''Estesia'' (in honour of

Richard Estes Richard Estes (born May 14, 1932 in Kewanee, Illinois) is an American artist, best known for his photorealist paintings. The paintings generally consist of reflective, clean, and inanimate city and geometric landscapes. He is regarded as one of ...

) is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

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'', ...

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 altho ...

found in the

Gobi Desert The Gobi Desert ( Chinese: 戈壁 (沙漠), Mongolian: Говь (ᠭᠣᠪᠢ)) () is a large desert or brushland region in East Asia, and is the sixth largest desert in the world. Geography The Gobi measures from southwest to northeast a ...

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million ...

. It was discovered in June 1990 by a joint expedition made up of Mongolian and American

palaeontologists Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

, and described in 1992 by Mark Norell, Malcolm McKenna and Michael Novacek. This animal is of interest to palaeontologists, not only because it is close to the lineage of modern Gila monsters (''

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'' ...

''), but also because its dentition shows evidence that it was

venomous Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

is ''E. mongoliensis'', after Mongolia, where it was found.

Material

Material for ''Estesia'' has been collected in various localities in the Gobi Desert, including the

Barun Goyot Formation The Barun Goyot Formation (also known as Baruungoyot Formation or West Goyot Formation) is a geological formation dating to the Late Cretaceous Period. It is located within and is widely represented in the Gobi Desert Basin, in the Ömnögovi Pr ...

, the Djadochta Formation and Ukhaa Tolgod. *IGM M3/14 (

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

): A well-preserved skull with mandible, from Lizard Hill, Khulsan (Barun Goyot Formation) *IGM 3/15: Partial skeleton with associated braincase, from Khermeen Tsav (Barun Goyot Formation), discovered in 1993 and described by Norell and Gao in 1997.

Systematics

In the description, ''Estesia'' was assigned 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 ...

, as the sister group 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 rel ...

, based on skull characters. However, the new material found in 1993 provided evidence that ''Estesia'' was not closely related to modern varanids, but rather a distant relative of Gila monsters. The phylogenetic analysis presented by Norell and Gao (1997) actually supported the creation of a new group that included modern Gila monsters and extinct pre-historic forms, the

Monstersauria Monstersauria is a clade of anguimorph lizards, defined as all taxa more closely related to ''Heloderma'' than '' Varanus''. It includes ''Heloderma'', as well as several extinct genera, such as '' Estesia'', '' Primaderma'' and '' Gobiderma'', ...

Palaeobiology

The teeth of ''Estesia'' were sharp and recurved, like in modern varanoids. These teeth possess longitudinal grooves that run both from the anterior and posterior tooth surfaces during the entire tooth length. Similar characteristics are present in the teeth of Gila monsters.

References

* Norell, M.A. and Gao, K. (1997). Braincase and phylogenetic relationships of ''Estesia mongoliensis'' from the Late Cretaceous of the Gobi Desert and the recognition of a new clade of lizards. ''American Museum Novitates'' 3211:1-25. * Norell, M.A., M.C. McKenna, and M.J. Novacek. (1992). ''Estesia mongoliensis'', a new fossil varanoid from the Cretaceous Barun Goyot Formation of Mongolia. ''American Museum Novitates'' 3045:1-24. {{Taxonbar, from=Q1114164 Late Cretaceous lepidosaurs of Asia Gobi Desert Fossil taxa described in 1992 Djadochta fauna Anguimorpha