Ancyloceratina
Encyclopedia
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 become 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 fossil
s. 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.
In the more primitive forms, the shell departs only slightly from being a perfect spiral, with only the last, outermost whorl being open, forming a hook underneath the main spiral. In such forms the spiral was the chambered, buoyant
part of the shell, and the hook was the living chamber in which the soft body of the ammonite resided. Examples of such types were Ancyloceras
, Protanisoceras, and Tropaeum
. The more advanced heteromorphs departed from such forms radically. The shells of Ptychoceras consisted of three or four shafts squashed together and connected with tight, 180 degree bends. Members of the genus Hamites
were much larger but had a similar sort of shape, though the shafts were open so that the whole thing looked rather like a big paper clip
.
The Late Cretaceous enjoyed the widest variety of heteromorphs, including the straight-shelled Baculites and Sciponoceras; the helically coiled Turrilites
; and the bizarre Nipponites
, which looked more like a ball of string than anything else. Some forms combined different coiling modes. For example, Nostoceras
started off with a helix like a Turrilites, but had a planar hook hanging underneath, more like an Ancyloceras.
Not all the Ancyloceratina had such strangely shaped shells; many of the earlier heteromorph forms had regularly coiled shells barely distinguishable from the homomorph ammonites (for example, the Lower Cretaceous genus Deshayesites). Some offshoots of the uncoiled varieties even went back to being regularly coiled. Most notable among these were the Scaphites
, Hoploscaphites
and their relatives, which were mostly regular spirals in shape except for a very slight hook at the end.
The biology of the heteromorph ammonites is not clear, but one certainty is that their uncoiled shells would have made these forms very poor swimmers. Open shells, particularly ones with spines and ribs, create a lot of drag; but more importantly, the orientation of the shell, with the body hanging below the buoyant part of the shell, would have created a serious impediment to efficient swimming. It's more likely these ammonites either drifted in the plankton
, collecting small animals on long tentacle
s like modern jellyfish
, or else they crawled along the sea floor feeding on sessile or slow-moving animals such as clam
s.
Ancyloceratida varied widely in size, ranging from diminutive Ptychoceras, which was barely 3 cm long, to Baculites and Diplomoceras, which could grow to 1–2 m in length. Some species were very widely distributed, for example some species of Hamites can be found in Eurasia
, South America
, Australia
, and Antarctica. Others, like those inhabiting the Western Interior Seaway
that covered much of the US, were much more localized.
The thin shelled heteromorphic ammonites probably lived at depths 36-183 m.
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
most closely related to the ammonites of order Lytoceratina
Lytoceratina
Lytoceratina is a suborder of Jurassic and Cretaceous ammonites that produced loosely coiled, evolute and gyroconic shells in which the sutural element are said to have complex moss-like endings.-Morphologic characteristics:...
. They evolved during the Late Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
but were not very common until the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period, when they rapidly diversified and become 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 fossil
Index fossil
Index fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...
s. 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.
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
part of the shell, and the hook was the living chamber in which the soft body of the ammonite resided. Examples of such types were Ancyloceras
Ancyloceras
Ancyloceras is an extinct genus of heteromorph ammonite cephalopod found throughout the world during the Lower Cretaceous, from the Lower Barremian epoch until the genus' extinction during the Lower Aptian....
, Protanisoceras, and Tropaeum
Tropaeum
Tropaeum is an extinct genus of ammonite cephalopod found throughout the oceans of the world during the Early Cretaceous. As with many other members of the family Ancyloceratidae, there was a trend among species within this genus to uncoil somewhat, in a very similar manner in the genus...
. The more advanced heteromorphs departed from such forms radically. The shells of Ptychoceras consisted of three or four shafts squashed together and connected with tight, 180 degree bends. Members of the genus Hamites
Hamites
Hamites is a genus of heteromorph ammonite that evolved late in the Aptian stage of the Early Cretaceous and lasted into the Cenomanian stage of the Late Cretaceous. The genus is almost certainly paraphyletic but remains in wide use as a "catch all" for heteromorph ammonites of the superfamily...
were much larger but had a similar sort of shape, though the shafts were open so that the whole thing looked rather like a big paper clip
Paper Clip
"Paper Clip" is a 1995 episode of The X-Files television series. It was the second episode broadcast in the show's third season. Paper Clip concludes the story regarding the agents' possession of a digital tape containing government secrets on extraterrestrials.- Plot :Continuing from the previous...
.
The Late Cretaceous enjoyed the widest variety of heteromorphs, including the straight-shelled Baculites and Sciponoceras; the helically coiled Turrilites
Turrilites
Turrilites is a helically coiled ammonoid cephalopod from the lower part of the Upper Cretaceous ; generally included in the Ancyloceratina. Previously it was included in the ammonoid suborder, Lytoceratina....
; and the bizarre Nipponites
Nipponites
Nipponites is an extinct genus of heteromorph ammonites. The species of Nipponites are famous for the way their shells form "ox-bow" bends, resulting in some of the most bizarre shapes ever seen among ammonites.The ecology of Nipponites, as with many other nostoceratids, is subject to much...
, which looked more like a ball of string than anything else. Some forms combined different coiling modes. For example, Nostoceras
Nostoceras
Nostoceras is an extinct genus of ammonite from the Nostoceratidae family....
started off with a helix like a Turrilites, but had a planar hook hanging underneath, more like an Ancyloceras.
Not all the Ancyloceratina had such strangely shaped shells; many of the earlier heteromorph forms had regularly coiled shells barely distinguishable from the homomorph ammonites (for example, the Lower Cretaceous genus Deshayesites). Some offshoots of the uncoiled varieties even went back to being regularly coiled. Most notable among these were the Scaphites
Scaphites
Scaphites is a genus of extinct cephalopod belonging to the family of heteromorph ammonites . They were a widespread genus that thrived during the Cretaceous period....
, Hoploscaphites
Hoploscaphites
Hoploscaphites is an extinct genus of ammonite....
and their relatives, which were mostly regular spirals in shape except for a very slight hook at the end.
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
, collecting small animals on long tentacle
Tentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
s like modern jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
, or else they crawled along the sea floor feeding on sessile or slow-moving animals such as clam
Clam
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...
s.
Ancyloceratida varied widely in size, ranging from diminutive Ptychoceras, which was barely 3 cm long, to Baculites and Diplomoceras, which could grow to 1–2 m in length. Some species were very widely distributed, for example some species of Hamites can be found in Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
, South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, and Antarctica. Others, like those inhabiting the Western Interior Seaway
Western Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
that covered much of the US, were much more localized.
The thin shelled heteromorphic ammonites probably lived at depths 36-183 m.
Classification
Suborder Ancyloceratina- Superfamily AncylocerataceaeAncylocerataceaeThe Ancylocerataceae is a superfamily of typically uncoilded and loosely coilded ammonoids, presently comprising nine families, the Acrioceratidae Ancyloceratidae Crioceratitidae, Hemihoplitidae, Heteroceratidae, Himantoceratidae, Labeceratidae, Leptoceratoididae, and Ptychoceratidae .The...
- Family Ancyloceratidae
- Family Bochianitidae
- Family Heteroceratidae
- Family Hemihoplitidae
- Family Hamulinidae
- Family Labeceratidae
- Family Macroscaphitidae
- Family Ptychoceratidae
- Superfamily Deshayesitaceae
- Family Deshayesitidae
- Family ParahoplitidaeParahoplitidaeParahoplitidae is an extinct family of Cretaceous ammonites with stoutly ribbed, compressed, generally involute shells lacking or with only minor tubercles included in the Deshayestaceae, a superfamily now separated from the Hoplitacaceae-References:...
- Superfamily Douvilleicerataceae
- Family Astiericeratidae
- Family Douvilleiceratidae
- Family Trochleiceratidae
- Superfamily Scaphitaceae
- Family Hoploscaphitidae
- Family Scaphitidae
- Superfamily TurrilitaceaeTurrilitaceaeThe Turrilitacaeae is a diverse superfamily of Cretaceous ammonites generally considered as heteromorphic and commonly included in the suborder Ancyloceratina...
- Family AnisoceratidaeAnisoceratidaeAnisoceratidae is an extinct family of heteromorph ammonoid cephalopods.-Referenceas:*http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=96545&is_real_user=1...
- Family BaculitidaeBaculitidaeBaculitidae is a family of extinct ammonoid cephalopods that lived mostly during the Late Cretaceous, and often included in the suborder Ancyloceratina....
- Family Diplomoceratidae
- Family Hamitidae
- Family NostoceratidaeNostoceratidaeFamily Nostoceratidae was a diverse group of heteromorph ammonites found throughout the oceans of the world during the Late Cretaceous. The nostoceratids are famous for the bizarre coiling of their shells...
- Family TurrilitidaeTurrilitidaeTurrilitidae is a family of extinct heteromorph ammonite cephalopods. All members had shells that coiled helically that tended to resemble auger shells....
- Family Anisoceratidae
Timescale
| Por. | Ber. | Val. | Hau. | Bar. | Apt. | Alb. | Cen. | Tur. | Con. | San. | Cam. | Maa. | |
| Bochianitidae | |||||||||||||
| Ancyloceratidae | |||||||||||||
| Ptychoceratidae | |||||||||||||
| Heteroceratidae | |||||||||||||
| Hemihoplitidae | |||||||||||||
| Hamulinidae | |||||||||||||
| Douvilleiceratidae | |||||||||||||
| Asteiriceratidae | |||||||||||||
| Trochleiceratidae | |||||||||||||
| Deshayesitidae | |||||||||||||
| Parahoplitidae | |||||||||||||
| Hamitidae | |||||||||||||
| Anisoceratidae | |||||||||||||
| Labeceratidae | |||||||||||||
| Turrilitidae | |||||||||||||
| Diplomoceratidae | |||||||||||||
| Nostoceratidae | |||||||||||||
| Baculitidae | |||||||||||||
| Scaphitidae | |||||||||||||
| Macroscaphitidae |
Reference
- Pasch, A. D., K. C. May. 2001. Taphonomy and paleoenvironment of hadrosaur (Dinosauria) from the Matanuska Formation (Turonian) in South-Central Alaska. In: Mesozioc Vertebrate Life. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press. Pages 219-236.