''Paleopsephurus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

paddlefish 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 elongated rost ...

(Polyodontidae). At present the genus contains the single species ''Paleopsephurus wilsoni''. The genus is known 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 ...

(

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 ...

) 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 (stratigraphy), formation s ...

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

History and classification

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

University of Michigan The University of Michigan (U-M, U of M, or Michigan) is a public university, public research university in Ann Arbor, Michigan, United States. Founded in 1817, it is the oldest institution of higher education in the state. The University of Mi ...

Museum of Paleontology in

Ann Arbor, Michigan Ann Arbor is a city in Washtenaw County, Michigan, United States, and its county seat. The 2020 United States census, 2020 census recorded its population to be 123,851, making it the List of municipalities in Michigan, fifth-most populous cit ...

, USA. Specimen number '' 22206 U.M.'' is a complete and well preserved

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

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 o ...

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 Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into th ...

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 Fort Peck is a town in Valley County, Montana, United States. The population was 239 at the 2020 census. History The name Fort Peck is associated with Col. Campbell K. Peck, the partner of Elias H. Durfee in the Leavenworth, Kansas trading fir ...

by a University of Michigan Museum of Paleontology expedition in 1938. the fossils were in close association with the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen of the extinct

sturgeon Sturgeon (from Old English ultimately from Proto-Indo-European language, Proto-Indo-European *''str̥(Hx)yón''-) is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the ...

'' Protoscaphirhynchus squamosus''. The ''Paleopsephurus'' specimens were first studied by American

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

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, 35,800 species of fish had been described as of March 2 ...

Archie Justus MacAlpin. He published his detailed 1947

type description A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differ ...

in the journal ''Contributions from the Museum of Paleontology, University of Michigan''.

Description

The skull is about long, suggesting a total body length of about . The skull roof is poorly preserved. The stellate bones are loosely packed and more poorly developed compared to the ones in ''

Crossopholis ''Crossopholis'' is an extinct 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 Polyodontidae. Hi ...

'' or ''

Polyodon 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 elongated rost ...

,'' but are similar to those of '' Psephurus''.

Ecology

Like other non-''Polyodon'' paddlefish, ''Paleopsephurus'' was likely piscivorous.

Phylogeny

''Paleopsephurus'' exhibits a combination of characters which suggests that it is more derived than ''

Protopsephurus ''Protopsephurus'' is an extinct genus of paddlefish containing the single species ''Protopsephurus liui,'' known from the Yixian, Jiufotang and Huajiying formations in Liaoning, northern China from the Barremian to Aptian ages of the Early Cr ...

'', but is more basal than ''Crossopholis'', ''Polyodon'', or ''Psephurus''. Relationships of the genera, after Grande et al. (2002).

References

Polyodontidae Monotypic prehistoric 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