Paleopsephurus

Paleopsephurus is an extinctgenus of paddlefish (Polyodontidae).^[1] At present the genus contains the single species Paleopsephurus wilsoni. The genus is known from the Late Cretaceous (Maastrichtian) aged Hell Creek Formation of Montana.

The genus was described from three partial specimens currently residing in the collections of the University of MichiganMuseum of Paleontology in Ann Arbor, Michigan, USA.^[1] Specimen number 22206 U.M. is a complete and well preserved skull with some denticles, pectoral girdle and pectoral fins.^[1] 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.^[1] The specimens were collected from a sandstone outcrop of the Hell Creek Formation 24 miles (39 km) 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 specimen of the extinct sturgeonProtoscaphirhynchus squamosus.^[1]

The Paleopsephurus specimens were first studied by American paleontologist and ichthyologistArchie Justus MacAlpin. He published his detailed 1947 type description in the journal Contributions from the Museum of Paleontology, University of Michigan.^[1]

El cráneo holotipo mide aproximadamente 274 milímetros (10,8 pulgadas) de largo. Grande y Bemis (1991) estimaron que la longitud total habría sido de unos 56 centímetros (22 pulgadas) , ^{[ 2 ]} mientras que la descripción original de MacAplin sugería una longitud total de 65 centímetros (26 pulgadas) . ^{[ 1 ]} El techo del cráneo está mal conservado. Los huesos estrellados están poco compactos y menos desarrollados en comparación con los de Crossopholis o Polyodon , pero son similares a los de Psephurus . ^{[ 2 ]}   

Al igual que otros peces espátula que no pertenecen al género Polyodon , es probable que Paleopsephurus fuera piscívoro . Se cree que, al igual que otros peces espátula, vivía en agua dulce. ^{[ 3 ]}

Paleopsephurus presenta una combinación de caracteres que sugiere que es más derivado que Protopsephurus , pero más basal que Crossopholis , Polyodon o Psephurus . Relaciones de los géneros, según Grande et al. (2002). ^{[ 4 ]}