Paleopsephurus

Paleopsephurus Temporal range:
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Acipenseriformes
Family:	Polyodontidae
Subfamily:	†Paleopsephurinae
Genus:	†Paleopsephurus MacAlpin, 1947
Species:	†P. wilsoni
Binomial name
†Paleopsephurus wilsoni MacAlpin,1947

Paleopsephurusis anextinctgenusofpaddlefish(Polyodontidae).At present the genus contains the single speciesPaleopsephurus wilsoni.The genus is known from theLate Cretaceous(Maastrichtian) agedHell Creek FormationofMontana.

History and classification

The genus was described from three partialspecimenscurrently residing in the collections of theUniversity of MichiganMuseum of PaleontologyinAnn Arbor, Michigan,USA.Specimen number22206 U.M.is a complete and well preservedskullwith somedenticles,pectoral girdleand pectoral fins.The second and third specimens were found in a block of matrix from the same location as2226 U.M..Specimen22207 U.M.is a portion of thecaudalregion of a paddlefish, while22208 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 24 miles (39 km) southeast ofFort Peck, Montanaby a University of Michigan Museum of Paleontology expedition in 1938. the fossils were in close association with theholotypespecimen of the extinctsturgeonProtoscaphirhynchus squamosus.

ThePaleopsephurusspecimens were first studied by AmericanpaleontologistandichthyologistArchie Justus MacAlpin.He published his detailed 1947type descriptionin the journalContributions from the Museum of Paleontology, University of Michigan.

Description

The skull is about 274 millimetres (10.8 in) long, suggesting a total body length of about 56 centimetres (22 in). The skull roof is poorly preserved. The stellate bones are loosely packed and more poorly developed compared to the ones inCrossopholisorPolyodon,but are similar to those ofPsephurus.

Ecology

Like other non-Polyodonpaddlefish,Paleopsephuruswas likely piscivorous.

Phylogeny

Paleopsephurusexhibits a combination of characters which suggests that it is morederivedthanProtopsephurus,but is more basal thanCrossopholis,Polyodon,orPsephurus.Relationships of the genera, after Grande et al. (2002).

	Polyodontidae †Protopsephurus †Paleopsephurus Polyodontinae †Psephurus †Crossopholis Polyodon