''Palaeopsephurus'' is an extinct

genus Genus ( plural genera ) 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 n ...

of paddlefish in the

Acipenseriformes Acipenseriformes is an order of basal ray-finned fishes that includes living and fossil sturgeons and paddlefishes (Acipenseroidei), as well as the extinct families Chondrosteidae and Peipiaosteidae. They are the second earliest diver ...

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Polyodontidae Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their titular elongl ...

. At present the genus contains the single species ''Palaeopsephurus wilsoni''. The genus is known primarily from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...

(

Maastrichtian The Maastrichtian () is, in the 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 Era or Erathem. It spanned the interv ...

) aged

Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of ...

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

. ''Palaeopsephurus'' is one of two extinct paddlefish genera to have been found in the North American fossil record, with the other genus and species ''

Crossopholis magnicaudatus ''Crossopholis'' is an extinct bony fish known from the early Eocene (Ypresian) of North America, approximately 52 million years ago. It is a close relative of the contemporary American paddlefish, belonging to the paddlefish family. History of ...

'' having been described and found in the

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

Green River Formation The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine ...

. A third extinct genus ''

Protopsephurus ''Protopsephurus'' is an extinct genus of paddlefish containing the single species ''Protopsephurus liui,'' known from the Yixian Formation in Liaoning, northern China from the Barremian to Aptian ages of the Early Cretaceous period around 125- ...

'' with the single species '' Protopsephurus liui'' was described from China in 1994. Only two modern paddle fish species are known, '' Polyodon spathula'' in the

Mississippi River System The Mississippi River System, also referred to as the Western Rivers, is a mostly riverine network of the United States which includes the Mississippi River and connecting waterways. The Mississippi River is the largest drainage basin in the Unit ...

of North America, and the extinct '' Psephurus gladius'' in the

Yangtze River The Yangtze or Yangzi ( or ; ) is the longest river in Asia, the third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in the Tanggula Mountains (Tibetan Plateau) and flow ...

of China.

History and classification

The genus was described from three partial specimens currently residing in the collections of the

University of Michigan , mottoeng = "Arts, Knowledge, Truth" , former_names = Catholepistemiad, or University of Michigania (1817–1821) , budget = $10.3 billion (2021) , endowment = $17 billion (2021)As o ...

Museum of Paleontology A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make these ...

in Ann Arbor, Michigan, USA. Specimen number '' 22206 U.M.'' is a complete and well preserved

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

with some denticles,

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists ...

and pectoral fins. The second and third specimens were found in a block of matrix from the same location as ''2226 U.M.''. Specimen ''22207 U.M.'' is a portion of the caudal region of a paddlefish, while ''22208 U.M.'' is a partial shoulder with associated pectoral fin. While the specimens were found close to each other, it is impossible to determine if they represent a single individual, and as such were described as three separate fish specimens. The specimens were collected from a sandstone outcrop of the Hell Creek Formation southeast of Fort Peck, Montana by a University of Michigan Museum of Paleontology expedition in 1938. the fossils were in close association with the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

specimen of the extinct sturgeon '' Protoscaphirhynchus squamosus''. The ''Palaeopsephurus'' specimens were first studied by American

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

and

ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of October ...

Archie Justus MacAlpin Archie is a masculine given name, a diminutive of Archibald. It may refer to: People Given name or nickname *Archie Alexander (1888–1958), African-American mathematician, engineer and governor of the US Virgin Islands * Archie Blake (mathematici ...

. He published his detailed 1947

type description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have ...

in the journal ''

Contributions from the Museum of Paleontology, University of Michigan Contribution or Contribute may refer to: * ''Contribution'' (album), by Mica Paris (1990) ** "Contribution" (song), title song from the album *Contribution (law), an agreement between defendants in a suit to apportion liability *Contributions, a ...

''.

References

Polyodontidae Monotypic fish genera Prehistoric ray-finned fish genera Cretaceous bony fish Turonian genus first appearances Maastrichtian genus extinctions Late Cretaceous fish of North America Hell Creek fauna Fossil taxa described in 1947 {{Cretaceous-fish-stub