Estesia mongoliensis (Dashzeveg et al., 1995), is a Late Cretaceous varanid originally considered similar to both Varanus and Heloderma. The dentition indicates that Estesia delivered venom. Norell and Keguin (1997) found a sisterhood with Heloderma. The erected the clade Monstersauria to include Estesia and Heloderma.

In the large reptile tree Estesia nests at the base of the varanids, far from Heloderma. Outgroups include Saniwa and Bahndwivici. A sister to Estesia was basal to Varanus.

The skull was narrow, but the muzzle was broad with wide maxillary palatal processes that narrowed the internal nares.

Dashzeveg DM, Novacek J, Norell MA, Clark JM, Chiappe, Davidson A, MeKenna MC, Dingus L, Swisher C ,and Altangerel P 1995. Extraordinary preservation in a new
vertebrate assemblage from the Late Cretaceous of Mongolia. Nature 374: 446-449.

Norell MA, McKenna MC, Novacek MJ 1992. Estesia mongoliensis, a New Fossil Varanoid from the Late Cretaceous Barun Goyot Formation of Mongolia. American Museum Novitates2045:1-24.

Norell MA and Keguin G 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: 25pp.

wiki/Estesia