''Pachydiscus'' is an extinct genus of

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

and

Early Paleocene The Danian is the oldest age (geology), age or lowest stage (stratigraphy), stage of the Paleocene Epoch or series (stratigraphy), Series, of the Paleogene Period or system (stratigraphy), System, and of the Cenozoic Era or Erathem. The beginnin ...

with a worldwide distribution, and

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

for the desmoceratacean family Pachydiscidae. The genus' type species is ''P. neubergicus''. Altogether some 28 species have been described. The shell of ''Pachydiscus'' is compressed and high-whorled, with an oval or flat sided section. Ribs tend to be differentiated into short umbilical and separate ventro-lateral sets, with a smooth area between. Some Hungarian specimens of this genus reached in diameter. ''Pachydiscus'' includes two subgenera, ''P. (Pachysiscus)'' from the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

in which the ribs persist, and ''P. (Neodesmoceras)'' from the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

in which ribs disappear early, leaving an almost smooth shell.

Biostratigraphic significance

The

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

(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 partic ...

of ''Pachydiscus neubergicus'' as the defining biological marker for the start of the

Maastrichtian Stage The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic E ...

of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

, 72.1 ± 0.2 million years ago.

Distribution

Fossils of ''Pachydiscus'' have been found in Antarctica, Australia, Austria, Belgium, Brazil, Canada (British Columbia), Chile, Denmark, France, Germany, Haiti, India, Iran, Japan, Mexico, the Netherlands, New Zealand, Nigeria, Oman, Romania, the Russian Federation, Poland, Saudi Arabia, South Africa, Spain, Turkey, Ukraine, the United Arab Emirates, and the United States (Alaska, Arkansas, California, Delaware, Mississippi, New Jersey, Oregon, Texas, Washington).''Pachydiscus''
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org

References

, Part L, Ammonoidea. R.C. Moore, ed. Geological Soc. of America and Univ. Kansas press. p L377-L380. * ''A Pictorial Guide to Fossils'' by Gerard Ramon Case * ''Cephalopods Present and Past: New Insights and Fresh Perspectives'' by Neil H. Landman, Richard Arnold Davis, and Royal H. Mapes * Kennedy, W. J. (1986). Campanian and Maastrichtian Ammonites from Northern Aquitaine, France (No. 36). Palaeontological association. page 30 Desmoceratoidea Ammonitida genera Campanian life Maastrichtian life Campanian genus first appearances Maastrichtian genus extinctions Cretaceous ammonites Index fossils Ammonites of Africa Cretaceous Africa Ammonites of Asia Cretaceous Asia Ammonites of Australia Cretaceous animals of Australia Late Cretaceous ammonites of Europe Cretaceous Europe Late Cretaceous ammonites of North America Cretaceous Canada Cretaceous Mexico Cretaceous United States Ammonites of South America Cretaceous Brazil Cretaceous Chile Cretaceous Caribbean Ammonites of Antarctica {{Ammonitina-stub

Biostratigraphic significance

Distribution

References

Further reading