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 ter ...

of anguimorph

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 altho ...

s, defined as all taxa 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'' ...

'' than '' Varanus''. It includes ''Heloderma'', as well as several extinct genera, such as '' Estesia'', '' Primaderma'' and '' Gobiderma'', 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 along with fossil genera such as '' Gobiderma'' and '' Estesia'' on the finding that it was a sister to Varanidae. But in more recent years, such as 2004 and 2008, more precise molecular studies have shown that the extant ''

'' 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. 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 ''

''. In total, three different possibilities exist: either ''

'' is sister to the rest of Neoanguimorpha and fossil monstersaurians nest within Varanoidea (based on molecular and combined; optimal arrangement); they both nest with each other in Neoanguimorpha (unlikely possibility based on parsimony analysis of combined data), or they both nest with each other in Varanoidea (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:

References

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