parent_taxon protoscaphirhynchus
Sturgeon is the common name for the 27 species of fish belonging to the family ___MASK27___ . Their evolution dates back to the Triassic some 245 to 208 million years ago . The family is grouped into four genera : " Acipenser ", " Huso ", " Scaphirhynchus " and " Pseudoscaphirhynchus ". Four species may now be extinct . Two closely related species , " Polyodon spathula " ( paddlefish ) and " Psephurus gladius " ( Chinese paddlefish , possibly extinct ) are of the same order , Acipenseriformes , but are in the family Polyodontidae and are not considered to be " true " sturgeons . Both sturgeons and paddlefish have been referred to as " primitive fishes " because their morphological characteristics have remained relatively unchanged since the earliest fossil record . Sturgeons are native to subtropical , temperate and sub - Arctic rivers , lakes and coastlines of Eurasia and North America . Sturgeons are long - lived , late - maturing fishes with distinctive characteristics , such as a heterocercal caudal fin similar to that of sharks , and an elongated spindle - like body that is smooth - skinned , scaleless and armored with 5 lateral rows of bony plates called scutes . Several species can grow quite large , typically ranging 7  12 feet ( 2 - 3 m ) in length . The largest sturgeon on record was a Beluga female captured in the Volga estuary in 1827 , weighing and long . Most sturgeons are anadromous bottom - feeders which migrate upstream to spawn but spend most of their lives feeding in river deltas and estuaries . Some species inhabit freshwater environments exclusively while others primarily inhabit marine environments near coastal areas , and are known to venture into open ocean . 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 interval from . The Maastrichtian was preceded by the Campanian and succeeded by the Danian ( part of the Paleogene and Paleocene ). 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 . 9 ± 0 . 8 Ma and 89 . 8 ± 1 Ma ( million years ago ). The Turonian is preceded by the Cenomanian stage and underlies the Coniacian stage . The Triassic is a geologic period and system which spans 50 . 9 million years from the end of the Permian Period million years ago ( ___MASK42___ ), to the beginning of the Jurassic Period ___MASK42___ . The Triassic is the first period of the Mesozoic Era . Both the start and end of the period are marked by major extinction events . The Triassic was named in 1834 by Friedrich von Alberti , after the three distinct rock layers (" tri " meaning " three ") that are found throughout Germany and northwestern Europe  red beds , capped by marine limestone , followed by a series of terrestrial mud - and sandstones  called the " Trias ". The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period million years ago ( ___MASK42___ ) to the beginning of the Paleogene Period ___MASK42___ . It is the last period of the Mesozoic Era . The Cretaceous Period is usually abbreviated K , for its German translation " Kreide " ( chalk ). ___MASK3___ is a genus of sturgeons . With 17 species , many of which are threatened , it is the largest genus in the order ___MASK9___ . Protoscaphirhynchus squamosus is an extinct sturgeon that lived from the Turonian to the Maastrichtian . ___MASK9___ is an order of basal ray - finned fishes that includes the sturgeons and paddlefishes , as well as some extinct families . ___MASK32___ is a genus of large sturgeons from Eurasia . It contains two species , which both are critically endangered : The Paleogene ( or ; also spelled Palaeogene or Palæogene ; informally Lower Tertiary ) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( ___MASK42___ ) to the beginning of the Neogene Period ___MASK42___ . It is the beginning of the Cenozoic Era of the present Phanerozoic Eon . The Paleogene is most notable for being the time during which mammals diversified from relatively small , simple forms into a large group of diverse animals in the wake of the Cretaceous  Paleogene extinction event that ended the preceding Cretaceous Period . ___MASK43___ is a genus of fishes in the ___MASK27___ family . The three species , all of which are threatened , are restricted to Central Asia . ___MASK100___ is a genus of sturgeons native to the United States of America . All species in this genus are considered to be threatened . The pallid sturgeon is Endangered and the Alabama sturgeon is Critically Endangered . The Cenomanian is , in the ICS ' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series . An age is a unit of geochronology : it is a unit of time ; the stage is a unit in the stratigraphic column deposited during the corresponding age . Both age and stage ___MASK4___ the same name .