Extinct species of lizard
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Varanus darevskii, also known as the Central Asian monitor, is an extinct species of monitor lizard from the Early Pliocene of Tajikistan, known from a partial skull. "V. darevskii" might have been a close relative of, and perhaps ancestral to, the modern desert monitor ("V. griseus"). 
Discovery and naming.
"Varanus darevskii" was described by the Russian palaeontologist Irina Levshakova in 1986, based on a partial skull in comparatively good condition from the Early Pliocene found near the village of Sor in the Sughd Region of Tajikistan. The skull preserved the snout in its entirety, alongside portions of the skull roof and palate.
The species name "darevskii" honors the Russian zoologist and herpetologist Ilya Darevsky. Levshakova also gave the species a common name, calling it the Central Asian monitor.
Description.
The skull of "V. darevskii" is similar to the modern desert monitor ("V. griseus"), but differs by having a broader parietal region and a more pointed tip of the snout. Though the fossil is incompletely preserved, it is also possible that the orbits of "V. darevskii" were larger than those of "V. griseus". "V. darevskii" was slightly smaller than "V. griseus" (which usually grow to about one meter in length), but had bigger teeth.
Classification.
Levshakova classified "V. darevskii" within the "Varanus" subgenus "Psammosaurus" (which also contains "V. griseus") on the basis of both anatomy and zoogeography. She believed "V. darevskii" to be closely related, perhaps ancestral, to "V. griseus". Levshakova further placed the extinct species "V. marathonensis" in the same subgenus, arguing that it too was a close relative of "V. darevskii". A 2018 analysis found "V. marathonensis" to fall outside of such a clade with "V. griseus", instead being more closely related to eastern "Varanus" species such as "V. flavescens" and "V. bengalensis".
According to the 2004 reference work "Varanoid Lizards of the World" by Eric R. Pianka, Dennis King and Ruth Allen King, Levshakova's classification of "V. darevskii" is sensible and it would not be surprising if "V. griseus" were a descendant of "V. darevskii", although no phylogenetic studies have yet taken "V. darevskii" into account and confirmed it. A 2016 analysis recovered "V. darevskii" as belonging to the subgenus "Polydaedalus", which includes modern species such as the Nile monitor ("V. niloticus"), rock monitor ("V. albigularis") and savannah monitor ("V. exanthematicus"). If this classification is correct, "V. darevskii" would be the first known occurrence of "Polydaedalus" in western Asia.
References.
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