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Ammonitida
Fossil range: 200–65.5 Ma
Early Jurassic – Late Cretaceous
Artist's reconstruction of Asteroceras
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Hyatt, 1889
Suborders

Ammonites, as they pertain specifically to the order Ammonitida, are an extinct group of marine animals belonging to the cephalopod subclass Ammonoidea. 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.

The closest living relative of the Ammonitida, is not the modern Nautilus which they somewhat outwardly resemble, but rather the subclass Coleoidea (octopus, squid, and cuttlefish).[citation needed]

Their fossil shells usually take the form of planispirals, although there were some helically-spiraled and non-spiraled forms (known as "heteromorphs"). Their name came from their spiral shape as their fossilized shells somewhat resemble tightly-coiled rams' horns. Pliny the Elder (d. 79 A.D. near Pompeii) called fossils of these animals ammonis cornua ("horns of Ammon") because the Egyptian god Ammon (Amun) was typically depicted wearing ram's horns.[1] Often the name of an ammonite genus ends in -ceras, which is Greek (κέρας) for "horn" (for instance, Pleuroceras).

Contents

Classification

Suborders

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.

Four suborders have been named for the Ammonitida.

  • Phylloceratina (Lower Triassic to Upper Cretaceous)
  • Ammonitina (Lower Jurassic to Upper Cretaceous) includes the true ammonites
  • Lytoceratina (Lower Jurassic to Upper Cretaceous)
  • Ancyloceratina (Upper Jurassic to Upper Cretaceous) the heteromorph ammonites

Taxonomy of the Treatise

The Treatise on Invertebrate Paleontology (1964) includes the Ammonitina, Lytoceratina, and Phylloceratina as separate suborders within the subclass Ammonoidea, without the use of orders, and divides them into superfamilies. In other, subsequent taxonomies the Ammonitina, Lytoceratina, and Phylloceratina are placed within the order, Ammonitida. The Ancyloceratina which is sometimes treated as a separate suborder is treated as a superfamily, the Ancylocerataceae in the Lytoceratina in the Treatise.

According to the Treatise, the Ammonitina are derived from the Phyllocerarina and Lytoceratina beginning in the Early Jurassic with the Psilocerataceae and ending with nine superfamilies, although not all extant at the same time. These are the Acanthocerataceae, Desmocerataceae, Eoderocerataceae, Haploceratacea, Hildocerataceae, Hoplitaceae, Perispinctaceae, Psilocerataceae, and Stephanocerataceae.

The Eoderocerataceae, Hildocerataceae, Psilocerataceae, and Stephanocerataceae are strictly Jurassic groups. The Acanthocerataceae, Desmocerataceae, and Hoplitaceae are known only from the Cretaceous. But the Haplocerataceae and Peripinctaceae extend from the Jurassic well into the Cretaceous.

Life

Jeletzkytes, a Cretaceous ammonite from the USA
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. This is suggested by the fact that their fossils are often found in rocks that were 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. Ammonites and their kin probably preyed on fish, crustaceans and other small creatures, while they themselves were preyed upon by such marine reptiles as mosasaurs. Fossilized ammonoids have been found showing teeth marks from such attacks. They may have avoided predation by squirting ink, much like modern cephalopods; ink is occasionally preserved in fossil specimens.[2]

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.[3]

Shell anatomy and diversity

Basic shell anatomy

A variety of ammonite forms, from Ernst Haeckel's 1904 Kunstformen der Natur (Artforms of Nature).

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 at any given moment. 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 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 that 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

Ammonite species, Jurassic period

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 (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.

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 ammonite species feature a shell that is a planispiral flat coil, but other species feature a shell that is nearly strght (as in baculites). Still other species' shells are coiled helically, superficially like that of a large gastropod (as in 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 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 (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 named "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 it was assumed that these plates served to close the opening of the shell in much the same way as an operculum, however more recently it has been postulated that they were instead a jaw apparatus.[citation needed]

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 symmetrical 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 an ammonite. What exact function they serve is however not certain. One long-standing and widespread interpretation of them as a form of operculum has more recently been contested. The latest studies suggest that the anaptychus may have in fact formed part of a special jaw apparatus[citation needed]).

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 many aptychi belong. 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.

Soft parts

Although ammonites do occur in exceptional lagerstatten such as the Solnhoffen, their soft part record is surprisingly bleak - beyond a tentative ink sac and possible digestive organs, no soft parts are known at all.[4] It can be tentatively assumed that they had numerous tentacles, each quite weak, and engulfed prey almost whole.[4]

Size

2-metre (6.5-foot) Parapuzosia seppenradensis cast in Germany

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 Parapuzosia seppenradensis of the Cretaceous period of Germany, which is one of the largest known ammonites, sometimes reaching 2 metres (6.5 feet) in diameter. The largest documented North American ammonite is Parapuzosia bradyi from the Cretaceous with specimens measuring 137 centimetres (4.5 feet) in diameter, although a new 2.3-metre (7.5-foot) British Columbian specimen, if authentic, would appear to trump even the European champion.[5]

Distribution

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

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 is called a concretion and 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.

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.

Ammonite fossils became less abundant during the latter part of the Mesozoic, with none surviving into the Cenozoic era. The last surviving lines disappeared along with the dinosaurs 65 million years ago in the Cretaceous-Tertiary extinction event. That no ammonites survived the extinction event at the end of the Cretaceous, while some nautiloid cousins survived, might be due to differences in ontogeny. If their extinction was due to a bolide strike, plankton around the globe could have been severely diminished, thereby dooming ammonite reproduction during its planktonic stage.

Mythology

In medieval Europe, fossilised ammonites were thought to be petrified snakes, and were called "snakestones" or, more commonly in medieval England, "serpentstones". They were taken to be evidence for the actions of saints such as Saint Hilda and Saint Patrick. Traders would occasionally carve the face of a snake into the empty, wide end of the ammonite fossil and sell them to the public. Ammonites from the Gandaki river in Nepal are known as saligrams, and are believed by Hindus to be a concrete manifestation of God or Vishnu.[6]

Terminological note

The words "ammonite" and "ammonoid" are both used quite loosely in common parlance to refer to any member of subclass Ammonoidea. However, in stricter usage the term "ammonite" is reserved for members of suborder Ammonitina (or sometimes even order Ammonitida).

See also


References and further reading

  1. ^ NH 37.40.167
  2. ^ Doguzhaeva, Larisa A.; Royal H. Mapes; Herbert Summesberger; and Harry Mutvei (2007). "The Preservation of Body Tissues, Shell, and Mandibles in the Ceratitid Ammonoid Austrotrachyceras (Late Triassic), Austria". in N.H.Landman et al.. Cephalopods Present and Past: New Insights and Fresh Perspectives. Dordrecht: Springer. pp. 221–238. doi:10.1007/978-1-4020-6806-5_11. ISBN 978-1-4020-6806-5.  edit
  3. ^ "Introduction to Ammonoidea". The Geology of Portsdown Hill. http://www.bbm.me.uk/portsdown/PH_232_Ammonites.htm. Retrieved 2007-04-26. 
  4. ^ a b Wippich, M. G. E. (2004). "Allocrioceras from the Cenomanian (mid-Cretaceous) of the Lebanon and its bearing on the palaeobiological interpretation of heteromorphic ammonites". Palaeontology 47: 1093–1107. doi:10.1111/j.0031-0239.2004.00408.x.  edit
  5. ^ "Ammonites". Hanman's Fossil Replicas and Minerals. http://web.archive.org/web/20030210130400/http://www.hanmansfossils.com/catalogs/fossils/ammonites/ammonites.shtml. 
  6. ^ "Fossils: myths, mystery, and magic". The Independent. http://news.independent.co.uk/sci_tech/article2259490.ece. 

External links


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also ammonite

English

Proper noun

Singular
Ammonite

Plural
Ammonites

Ammonite (plural Ammonites)

  1. Extinct Canaanite language of the Ammonite people who used to live in modern-day northwest Jordan, and after whom its capital Amman is named. Extinct since 5th century BCE.

Bible wiki

Up to date as of January 23, 2010

From BibleWiki

the usual name of the descendants of Ammon, the son of Lot (Gen 19:38). From the very beginning (Deut 2:16-20) of their history till they are lost sight of (Jdg 5:2), this tribe is closely associated with the Moabites (Jdg 10:11; 2Chr 20:1; Zeph 2:8). Both of these tribes hired Balaam to curse Israel (Deut 23:4). The Ammonites were probably more of a predatory tribe, moving from place to place, while the Moabites were more settled. They inhabited the country east of the Jordan and north of Moab and the Dead Sea, from which they had expelled the Zamzummims or Zuzims (Deut 2:20; Gen 14:5). They are known as the Beni-ammi (Gen 19:38), Ammi or Ammon being worshipped as their chief god. They were of Semitic origin, and closely related to the Hebrews in blood and language. They showed no kindness to the Israelites when passing through their territory, and therefore they were prohibited from "entering the congregation of the Lord to the tenth generation" (Deut 23:3). They afterwards became hostile to Israel (Jdg 3:13). Jephthah waged war against them, and "took twenty cities with a very great slaughter" (Jdg 11:33). They were again signally defeated by Saul (1Sam 11:11). David also defeated them and their allies the Syrians (2 Sam 10:6-14), and took their chief city, Rabbah, with much spoil (2 Sam 10:14; 12:26-31). The subsequent events of their history are noted in 2Chr 20:25; 26:8; Jer 49:1; Ezek 25:3, 6. One of Solomon's wives was Naamah, an Ammonite. She was the mother of Rehoboam (1 Kg 14:31; 2Chr 12:13).

The prophets predicted fearful judgments against the Ammonites because of their hostility to Israel (Zeph 2:8; Jer 49:1-6; Ezek 25:1-5, 10; Amos 1:13-15).

The national idol worshipped by this people was Molech or Milcom, at whose altar they offered human sacrifices (1 Kg 11:5, 7). The high places built for this idol by Solomon, at the instigation of his Ammonitish wives, were not destroyed till the time of Josiah (2Kg 23:13).

This entry includes text from Easton's Bible Dictionary, 1897.

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The Ammonites were a race very closely allied to the Hebrews. One use of their name itself in the Bible indicates the ancient Hebrew belief of this near relationship, for they are called Bén`ámmî or "Son of my people", meaning that that race is regarded as descended from Israel's nearest relative. This play of words on the name Ammon did not arise from the name itself, but presupposes the belief in the kinship of Israel and Ammon. The name Ammon itself cannot be accepted as proof of this belief, for it is obscure in origin, derived perhaps from the name of a tribal deity. A strong proof of their common origin is found in the Ammonite language. No Ammonite inscription, it is true, has come down to us, but the Ammonite names that have been preserved belong to a dialect very nearly akin to the Hebrew; moreover, the close blood relationship of Moab and Ammon being admitted by all, the language of the Moabite Stone, almost Hebrew in form, is a strong witness to the racial affinity of Israel and Ammon. This linguistic argument vindicates the belief that Israel always entertained of his kinship with the Ammonites. The belief itself has found expression in an unmistakable manner in Gen. xix, where the origin of Ammon and his brother, Moab, is ascribed to Lot, the nephew of Abraham. This revolting narrative has usually been considered to give literal fact, but of late years it has been interpreted, e.g. by Father Lagrange, O.P., as recording a gross popular irony by which the Israelites expressed their loathing of the corrupt morals of the Moabites and Ammonites. It may be doubted, however, that such an irony would be directed against Lot himself. Other scholars see in the very depravity of these peoples a proof of the reality of the Biblical story of their incestuous origin. Ethnologists, interpreting the origin from the nephew of Abraham by the canons usually found true in their science, hold it as indicating that the Israelites are considered the older and more powerful tribe, while the Ammonites and Moabites are regarded as offshoots of the parent stem. The character of Genesis, which at times seems to preserve popular traditions rather than exact ethnology, is taken as a confirmation of this position. But it is not denied, at any rate, that the Hebrew tradition of the near kinship of Israel, Ammon, and Moab is correct. All three, forming together a single group, are classified as belonging to the Aramæan branch of the Semitic race.

THEIR COUNTRY AND CIVILIZATION

The Ammonites were settled to the east of the Jordan, their territory originally comprising all from the Jordan to the wilderness, and from the River Jabbok south to the River Arnon (Jud., xi, 13-22) which later fell to the lot of Reuben and Gad. "It was accounted a land of giants; and giants formerly dwelt in it, whom the Ammonites called Zomzommims" (Deut, ii, 20), of whom was Og, King of Basan, who perished before the children of Israel in the days of Moses (iii). The Ammonites were, however, a short time before the invasion of the Hebrews under Josue, driven away by the Amorites from the rich lands near the Jordan and retreated to the mountains and valleys which form the eastern part of the district now known as El­Belka. They still continued to regard their original territory as rightfully theirs, and in later times regained it and held it for a considerable period. Their land, in general, while not very fertile, was well watered and excellent for pasture. Jeremiah speaks of Ammon glorying in her valleys and trusting in her treasures (Jer., xlix). Her chief city, Rabbath, or Rabbath­Ammon, to distinguish it from a city of the same name in Moab, lay in the midst of a fertile and well tilled valley. It was the royal city; in the time of David it was flourishing under a wealthy king and was well fortified, though it succumbed before the attack of Joab, his general (II K., xi-xii). Later rebuilt by Ptolemy II (Philadelphus) and called after him Philadelphia, it still retains something of its original name, being knows at present to the Arabs as Ammân. Its ruins to­day are among the most imposing beyond the Jordan, and are said, despite the many vicissitudes of the city, to lend light and vividness to the already vivid narrative of Joab's assault. The Ammonites had many other cities besides Rabbath (see Jud., xi, 33, and II K., xii, 31), but their names have perished. They indicate, at least, a considerable degree of civilization and show that the Ammonites should not be placed, as is sometimes done, almost on the plane of nomads. In religion they practised the idolatries and abominations common to the Semitic races surrounding Israel; their god was called Milcom, supposed to be another form of Moloch. They seem with the Moabites to have been held in special loathing by the Hebrews. No man of either race, even when converted to the religion of Jehovah, was allowed to enter the Tabernacle; nor his children even after the tenth generation (Deut., xxiii).

AMMON AND ISRAEL

This distinction against his nearest relatives was due to the treatment accorded by them to Israel during the march to Palestine, when Israel was struggling towards nationhood. The Hebrews had no intention of taking the land of the children of Lot, either of Moab or of Ammon and were expressly warned against it; this special friendliness and recognition of consanguinity obtained no return from either, who refused provisions to the Israelites and hired Balaam, who was an Ammonite, or at least dwelt among the Ammonites, to curse the host of Israel; though, as is well known, Balaam was forced to deliver instead a blessing (Deut., xxiii, 4, 5; Num. xxii-xxiv). For this lack of brotherly spirit, the ban was put upon the Ammonites; but no attempt was made to seize their land, the Israelites turning aside when they reached the border of the Ammonites. The stretch of land along the Jordan, however, to which they laid claim, was taken from the Amorites who had dispossessed them. Half the land of Ammon, too, is said to have been assigned by Moses to the tribe of Gad (Jos. xiii, 25); but there is no record of its alienation from the Ammonites, which moreover would be in contradiction with the divine command already mentioned. It appears to have been territory from which they were already driven. Shortly after the death of Josue, when the Israelites were established beyond the Jordan, the Ammonites allied themselves with the Moabites under King Eglon in a successful attack upon Israel; but the Moabites were in turn defeated and a long peace set in (Jud. iii, 30). Later, after the judgeship of Jair, the Hebrews were simultaneously attacked by the Philistines from the southwest and the Ammonites from the east. Gad especially, whose dwelling was east of the Jordan, suffered from the incursions of the Ammonites which continued eighteen years; but the victorious enemy pushed beyond the Jordan and laid waste the country of Juda, Benjamin, and Ephraim (Jud., x). At this crisis, Israel was in terror; but a deliverer was raised up in the person of Jephte, who was chosen leader. The Ammonites demanded the cession of the territory beyond the Jordan from the Arnon to the Jabbok, of which they had been dispossessed; but Jephte refused since the Israelites had, three hundred years previously, taken the land from the Amorites and not from the Ammonites; he boldly carried the war into the invaders' country, and completely defeated them, taking as many as twenty cities (Jud., xi, 33). By the time of Saul, the Ammonites had again grown to great power and under their King Naas (Nahash) had laid siege to Jabes Galaad. Saul had been chosen king by Samuel only one month before and his election was not yet ratified by the people; but as soon as he heard of the siege, he summoned a large army and defeated the Ammonites, inflicting heavy loss (I K., xi). This victory established him in the monarchy. Further operations by Saul against the Ammonites are mentioned without detail (xiv, 47), as likewise the kindness of Naas to David (II K., x, 2), probably before his accession. David signalized the beginning of his reign by military exploits and is said to have dedicated to the Lord the spoils of Ammon (viii, 11); however, there is no mention of a war, which seems inconsistent with the friendliness of David to Hanon, the successor of Naas (x, 2). David's proffer of friendship to Ammon was suspected and rejected and his ambassadors maltreated. War ensued. The Ammonites were joined by the Syrians, and both were attacked and routed by Joab, David's leading general. The next year Joab again invaded the territory of the Ammonites and, pursuing them as far as Rabbath, laid siege to the royal city. It was during this siege that the incident of David and Bethsabee happened, which resulted in David sending the faithful Urias to his death at Rabbath and incurring the deepest stain upon his character. When Joab had reduced the city to the point of surrender, he sent for David who came and reaped the glory of it, transferred the king's massive crown to his own head, sacked the city and slaughtered its inhabitants; and did likewise to all the cities of the Ammonites (x-xii). The power of the Ammonites was now broken, Ammon apparently becoming a vassal of Israel; later, towards the end of David's reign, another son of King Naas, either through lack of spirit or genuine humanity, heaped kindness upon David, when the distressed old king was at war with his son Absalom (xvii). Some of the Ammonites seem to have enrolled themselves in David's service; one is mentioned among his thirty­seven most valiant warriors (xxiii, 37). No hostilities are narrated during the reign of Solomon; he chose Ammonite women as his wives, worshipped their god and built a high­place in his honour (III K., xi), which Josias destroyed (IV K., xxiii, 13). When Solomon died and his kingdom was divided, the Ammonites regained their independence and allied themselves with the Assyrians, joining with them in an attack on Gilead by which their territory was increased. Their barbarous cruelty on this occasion called forth the denunciation of Amos, who foretold the destruction of Rabbath (Amos, i, 13). During the Assyrian invasion under Theglathphalasar, when their neighbours, the Reubenites and the Gaddites, were carried into captivity, they regained some of their old territory along the Jordan (IV K., xv, 29; Jer. xlix, 1-6). In the time of Josaphath, King of Judah, when the Israelites were greatly weakened, the Ammonites put themselves at the head of a confederacy of nations for the subjugation of Israel; but suspicion awakening among the allies, they turned to destroying one another and Israel miraculously escaped (II Par., xx, 23). After nearly one hundred and fifty years, Joatham, King of Judah, ventured an attack upon the Ammonites, conquering them and subjecting them to a yearly tribute (II Par., xxvii), which, however, was enforced for only three years. But the doom of the Hebrew monarchy was approaching and the Ammonites had a part to play. With others of the surrounding nations, they were employed by Nabuchodonosor, King of Babylon, to overrun the kingdom of Judah (IV K., xxiv); and when the fall finally came, it was the king of the Ammonites who sent assassins into Judea to murder the governor who had gathered together the remnant of Judah (IV K., xxv; Jer., xl, 14). After the return the old hatred is still seen to live (II Esd., iv). In the time of Judas Maccabeus, the Ammonites are still a strong people, and the great leader had to fight many battles before he conquered them (I Mach., v). No further mention of them occurs in biblical times; Justin Martyr refers to them as a numerous people in his day, but in the course of the next century they vanish completely from the view of history.

Portions of this entry are taken from The Catholic Encyclopedia, 1907.

Simple English

Ammonoidea
Fossil range: Devonian - Cretaceous
File:Asteroceras
Asteroceras
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Zittel, 1884
Orders

Anarcestida; Clymeniida; Goniatitida; Prolecanitida; Ceratitida; Phylloceratida; Lytoceratida; Ammonitida; Ancyloceratina

File:Vitoria - Museo Ciencias
Showing some of the variety of ammonite body shapes.

Ammonites[1] were marine cephalopod molluscs of the subclass Ammonoidea.

Their widely-known fossils show a ribbed spiral-form shell, in the end compartment of which lived the tentacled animal. These creatures lived in the seas from at least 400 to 65 million years ago. They became extinct at the K/T extinction event. Their nearest living relatives are the octopus, squid, cuttlefish and Nautilus.

Nine orders are recognised in the Ammonoidea: five in the Palaeozoic and four in the Mesozoic.

Evolution

Ammonites first appeared in the early Devonian period. They evolved from a small, straight shelled Bactridian, which was an early Nautiloid. They quickly evolved into a variety of shapes and sizes, including some shaped like hairpins. During their evolution the ammonites faced no fewer than four catastrophic events that would eventually lead to their extinction. The first event occurred in the Upper Devonian, and the second at the end of the Permian (250 million years ago), when only two lines survived the P/Tr extinction event. The surviving species radiated and flourished throughout the Triassic perod. At the end of this period (206 million years ago) they faced near extinction again, when only one genus survived. This event marked the end of the Triassic and the beginning of the Jurassic, during which time the number of ammonite species grew once more. The final catastrophe occurred at the end of the Cretaceous period when all species were annihilated and the ammonites became extinct.

The young ammonites lived in the plankton, near the sea surface. They ate mostly small fry as they were growing. This made them especially vulnerable to any event which upset the plankton zone.

Life

Ammonites began life as tiny planktonic creatures less than 1mm in diameter. In their infancy they would have been vulnerable to attack from other predators, including mosasaurs and fish. However, their shell gave their soft parts some protection. The existence of sexual dimorphism, with larger females and smaller males, has been much discussed.[2]p244 The matter is still open, but at least in some species deposits are found with two sizes and no intermediates.

As the shell grew, the back compartments were sealed with a semi-permeable membrane. A single tube, the siphuncle, passed through the centre of each septum and connected the chambers The animal could add or withdraw gas as it needed for buoyancy. On the inside of the shell, the compartments are marked by elaborate sutures. These can be seen easily on those fossils which are internal moulds, as most are.[2]p241 Ammonites were active predators, and they themselves were often eaten by fish and marine reptiles. The fossils are almost always found with the outer compartment broken off, probably as a result of just such an attack.

Ammonoid shells are always thinner than the shells of Nautilus, and their siphuncles were usually ventral. They swam by jet propulsion, as do most other cepalopods. Water would have come into the mantle cavity, passed over the gills, and was squirted out. Nautilus also has an escape mechanism, where a contraction of the branchial (gill) chamber causes the animal to jump out of the way of a predator.[2]p232 It would be reasonable to suppose that ammonites had a similar mechanism.

References

  1. meaning 'ram-horned', from the Egyptian god Amun.
  2. 2.0 2.1 2.2 Clarkson E.N.K. Invertebrate palaeontology and evolution. Blackwell, Oxford.
Look up Ammonoidea in Wikispecies, a directory of species








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