''Estesia'' (in honour of Richard Estes) is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

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 ...

found in the

Gobi Desert The Gobi Desert (, , ; ) is a large, cold desert and grassland region in North China and southern Mongolia. It is the sixth-largest desert in the world. The name of the desert comes from the Mongolian word ''gobi'', used to refer to all of th ...

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

Discovery

It was discovered in June 1990 by a joint expedition made up of Mongolian and American palaeontologists, and described in 1992 by Mark Norell,

Malcolm McKenna Malcolm Carnegie McKenna (1930–2008) was an American paleontologist and author on the subject. Paleontologist McKenna began his paleontology career at the Webb School of California (grades 9-12) in Claremont, California, under noted paleontolo ...

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'') a ...

''), 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 International_Code_of_Zoological_Nomenclature, 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 spe ...

is ''E. mongoliensis'', after Mongolia, where it was found. Material for ''Estesia'' has been collected in various localities in the Gobi Desert, including the

Barun Goyot Formation The Baruungoyot Formation (also known as Barun Goyot) 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 Province of Mongolia. Descriptio ...

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

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

): 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 Gao (or Gawgaw/Kawkaw) is a city in Mali and the capital of the Gao Region. The city is located on the River Niger, east-southeast of Timbuktu on the left bank at the junction with the Tilemsi valley. For much of its history Gao was an imp ...

in 1997.

Classification

In the description, ''Estesia'' was assigned to Varanoidea, as the sister group to Varanidae, 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 Anguimorpha, 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 ''Gobid ...

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