Estesia

Taxobox
name = "Estesia"
fossil_range = Late Cretaceous


image_caption = Skull from the American Museum of Natural History
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Lepidosauria
infraordo = Anguimorpha
superfamilia = Helodermatoidea
tribus =
genus = "Estesia"
binomial = "Estesia mongoliensis"
binomial_authority = Norell, McKenna & Novacek, 1992

"Estesia" (in honour of Richard Estes) 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.

Material

Material for Estesia has been collected in various localities in the Gobi Desert, including the Barun Goyot Formation, the Djadoktha Formation and Ukhaa Tolgod.

*IGM M3/14 (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 Varanoidea, 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.

Palaeobiology

The teeth of "Estesia" were sharp and recurved, like in modern varanoids. Interestingly, 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.