Paleopsephurus
Encyclopedia
Paleopsephurus is an extinct genus
of paddlefish
in the Acipenseriformes
family
Polyodontidae. At present the genus contains the single species Paleopsephurus wilsoni.
The genus is known primarily from the Late Cretaceous
, Turonian
to the Campanian
stage, Hell Creek Formation
deposits. Paleopsephurus is one of only two known paddlefish genera to have been found in the North American fossil record, with the genus and species Crossopholis magnicaudatus only being described and found in the Early Eocene Green River Formation
. A third extinct genus Protopsephurus 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
of North America, and the possibly extinct Psephurus gladius in the Yangtze River
of China.
currently residing in the collections of the University of Michigan
Museum of Paleontology in Ann Arbor, Michigan
, USA. Specimen number 22206 U.M. is a complete and well preserved skull
with some denticles, pectoral girdle 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 24 miles (38.6 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 sturgeon
Protoscaphirhynchus squamosus
.
The Paleopsephurus specimens were first studied by American paleontologist and ichthyologist Archie Justus MacAlpin. He published his detailed 1947 type description in the journal Contributions from the Museum of Paleontology, University of Michigan.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of paddlefish
Paddlefish
Paddlefish are primitive Chondrostean ray-finned fishes. The paddlefish can be distinguished by its large mouth and its elongated, spatula-like snout, called a rostrum, which is longer than the rest of the head...
in the Acipenseriformes
Acipenseriformes
Acipenseriformes are an order of primitive ray-finned fishes that includes the sturgeons and paddlefishes, as well as some extinct families.Notable characteristics of Acipenseriformes include:* Cartilaginous endoskeleton* Lack of vertebral centrum...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Polyodontidae. At present the genus contains the single species Paleopsephurus wilsoni.
The genus is known primarily from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
, Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
to the Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stage, Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
deposits. Paleopsephurus is one of only two known paddlefish genera to have been found in the North American fossil record, with the genus and species Crossopholis magnicaudatus only being described and found in the Early Eocene Green River Formation
Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...
. A third extinct genus Protopsephurus 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
Mississippi River System
The Mississippi River System, also referred to as the Western Rivers, is a mostly riverine network which includes the Mississippi River and connecting waterways....
of North America, and the possibly extinct Psephurus gladius in the Yangtze River
Yangtze River
The Yangtze, Yangzi or Cháng Jiāng is the longest river in Asia, and the third-longest in the world. It flows for from the glaciers on the Tibetan Plateau in Qinghai eastward across southwest, central and eastern China before emptying into the East China Sea at Shanghai. It is also one of the...
of China.
History and classification
The genus was described from three partial specimensHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
currently residing in the collections of the University of Michigan
University of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...
Museum of Paleontology in Ann Arbor, Michigan
Ann Arbor, Michigan
Ann Arbor is a city in the U.S. state of Michigan and the county seat of Washtenaw County. The 2010 census places the population at 113,934, making it the sixth largest city in Michigan. The Ann Arbor Metropolitan Statistical Area had a population of 344,791 as of 2010...
, USA. Specimen number 22206 U.M. is a complete and well preserved skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
with some denticles, pectoral girdle 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 24 miles (38.6 km) southeast of Fort Peck, Montana
Fort Peck, Montana
Fort Peck is a town in Valley County, Montana, United States. The population was 240 at the 2000 census.-History:The name Fort Peck is associated with Col. Campbell K. Peck, the partner of Elias H. Durfee in the Leavenworth, Kansas, trading firm of Durfee and Peck...
by a University of Michigan Museum of Paleontology expedition in 1938. the fossils were in close association with the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen of the extinct sturgeon
Sturgeon
Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common...
Protoscaphirhynchus squamosus
Protoscaphirhynchus
Protoscaphirhynchus squamosus is an extinct sturgeon that lived from the Turonian to the Campanian.-See also:* Prehistoric fish* List of prehistoric bony fish...
.
The Paleopsephurus specimens were first studied by American paleontologist and ichthyologist Archie Justus MacAlpin. He published his detailed 1947 type description in the journal Contributions from the Museum of Paleontology, University of Michigan.