''Liodon'' is a
dubious
Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them.
Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty ...
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
mosasaur
Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and 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 Maastricht on th ...
from the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', the ...
, known from fragmentary fossils discovered in
St James' Pit
St James' Pit is a geological Site of Special Scientific Interest in Norwich in Norfolk. It is a Geological Conservation Review site and part of Mousehold Heath Local Nature Reserve.
This site has been designated because of its jaw and verteb ...
,
England
England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
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 a ...
of
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 to ...
.
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 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 anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils.
Owe ...
in 1841, based only on two tooth fragments and a minor portion of the corresponding jaw bone
discovered in
Essex
Essex () is a county in the East of England. One of the home counties, it borders Suffolk and Cambridgeshire to the north, the North Sea to the east, Hertfordshire to the west, Kent across the estuary of the River Thames to the south, and G ...
, 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") is the type genus (defining example) of the mosasaurs, an extinct group of aquatic squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian and Maastrichtian stages o ...
'' than any other reptile and in 1851 placed both genera in the new clade Natantia within the suborder
Lacertilia
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...
.
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 rec ...
noted that the generic name ''Leiodon'' was already
preoccupied
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linn ...
by the fish ''
Leiodon'' (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 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 medicine ...
. The other genera initially included in the family were ''
Mosasaurus
''Mosasaurus'' (; "lizard of the Meuse River") is the type genus (defining example) of the mosasaurs, an extinct group of aquatic squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian and Maastrichtian stages o ...
'', ''
Onchosaurus
''Onchosaurus'' is an extinct genus of sclerorhynchid sawfish from the Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata fro ...
'' (later recognized to have been a
batoid
Batoidea is a superorder of cartilaginous fishes, commonly known as rays. They and their close relatives, the sharks, comprise the subclass Elasmobranchii. Rays are the largest group of cartilaginous fishes, with well over 600 species in 26 fam ...
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
), ''
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 bo ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
), ''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 sole purpose of classifying organisms that do not fit anywhere else. They are typically defined ...
") 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 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 only pseudo ...
).
Over the course of the later nineteenth century, more species of ''Liodon'' were described.
In addition to material later assigned to ''
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 ...
'',
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 state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
and the Netherlands.
Another species, ''L. asiaticum'', was described in 1915 based on fragmentary fossils found near
Jerusalem
Jerusalem (; he, יְרוּשָׁלַיִם ; ar, القُدس ) (combining the Biblical and common usage Arabic names); grc, Ἱερουσαλήμ/Ἰεροσόλυμα, Hierousalḗm/Hierosóluma; hy, Երուսաղեմ, Erusałēm. i ...
.
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''. A review of the Moroccan mosasaur material conducted in 2015 by Nathalie Bardet and colleagues determined that no material assignable to ''Liodon'' was present, referring the small teeth assigned to ''L. anceps'' by Arambourg to ''
Eremiasaurus heterodontus'' and the large teeth to an as of yet undescribed species of ''
Prognathodon
''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 depos ...
''.
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 s ...
'', 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 s ...
and reclassified its fossils as
Mosasaurini
Mosasaurini is a 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 mosasaur from the Upper Cretaceous (Maastrichtian) of Fresno County, California. Originally named ''Kolposaurus'' (meaning "bay lizard") by Berkeley paleontologist Charles Lewis Camp in 19 ...
''.
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 a ...
classified ''Liodon'' within the Mosasaurini tribe of the
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 except ...
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 in 1892 and Per-Ove Persson in 1959, suggested that ''L. anceps'' (but not any of the other species) were congeneric with the
tylosaurine genus ''
Hainosaurus
''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
...
'', 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, Cretaceous
Mosasaurids
Mosasaurs of Europe
Fossil taxa described in 1846
Taxa named by Louis Agassiz