Halisaurus Temporal range: Late Cretaceous | |
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Mounted skeleton in Thermopolis, Wyoming. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | Squamata |
Clade: | † Mosasauria |
Family: | † Mosasauridae |
Tribe: | † Halisaurini |
Genus: | † Halisaurus Marsh, 1869 |
Type species | |
†Halisaurus platyspondylus | |
Species | |
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Halisaurus is an extinct genus of mosasaur named by Othniel Charles Marsh in 1869. The holotype, consisting of an angular and a basicranium fragment discovered near Hornerstown, New Jersey, already revealed a relatively unique combination of features and prompted a new genus to be described. Its name is a portmanteau of the Ancient Greek ἅλς (háls; "sea") and σαῦρος (saûros; "lizard"). [1] 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 North America and North Africa. 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.
With a length of 3–4 m (9.8–13.1 ft), Halisaurus was comparatively small by mosasaur standards. Though bigger than earlier and more basal mosasaurs, such as Dallasaurus , the sleek Halisaurus would have been dwarfed by many of its contemporaries, such as Tylosaurus and larger species of Clidastes .
Halisaurus appeared relatively early in the evolutionary history of the mosasaurs, during the Santonian. As such, the genus retains many primitive characteristics, as does the Halisaurinae at large. It was a medium-sized mosasaur about 3–4 m (9.8–13.1 ft) long. [2] 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 Halisaurinae, was highly specialized to compensate for its lack of hydrophalangy. [3]
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) that the angular resembles that of Platecarpus 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 Clidastes . The similarities with both Platecarpus and Clidastes were problematic, as said genera have always been classified in separate subfamilies, the Plioplatecarpinae and Mosasaurinae respectively. Russell referred the genus to the Plioplatecarpinae on the basis of a Platecarpus-like suprastapedial process in specimens referred to H. onchognathus. [4]
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). [5] In 2005, the species Halisaurus sternbergii was reassigned to its own genus, Eonatator , 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 Halisaurinae, which was then believed to be a sister-group to more advanced mosasaurs. [2]
The most recent major phylogenetic analysis of mosasaurs, conducted by Tiago R. Simões and colleagues in May 2017, recovered Halisaurus and the rest of the Halisaurinae as a sister group to the Mosasaurinae. This would mean that the halisaurines are more closely related to the mosasaurines than the russellosaurines (genera such as Tylosaurus and Plesiopatecarpus ) are. [6]
Below is a cladogram following an analysis by Takuya Konishi and colleagues (2015) done during the description of Phosphorosaurus ponpetelegans , which showcases the internal relationships within the Halisaurinae, showing Halisaurus as the basalmost genus of the subfamily. [3] The analysis excluded the dubious H. onchognathus and the genus Pluridens .
Halisaurinae |
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At least three species of Halisaurus are considered valid; H. platyspondylus, H. arambourgi, and H. hebae. The species H. onchognathus, known from Campanian or Santonian deposits that were once part of the Western Interior Seaway, is considered dubious due to all the known remains of the species having been destroyed in the Second World War. 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 Campanian of Texas, the Maastrichtian of California and the Santonian of Peru (which significantly expands the known temporal range of the genus). [7]
In 2023, Shaker et al. named H. hebae, a new species of Halisaurus from the Late Cretaceous Dakhla Formation of Egypt, on the basis of disarticulated cranial elements, teeth, and vertebrae from the neck and back. After performing a phylogenetic analyses of Halisaurus and closely related taxa, they suggested that Phosphorosaurus ponpetelegans and Eonatator coellensis were more closely related to the genus Halisaurus than the type species of their respective genera. They tentatively assigned these species to Halisaurus, with H. ("Phosphorosaurus") ponpetelegans possibly representing a distinct genus in need of a new name. The results of their analyses are displayed in the cladogram below: [8]
Halisaurini |
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Halisaurus platyspondylus is the type species of Halisaurus, having been named by Othniel Charles Marsh 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 (New Jersey), which is Maastrichtian in age. Important subsequent specimens include NJSM 12146 (an incomplete cranium from the Navesink Formation, New Jersey), USNM 442450 (an incomplete skeleton from the Severn Formation of Maryland). [2] The species is also known from the Mount Laurel and Merchantville Formations of Delaware, implying that the species ranged across the eastern coast of North America during the Middle to Late Maastrichtian. [9]
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 preserving nine teeth. [2]
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 and the Middle East.
Like H. platyspondylus, H. arambourgi is Late Maastrichtian in age, though specimens of this species have been found across northern Africa and potentially in the Middle East. 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 in central Morocco.
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). [2]
Mosasaurs are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. They belong to the order Squamata, which includes lizards and snakes.
Selmasaurus is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Plioplatecarpinae subfamily alongside genera like Angolasaurus and Platecarpus. Two species are known, S. russelli and S. johnsoni; both are exclusively known from Santonian deposits in the United States.
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 except for South America.
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 occurrences in Australia remain questionable. The subfamily includes the genera Latoplatecarpus, Platecarpus, Plioplatecarpus and Plesioplatecarpus.
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. They tended to have relatively slender jaws and small, numerous teeth, suggesting a diet of small fish and other prey. Although the skeleton is primitive compared to other Mosasauridae in many respects, halisaurines had the distinctive hypocercal tail of other mosasaurids suggesting good swimming ability, and they persisted alongside other mosasaurs until the end of the Cretaceous. The earliest known remains of halisaurines occur in rocks of Santonian age and the subfamily persists until the latest Maastrichtian. Halisaurines are known from North and South America, Europe, Asia and Africa, indicating a more or less global distribution in the Late Cretaceous. Four genera are currently recognized: Eonatator, Halisaurus, Phosphorosaurus and Pluridens.
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 Sweden. Originally, this taxon was included within Halisaurus, but was placed in its own genus, which also led to the subfamily Halisaurinae being created for the two genera.
Platecarpus 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 found in the United States and possible specimens in Belgium and Africa. A well-preserved specimen of Platecarpus shows that it fed on moderate-sized fish, and it has been hypothesized to have fed on squid, and ammonites as well. Like other mosasaurs, it was initially thought to have swum in an eel-like fashion, although another study suggests that it swam more like modern sharks. An exceptionally well-preserved specimen of P. tympaniticus known as LACM 128319 shows skin impressions, pigments around the nostrils, bronchial tubes, and the presence of a high-profile tail fluke, showing that it and other mosasaurs did not necessarily have an eel-like swimming method, but were more powerful, fast swimmers. It is held in the Natural History Museum of Los Angeles County. Isotopic analysis on teeth specimens has suggested that this genus and Clidastes may have entered freshwater occasionally, just like modern sea snakes.
Globidens is an extinct genus of mosasaurid oceanic lizard classified as part of the Globidensini tribe in the Mosasaurinae subfamily. Globidens belongs to the family Mosasauridae, which consists of several genera of predatory marine lizards of various sizes that were prevalent during the Late Cretaceous. Specimens of Globidens have been discovered in Angola, Brazil, Morocco, Syria and the United States. Among mosasaurs, Globidens is probably most well known for the highly rounded, globe-like teeth that give it its name.
Prognathodon 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 Clidastes. Prognathodon has been recovered from deposits ranging in age from the Campanian to the Maastrichtian in the Middle East, Europe, New Zealand, and North America.
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 in age from the Coniacian to the early Campanian in the United States.
Pluridens is an extinct genus of marine lizard belonging to the Mosasauridae. Pluridens is placed in the subfamily Halisaurinae with the genera Phosphorosaurus, Eonatator and Halisaurus. Compared to related halisaurines, Pluridens had longer jaws with more teeth, and smaller eyes. It also grew large size, measuring 5–6 m (16–20 ft) long and perhaps over 9 m (30 ft) in some individuals. The jaws in some specimens are robust, and sometimes show injuries suggestive of combat. The jaws may have been used for fighting over mates or territories.
Goronyosaurus is an extinct genus of marine lizard belonging to the mosasaur family. Fossils of Goronyosaurus are exclusively known from the Late Maastrichtian of the Iullemmeden Basin in West Africa, specifically the Dukamaje Formation of Niger and Nigeria and Farin Doutchi Formation of Niger. The type specimen was first described in 1930 as Mosasaurus nigeriensis, but subsequent remains revealed a highly unique set of adaptations that prompted the species to be reclassified as the only species of the new genus Goronyosaurus in 1972. These unique adaptations have made Goronyosaurus notoriously difficult to classify within the Mosasauridae and it is often left out of phylogenetic analyses, although most authors agree that Goronyosaurus belonged to Mosasauridae.
The Mooreville Chalk is a geological formation in North America, within the U.S. states of Alabama and Mississippi, which were part of the subcontinent of Appalachia. 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 the Mississippi embayment. It is a unit of the Selma Group and consists of the upper Arcola Limestone Member and an unnamed lower member. Dinosaur, mosasaur, and primitive bird remains are among the fossils that have been recovered from the Mooreville Chalk Formation.
Ectenosaurus is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Plioplatecarpinae subfamily alongside genera like Angolasaurus and Platecarpus. Ectenosaurus is known from the Santonian and Campanian of Kansas, Alabama, and Texas.
Angolasaurus is an extinct genus of mosasaur. Definite remains from this genus have been recovered from the Turonian and Coniacian of Angola, and possibly the Coniacian of the United States, the Turonian of Brazil, and the Maastrichtian of Niger. While at one point considered a species of Platecarpus, recent phylogenetic analyses have placed it between the (then) plioplatecarpines Ectenosaurus and Selmasaurus, maintaining a basal position within the plioplatecarpinae.
Phosphorosaurus is an extinct genus of marine lizard belonging to the mosasaur family. Phosphorosaurus is classified within the Halisaurinae subfamily alongside the genera Pluridens, Eonatator, and Halisaurus.
Plesioplatecarpus is an extinct genus of plioplatecarpine mosasaur known from the Late Cretaceous of the northern Gulf of Mexico and the Western Interior Basin of North America.
This timeline of mosasaur research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, and taxonomic revisions of mosasaurs, a group of giant marine lizards that lived during the Late Cretaceous Epoch. Although mosasaurs went extinct millions of years before humans evolved, humans have coexisted with mosasaur fossils for millennia. Before the development of paleontology as a formal science, these remains would have been interpreted through a mythological lens. Myths about warfare between serpentine water monsters and aerial thunderbirds told by the Native Americans of the modern western United States may have been influenced by observations of mosasaur fossils and their co-occurrence with creatures like Pteranodon and Hesperornis.