''Halisaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of marine reptile belonging to the

mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Ma ...

family. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

, consisting of an angular and a basicranium fragment discovered near Hornerstown,

New Jersey New Jersey is a U.S. state, state in the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. It is bordered on the north and east by the state of New York (state), New York; on the ea ...

, already revealed a relatively unique combination of features and prompted a new genus to be described. It was named by

Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...

in 1869 and means "ocean lizard". It was renamed by Marsh to ''Baptosaurus'' in 1870, since he believed the name to already be preoccupied by the fish '' Halosaurus''. According to modern rules, a difference of a letter is enough and the substitute name is unneeded, making "''Baptosaurus''" a junior synonym. Since its description, more complete remains have been uncovered from fossil deposits throughout the world with particularly complete remains found in

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria ...

and the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...

. The genus remains a key taxon in mosasaur systematics due to its unique set of features and as the most complete representative of its subfamily, the

Halisaurinae The Halisaurinae are a subfamily of mosasaurs, a group of Late Cretaceous marine lizards. They were small to medium-sized, ranging from just under 3 meters in ''Eonatator sternbergi'' to as much as 8 or 9 meters in ''Pluridens serpentis''. Th ...

. With a length of , ''Halisaurus'' was comparatively small by mosasaur standards. Though bigger than earlier and more basal mosasaurs, such as ''

Dallasaurus ''Dallasaurus'' ("Dallas lizard") is a basal mosasauroid from the Upper Cretaceous of North America. Along with '' Russellosaurus'', ''Dallasaurus'' is one of the two oldest mosasauroid taxa currently known from North America. It is also the sma ...

'', the sleek ''Halisaurus'' would have been dwarfed by many of its contemporaries, such as ''

Tylosaurus ''Tylosaurus'' (from the ancient Greek (') 'protuberance, knob' + Greek (') 'lizard') is a genus of mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and to snakes, from the Late Cretaceous. Description A ...

'' and larger species of ''

Clidastes ''Clidastes'' is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like ''Mosasaurus'' and ''Prognathodon''. ''Clidastes'' is known from deposits ranging i ...

''.

Description

''Halisaurus'' appeared relatively early in the evolutionary history of the mosasaurs, during the

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. ...

. As such, the genus retains many primitive characteristics, as does the

at large. It was a medium-sized mosasaur about long. The length of the dubious ''H. onchognathus'' is difficult to tell due to the lack of remains, but was likely similar. As in other halisaurines, the flippers of ''Halisaurus'' are poorly differentiated which means that the genus lacked the hydrophalangy of more advanced mosasaurs. That ''Halisaurus'' was a relatively poor swimmer is relatively surprising considering its small size, since other small and medium-sized mosasaurs were mostly adept swimmers. The description of '' Phosphorosaurus ponpetelegans'' revealed that '' Phosphorosaurus'', another member of the

, was highly specialized to compensate for its lack of hydrophalangy.Takuya Konishi, Michael W. Caldwell, Tomohiro Nishimura, Kazuhiko Sakurai & Kyo Tanoue (2015) A new halisaurine mosasaur (Squamata: Halisaurinae) from Japan: the first record in the western Pacific realm and the first documented insights into binocular vision in mosasaurs. Journal of Systematic Palaeontology (advance online publication) DOI:10.1080/14772019.2015.1113447 http://www.tandfonline.com/doi/full/10.1080/14772019.2015.1113447#abstract

Classification and species

The exact position of ''Halisaurus'' within the larger mosasaur family tree has long been considered controversial. The type specimen of ''H. platyspondylus'' is not comprehensive and only preserves an angular and a basicranium fragment. Though the specimen does not reveal much about the mosasaur, it was noted by D.A. Russell in his ''Systematics and Morphology of American Mosasaurs'' (

1967 Events January * January 1 – Canada begins a year-long celebration of the 100th anniversary of Canadian Confederation, Confederation, featuring the Expo 67 World's Fair. * January 5 ** Spain and Romania sign an agreement in Paris, establ ...

) that the angular resembles that of ''

Platecarpus ''Platecarpus'' ("flat wrist") is an extinct genus of aquatic lizards belonging to the mosasaur family, living around 84–81 million years ago during the middle Santonian to early Campanian, of the Late Cretaceous period. Fossils have been fou ...

'' but is more symmetrically heart-shaped in anterior aspect and appears slightly inflated in later profile with a convex anteroventral outline that is continuous with the anteroexternal margin of the articular surface, as in the genus ''

''. The similarities with both ''

'' and ''

'' were problematic, as said genera have always been classified in separate subfamilies, the

Plioplatecarpinae Plioplatecarpinae is a subfamily of mosasaurs, a diverse group of Late Cretaceous marine squamates. Members of the subfamily are informally and collectively known as "plioplatecarpines" and have been recovered from all continents, though the occ ...

and

Mosasaurinae The Mosasaurinae are a subfamily of mosasaurs, a diverse group of Late Cretaceous marine squamates. Members of the subfamily are informally and collectively known as "mosasaurines" and their fossils have been recovered from every continent excep ...

respectively. Russell referred the genus to the Plioplatecarpinae on the basis of a ''Platecarpus''-like suprastapedial process in specimens referred to ''H. onchognathus''. Several discoveries throughout the 1980s and 1990s helped shed light on ''Halisaurus'', with more complete specimens of the type species ''H. platyspondylus'' being discovered and '' Phosphorosaurus ortliebi'' being momentarily reassigned to the genus by Lingham-Soliar (1996). In 2005, the species ''Halisaurus sternbergii'' was reassigned to its own genus, ''

Eonatator ''Eonatator'' is an extinct genus of marine lizard belonging to the mosasaur family. It is a close relative of ''Halisaurus'', and part of the same subfamily, the Halisaurinae. It is known from the Late Cretaceous of North America, Colombia and ...

'', along with the description of the new species ''Halisaurus arambourgi'' by Nathalie Bardet and colleagues. With the description of ''Eonatator'' as a closely related genus to ''Halisaurus'', the two genera were grouped into the new subfamily

, which was then believed to be a sister-group to more advanced mosasaurs.Bardet, N., Pereda Suberbiola, X., Iarochene, M., Bouya, B. & Amaghzaz, M. 2005. A new species of Halisaurus from the Late Cretaceous phosphates of Morocco, and the phylogenetical relationships of the Halisaurinae (Squamata: Mosasauridae). Zoological Journal of the Linnean Society, 143, 447–472. The most recent major phylogenetic analysis of mosasaurs, conducted by Tiago R. Simões and colleagues in May

2017 File:2017 Events Collage V2.png, From top left, clockwise: The War Against ISIS at the Battle of Mosul (2016-2017); aftermath of the Manchester Arena bombing; The Solar eclipse of August 21, 2017 ("Great American Eclipse"); North Korea tests a ser ...

, recovered ''Halisaurus'' and the rest of the Halisaurinae as a sister group to the

. This would mean that the halisaurines are more closely related to the mosasaurines than the russellosaurines (genera such as ''

'' and '' Plesiopatecarpus'') are. Halisaurus arambourgi forelimb

Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

following an analysis by Takuya Konishi and colleagues (

2015 File:2015 Events Collage new.png, From top left, clockwise: Civil service in remembrance of November 2015 Paris attacks; Germanwings Flight 9525 was purposely crashed into the French Alps; the rubble of residences in Kathmandu following the April ...

) done during the description of '' Phosphorosaurus ponpetelegans'', which showcases the internal relationships within the

, showing ''Halisaurus'' as the basalmost genus of the subfamily. The analysis excluded the dubious ''H. onchognathus'' and the genus '' Pluridens''. Two species of ''Halisaurus'' are considered valid; ''H. platyspondylus'' and ''H. arambourgi''. The species ''H. onchognathus'', known from

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

deposits that were once part of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient se ...

, is considered dubious due to all the known remains of the species having been destroyed in the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

. Apart from the named species, fragmentary remains have been referred to the genus from across the world. Though the designation of these remains as ''Halisaurus'' is debatable in most cases, unnamed species are known from the

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

, the

Maastrichtian 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 interv ...

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

and the

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

(which significantly expands the known temporal range of the genus).

''Halisaurus platyspondylus''

''Halisaurus platyspondylus'' is the type species of ''Halisaurus'', having been named by

in 1869. The species name means "flat-spined". Referred specimens include the type specimen YPM 444 (consisting of an angular and a basicranium fragment) from the New Egypt Formation (

), which is Maastrichtian in age. Important subsequent specimens include NJSM 12146 (an incomplete cranium from the

Navesink Formation The Navesink Formation is a 66 to 70 mya greensand glauconitic marl and sand geological formation in New Jersey. It is known for its Cretaceous period fossil shell beds and dinosaur bones. Description The Navesink Formation, named after Nave ...

), USNM 442450 (an incomplete skeleton from the Severn Formation of

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; ...

). The species is also known from the Mount Laurel and

Merchantville Formation The Merchantville Formation is a geological formation in the northeastern United States whose strata date back to the Late Cretaceous, around the time of the Santonian and Campanian age. Dinosaur remains are among the fossils that have been rec ...

s of

Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacen ...

, implying that the species ranged across the eastern coast of North America during the Middle to Late

. This species is differentiated from other species by the narrow and oblique shape of its quadrate, the broadly rounded and posteriorly rounded external nares and the lack of anterior ridges on its frontal as well as its

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Med ...

preserving nine teeth.

''Halisaurus arambourgi''

''Halisaurus arambourgi'' means "Arambourg's ocean lizard" and is named in honor of Professor Camille Arambourg due to his work on fossil vertebrates in

North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in t ...

and the

Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europ ...

. Like ''H. platyspondylus'', ''H. arambourgi'' is Late

in age, though specimens of this species have been found across northern

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

and potentially in the

. The type specimen, MNHN PMC 14, is an incomplete skeleton that includes a disarticulated skull and 27 associated articulated vertebrae from the Grand Daoui area near

Khouribga Khouribga ( ber, ⵅⵯⵔⵉⴱⴳⴰ, xʷribga; ar, خريبڭة, ḵurībga, ) is the capital of Khouribga Province in the Béni Mellal-Khénifra region, Morocco. With a population of 196,196 (2014 census), Khouribga owes its growth to the ph ...

in central

. The fossils of ''H. arambourgi'' preserve several features that distinguish it from ''H. platyspondylus'', among them the shape of its external nares (V-shaped anteriorly and U-shaped posteriorly), the shape of its quadrate (which has an oval vertical stapedial notch) and the presence of anterior ridges on the frontal. Its pterygoid bone also preserves twelve teeth (three more than in ''H. platyspondylus'').

References

* ''Sea Dragons: Predators Of The Prehistoric Oceans'' by Richard Ellis page (p. 214) * ''Ancient Marine Reptiles'' by Jack M. Callaway and

Elizabeth L. Nicholls Elizabeth (Betsy) Laura Nicholls (January 31, 1946 – October 18, 2004) was an American-Canadian paleontologist who specialized in Triassic marine reptiles. She was a paleontologist at the Royal Tyrrell Museum in Alberta, Canada. Early ...

page (p. 283) {{Taxonbar, from=Q134622 Mosasaurs of North America Fossil taxa described in 1869 Taxa named by Othniel Charles Marsh Mosasaurids