''Stratodus'' is a genus of giant prehistoric aulopiform fish found in

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

-aged marine strata of

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Niger Niger, officially the Republic of the Niger, is a landlocked country in West Africa. It is a unitary state Geography of Niger#Political geography, bordered by Libya to the Libya–Niger border, north-east, Chad to the Chad–Niger border, east ...

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, and Jordan. It has also been found in the Tamaguélelt Formation of

Mali Mali, officially the Republic of Mali, is a landlocked country in West Africa. It is the List of African countries by area, eighth-largest country in Africa, with an area of over . The country is bordered to the north by Algeria, to the east b ...

, dating to the Lower

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

, indicating that ''Stratodus'' survived the Cretaceous-Paleogene extinction event. This sleek fish has an upper jaw filled with multiple rows of tiny teeth and was the largest aulopiform, reaching 5 meters in length.

History of Discovery

''Stratodus'' was initially described by

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...

in Kansas during 1872, naming the type species ''S. apicalis'', and described a second species in 1877, ''S. oxypogon'', both species being assigned to the family Stratodontidae. ''S. oxypogon'' is now often considered a synonym of ''S. apicalis'', and the family was shifted from Stratodontidae to Dercetidae, some has gone back to Stratodontidae while others support attribution to Dercetidae. For the 19th and 20th centuries, ''Stratodus'' was only known from poor fossils, usually of the skull. It wasn't until 2006 that a nearly complete skeleton of ''S. apicalis'' in the Upper Niobrara Formation was discovered by Dave Palmquist, along the bank of the

Missouri River The Missouri River is a river in the Central United States, Central and Mountain states, Mountain West regions of the United States. The nation's longest, it rises in the eastern Centennial Mountains of the Bitterroot Range of the Rocky Moun ...

of Oacoma, South Dakota, and other well preserved remains have subsequently been found in the

Muwaqqar Chalk Marl Formation The Muwaqqar Chalk-Marl Formation or Muwaqqar Formation is a Late Cretaceous (Maastrichtian) and early Paleogene-aged geological formation in Jordan, cropping out across the Jordanian Highlands from north to south. It is the geological formation c ...

of Harrana, Jordan. Marc Michaut described second species ‘''S. indamanensis''‘ from Mt Indamane (Mont In Daman) site in Niger in 2002, along with smaller relative named ‘''Ministratodus''‘. However, the publication that described these taxa is not ascertained to be valid publication under the

International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific naming of organisms treated as animals. It is also informally known as the I ...

, same as a turtle ‘''Kaosaurus''‘ Michaut described from same site. Paper in 2020 considered that remains from Mt Indamane is ''S. apicalis'' or "species not verified" instead. In 2019, fossils of ''S. apicalis'' were found in Mali dating to the Eocene.

Description

''Stratodus'' in many respects is similar in appearance to other lizardfish but much larger, as ''S. apicalis'' could grow to over a meter while ‘''S. indamanensis''‘ could reach lengths of . Remains that was once considered as ''S. apicalis'' from Israel shows its skull may exceeded . The body is long and slender, anguiliform in shape, and is covered in thick, spiny

scutes A scute () or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterio ...

. An elongated dorsal fin runs down the back. Perhaps the most striking feature of ''Stratodus'' were its conical, inward pointing teeth. ''Stratodus'' possessed multiple rows of these teeth which could reach . These teeth were extremely numerous, with at least 6,000 being present in the fish's mouth, to the point that over 1,000 of the teeth are oriented outside of the jaws on the lips of the fish.

Paleoecology

During the Late Cretaceous, ''Stratodus'' had a

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distribution on both sides of the

North Atlantic Ocean The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

, along with North Africa and Arabia. It lived in shallow, epicontinental waters only a few meters deep. While modern aulopiformes are often ambush predators, ''Stratodus'' appears capable of active hunting, owing to a muscular and hydrodynamic body, and swam in an anguilliform-esque fashion. Its hunting strategy has been hypothesized to resemble that of

billfish The billfish are a group (Xiphioidea) of saltwater fish, saltwater predatory fish characterised by prominent pointed beak, bills (rostrum (anatomy), rostra), and by their large size; some are longer than . Extant billfish include sailfish and m ...

, using its external teeth to injure prey before returning to devour them, indicated by its external teeth and club-like protrusion at the end of its skull. ''Stratodus'' is one of the few large fish to exist on both sides of the K-Pg boundary, surviving the asteroid that caused the extinction of most other megafauna. In the Eocene, ''Stratodus'' inhabited brackish-to-marine tropical waters in the

Trans-Saharan Seaway The Trans-Saharan seaway was a sea in the present-day Sahara in the Late Cretaceous period to the Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eoce ...

, living alongside animals like '' Palaeophis colossaeus'' and '' Rhabdognathus''.

References

{{Taxonbar, from=Q7622223 Paleocene fish Dercetidae Prehistoric ray-finned fish genera Cretaceous bony fish Prehistoric fish of Asia Prehistoric fish of Africa Prehistoric fish of North America Mooreville Chalk Fossils of Mali Fossils of Morocco Fossils of Israel Fossils of Niger Eocene Africa Taxa named by Edward Drinker Cope