Estesia
Encyclopedia
Estesia is an extinct genus
of Late Cretaceous
helodermatoid 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 described in 1992 by Mark Norell, Malcolm McKenna
and Michael Novacek. This animal is very interesting, not only because it's a close, albeit distant in time, relative to modern Gila monsters (Heloderma
), but also because its dentition shows evidence that it was venomous.
The type species
is E. mongoliensis, after Mongolia, where it was found.
, the Djadochta Formation
and Ukhaa Tolgod.
, as the sister group to Varanidae
, based on skull characters. However, the new material found in 1993 provided evidence that not only Estesia was not closely related to modern varanids, it was actually 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
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
helodermatoid lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
found in the Gobi Desert
Gobi Desert
The Gobi is a large desert region in Asia. It covers parts of northern and northwestern China, and of southern Mongolia. The desert basins of the Gobi are bounded by the Altai Mountains and the grasslands and steppes of Mongolia on the north, by the Hexi Corridor and Tibetan Plateau to the...
in Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
. 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 McKenna
Malcolm Carnegie McKenna was an American paleontologist. He was the curator of vertebrate paleontology at the American Museum of Natural History and co-authored the book Classification of Mammals along with Susan K. Bell...
and Michael Novacek. This animal is very interesting, not only because it's a close, albeit distant in time, relative to modern Gila monsters (Heloderma
Heloderma
Heloderma, the only genus of the family Helodermatidae, consists of venomous lizards native to the southwestern United States, Mexico and as far south as Guatemala. It includes two separate species, with six subspecies...
), but also because its dentition shows evidence that it was venomous.
The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
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 FormationBarun Goyot Formation
The Barun Goyot Formation , dating from the Late Cretaceous Period, is located within and is widely represented in the Gobi Desert basin, in the Ömnögovi Province of Mongolia....
, the Djadochta Formation
Djadochta Formation
The Djadochta Formation is situated in central Asia and dates from the Late Cretaceous Period. Laid down in the early Campanian, possibly starting in the latest Santonian, it is dated somewhat uncertainly at about 84-75 mya...
and Ukhaa Tolgod.
- IGM M3/14 (holotypeHolotypeA holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
): 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 VaranoideaVaranoidea
Varanoidea is a superfamily of lizards, including the well-known family Varanidae . Also included in the Varanoidea are such extinct marine and semi-aquatic forms as mosasaurs and dolichosaurs, the venomous helodermatids , the Lanthanotidae , and the extinct Necrosauridae.Throughout their long...
, as the sister group to Varanidae
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa...
, based on skull characters. However, the new material found in 1993 provided evidence that not only Estesia was not closely related to modern varanids, it was actually 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
Monstersauria is a clade of Varanoid lizards, defined as all taxa more closely related to Heloderma than Varanus. It includes Heloderma, as well as several extinct taxa, such as Estesia and Gobiderma....
.