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Monstersauria is a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of anguimorph
lizard 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 ...
s, defined as all
taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
more closely related to ''
Heloderma ''Heloderma'' is a genus of toxicoferan lizards that contains five species, all of which are venomous. It is the only extant genus of the family Helodermatidae. Description The genus ''Heloderma'' contains the Gila monster (''H. suspectum'') a ...
'' than '' Varanus''. It includes ''Heloderma'', as well as several extinct genera, such as ''
Estesia ''Estesia'' (in honour of Richard Estes) is an extinct genus of Late Cretaceous anguimorph lizard found in the Gobi Desert in Mongolia. Discovery It was discovered in June 1990 by a joint expedition made up of Mongolian and American palaeon ...
'', '' Primaderma'' and ''
Gobiderma ''Gobiderma'' is an extinct genus of Late Cretaceous lizard whose fossils are known from the Gobi Desert in southern Mongolia. It was first discovered as a result of a joint Polish-Mongolian Paleontological Expedition, and formally named in 1984 ...
'', but this group was found to be polyphyletic in the most recent and complete squamate phylogenetic analysis by Reeder ''et al.'' (2015).


Classification

Traditionally, Monstersauria was thought to include the modern
Helodermatidae The Helodermatidae or beaded lizards are a small family of lizards endemic to North America today, mainly found in the Isthmus of Tehuantepec in Oaxaca, the central lowlands of Chiapas, on the border of Guatemala, and in the Nentón River Valley, ...
along with fossil genera such as ''
Gobiderma ''Gobiderma'' is an extinct genus of Late Cretaceous lizard whose fossils are known from the Gobi Desert in southern Mongolia. It was first discovered as a result of a joint Polish-Mongolian Paleontological Expedition, and formally named in 1984 ...
'' and ''
Estesia ''Estesia'' (in honour of Richard Estes) is an extinct genus of Late Cretaceous anguimorph lizard found in the Gobi Desert in Mongolia. Discovery It was discovered in June 1990 by a joint expedition made up of Mongolian and American palaeon ...
'' on the finding that it was a sister to
Varanidae The Varanidae are a family of lizards in the superfamily Varanoidea and order Anguimorpha. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely related ...
. But in more recent years, such as 2004 and 2008, more precise molecular studies have shown that the extant ''
Heloderma ''Heloderma'' is a genus of toxicoferan lizards that contains five species, all of which are venomous. It is the only extant genus of the family Helodermatidae. Description The genus ''Heloderma'' contains the Gila monster (''H. suspectum'') a ...
'' is closer to
Anguidae Anguidae refers to a large and diverse family of lizards native to the Northern Hemisphere. It contains 9 genera and 89 extant species. Common characteristics of this group include a reduced supratemporal arch, striations on the medial faces of t ...
& kin than to
Varanoidea Varanoidea is a superfamily of lizards, including the well-known family Varanidae (the monitors and goannas). Also included in the Varanoidea are the Lanthanotidae ( earless monitor lizards), and the extinct Palaeovaranidae. Throughout their ...
. A large-scale integrated analysis on squamate phylogeny incorporating 737 characters of morphological and molecular data in 2015 analyzed the traditionally-monstersaurian fossil taxa along with the rest of the dataset, and what it found was a well-supported separation of the extinct monstersaurians from the extant ''
Heloderma ''Heloderma'' is a genus of toxicoferan lizards that contains five species, all of which are venomous. It is the only extant genus of the family Helodermatidae. Description The genus ''Heloderma'' contains the Gila monster (''H. suspectum'') a ...
''. In total, three different possibilities exist: either ''
Heloderma ''Heloderma'' is a genus of toxicoferan lizards that contains five species, all of which are venomous. It is the only extant genus of the family Helodermatidae. Description The genus ''Heloderma'' contains the Gila monster (''H. suspectum'') a ...
'' is sister to the rest of
Neoanguimorpha Neoanguimorpha is a clade of anguimorphs comprising Monstersauria (represented today by helodermatids) and Diploglossa (Xenosauridae Xenosauridae is a family of anguimorph lizards whose only living representative is the genus '' Xenosaurus' ...
and fossil monstersaurians nest within
Varanoidea Varanoidea is a superfamily of lizards, including the well-known family Varanidae (the monitors and goannas). Also included in the Varanoidea are the Lanthanotidae ( earless monitor lizards), and the extinct Palaeovaranidae. Throughout their ...
(based on molecular and combined data; optimal arrangement); they both nest with each other in
Neoanguimorpha Neoanguimorpha is a clade of anguimorphs comprising Monstersauria (represented today by helodermatids) and Diploglossa (Xenosauridae Xenosauridae is a family of anguimorph lizards whose only living representative is the genus '' Xenosaurus' ...
(unlikely possibility based on parsimony analysis of combined data), or they both nest with each other in
Varanoidea Varanoidea is a superfamily of lizards, including the well-known family Varanidae (the monitors and goannas). Also included in the Varanoidea are the Lanthanotidae ( earless monitor lizards), and the extinct Palaeovaranidae. Throughout their ...
(based on morphology only). The most likely tree chosen by the authors, based on the combined dataset of 691 morphological characters and 46 molecular characters across 210 operational taxonomic units, is as shown, focusing on
Anguimorpha The Anguimorpha is a suborder of Squamata, squamates. The group was named by Fürbringer in 1900 to include all autarchoglossans closer to ''Varanus'' and ''Anguis'' than ''Scincus''. These lizards, along with iguanians and snakes, constitute the ...
:


References

Anguimorpha Neogene reptiles Extant Neogene first appearances Tetrapod unranked clades {{lizard-stub