Halisaurinae
Encyclopedia
Halisaurinae is a subfamily of mosasaur
s, a diverse group of Late Cretaceous
marine squamates.
Bardet et al. (2005, p. 464) diagnosed the Halsaurinae as all mosasaurs more closely related to Halisaurus than Moanasaurus. Unambiguous character states were listed as follows: "premaxilla
-maxilla
sutural contact vertical anteriorly, oblique at midpoint and horizontal posteriorly; contact plane between the parietal
and the supratemporal oblique; preaxial ridge extending on two-thirds of the length of the radius; tibia
and fibula long and slender with slightly expanded extremities. Ambiguous characters include "dorsal
median ridge borne on the anterior two-thirds of the frontal
; frontal with ventral boss; parietal foramen surrounded by a ventral boss; quadrate with large infrastapedial process; coalescent infra- and suprastapedial processes of quadrate; zygosphene-zygantrum complex absent; synapophyses of the cervical vertebrae
extending ventrally to the ventral surface of the centrum; fused haemal spines."
Designation of this subfamily followed many decades of confusion surrounding the type genus
, Halisaurus, especially H. sternbergii, a species from the Mooreville Chalk Formation
of Alabama
and the Niobrara Chalk of Kansas
. Originally, the species
had been referred to the mosasaurine Clidastes , then to Halisaurus (Russell, 1967; p. 369 ), which was also considered a member of the Mosasaurinae
at that time. Later workers questioned the phylogenetic position and monophyly
of Halisaurus, in part because of striking morphological
differences between H. sternbergii and the other known species of the taxon
. Finally, Bardet et al. (2004) determined that H. sternbergii was not conspecific with the other members of the genus
and erected a new genus, Eonatator
, as well a new new subfamily, consisting of Eonatator and Halisaurus. Halisaurines (as members of this subfamily are collectively and informally known) were small to medium-sized mosasaurs averaging 4.5-6+ meters in length. Of all known mosasaurids, they were the least adapted to a marine lifestyle. Halisaurines are known from North America
, Europe
, South America
, and Africa
. The earliest known remains of halisaurines occur in rocks of Santonian
age and the subfamily persists until the latest Maastrichtian
. The etymology
of this group derives from the genus Halisaurus (Greek
halis = "sea" + Greek
sauros = "lizard").
composed of Halisaurus
and Eonatator
was christened the Halisaurinae, "the sister group of more advanced mosasaurids."
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
s, a diverse group of Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
marine squamates.
Bardet et al. (2005, p. 464) diagnosed the Halsaurinae as all mosasaurs more closely related to Halisaurus than Moanasaurus. Unambiguous character states were listed as follows: "premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
-maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
sutural contact vertical anteriorly, oblique at midpoint and horizontal posteriorly; contact plane between the parietal
Parietal
Parietal may refer to:*Parietal placentation*Parietal lobe of the brain*Parietal bone of the skull*Parietal scales of a snake lie in the general region of the parietal bone*Parietal cell in the stomach*Parietal pleura...
and the supratemporal oblique; preaxial ridge extending on two-thirds of the length of the radius; tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
and fibula long and slender with slightly expanded extremities. Ambiguous characters include "dorsal
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
median ridge borne on the anterior two-thirds of the frontal
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
; frontal with ventral boss; parietal foramen surrounded by a ventral boss; quadrate with large infrastapedial process; coalescent infra- and suprastapedial processes of quadrate; zygosphene-zygantrum complex absent; synapophyses of the cervical vertebrae
Cervical vertebrae
In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...
extending ventrally to the ventral surface of the centrum; fused haemal spines."
Designation of this subfamily followed many decades of confusion surrounding the type genus
Type genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
, Halisaurus, especially H. sternbergii, a species from the Mooreville Chalk Formation
Mooreville Chalk Formation
The Mooreville Chalk Formation is a geological formation in North America, within the U.S. states of Alabama and Mississippi. The strata date back to the early Santonian to the early Campanian stage of the Late Cretaceous. The chalk was formed by pelagic sediments deposited along the eastern edge...
of Alabama
Alabama
Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...
and the Niobrara Chalk of Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
. Originally, the species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
had been referred to the mosasaurine Clidastes , then to Halisaurus (Russell, 1967; p. 369 ), which was also considered a member of the Mosasaurinae
Mosasaurinae
Mosasaurinae is a subfamily of mosasaurs, a diverse group of Late Cretaceous marine squamates.Russell defined the Mosasurinae as differing from all other mosasaurs as follows: "Small rostrum present or absent anterior to premaxillary teeth. Fourteen or more teeth present in dentary and maxilla...
at that time. Later workers questioned the phylogenetic position and monophyly
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
of Halisaurus, in part because of striking morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
differences between H. sternbergii and the other known species of the taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
. Finally, Bardet et al. (2004) determined that H. sternbergii was not conspecific with the other members of the genus
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...
and erected a new genus, Eonatator
Eonatator
Eonatator is a genus of halisaurine mosasaur from the Upper Cretaceous of North America and Europe. Originally, this taxon was included within Halisaurus, but was placed in its own genus...
, as well a new new subfamily, consisting of Eonatator and Halisaurus. Halisaurines (as members of this subfamily are collectively and informally known) were small to medium-sized mosasaurs averaging 4.5-6+ meters in length. Of all known mosasaurids, they were the least adapted to a marine lifestyle. Halisaurines are known from North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. The earliest known remains of halisaurines occur in rocks of Santonian
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 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
age and the subfamily persists until the latest Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
. The etymology
Etymology
Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...
of this group derives from the genus Halisaurus (Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
halis = "sea" + Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
sauros = "lizard").
Phylogeny and Taxonomy
Halisaurus is an important taxon in studies of mosasaur phylogeny as it has been repeatedly considered the sister group to all other mosasaurs. A cladistic analysis by Bardet et al. (2005, p. 462-463 ) supported this model and the cladeClade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
composed of Halisaurus
Halisaurus
Halisaurus is an extinct genus of marine lizard belonging to the mosasaur family. With a length of 3–4 m , it was small compared to most other mosasaurs. It was named by Othniel Charles Marsh in 1869, but renamed Baptosaurus by Marsh in 1870, who thought the name was already in use by a fish...
and Eonatator
Eonatator
Eonatator is a genus of halisaurine mosasaur from the Upper Cretaceous of North America and Europe. Originally, this taxon was included within Halisaurus, but was placed in its own genus...
was christened the Halisaurinae, "the sister group of more advanced mosasaurids."
- Halisaurinae
- HalisaurusHalisaurusHalisaurus is an extinct genus of marine lizard belonging to the mosasaur family. With a length of 3–4 m , it was small compared to most other mosasaurs. It was named by Othniel Charles Marsh in 1869, but renamed Baptosaurus by Marsh in 1870, who thought the name was already in use by a fish...
- H. platyspondylus
- H. ortlebi
- H. arambourgi
- H. onchognathus (nomen dubiumNomen dubiumIn zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
; holotype destroyed during World War IIWorld War IIWorld War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
)
- EonatatorEonatatorEonatator is a genus of halisaurine mosasaur from the Upper Cretaceous of North America and Europe. Originally, this taxon was included within Halisaurus, but was placed in its own genus...
- E. sternbergii
- Halisaurus