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Monstersauria is a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
of
anguimorph The Anguimorpha is a suborder of 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 propo ...
lizard 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 alt ...
s, defined as all
taxa In biology, a taxon (back-formation from ''taxonomy''; plural 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 nam ...
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. It was discovered in June 1990 by a joint expedition made up of Mongolian and American palaeontologists, and d ...
'', '' Primaderma'' and ''
Gobiderma ''Gobiderma'' is an extinct genus of Late Cretaceous lizard whose fossils are known from the Gobi Desert in southern Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country i ...
'', but it 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, but formerly more widespread in the ancient past. Traditionally, the Gila monster and the Mexican beaded lizard were the only species recognized, al ...
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 Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country i ...
'' and ''
Estesia ''Estesia'' (in honour of Richard Estes) is an extinct genus of Late Cretaceous anguimorph lizard found in the Gobi Desert in Mongolia. It was discovered in June 1990 by a joint expedition made up of Mongolian and American palaeontologists, and d ...
'' on the finding that it was a sister to
Varanidae The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely relat ...
. 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. Common characteristics of this group include a reduced supratemporal arch, striations on the medial faces of tooth crowns, osteoderms, and a lateral fold ...
& 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 lon ...
. 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 and Anguioidea). Morphological studies in the past had classified helodermatids with the varanoids in the clade ...
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 lon ...
(based on molecular and combined; 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 and Anguioidea). Morphological studies in the past had classified helodermatids with the varanoids in the clade ...
(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 lon ...
(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 squamates. The group was named by Fürbringer in 1900 to include all autarchoglossans closer to '' Varanus'' and '' Anguis'' than ''Scincus ''Scincus'' is a genus of skinks, lizards in the family Scincidae. Th ...
:


References

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