Liodon
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''Liodon'' is a dubious
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains wer ...
from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
, known from fragmentary fossils discovered in
St James' Pit St James' Pit is a geological Site of Special Scientific Interest in Norwich in Norfolk, England. It is a Geological Conservation Review site within Mousehold Heath, which is a Local Nature Reserve. This site has been designated because of it ...
,
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
and possibly also the
Ouled Abdoun Basin The Oulad Abdoun Basin (also known as the Ouled Abdoun Basin or Khouribga Basin) is a phosphate sedimentary basin located in Morocco, near the city of Khouribga. It is the largest in Morocco, comprising 44% of Morocco's phosphate reserves, and at ...
of
Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...
. Though dubious and of uncertain phylogenetic affinities, ''Liodon'' was historically a highly important taxon in mosasaur systematics, being one of the genera on which the family
Mosasauridae Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') 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 ...
was based.


History

''Liodon anceps'' was first described as "''Leiodon anceps''" by
Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomy, comparative anatomist and paleontology, palaeontologist. Owen is generally considered to have been an outstanding naturalist with a remarkabl ...
in 1841, based only on two tooth fragments and a minor portion of the corresponding jaw bone discovered in
Essex Essex ( ) is a Ceremonial counties of England, ceremonial county in the East of England, and one of the home counties. It is bordered by Cambridgeshire and Suffolk to the north, the North Sea to the east, Kent across the Thames Estuary to the ...
, England.Benjamin Creisler
Mosasauridae Translation and Pronunciation Guide
. Dinosauria.com. Retrieved 2008-04-07.
The name ''Leiodon'' derived from the Greek ''leios'' ("smooth") and ''-odon'' ("tooth"), meaning "smooth tooth" on account of the "smooth and polished surface" of the fossil teeth. The specific name ''anceps'' means "two-edged", referencing the carinae (cutting edges) on both the front and back of the teeth. In 1845, Owen noted that the teeth he assigned to ''Leiodon'' were more reminiscent of those of ''
Mosasaurus ''Mosasaurus'' (; "lizard of the Meuse (river), Meuse River") is the type genus (defining example) of the mosasaurs, an extinct group of aquatic Squamata, squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian an ...
'' than any other reptile and in 1851 placed both genera in the new clade Natantia within the suborder
Lacertilia Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
. In 1846,
Louis Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he recei ...
noted that the generic name ''Leiodon'' was already
preoccupied In biology, a homonym is a name for a taxon that is identical in spelling to another such name, that belongs to a different taxon. The rule in the International Code of Zoological Nomenclature is that the first such name to be published is the s ...
by the fish ''
Leiodon ''Leiodon'' is a genus of pufferfish Tetraodontidae is a family of marine and freshwater fish in the order Tetraodontiformes. The family includes many familiar species variously called pufferfish, puffers, balloonfish, blowfish, blowers, ...
'' (described in 1839) and consequently changed the spelling to ''Liodon'', which carries the same meaning. In 1853, ''Liodon'' was one of the original genera included in the definition of the family
Mosasauridae Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') 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 ...
by
Paul Gervais Paul Gervais (full name: François Louis Paul Gervais) (26 September 1816 – 10 February 1879) was a French palaeontologist and entomologist. Biography Gervais was born in Paris, where he obtained the diplomas of doctor of science and of medic ...
. The other genera initially included in the family were ''
Mosasaurus ''Mosasaurus'' (; "lizard of the Meuse (river), Meuse River") is the type genus (defining example) of the mosasaurs, an extinct group of aquatic Squamata, squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian an ...
'', '' Onchosaurus'' (later recognized to have been a batoid
fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
), ''
Oplosaurus ''Oplosaurus'' (meaning "armed or weapon lizard" or "armoured lizard"; see below for discussion) was a genus of sauropod dinosaur from the Barremian-age Lower Cretaceous Wessex Formation of the Isle of Wight, England. It is known from a single to ...
'' (a
sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
), ''Macrosaurus'' (a historical mosasaur "
wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...
") and ''
Geosaurus ''Geosaurus'' is an extinct genus of marine crocodyliform within the family Metriorhynchidae, that lived during the Late Jurassic and the Early Cretaceous. ''Geosaurus'' was a carnivore that spent much, if not all, its life out at sea. No ''Geosa ...
'' (a thalattosuchian
crocodyliform Crocodyliformes is a clade of Crurotarsi, crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the ...
). Over the course of the later nineteenth century, more species of ''Liodon'' were described. In addition to material later assigned to ''
Tylosaurus ''Tylosaurus'' (; "knob lizard") is a genus of Russellosaurina, russellosaurine mosasaur (an extinct group of predatory marine Squamata, lizards) that lived about 92 to 66 million years ago during the Turonian to Maastrichtian stages of the Late ...
'', the three most enduring species assigned to ''Liodon'' were ''L. sectorius'' in 1871 and ''L. mosasauroides'' and ''L. compressidens'' in 1892. These species were based on more well-preserved material than ''L. anceps'' and gave ''Liodon'' a worldwide distribution, with material being assigned to ''L. mosasauroides'' from France and ''L. sectorius'' from
New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...
and the Netherlands. Another species, ''L. asiaticum'', was described in 1915 based on fragmentary fossils found near
Jerusalem Jerusalem is a city in the Southern Levant, on a plateau in the Judaean Mountains between the Mediterranean Sea, Mediterranean and the Dead Sea. It is one of the List of oldest continuously inhabited cities, oldest cities in the world, and ...
. In addition to these species, isolated teeth from various locations, including Poland, the Netherlands and Morocco, have also been assigned to ''Liodon'' in the past. In 1952,
Camille Arambourg Camille Arambourg (February 3, 1885 – November 19, 1969) was a French vertebrate paleontologist. He conducted extensive field work in North Africa. In the 1950s, he argued against the prevailing model of Neanderthals as brutish and simian. Du ...
assigned isolated fossil teeth discovered in the Maastrichtian-age phosphates of Morocco to ''Mosasaurus'' (''Leiodon'') cf. ''anceps''. It has since been accepted that the small teeth previously attributed to this taxon actually belong to '' Eremiasaurus heterodontus'', while the larger ones likely belong to ''
Thalassotitan ''Thalassotitan'' ("titan of the seas") is an extinct genus of large mosasaurs (a group of extinct marine lizards) that lived during the late Maastrichtian of the Cretaceous period in what is now Morocco, around 67 to 66 million years ago. The on ...
''. In 1993, Theagarten Lingam-Soliar argued that ''Liodon'' was a distinct genus and definable on account of its highly specialized teeth, which Lingham-Soliar believed made it "probably the most efficient in the Mosasauridae for tearing off chunks of soft bodied prey such as fishes and other marine reptiles". Lingham-Soliar also suggested that a mosasaur skeleton from Japan otherwise identified as '' Mosasaurus hobetsuensis'' could be a ''Liodon'' specimen. ''L. compressidens'', ''L. mosasauroides'' and ''L. sectorius'' were reassigned as species of ''Prognathodon'' by Schulp ''et al''. (2008). This reassignment followed from the discovery that the ''L. anceps'' type specimen was presently missing all tooth material (and as a result all of its supposedly diagnostic features), rendering it a ''
nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...
'', and from the description of the ''Prognathodon'' species ''P. kianda'' from Angola. The teeth of ''P. kianda'' had a highly similar morphology to those of the three ''Liodon'' species, meaning that they were determined as falling within the range of variation of the genus. In 2014, Palci et al. suggested that ''Liodon'' should be synonymized with ''Mosasaurus'' on account of the differences between the two mostly being in the form of tooth morphology, otherwise "consistent with differentiation at the species level only". Palci et al. also put forth the idea that ''L. anceps'' and the three species assigned to ''Prognathodon'' in 2008 were more closely related to each other and to ''Mosasaurus'' than either was to ''Prognathodon'', though made no formal taxonomic revisions. A 2021 analysis of the ''L. asiaticum'' material determined ''L. asiaticum'' to be a
nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...
and reclassified its fossils as
Mosasaurini Mosasaurini is an extinct tribe of mosasaurine mosasaurs who lived during the Late Cretaceous and whose fossils have been found in North America, South America, Europe, Africa and Oceania, with questionable occurrences in Asia. They are highly d ...
''incertae sedis'' after determining them to be non-diagnostic and close to ''Mosasaurus'' and ''
Plotosaurus ''Plotosaurus'' ("swimmer lizard") is an extinct genus of large mosasaurs which lived during the Upper Cretaceous (Maastrichtian) in what is now North America. The taxon was initially described by University of California, Berkeley, Berkeley pale ...
''.


Classification

Dale Russell Dale Alan Russell (27 December 1937 – 21 December 2019) was an American-Canadian geologist and palaeontologist. Throughout his career Russell worked as the Curator of Fossil Vertebrates at the Canadian Museum of Nature, Research Professor at ...
classified ''Liodon'' within the Mosasaurini tribe of the
Mosasaurinae The Mosasaurinae are a subfamily of mosasaurs, a diverse group of Late Cretaceous marine Squamata, squamates. Members of the subfamily are informally and collectively known as "mosasaurines" and their fossils have been recovered from every contin ...
subfamily in 1967 owing to the "great resemblance" of the fossils of ''L. mosasauroides'' to ''Mosasaurus''. Over the course of the late 19th and early 20th century, several researchers, including
Albert Gaudry Jean Albert Gaudry (16 September 1827 – 27 November 1908) was a French geologist and palaeontologist. He was born at St Germain-en-Laye, and was educated at the Catholic Collège Stanislas de Paris. He was a notable proponent of theistic evolu ...
in 1892 and Per-Ove Persson in 1959, suggested that ''L. anceps'' (but not any of the other species) were congeneric with the
tylosaurine The Tylosaurinae are a subfamily of mosasaurs,Williston, S. W. 1897. Range and distribution of the mosasaurs with remarks on synonymy. ''Kansas University Quarterly'' 4(4):177-185. a diverse group of Late Cretaceous marine Squamata, squamates. Me ...
genus ''
Hainosaurus ''Tylosaurus'' (; "knob lizard") is a genus of russellosaurine mosasaur (an extinct group of predatory marine lizards) that lived about 92 to 66 million years ago during the Turonian to Maastrichtian stages of the Late Cretaceous. Its fossils h ...
'', which Russell also believed was a possibility.'''' Despite this, ''Liodon'' is traditionally (with or without any species in addition to ''L. anceps'') maintained in the Mosasaurinae on account of the small differences separating it from ''Mosasaurus''. Schulp et al. conceived ''L. anceps'' as a basally branching close relative of ''Prognathodon''.


See also

* List of mosasaur genera * Timeline of mosasaur research


References

{{Portal bar, Paleontology Mosasaurids Mosasaurs of Europe Fossil taxa described in 1846 Taxa named by Louis Agassiz