautilus stenomphalus The nautilus is a marine creature of the class Cephalopoda. ... FOSSIL is a standard for allowing serial communication for telecommunications programs under DOS. FOSSIL stands for Fido Opus Seadog Standard Interface Layer and was made by a group of Fidonet sysops to make their software work on different machines. ... Binomial name Ovis aries Linnaeus, 1758 A sheep is any of several woolly ruminant quadrupeds, but most commonly the Domestic Sheep (Ovis aries), which probably descends from the wild moufflon of south-central and south-west Asia. ... For the people in the Bible, see Ammon (nation). ... Gaius Plinius Secundus, (23–79) better known as Pliny the Elder, was an ancient author and scientist of some importance who wrote Naturalis Historia. ...

Classification

Ammonites first appeared in the late Silurian to early Devonian (~400 million years ago) and became extinct at the close of the Cretaceous along with the dinosaurs (65 million years ago). The classification of ammonites is based in part on the ornamentation and structure of their shells, which divide this subclass into three orders and eight known suborders. Unlike the nautiloids, all of which have gently curving sutures, the suture line between the chamber wall and the outer ammonite shell was folded, forming saddles (or peaks) and lobes (or valleys). Here they are listed from most primitive to more advanced: Alternate use: The Silurians, a reptilian race from the science fiction series Doctor Who. The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 439 million years before the present (BP), to the beginning of the Devonian period, about 408. ... The Devonian is a major division of the geologic timescale that extends from the end of the Silurian period (360 million years ago (mya)) to the beginning of the Mississippian subperiod of the Carboniferous (408. ... In biology and ecology, extinction is the ceasing of existence of a species or group of species. ... The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period (about 135 mya) to the beginning of the Paleocene epoch of the Tertiary period (65 mya). ... Orders Saurischia    Sauropodomorpha    Theropoda Ornithischia Dinosaurs are reptiles that dominated the terrestrial ecosystem for most of their 165-million year existence. ... Ornament is frequently used to denote: An element of decoration. ...

Orders and suborders:

• Goniatitida (Devonian to Permian) - round saddles, pointed lobes
  • Anarcestina (Devonian only)
  • Clymeniina (Upper Devonian only)
  • Goniatitina (Devonian to Upper Permian)
• Ceratida (Carboniferous to Triassic) - round saddles, serrated lobes
  • Prolecanitina (Upper Devonian to Upper Triassic)
  • Ceratitina (Permian to Triassic)
• Ammonitida (Permian to Cretaceous) - folded saddles and lobes, fractal patterns
  • Phylloceratina (Lower Triassic to Upper Cretaceous)
  • Ammonitina (Lower Jurassic to Upper Cretaceous)
  • Lytoceratina (Lower Jurassic to Upper Cretaceous)
  • Ancyloceratina (Upper Jurassic to Upper Cretaceous) - the heteromorph ammonites

Life

Jeletzkytes, a Cretaceous ammonite from the USA

Because ammonites and their close relatives are extinct, little is known about their way of life. Their soft body parts are practically never preserved in any detail. Nonetheless, a lot has been worked out by examining ammonite shells and by using models of these shells in water tanks. Photograph of the ammonite Jeletzkytes spedeni taken by Dlloyd. ... Photograph of the ammonite Jeletzkytes spedeni taken by Dlloyd. ...

Most ammonites probably lived at the surface of ancient seas; this is suggested by the fact that their fossils are often found in rocks that were laid down under conditions where no benthic (bottom-dwelling) life is found. Many of them are thought to have been good swimmers with flattened, discus-shaped, streamlined shells (such as Oxynoticeras), although some were less effective swimmers and were likely to have been bottom dwellers. Ammonites probably preyed on fishes and crustaceans and were themselves preyed upon by marine reptiles (such as Mosasaurs). Fossilized shells are sometimes found showing teeth marks from such attacks. Atlantic herring, Clupea harengus, the most abundant fish species in the world. ... Classes Remipedia Cephalocarida Branchiopoda Ostracoda Maxillopoda Malacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum. ... Orders  Crocodylia - Crocodilians  Rhynchocephalia - Tuataras  Squamata   Suborder Sauria - Lizards   Suborder Serpentes - Snakes Testudines - Turtles Superorder Dinosauria  Saurischia  Ornithischia The reptiles are a group of vertebrate animals. ... Subfamilies Mosasaurinae Plioplatecarpinae Tylosaurinae A mosasaur was not a dinosaur, but rather an ocean-dwelling serpentine marine reptile related to varanids like monitor lizards. ...

Shell anatomy and diversity

Basic shell anatomy

The chambered part of the ammonite shell is called a phragmocone. The phragmocone contains a series of progressively larger chambers, called camerae (sing. camera) that are divided by thin walls called septa (sing. septum). Only the last and largest chamber, the body chamber, was occupied by the living animal. As it grew, it added newer and larger chambers to the open end of the coil.

A thin living tube called a siphuncle passed through the septa, extending from the ammonite's body into the empty shell chambers. Through an osmotic process, the ammonite emptied water out of and secreted gas into these shell chambers. This enabled it to control the buoyancy of the shell. The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. ... In physics, buoyancy is an upward force on an object immersed in a fluid (i. ...

A primary difference between ammonites and nautiloids is that the siphuncle of ammonites runs along the inside of the outer axis of the shell, while the siphuncle of nautiloids runs through the center of the septa and camerae.

Sexual dimorphism

Ammonite species, Jurassic era

One feature found in shells of the modern nautilus is the variation in the size of the shell according to the gender of the animal, the shell of the male being slightly smaller than that of the female. This sexual dimorphism is thought to be an explanation to the variation in size of certain ammonite shells of the same species, the larger shell (called a macroconch) being female, and the smaller shell (called a microconch) being male. This is thought to be because the female required a larger body size for egg production. A good example of this sexual variation is found in Bifericeras from the early part of the Jurassic period of Europe. Gender, for the purposes of this article, is the perceived or projected (self-identified) masculinity or femininity of a person or characteristic. ... Female (left) and male Common Pheasant, illustrating the large degree of sexual dimorphism between the sexes Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species. ... The Jurassic period is a major unit of the geologic timescale that extends from about 195 million years BP at the end of the Triassic to 135 million years BP at the beginning of the Cretaceous. ... World map showing location of Europe A satellite composite image of Europe Europe is geologically and geographically a peninsula, forming the westernmost part of Eurasia. ...

It is only in relatively recent years that the sexual variation in the shells of ammonites has been recognized. The macroconch and microconch of one species were often previously mistaken for two closely related but different species occurring in the same rocks. However, these "pairs" were so consistently found together that it became apparent that they were in fact sexual forms of the same species.

Variations in shape

The majority of ammonites have a shell that is a planispiral flat coil, but some have a shell that is partially uncoiled, partially coiled and partially straight (as in Australiceras), nearly straight (as in baculites and belemnites), or coiled helically - superficially like that of a large gastropod (as in Turrilites and Bostrychoceras). These partially uncoiled and totally uncoiled forms began to appear during the early part of the Cretaceous and are known as heteromorphs. Species all extinct Baculites (walking stick rock) is a genus of extinct marine animals in the phylum Mollusca and class Cephalopoda. ... Extinct Orders Aulacocerida Phragmoteuthida Belemnitida Diplobelida Belemnoteuthina Belemnites (or belemnoids) are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the modern cuttlefish. ... Subclass Subclass Eogastropoda     Patellogastropoda Subclass Orthogastropoda   Superorder Cocculiniformia   Superorder Hot Vent Taxa     Neomphaolida   Superorder Vetigastropoda   Superorder Neritaemorphi     Neritopsina   Superorder Caenogastropoda     Architaenioglossa     Sorbeoconcha   Superorder Heterobranchia     Heterostropha     Opisthobranchia     Pulmonata The gastropods, or univalves, are the largest and most successful class of mollusks, with 60,000-75,000 species, and second largest class...

Perhaps the most extreme and bizarre looking example of a heteromorph is Nipponites, which appears to be a tangle of irregular whorls lacking any obvious symmetrical coiling. However, upon closer inspection the shell proves to be a three-dimensional network of connected "U" shapes. Nipponites occurs in rocks of the upper part of the Cretaceous in Japan and the USA.

Ammonites vary greatly in the ornamentation of their shells. Some may be smooth and relatively featureless, except for growth lines, and resemble that of the modern nautilus. In others various patterns of spiral ridges and ribs or even spines are shown. This type of ornamentation of the shell is especially evident in the later ammonites of the Cretaceous.

The aptychus

Like the modern nautilus, many ammonites were probably able to withdraw their body into the living chamber of the shell and developed either a single horny plate or a pair of calcitic plates with which they were able to close the opening of the shell. The opening of the shell is called the aperture. The plates are collectively termed the aptychus or aptychii in the case of a pair of plates, and anaptychus in the case of a single plate. The aptychus were identical and equal in size.

Asteroceras, a Jurassic ammonite from England

Anaptychi are rare as fossils. They are found in ammonites from the Devonian period through those of the Cretaceous period. Photograph of the ammonite Asteroceras obtusum taken by Dlloyd. ... Photograph of the ammonite Asteroceras obtusum taken by Dlloyd. ...

Aptychi only occur in ammonites from the Mesozoic era and are normally found detached the shell and are rarely preserved in place. Still, sufficient numbers have been found closing the apertures of fossil ammonite shells as to leave no doubt as to their intended purpose. (This long standing and wide-spread interpretation of the function of the aptychus has recently been disputed. The latest studies suggest that the apatychus may have in fact formed part of a special jaw apparatus). The Mesozoic is one of three geologic eras of Phanerozoic eon. ...

Large numbers of detached aptychi occur in certain beds of rock (such as those from the Mesozoic in the Alps). These rocks are usually accumulated at great depths. The modern nautilus lacks any calcitic plate for closing its shell, and none has been found in any of the extinct nautiloids. It does, however, have a leathery head shield it uses to cover the opening when it retreats inside. The Alps is the collective name for one of the great mountain range systems of Europe, stretching from Austria in the east, Slovenia, Italy, Switzerland, Liechtenstein and Germany, through to France in the west. ... Orders Nautilida Bactrida Nautiloids are a group of marine animals which all possess an external shell, the most well known example being the modern nautiluses. ...

There are many forms of aptychus, varying in shape and the sculpture of the inner and outer surfaces, but because they are so rarely found in position within the shell of the ammonite it is unclear as to which species of ammonite many aptychi belong.

Size

Few of the ammonites occurring in the lower and middle part of the Jurassic period reach a size exceeding 23 centimetres (9 inches) in diameter. Much larger forms are found in the later rocks of the upper part of the Jurassic and the lower part of the Cretaceous, such as Titanites from the Portland Stone of Jurassic of southern England, which is often 53 centimetres (2 feet) in diameter, and Pachydiscus seppenradensis of the Cretaceous period of Germany, which is the largest known ammonite sometimes reaching 2 metres (6.5 feet) in diameter. The largest known North American ammonite is Parapuzosia bradyi from the Cretaceous with specimens measuring 137 centimetres (4.5 feet) in diameter. World map showing location of North America A satellite composite image of North America North America is the third largest continent in area and in population after Eurasia and Africa. ...

Ammonite distribution

A specimen of Hoploscaphites from the Pierre Shale of South Dakota. Much of the original shell has survived.

Starting from the late Silurian, ammonites were extremely abundant, especially in the Mesozoic seas. Many genera evolved and ran their course quickly, becoming extinct in a few million years. Due to their rapid evolution and widespread distribution, ammonites are useful for geologists and paleontologists for biostratigraphy. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods. Charles Darwin, the father of evolutionary theory Although generally, evolution is taken to mean any process of change over time, in the context of life science, evolution is a change in the traits of living organisms over generations, including the emergence of new species. ... A geologist is a contributor to the science of geology. ... A paleontologist carefully chips rock from a column of dinosaur vertebrae. ... Biostratigraphy is the science of dating rocks by using the fossils contained within them. ... Index fossils (or zone fossils) are fossils used to define and identify geologic periods (or faunal stages). ... The geologic timescale is used by geologists and other scientists to describe the timing and relationships between events that have occured during the history of the Earth. ...

An iridescent ammonite from Madagascar.

When ammonites are found in clays their original mother-of-pearl coating is often preserved. This type of preservation is found in ammonites such as Hoplites from the Cretaceous Gault clay of Folkestone in Kent, England. Clay is a generic term for an aggregate of hydrous silicate particles less than 4 μm (micrometres) in diameter. ... A piece of nacre Nacre, also known as mother of pearl, is an organic mixture of calcium carbonate (CaCO3) in the form of platy crystals of aragonite and conchiolin (a scleroprotein). ... The Gault Clay is a formation of stiff blue clay deposited in a calm, fairly deep water marine environment during the Lower Cretaceous Period (Upper and Middle Albian). ... Royal motto: Dieu et mon droit (French: God and my right) Englands location within the UK Official language English de facto Capital London de facto Largest city London Area  - Total Ranked 1st UK 130,395 km² Population  - Total (2001)  - Density Ranked 1st UK 49,138,831 377/km² Religion...

The Cretaceous Pierre Shale formation of the United States and Canada is well known for the abundant ammonite fauna it yields, including Baculites, Placenticeras, Scaphites, Hoploscaphites, and Jeletzkytes, as well as many uncoiled forms. Many of these also have much or all of the original shell still intact. Species all extinct Scaphites (Greek skafh, a boat or anything dug or scooped out) is a genus of extinct cephalopod belonging to the ammonite family (order Ancyloceratida). ...

Other fossils, such as many found in Madagascar, display iridescence. These iridescent ammonites are often of gem quality when polished. The iridescence of the Blue Morpho butterfly wings. ...

The ammonites survived several major extinction events, with often only a few species surviving. But each time, this handful would diversify into a multitude of forms. Ammonites fossils become less abundant during the upper part of the Cretaceous, and none survive into the Cenozoic era. The last surviving lines died out about 65 million years ago along with the dinosaurs in the Cretaceous-Tertiary extinction event. An extinction event (also extinction-level event, ELE) is a period in time when a large number of species die out. ... The Cenozoic or Cainozoic era (sometimes Caenozoic Era) is the most recent of the four classic geological eras. ... The Cretaceous-Tertiary (K-T or KT) extinction event, also known as the KT boundary (the K is from kreta, the greek root of the word cretaceous, meaning chalk), was a period of massive extinction of species, about 65. ...

Trivia

In medieval times, ammonites were believed to be petrified snakes. They were frequently fitted with carved snake-like heads and sold to pilgrims. Superfamilies and Families Henophidia Aniliidae Anomochilidae Boidae Bolyeriidae Cylindrophiidae Loxocemidae Pythonidae Tropidophiidae Uropeltidae Xenopeltidae Typhlopoidea Anomalepididae Leptotyphlopidae Typhlopidae Xenophidia Acrochordidae Atractaspididae Colubridae Elapidae Hydrophiidae Viperidae Snakes are cold blooded legless reptiles closely related to lizards, which share the order Squamata. ...

References and further reading

• Neal L Larson, Steven D Jorgensen, Robert A Farrar and Peter L Larson. Ammonites and the other Cephalopods of the Pierre Seaway. Geoscience Press, 1997.
• Monks, Neale and Palmer, Phil. Ammonites. Natural History Museum, 2002.
• Walker, Cyril and Ward, David. Fossils. Dorling, Kindersley Limited, London, 2002.
• A Broad Brush History of the Cephalopoda (http://is.dal.ca/~ceph/TCP/evolution.html) by Dr. Neale Monks, from The Cephalopod Page.
• Ammonite maturity, pathology and old age (http://is.dal.ca/%7Eceph/TCP/ammonage.html) By Dr. Neale Monks, from The Cephalopod Page. Essay about the life span of Ammonites.
• Cretaceous Fossils Taxonomix Index for Order Ammonoitida (http://www.cretaceousfossils.com/invertebrates/ammonites/ammonites_index.htm)

See also

• Fossils and the geological timescale
• Belemnoidea
• Nautiloidea
• Ammolite - a gemstone formed from fossil ammonite shells.

Precambrian (3. ... Extinct Orders Aulacocerida Phragmoteuthida Belemnitida Diplobelida Belemnoteuthina Belemnites (or belemnoids) are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the modern cuttlefish. ... Orders Nautilida Bactrida Nautiloids are a group of marine animals which all possess an external shell, the most well known example being the modern nautiluses. ... Ammolite is a very rare and precious opal-like organic gemstone found only along the eastern slopes of the United States and Canada. ... A gemstone is a mineral, rock (as in lapis lazuli) or petrified material that when cut or faceted and polished is collectible or can be used in jewellery. ...

External links

• Photos of Ammonites at Lyme Regis, UK (http://y2u.co.uk/&002_Images/Lyme%20Regis%20Fossils%20%2001.htm)