Monstersauria

Monstersauria Temporal range:
Gila monster,Heloderma suspectum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Infraorder:	Neoanguimorpha
Clade:	Monstersauria NorellandGao,1997
Subgroups
†Palaeosaniwa? †Asprosaurus? †Chianghsia? †Gobiderma? †Morohasaurus? †Paraderma? †Primaderma? †Estesia? †Eurheloderma? †Lowesaurus? Helodermatidae

Monstersauriais acladeofanguimorphlizards,defined as alltaxamore closely related toHelodermathanVaranus.It includesHeloderma,as well as several extinct genera, such asEstesia,PrimadermaandGobiderma,but this group was found to be polyphyletic in the most recent and complete squamate phylogenetic analysis by Reederet al.(2015).

Classification

Traditionally, Monstersauria was thought to include the modernHelodermatidaealong with fossil genera such asGobidermaandEstesiaon the finding that it was a sister toVaranidae.But in more recent years, such as 2004 and 2008, more precise molecular studies have shown that the extantHelodermais closer toAnguidae& kin than toVaranoidea.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 extantHeloderma.In total, three different possibilities exist: eitherHelodermais sister to the rest ofNeoanguimorphaand fossil monstersaurians nest withinVaranoidea(based on molecular and combined data; optimal arrangement); they both nest with each other inNeoanguimorpha(unlikely possibility based on parsimony analysis of combined data), or they both nest with each other inVaranoidea(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 onAnguimorpha:

Squamata

~†Huehuecuetzpalli ~†Eichstaetisaurus Dibamidae Gekkota Scincomorpha Lacertoidea Amphisbaenia Teiidae Toxicofera †Mosasauria Serpentes †Polyglyphanodontia Iguania Anguimorpha Paleoanguimorpha Shinisauridae †Gobiderma †Aiolosaurus †Estesia Varanoidea Lanthanotus Varanidae †Saniwa Varanus sensu Estes 1998 sensu Lee 1997 Neoanguimorpha Monstersauria Heloderma Diploglossa Xenosauridae Anguioidea †Glyptosauridae Diploglossidae Anniellidae Anguidae