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Ammonoidea

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Ammonoids
Temporal range: 409–66 Ma Devonian-Late Cretaceous
Pleuroceras solare, Little Switzerland, Bavaria, Germany.jpg
Specimen of Pleuroceras solare, from the Lower Jurassic of Bavaria, Germany
Scientific classification e
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Zittel, 1884
Orders
Ammonite clean cut
Ammonite clean cut

Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) than they are to shelled nautiloids such as the living Nautilus species.[1] The earliest ammonites appeared during the Devonian, with the last species vanishing during the Cretaceous–Paleogene extinction event.

Ammonites are excellent index fossils, and linking the rock layer in which a particular species or genus is found to specific geologic time periods is often possible. Their fossil shells usually take the form of planispirals, although some helically spiraled and nonspiraled forms (known as heteromorphs) have been found.

The name "ammonite", from which the scientific term is derived, was inspired by the spiral shape of their fossilized shells, which somewhat resemble tightly coiled rams' horns. Pliny the Elder (d. 79 AD near Pompeii) called fossils of these animals ammonis cornua ("horns of Ammon") because the Egyptian god Ammon (Amun) was typically depicted wearing rams' horns.[2] Often, the name of an ammonite genus ends in -ceras, which is from κέρας (kéras) meaning "horn".

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Class (biology)

Class (biology)

In biological classification, class is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order.

Cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, cuttlefish, or nautilus. 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. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

Octopus

Octopus

An octopus is a soft-bodied, eight-limbed mollusc of the order Octopoda. The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, and nautiloids. Like other cephalopods, an octopus is bilaterally symmetric with two eyes and a beaked mouth at the center point of the eight limbs. The soft body can radically alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight appendages behind them as they swim. The siphon is used both for respiration and for locomotion, by expelling a jet of water. Octopuses have a complex nervous system and excellent sight, and are among the most intelligent and behaviourally diverse of all invertebrates.

Cuttlefish

Cuttlefish

Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of buoyancy.

Nautiloid

Nautiloid

Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living Nautilus and Allonautilus. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. They flourished during the early Paleozoic era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms (orthocones). Only a handful of rare coiled species, the nautiluses, survive to the present day.

Nautilus

Nautilus

The nautilus is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.

Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, England, where rocks from this period were first studied.

Cretaceous–Paleogene extinction event

Cretaceous–Paleogene extinction event

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kilograms also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous Period, and with it the Mesozoic era, while heralding the beginning of the Cenozoic era, which continues to this day.

Geologic time scale

Geologic time scale

The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy and geochronology. It is used primarily by Earth scientists to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardized international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units.

Fossil

Fossil

A fossil 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 in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the fossil record.

Horns of Ammon

Horns of Ammon

The horns of Ammon were curling ram horns, used as a symbol of the Egyptian deity Ammon. Because of the visual similarity, they were also associated with the fossils shells of ancient snails and cephalopods, the latter now known as ammonite because of that historical connection.

Amun

Amun

Amun was a major ancient Egyptian deity who appears as a member of the Hermopolitan Ogdoad. Amun was attested from the Old Kingdom together with his wife Amunet. With the 11th Dynasty, Amun rose to the position of patron deity of Thebes by replacing Montu.

Diagnostic characters

Ammonites (subclass Ammonoidea) can be distinguished by their septa, the dividing walls that separate the chambers in the phragmocone, by the nature of their sutures where the septa join the outer shell wall, and in general by their siphuncles.

Septa

Ammonoid septa characteristically have bulges and indentations and are to varying degrees convex when seen from the front, distinguishing them from nautiloid septa, which are typically simple concave, dish-shaped structures. The topology of the septa, especially around the rim, results in the various suture patterns found.[3]

Suture patterns

Regions of the suture line and variants in suture patterns
Regions of the suture line and variants in suture patterns

While nearly all nautiloids show gently curving sutures, the ammonoid suture line (the intersection of the septum with the outer shell) is variably folded, forming saddles ("peaks" that point towards the aperture) and lobes ("valleys" which point away from the aperture). The suture line has four main regions. The external or ventral region refers to sutures along the lower (outer) edge of the shell, where the left and right suture lines meet. The external saddle lies directly on the lower midline of the shell and is edged by external lobes. On suture diagrams the external saddle is supplied with an arrow which typically points towards the aperture. The lateral region involves the first saddle and lobe pair past the external region as the suture line extends up the side of the shell. Additional lobes developing towards the inner edge of a whorl are labelled umbilical lobes, which increase in number through ammonoid evolution as well as an individual ammonoid's development. Lobes and saddles which are so far towards the center of the whorl that they are covered up by succeeding whorls are labelled internal lobes and saddles. Three major types of suture patterns are found in the Ammonoidea:

  • Goniatitic – numerous undivided lobes and saddles; typically 8 lobes around the conch. This pattern is characteristic of the Paleozoic ammonoids.
  • Ceratitic – lobes have subdivided tips, giving them a saw-toothed appearance and rounded, undivided saddles. This suture pattern is characteristic of Triassic ammonoids and appears again in the Cretaceous "pseudoceratites".
  • Ammonitic – lobes and saddles are much subdivided (fluted); subdivisions are usually rounded instead of saw-toothed. Ammonoids of this type are the most important species from a biostratigraphical point of view. This suture type is characteristic of Jurassic and Cretaceous ammonoids, but extends back all the way to the Permian.

Siphuncle

The siphuncle in most ammonoids is a narrow tubular structure that runs along the shell's outer rim, known as the venter, connecting the chambers of the phragmocone to the body or living chamber. This distinguishes them from living nautiloides (Nautilus and Allonautilus) and typical Nautilida, in which the siphuncle runs through the center of each chamber. However the very earliest nautiloids from the Late Cambrian and Ordovician typically had ventral siphuncles like ammonites, although often proportionally larger and more internally structured. The word "siphuncle" comes from the New Latin siphunculus, meaning "little siphon".

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Goniatite

Goniatite

Goniatids, informally goniatites, are ammonoid cephalopods that form the order Goniatitida, derived from the more primitive Agoniatitida during the Middle Devonian some 390 million years ago. Goniatites (goniatitids) survived the Late Devonian extinction to flourish during the Carboniferous and Permian only to become extinct at the end of the Permian some 139 million years later.

Ceratites

Ceratites

Ceratites is an extinct genus of ammonite cephalopods. These nektonic carnivores lived in marine habitats in what is now Europe, during the Triassic, from the upper-most Anisian to the lower Ladinian age.

Cretaceous

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 the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

Jurassic

Jurassic

The Jurassic is a geologic period and stratigraphic system that spanned from the end of the Triassic Period 201.4 million years ago (Mya) to the beginning of the Cretaceous Period, approximately 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era and is named after the Jura Mountains, where limestone strata from the period were first identified.

Permian

Permian

The Permian is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia.

Goniatites

Goniatites

Goniatites is a genus of extinct cephalopods belonging to the family Goniatitidae, included in the superfamily Goniatitaceae. Hibernicoceras and Hypergoniatites are among related genera.

Protrachyceras

Protrachyceras

Protrachyceras is a genus of ceratitid ammonoid cephalopods belonging to the family Trachyceratidae.

Lytoceras sutile

Lytoceras sutile

Lytoceras sutile is an ammonite species belonging to the family Lytoceratidae. These cephalopods were fast-moving nektonic carnivores.

Phragmocone

Phragmocone

The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae.

Allonautilus

Allonautilus

The genus Allonautilus contains two species of nautiluses, which have a significantly different morphology from those placed in the sister taxon Nautilus. Allonautilus is now thought to be a descendant of Nautilus, rendering the latter genus paraphyletic.

Nautilida

Nautilida

The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, Nautilus and Allonautilus, with six species. All told, between 22 and 34 families and 165 to 184 genera have been recognised, making this the largest order of the subclass Nautiloidea.

New Latin

New Latin

New Latin is the revival of Literary Latin used, in original, scholarly, and scientific works, first in Italy in the fourteenth and fifteenth centuries' Italian Renaissance, and then across northern Europe after about 1500, as a key feature of the humanist movement. Neo Latin's adoption throughout Europe was coincident with the rise of the printing press and of early modern schooling. Latin was learnt as a spoken language as well as written, as the vehicle of schooling and University education, while vernacular languages were still infrequently used in such settings. As such, Latin dominated early publishing, and made a signficant portion of printed works until the nineteenth century.

Classification

An ammonite shell viewed in section, revealing the internal chambers and septa. Large polished examples are prized for both their aesthetic and scientific value.
An ammonite shell viewed in section, revealing the internal chambers and septa. Large polished examples are prized for both their aesthetic and scientific value.

Originating from within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian (circa 409 million years ago (Mya)) and became extinct shortly after Cretaceous (66 Mya). The classification of ammonoids is based in part on the ornamentation and structure of the septa comprising their shells' gas chambers.

Orders and suborders

An ammonitic ammonoid with the body chamber missing, showing the septal surface (especially at right) with its undulating lobes and saddles.
An ammonitic ammonoid with the body chamber missing, showing the septal surface (especially at right) with its undulating lobes and saddles.
Iridescent ancient ammonite fossil on display at the American Museum of Natural History, New York City, around 2.5 feet in diameter
Iridescent ancient ammonite fossil on display at the American Museum of Natural History, New York City, around 2.5 feet in diameter

The Ammonoidea can be divided into six orders, listed here starting with the most primitive and going to the more derived:

In some classifications, these are left as suborders, included in only three orders: Goniatitida, Ceratitida and Ammonitida.

Taxonomy of the Treatise on Invertebrate Paleontology

The Treatise on Invertebrate Paleontology (Part L, 1957) divides the Ammonoidea, regarded simply as an order, into eight suborders, the Anarcestina, Clymeniina, Goniatitina and Prolecanitina from the Paleozoic; the Ceratitina from the Triassic; and the Ammonitina, Lytoceratina and Phylloceratina from the Jurassic and Cretaceous. In subsequent taxonomies, these are sometimes regarded as orders within the subclass Ammonoidea.

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List of ammonite genera

List of ammonite genera

This list of ammonites is a comprehensive listing of genera that are included in the subclass †Ammonoidea, excluding purely vernacular terms. The list includes genera that are commonly accepted as valid, as well those that may be invalid or doubtful, or were not formally published, as well as junior synonyms of more established names, and genera that are no longer considered ammonites.

Bactritida

Bactritida

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 with questionable origins in Pragian stage before 409 million years ago, and persisted until Carnian pluvial event in the upper middle Carnian stage of the Triassic period. They are considered ancestors of the ammonoids, as well as of the coleoids.

Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, England, where rocks from this period were first studied.

Cretaceous

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 the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

Biological ornament

Biological ornament

A biological ornament is a characteristic of an animal that appears to serve a decorative function rather than a utilitarian function. Many are secondary sexual characteristics, and others appear on young birds during the period when they are dependent on being fed by their parents. Ornaments are used in displays to attract mates, which may lead to the evolutionary process known as sexual selection. An animal may shake, lengthen, or spread out its ornament in order to get the attention of the opposite sex, which will in turn choose the most attractive one with which to mate. Ornaments are most often observed in males, and choosing an extravagantly ornamented male benefits females as the genes that produce the ornament will be passed on to her offspring, increasing their own reproductive fitness. As Ronald Fisher noted, the male offspring will inherit the ornament while the female offspring will inherit the preference for said ornament, which can lead to a positive feedback loop known as a Fisherian runaway. These structures serve as cues to animal sexual behaviour, that is, they are sensory signals that affect mating responses. Therefore, ornamental traits are often selected by mate choice.

Iridescence

Iridescence

Iridescence is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfly wings and seashell nacre, and minerals such as opal. It is a kind of structural coloration that is due to wave interference of light in microstructures or thin films.

American Museum of Natural History

American Museum of Natural History

The American Museum of Natural History is a private 501(c)(3) natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 interconnected buildings housing 45 permanent exhibition halls, in addition to a planetarium and a library. The museum collections contain over 34 million specimens of plants, animals, fungi, fossils, minerals, rocks, meteorites, human remains, and human cultural artifacts, as well as specialized collections for frozen tissue and genomic and astrophysical data, of which only a small fraction can be displayed at any given time. The museum occupies more than 2×10^6 sq ft (190,000 m2). AMNH has a full-time scientific staff of 225, sponsors over 120 special field expeditions each year, and averages about five million visits annually.

Agoniatitida

Agoniatitida

Agoniatitida, also known as the Anarcestida, is the ancestral order within the cephalopod subclass Ammonoidea originating from bactritoid nautiloids, that lived in what would become Africa, Asia, Australia, Europe, and North America during the Devonian from about the lower boundary of Zlichovian stage into Taghanic event during upper middle Givetian, existing for approximately 25 million years.

Clymeniida

Clymeniida

Clymeniida is an order of ammonoid cephalopods from the Upper Devonian characterized by having an unusual dorsal siphuncle. They measured about 4 cm (1.6 in) in diameter and are restricted to Europe, North Africa, and possibly Australia.

Prolecanitida

Prolecanitida

Prolecanitida is an order of extinct ammonoid cephalopods with discoidal to thinly lenticular shells with goniatitic or ceratitic sutures and which retained the simple retrochoanitic siphuncle with backward extending septal necks. As typical for ammonoids the siphuncle is along the ventral margin. Prolecanitids form a relatively small and stable order within the Ammonoidea with 43 named genera and about 1250 species, but with a long-ranging lineage of about 108 m.y. stretching from the Lower Carboniferous to the Triassic. Although not as diverse as their goniatitid contemporaries, the Prolecanatida provided the stock from which all later Mesozoic ammonoids were derived.

Ceratitida

Ceratitida

Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post-Triassic ammonites.

Ammonitida

Ammonitida

Ammonitida is an order of ammonoid cephalopods that lived from the Jurassic through Paleocene time periods, commonly with intricate ammonitic sutures.

Life

Asteroceras, a Jurassic ammonite from England
Asteroceras, a Jurassic ammonite from England

Because ammonites and their close relatives are extinct, little is known about their way of life. Their soft body parts are very rarely preserved in any detail. Nonetheless, much has been worked out by examining ammonoid shells and by using models of these shells in water tanks.

Many ammonoids probably lived in the open water of ancient seas, rather than at the sea bottom, because their fossils are often found in rocks laid down under conditions where no bottom-dwelling life is found. Many of them (such as Oxynoticeras) are thought to have been good swimmers, with flattened, discus-shaped, streamlined shells, although some ammonoids were less effective swimmers and were likely to have been slow-swimming bottom-dwellers. Synchrotron analysis of an aptychophoran ammonite revealed remains of isopod and mollusc larvae in its buccal cavity, indicating at least this kind of ammonite fed on plankton.[4] They may have avoided predation by squirting ink, much like modern cephalopods; ink is occasionally preserved in fossil specimens.[5]

The soft body of the creature occupied the largest segments of the shell at the end of the coil. The smaller earlier segments were walled off and the animal could maintain its buoyancy by filling them with gas. Thus, the smaller sections of the coil would have floated above the larger sections.[6]

Many ammonite shells have been found with round holes once interpreted as a result of limpets attaching themselves to the shells. However, the triangular formation of the holes, their size and shape, and their presence on both sides of the shells, corresponding to the upper and lower jaws, is more likely evidence of the bite of a medium-sized mosasaur preying upon ammonites.

Some ammonites appear to have lived in cold seeps and even reproduced there.[7]

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Asteroceras

Asteroceras

Asteroceras is an extinct genus of cephalopod belonging to the Ammonite subclass. These fast-moving nektonic carnivores lived during the Triassic and Jurassic periods.

Benthic zone

Benthic zone

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "the depths." Organisms living in this zone are called benthos and include microorganisms as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.

Oxynoticeras

Oxynoticeras

Oxynoticeras is an extinct genus of ammonite from the Early Jurassic of Europe and North America. This genus is characterized by its smooth shell, with almost invisible undulations on the flank, and a sharp keel.

Synchrotron

Synchrotron

A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The magnetic field which bends the particle beam into its closed path increases with time during the accelerating process, being synchronized to the increasing kinetic energy of the particles. The synchrotron is one of the first accelerator concepts to enable the construction of large-scale facilities, since bending, beam focusing and acceleration can be separated into different components. The most powerful modern particle accelerators use versions of the synchrotron design. The largest synchrotron-type accelerator, also the largest particle accelerator in the world, is the 27-kilometre-circumference (17 mi) Large Hadron Collider (LHC) near Geneva, Switzerland, built in 2008 by the European Organization for Nuclear Research (CERN). It can accelerate beams of protons to an energy of 6.5 tera electronvolts (TeV or 1012 eV).

Plankton

Plankton

Plankton are the diverse collection of organisms found in water that are unable to propel themselves against a current. The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish and whales.

Cephalopod ink

Cephalopod ink

Cephalopod ink is a dark-coloured or luminous ink released into water by most species of cephalopod, usually as an escape mechanism. All cephalopods, with the exception of the Nautilidae and the Cirrina, are able to release ink to confuse predators.

Mosasaur

Mosasaur

Mosasaurs comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. They belong to the order Squamata, which includes lizards and snakes.

Cold seep

Cold seep

A cold seep is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. Cold does not mean that the temperature of the seepage is lower than that of the surrounding sea water. On the contrary, its temperature is often slightly higher. The "cold" is relative to the very warm conditions of a hydrothermal vent. Cold seeps constitute a biome supporting several endemic species.

Shell anatomy and diversity

Fossil shell of ammonite Placenticeras whitfieldi showing punctures caused by the bite of a mosasaur, Peabody Museum of Natural History, Yale
Fossil shell of ammonite Placenticeras whitfieldi showing punctures caused by the bite of a mosasaur, Peabody Museum of Natural History, Yale
Orthosphynctes, a Jurassic ammonite from Portugal
Orthosphynctes, a Jurassic ammonite from Portugal

Basic shell anatomy

Jeletzkytes, a Cretaceous ammonite from South Dakota, US
Jeletzkytes, a Cretaceous ammonite from South Dakota, US
A variety of ammonite forms, from Ernst Haeckel's 1904 Kunstformen der Natur (Art Forms of Nature)
A variety of ammonite forms, from Ernst Haeckel's 1904 Kunstformen der Natur (Art Forms of Nature)
Baculites ammonite from the Late Cretaceous of Wyoming, US: The original aragonite of the outer conch and inner septa has dissolved away, leaving this articulated internal mold.
Baculites ammonite from the Late Cretaceous of Wyoming, US: The original aragonite of the outer conch and inner septa has dissolved away, leaving this articulated internal mold.

The chambered part of the ammonite shell is called a phragmocone. It 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 at any given moment. As it grew, it added newer and larger chambers to the open end of the coil. Where the outer whorl of an ammonite shell largely covers the preceding whorls, the specimen is said to be involute (e.g., Anahoplites). Where it does not cover those preceding, the specimen is said to be evolute (e.g., Dactylioceras).

A thin living tube called a siphuncle passed through the septa, extending from the ammonite's body into the empty shell chambers. Through a hyperosmotic active transport process, the ammonite emptied water out of these shell chambers. This enabled it to control the buoyancy of the shell and thereby rise or descend in the water column.

A primary difference between ammonites and nautiloids is the siphuncle of ammonites (excepting Clymeniina) runs along the ventral periphery of the septa and camerae (i.e., the inner surface of the outer axis of the shell), while the siphuncle of nautiloids runs more or less through the center of the septa and camerae.

Sexual dimorphism

Discoscaphites iris, Owl Creek Formation (Upper Cretaceous), Ripley, Mississippi, US
Discoscaphites iris, Owl Creek Formation (Upper Cretaceous), Ripley, Mississippi, US

One feature found in shells of the modern Nautilus is the variation in the shape and size of the shell according to the sex of the animal, the shell of the male being slightly smaller and wider than that of the female. This sexual dimorphism is thought to be an explanation for the variation in size of certain ammonite shells of the same species, the larger shell (the macroconch) being female, and the smaller shell (the 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.

Only recently has sexual variation in the shells of ammonites 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, because the dimorphic sizes are so consistently found together, they are more likely an example of sexual dimorphism within the same species.

Whorl width in the body chamber of many groups of ammonites, as expressed by the width:diameter ratio, is another sign of dimorphism. This character has been used to separate "male" (Largiventer conch "L") from "female" (Leviventer conch "l").[8]

Variations in shape

Heteromorph ammonite Didymoceras stevensoni
Heteromorph ammonite Didymoceras stevensoni

The majority of ammonite species feature planispiral, flat-coiled shells, but other species feature nearly straight (as in baculites) shells. Still other species' shells are coiled helically, similar in appearance to some gastropods (e.g., Turrilites and Bostrychoceras). Some species' shells are even initially uncoiled, then partially coiled, and finally straight at maturity (as in Australiceras). These partially uncoiled and totally uncoiled forms began to diversify mainly during the early part of the Cretaceous and are known as heteromorphs.

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 symmetric coiling. Upon closer inspection, though, 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 United States.

Ammonites vary greatly in the ornamentation (surface relief) 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.

Aptychus

A drawing of an aptychus which was mistakenly described as a bivalve and given the name "Trigonellites latus", from the Kimmeridge Clay Formation in England
A drawing of an aptychus which was mistakenly described as a bivalve and given the name "Trigonellites latus", from the Kimmeridge Clay Formation in England

Some ammonites have been found in association with a single horny plate or a pair of calcitic plates. In the past, these plates were assumed to serve in closing the opening of the shell in much the same way as an operculum, but more recently they are postulated to have been a jaw apparatus.[9][10][11][12]

The plates are collectively termed the aptychus or aptychi in the case of a pair of plates, and anaptychus in the case of a single plate. The paired aptychi were symmetric to one another and equal in size and appearance.

Anaptychi are relatively rare as fossils. They are found representing ammonites from the Devonian period through those of the Cretaceous period.

Calcified aptychi only occur in ammonites from the Mesozoic era. They are almost always found detached from the shell, and are only very 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 identity as part of the anatomy of an ammonite.

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 only one extinct nautiloid genus is known to have borne anything similar. Nautilus does, however, have a leathery head shield (the hood) which it uses to cover the opening when it retreats inside.

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 often unclear to which species of ammonite one kind of aptychus belongs. A number of aptychi have been given their own genus and even species names independent of their unknown owners' genus and species, pending future discovery of verified occurrences within ammonite shells.

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Mosasaur

Mosasaur

Mosasaurs comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. They belong to the order Squamata, which includes lizards and snakes.

Peabody Museum of Natural History

Peabody Museum of Natural History

The Peabody Museum of Natural History at Yale University is among the oldest, largest, and most prolific university natural history museums in the world. It was founded by the philanthropist George Peabody in 1866 at the behest of his nephew Othniel Charles Marsh, the early paleontologist. Most known to the public for its Great Hall of Dinosaurs, which includes a mounted juvenile Brontosaurus and the 110-foot-long (34 m) mural The Age of Reptiles, it also has permanent exhibits dedicated to human and mammal evolution; wildlife dioramas; Egyptian artifacts; and the birds, minerals and Native Americans of Connecticut.

Jeletzkytes

Jeletzkytes

Jeletzkytes is an extinct genus of scaphatoid ammonite from the Upper Cretaceous (Maastrichtian) of North America named and described by Riccardi, 1983. In overall form Jeletzkytes closely resembles the genus Scaphites.

Ernst Haeckel

Ernst Haeckel

Ernst Heinrich Philipp August Haeckel was a German zoologist, naturalist, eugenicist, philosopher, physician, professor, marine biologist and artist. He discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms and coined many terms in biology, including ecology, phylum, phylogeny, and Protista. Haeckel promoted and popularised Charles Darwin's work in Germany and developed the influential but no longer widely held recapitulation theory claiming that an individual organism's biological development, or ontogeny, parallels and summarises its species' evolutionary development, or phylogeny.

Baculites

Baculites

Baculites is an extinct genus of cephalopods with a nearly straight shell, included in the heteromorph ammonites. The genus, which lived worldwide throughout most of the Late Cretaceous, and which briefly survived the K-Pg mass extinction event, was named by Lamarck in 1799.

Cretaceous

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 the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

Aragonite

Aragonite

Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, CaCO3. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.

Camera (cephalopod)

Camera (cephalopod)

Camerae are the spaces or chambers enclosed between two adjacent septa in the phragmocone of a nautiloid or ammonoid cephalopod molluscus. These can be seen in cross-sections of a nautilus shell and in the polished cross-sections of ammonites. In life these chambers are filled with gas, mediated by the siphuncle, and used to control buoyancy.

Anahoplites

Anahoplites

Anahoplites is a genus of rather involute, compressed hoplitid ammonites with flat sides, narrow flat or grooved venters, and flexious ribs or striae arising from weak umbilicle tubercles that end in fine dense ventrolateral nodes. The elements of their sutures are short, wide and jaggedy. Specimens of Annahoplites have diameters typically in the range of 4–6 centimetres (1.6–2.4 in) although some with diameters of as much as 19 centimetres (7.5 in) have been reported. The genus lived during the Cretaceous, from the Middle to the late Albian.

Dactylioceras

Dactylioceras

Dactylioceras was a widespread genus of ammonites from the Lower Jurassic period, approximately 180 million years ago (mya).

Buoyancy

Buoyancy

Buoyancy, or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and is equivalent to the weight of the fluid that would otherwise occupy the submerged volume of the object, i.e. the displaced fluid.

Clymeniina

Clymeniina

Clymeniina is an extinct suborder of ammonites that existed during the Devonian.

Soft-part anatomy

Although ammonites do occur in exceptional lagerstatten such as the Solnhofen Limestone, their soft-part record is surprisingly bleak. Beyond a tentative ink sac and possible digestive organs, no soft parts were known until 2021.[13][14] They likely bore a radula and beak, a marginal siphuncle and ten arms.[15] They operated by direct development with sexual reproduction, were carnivorous, and had a crop for food storage. They are unlikely to have dwelt in fresh or brackish water.[15] Many ammonites were likely filter feeders, so adaptations associated with this lifestyle like sieves probably occurred.[4]

A 2021 study found ammonite specimens with preserved hook-like suckers, providing a general shape to ammonite tentacles.[16] A contemporary study found an ammonite isolated body, offering for the first time a glimpse into these animals' organs.[14]

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Solnhofen Limestone

Solnhofen Limestone

The Solnhofen Limestone or Solnhofen Plattenkalk, formally known as the Altmühltal Formation, is a Jurassic Konservat-Lagerstätte that preserves a rare assemblage of fossilized organisms, including highly detailed imprints of soft bodied organisms such as sea jellies. The most familiar fossils of the Solnhofen Plattenkalk include the early feathered theropod dinosaur Archaeopteryx preserved in such detail that they are among the most famous and most beautiful fossils in the world. The Solnhofen beds lie in the German state of Bavaria (Bayern), halfway between Nuremberg (Nürnberg) and Munich (München) and were originally quarried as a source of lithographic limestone. The Jura Museum situated in Eichstätt, Germany has an extensive exhibit of Jurassic fossils from the quarries of Solnhofen and surroundings, including marine reptiles, pterosaurs, and one specimen of the early bird Archaeopteryx.

Crop (anatomy)

Crop (anatomy)

A crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion. This anatomical structure is found in a wide variety of animals. It has been found in birds, and in invertebrate animals including gastropods, earthworms, leeches, and insects.

Filter feeder

Filter feeder

Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish. Some birds, such as flamingos and certain species of duck, are also filter feeders. Filter feeders can play an important role in clarifying water, and are therefore considered ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.

Size

2-metre (6.6 ft) Parapuzosia seppenradensis cast in Germany
2-metre (6.6 ft) Parapuzosia seppenradensis cast in Germany

The smallest ammonoid was Maximites from the Upper Carboniferous. Adult specimens reached only 10 mm (0.39 in) in shell diameter.[17] Few of the ammonites occurring in the lower and middle part of the Jurassic period reached a size exceeding 23 cm (9.1 in) 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 cm (1.74 ft) in diameter, and Parapuzosia seppenradensis of the Cretaceous period of Germany, which is one of the largest-known ammonites, sometimes reaching 2 m (6.6 ft) in diameter. The largest-documented North American ammonite is Parapuzosia bradyi from the Cretaceous, with specimens measuring 137 cm (4.5 ft) in diameter.

Ammonoidea in Iran
Ammonoidea in Iran

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Cephalopod size

Cephalopod size

Cephalopods, which include squids and octopuses, vary enormously in size. The smallest are only about 1 centimetre (0.39 in) long and weigh less than 1 gram (0.035 oz) at maturity, while the largest—the giant and colossal squids—can exceed 10 metres (33 ft) in length and weigh close to half a tonne (1,100 lb), making them the largest living invertebrates. Living species range in mass more than three-billion-fold, or across nine orders of magnitude, from the lightest hatchlings to the heaviest adults. Certain cephalopod species are also noted for having individual body parts of exceptional size. The giant and colossal squids, for example, have the largest known eyes among living animals.

Parapuzosia seppenradensis

Parapuzosia seppenradensis

Parapuzosia seppenradensis is the largest known species of ammonite. It lived during the Lower Campanian Epoch of the Late Cretaceous period, in marine environments in what is now Westphalia, Germany. A specimen, found in Seppenrade near Lüdinghausen, Germany in 1895 measures 1.8 m (5.9 ft) in diameter, although the living chamber is incomplete.

Maximites

Maximites

Maximites is a genus of Late Carboniferous ammonoids. Adult specimens were the smallest known ammonoids, only at about 1 cm (0.39 in) in diameter of shells. Fossils are found in various Late Carboniferous marine strata in North America. Maximites is the sole genus of Maximitidae, one of two families of the Superfamily Pseudohaloritoidea, an important subgroup of the order Goniatitida.

Titanites

Titanites

Titanites is an extinct ammonite cephalopod genus within the family Dorsoplanitidae, that lived during the late Tithonian of the Late Jurassic.

North America

North America

North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Caribbean Sea, and to the west and south by the Pacific Ocean. Because it is on the North American Tectonic Plate, Greenland is included as a part of North America geographically.

Parapuzosia bradyi

Parapuzosia bradyi

Parapuzosia bradyi is a gigantic species of ammonite, reaching diameters of more than 4.5 ft (1.4 m) by 6 ft (1.8 m). It is the largest species of ammonite in North America. It had a moderately involute shell with flat sides. The inner whorls are slightly oval-shaped with prominent ribbing. They are only known from the upper layers of the Eagle Sandstone and Cody Shale formations.

Iran

Iran

Iran, officially the Islamic Republic of Iran and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmenistan to the north, by Afghanistan and Pakistan to the east, and by the Gulf of Oman and the Persian Gulf to the south. It covers an area of 1.64 million square kilometres, making it the 17th-largest country. Iran has an estimated population of 86.8 million, making it the 17th-most populous country in the world, and the second-largest in the Middle East. Its largest cities, in descending order, are the capital Tehran, Mashhad, Isfahan, Karaj, Shiraz, and Tabriz.

Distribution

Starting from the mid-Devonian, ammonoids were extremely abundant, especially as ammonites during the Mesozoic era. Many genera evolved and ran their course quickly, becoming extinct in a few million years. Due to their rapid evolution and widespread distribution, ammonoids are used by 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 geologic time periods.

Due to their free-swimming and/or free-floating habits, ammonites often happened to live directly above seafloor waters so poor in oxygen as to prevent the establishment of animal life on the seafloor. When upon death the ammonites fell to this seafloor and were gradually buried in accumulating sediment, bacterial decomposition of these corpses often tipped the delicate balance of local redox conditions sufficiently to lower the local solubility of minerals dissolved in the seawater, notably phosphates and carbonates. The resulting spontaneous concentric precipitation of minerals around a fossil, a concretion, is responsible for the outstanding preservation of many ammonite fossils.

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.

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, as well as the complete body chamber, still intact. Many Pierre Shale ammonites, and indeed many ammonites throughout earth history, are found inside concretions.

An iridescent ammonite from Madagascar
An iridescent ammonite from Madagascar

Other fossils, such as many found in Madagascar and Alberta, Canada display iridescence. These iridescent ammonites are often of gem quality (ammolite) when polished. In no case would this iridescence have been visible during the animal's life; additional shell layers covered it.

The majority of ammonoid specimens, especially those of the Paleozoic era, are preserved only as internal molds; the outer shell (composed of aragonite)[18] has been lost during the fossilization process. Only in these internal-mould specimens can the suture lines be observed; in life, the sutures would have been hidden by the outer shell.

The ammonoids as a group continued through several major extinction events, although often only a few species survived. Each time, however, this handful of species diversified into a multitude of forms. Ammonite fossils became less abundant during the latter part of the Mesozoic, and although they seemingly survived the Cretaceous–Paleogene extinction event, all known Paleocene ammonite lineages are restricted to the Paleocene epoch (65–61 Ma).[19][20]

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Mesozoic

Mesozoic

The Mesozoic Era is the second-to-last era of Earth's geological history, lasting from about 252 to 66 million years ago, comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of archosaurian reptiles, like the dinosaurs; an abundance of conifers and ferns; a hot greenhouse climate; and the tectonic break-up of Pangaea. The Mesozoic is the middle of the three eras since complex life evolved: the Paleozoic, the Mesozoic, and the Cenozoic.

Genus

Genus

Genus is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera. Panthera is a genus within the family Felidae.

Evolution

Evolution

In biology, evolution is the change in heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation tends to exist within any given population as a result of genetic mutation and recombination. Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or more rare within a population. The evolutionary pressures that determine whether a characteristic is common or rare within a population constantly change, resulting in a change in heritable characteristics arising over successive generations. It is this process of evolution that has given rise to biodiversity at every level of biological organisation.

Geologist

Geologist

A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, although backgrounds in physics, chemistry, biology, and other sciences are also useful. Field research is an important component of geology, although many subdisciplines incorporate laboratory and digitalized work. Geologists can be classified in a larger group of scientists, called geoscientists.

Biostratigraphy

Biostratigraphy

Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. The primary objective of biostratigraphy is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at a different section. Fossils within these strata are useful because sediments of the same age can look completely different, due to local variations in the sedimentary environment. For example, one section might have been made up of clays and marls, while another has more chalky limestones. However, if the fossil species recorded are similar, the two sediments are likely to have been laid down around the same time. Ideally these fossils are used to help identify biozones, as they make up the basic biostratigraphy units, and define geological time periods based upon the fossil species found within each section.

Geologic time scale

Geologic time scale

The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy and geochronology. It is used primarily by Earth scientists to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardized international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units.

Nekton

Nekton

Nekton or necton refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms that were carried along by the current, the plankton. As a guideline, nektonic organisms have a high Reynolds number and planktonic organisms a low one. However, some organisms can begin life as plankton and transition to nekton later on in life, sometimes making distinction difficult when attempting to classify certain plankton-to-nekton species as one or the other. For this reason, some biologists choose not to use this term.

Carbonate

Carbonate

A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula CO2−3. The word carbonate may also refer to a carbonate ester, an organic compound containing the carbonate group C(=O)(O–)2.

Concretion

Concretion

A concretion is a hard, compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin concretio "(act of) compacting, condensing, congealing, uniting", itself from con meaning 'together' and crescere meaning "to grow". Concretions form within layers of sedimentary strata that have already been deposited. They usually form early in the burial history of the sediment, before the rest of the sediment is hardened into rock. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum.

Clay

Clay

Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2Si2O5(OH)4).

Hoplites (ammonite)

Hoplites (ammonite)

Hoplites is a genus of ammonite that lived from the Early Albian to the beginning of the Middle Albian. Its fossils have been found in Europe, Transcaspia and Mexico. Shell has compressed, rectangular till depressed and trapezoidal whorl section. There are strong umbilical bullae from which, prominent ribs are branching and these are interrupted on venter. Ends of ribs on the venter are prominent and can be both alternate or opposite. Some species have zigzagging ribs and these ribs ends usually thickened, or they can be raised into ventrolateral tubercles. These tubercles are mostly oblique clavi.

Baculites

Baculites

Baculites is an extinct genus of cephalopods with a nearly straight shell, included in the heteromorph ammonites. The genus, which lived worldwide throughout most of the Late Cretaceous, and which briefly survived the K-Pg mass extinction event, was named by Lamarck in 1799.

Evolutionary history

Goniatites, which were a dominant component of Early and Middle Permian faunas, became rare in the Late Permian, and no goniatite is thought to have crossed into the Triassic.[21]

Ceratitida originated during the Middle Permian, likely from the Daraelitidae, and radiated in the Late Permian. In the aftermath of the Permian–Triassic extinction event, Ceratitids represent the dominant group of Triassic ammonites.[21]

Ammonites were devastated by the end-Triassic extinction, with only a handful of genera belonging to the family Psiloceratidae of the suborder Phylloceratina surviving and becoming ancestral to all later Jurassic and Cretaceous ammonites. Ammonites explosively diversified during the Early Jurassic, with the orders Psiloceratina, Ammonitina, Lytoceratina, Haploceratina, Perisphinctina and Ancyloceratina all appearing during the Jurassic.[22]

Heteromorph ammonites (ammonites with open or non-spiral coiling) of the order Ancyloceratina became common during the Cretaceous period.[23]

Ammonites in the permanent collection of The Children's Museum of Indianapolis
Ammonites in the permanent collection of The Children's Museum of Indianapolis

At least 57 species of ammonites, which were widespread and belonged to six superfamilies, were extant during the last 500,000 years of the Cretaceous, indicating that ammonites remained highly diverse until the very end of their existence. All ammonites were wiped out during or shortly after the K-Pg extinction event, caused by the Chicxulub impact. It has been suggested that ocean acidification generated by the impact played a key role in their extinction, as the larvae of ammonites were likely small and planktonic, and would have been heavily affected.[19] Nautiloids, exemplified by modern nautiluses, are conversely thought to have had a reproductive strategy in which eggs were laid in smaller batches many times during the lifespan, and on the sea floor well away from any direct effects of such a bolide strike, and thus survived.[24] Many ammonite species were filter feeders, so they might have been particularly susceptible to marine faunal turnovers and climatic change.[4] Some reports suggest that a few ammonite species may have persisted into the very early Danian stage of the Paleocene, before going extinct.[25][26]

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Daraelitidae

Daraelitidae

The Daraelitidae form a family in the ammonoid order Prolecanitida from the Upper Mississippian - Middle Permian characterized by discoidal shells with no prominent sculpture, moderately large umbilicus, and goniatitic or ceratitic sutures with a trifid ventral lobe and few auxiliary lobes.

Permian–Triassic extinction event

Permian–Triassic extinction event

The Permian–Triassic extinction event, also known as the End-Permian extinction event and colloquially as the Great Dying, forms the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras respectively, approximately 251.9 million years ago. As the largest of the "Big Five" mass extinctions of the Phanerozoic, it is the Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It is the largest known mass extinction of insects. There is evidence for one to three distinct pulses, or phases, of extinction.

Psiloceratidae

Psiloceratidae

Psiloceratidae is an extinct family of cephalopods belonging to the ammonite subclass.

Phylloceratina

Phylloceratina

The Phyllocertina comprise a suborder of ammonoid cephalopods, belonging to the Ammonitida, whose range extends from the Lower Triassic to the Upper Cretaceous. Shells of the Phylloceratina are generally smooth with small to large umbilici and complex sutures with leaf-like phylloid saddle endings and lobes with thorn-like projections.

Ancyloceratina

Ancyloceratina

The Ancyloceratina were a diverse suborder of ammonite most closely related to the ammonites of order Lytoceratina. They evolved during the Late Jurassic but were not very common until the Cretaceous period, when they rapidly diversified and became one of the most distinctive components of Cretaceous marine faunas. They have been recorded from every continent and many are used as zonal or index fossils. The most distinctive feature of the majority of the Ancyloceratina is the tendency for most of them to have shells that are not regular spirals like most other ammonites. These irregularly-coiled ammonites are called heteromorph ammonites, in contrast to regularly coiled ammonites, which are called homomorph ammonites.

Cretaceous

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 the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

Ocean acidification

Ocean acidification

Ocean acidification is the decrease in the pH of the Earth’s ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide (CO2) levels exceeding 410 ppm (in 2020). CO2 from the atmosphere is absorbed by the oceans. This produces carbonic acid (H2CO3) which dissociates into a bicarbonate ion (HCO−3) and a hydrogen ion (H+). The presence of free hydrogen ions (H+) lowers the pH of the ocean, increasing acidity (this does not mean that seawater is acidic yet; it is still alkaline, with a pH higher than 8). Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.

Plankton

Plankton

Plankton are the diverse collection of organisms found in water that are unable to propel themselves against a current. The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish and whales.

Nautiloid

Nautiloid

Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living Nautilus and Allonautilus. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. They flourished during the early Paleozoic era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms (orthocones). Only a handful of rare coiled species, the nautiluses, survive to the present day.

Nautilus

Nautilus

The nautilus is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.

Bolide

Bolide

A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a synonym for a fireball, sometimes specific to those with an apparent magnitude of −14 or brighter.

Paleocene

Paleocene

The Paleocene, or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek παλαιός palaiós meaning "old" and the Eocene Epoch, translating to "the old part of the Eocene".

Cultural significance

In medieval Europe, fossilised ammonites were thought to be petrified coiled snakes, and were called "snakestones" or, more commonly in medieval England, "serpentstones". They were considered to be evidence for the actions of saints, such as Hilda of Whitby, a myth referenced in Sir Walter Scott's Marmion,[27] and Saint Patrick, and were held to have healing or oracular powers. Traders would occasionally carve the head of a snake onto the empty, wide end of the ammonite fossil, and then sell them as petrified snakes. In other cases, the snake's head would be simply painted on.[28][29]

Ammonites from the Gandaki River in Nepal are known as saligrams, and are believed by Hindus to be a concrete manifestation of Vishnu.[30]

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Hilda of Whitby

Hilda of Whitby

Hilda of Whitby was a Christian saint and the founding abbess of the monastery at Whitby, which was chosen as the venue for the Synod of Whitby in 664. An important figure in the Christianisation of Anglo-Saxon England, she was abbess at several monasteries and recognised for the wisdom that drew kings to her for advice.

Walter Scott

Walter Scott

Sir Walter Scott, 1st Baronet, was a Scottish historian, novelist, poet, and playwright. Many of his works remain classics of European and Scottish literature, notably the novels Ivanhoe (1819), Rob Roy (1817), Waverley (1814), Old Mortality (1816), The Heart of Mid-Lothian (1818), and The Bride of Lammermoor (1819), along with the narrative poems Marmion (1808) and The Lady of the Lake (1810). He had a major impact on European and American literature.

Marmion (poem)

Marmion (poem)

Marmion: A Tale of Flodden Field is a historical romance in verse of 16th-century Scotland and England by Sir Walter Scott, published in 1808. Consisting of six cantos, each with an introductory epistle, and copious antiquarian notes, it concludes with the Battle of Flodden in 1513.

Saint Patrick

Saint Patrick

Saint Patrick was a fifth-century Romano-British Christian missionary and bishop in Ireland. Known as the "Apostle of Ireland", he is the primary patron saint of Ireland, the other patron saints being Brigid of Kildare and Columba. Patrick was never formally canonised, having lived before the current laws of the Catholic Church in these matters. Nevertheless, he is venerated as a saint in the Catholic Church, the Lutheran Church, the Church of Ireland, and in the Eastern Orthodox Church, where he is regarded as equal-to-the-apostles and Enlightener of Ireland.

Divination

Divination

Divination is the attempt to gain insight into a question or situation by way of an occultic, standardized process or ritual. Used in various forms throughout history, diviners ascertain their interpretations of how a querent should proceed by reading signs, events, or omens, or through alleged contact or interaction with a supernatural agency.

Gandaki River

Gandaki River

The Gandaki River, also known as the Narayani and the Gandak, is one of the major rivers in Nepal and a left bank tributary of the Ganges in India. Its total catchment area amounts to 46,300 km2 (17,900 sq mi), most of it in Nepal. In the Nepal Himalayas, it is notable for its deep canyon. The basin also contains three mountains over 8,000 m (26,000 ft), namely Dhaulagiri, Manaslu and Annapurna I. Dhaulagiri is the highest point of the Gandaki basin.

Nepal

Nepal

Nepal, officially the Federal Democratic Republic of Nepal, is a landlocked country in South Asia. It is mainly situated in the Himalayas, but also includes parts of the Indo-Gangetic Plain, bordering the Tibet Autonomous Region of China to the north, and India in the south, east, and west, while it is narrowly separated from Bangladesh by the Siliguri Corridor, and from Bhutan by the Indian state of Sikkim. Nepal has a diverse geography, including fertile plains, subalpine forested hills, and eight of the world's ten tallest mountains, including Mount Everest, the highest point on Earth. Nepal is a multi-ethnic, multi-lingual, multi-religious and multi-cultural state, with Nepali as the official language. Kathmandu is the nation's capital and the largest city.

Vishnu

Vishnu

Vishnu, also known as Narayana and Hari, is one of the principal deities of Hinduism. He is the supreme being within Vaishnavism, one of the major traditions within contemporary Hinduism.

Source: "Ammonoidea", Wikipedia, Wikimedia Foundation, (2023, March 16th), https://en.wikipedia.org/wiki/Ammonoidea.

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See also
References
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