''Acanthodiscus'' is an extinct

ammonoid 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 cuttlefi ...

cephalopod genus from the order

Ammonitida Ammonitida is an order of ammonoid cephalopods that lived from the Jurassic through Paleocene time periods, commonly with intricate ammonitic sutures. Ammonitida is divided into four suborders, the Phylloceratina, Lytoceratina, Ancylocerati ...

and included in the persphinctacean family

Berriasellidae Berriasellinae is a subfamily of very late Jurassic and very early Cretaceous perisphinctoid ammonites in the family Neocomitidae. Berriasellinae comprises generally compressed, evolute genera, typically with furcated ribbing, and in some a smo ...

. The type species, named by Bruguière, 1792, is ''Acanthodiscus radiatus''.''Acanthodiscus''
at

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.org

Description

The shell of ''Acanthodiscus'' (''A. radiatus'') is of modest size, slightly more than in diameter, coiled with the outer whorl covering about a third of the next inner whorl. The lower (2/3) flanks bear strong, wide spaced, radial ribs with large nodes at either end, and become weaker on the mature body chamber. Outer flanks (approx. 1/3) slope toward a narrow, flat to concave venter lined on either side by a series of smaller nodes. the mature whorl section is higher than wide.

Biostratigraphic significance

''Acanthodiscus'' is found in shallow water sediments in both the Tethyan and

Boreal Boreal may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a climate characterized by long winters and short, cool to mild ...

realms where it is used as an

index fossil 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.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Bio ...

. In fact, the

International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...

(ICS) has assigned the

First Appearance Datum First appearance datum (FAD) is a term used by geologists and paleontologists to designate the first appearance of a species in the geologic record. FADs are determined by identifying the geologically oldest fossil discovered, to date, of a part ...

of ''Acanthodiscus radiatus'', the first species of the genus, as the defining biological marker for the start of the

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by t ...

stage of the

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 ...

, ~132.9 million years ago.

Species

* ''A. radiatus'' ; type species * ''A. octagonus'' * ''A. ottmeri'' * ''A. rollieri'' * ''A. schmidtii''; Found on the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

* ''A. subradiatus''

Distribution

''Acanthodiscus'' fossils can be found in the Agrio Formation of the

Neuquén Basin Neuquén Basin ( es, Cuenca Neuquina) is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The ba ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

. Also in the Macanal Formation of the

Eastern Ranges The Eastern Ranges is an Australian rules football team in the NAB League, the Victorian statewide under-18s competition. The club is a founding member of the competition (1992) and has produced several players for the Australian Football Le ...

of the Colombian

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

, fossils of ''Acanthodiscus'' have been found.Piraquive ''et al.'', 2011, p.204 Other occurrences of the genus are in: * Abundancia Formation, Chile * Guchuochun Formation, China * Kaliste Formation, the Czech Republic * France * Giumal Sandstone Formation, India * Chia Gara Formation, Iraq *

Sardinia Sardinia ( ; it, Sardegna, label= Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label= Algherese and Catalan) is the second-largest island in the Mediterranean Sea, af ...

, Italy *

Sabinal Formation Sabinal may refer to: * Cayo Sabinal, island in Cuba * Rio Sabinal Group Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for "river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or R ...

and Barril Viejo Shale Member, Mexico * Myrtle Formation, Oregon, United States

References

Bibliography

External links

Acanthodiscus-Paleodb

in French * T. Birkelund, et al.: Cretaceous Stage Boundaries - Proposals. Bulletin of the Geological Society of Denmark, vol. 33 198

Ammonitida genera Prehistoric cephalopod genera Index fossils Ammonites of Asia Cretaceous China Fossils of China Cretaceous India Fossils of India Fossils of Iraq Ammonites of Europe Fossils of the Czech Republic Cretaceous France Fossils of France Cretaceous Italy Fossils of Italy Ammonites of North America Cretaceous Mexico Fossils of Mexico Fossils of the United States Ammonites of South America Cretaceous Argentina Fossils of Argentina Cretaceous Chile Fossils of Chile Cretaceous Colombia Fossils of Colombia Extinct animals of Antarctica Fossil taxa described in 1792 Fossil taxa described in 1905 Perisphinctoidea {{Ammonitida-stub