Vasuki indicus

Vasuki is an extinct genus of madtsoiid snake from the Middle Eocene Naredi Formation of India. The genus contains a single species, V. indicus, known from several vertebrae. Vasuki has an estimated body length between 10.9 - 15.2 m, making it the largest known madtsoiid. The upper bounds of the length estimates would make Vasuki the longest snake ever discovered.

Discovery and naming
The Vasuki holotype specimen, IITR/VPL/SB 3102-1-21, was discovered in the sedimentary layers of the Naredi Formation in the Panadhro Lignite Mine in the Kutch district of Gujarat State, western India. The specimen consists of 27 pre-cloacal vertebrae, some of which were found in articulation. The fossil material was found some time after 2004, and preliminary analyses suggested crocodilian affinities for the fossil material without further review.

In 2024, Vasuki indicus was described as a new genus and species of madtsoiid snake based on these fossil remains. The generic name, Vasuki, references the divine serpent of the same name from Hindu mythology. The specific name, indicus, references India, the country where the Vasuki fossils were found.

Description
The body length estimations of Vasuki are derived from predictive regression equations: one based on postzygapophyseal width, and the other based on prezygapophyseal width. The former equation resulted in a body length range of 10.9 - 12.2 m, while the latter equation resulted in a body length range of 14.5 - 15.2 m. Although the vertebral dimensions of Vasuki are smaller than those of Titanoboa, the largest length estimates indicate a longer body than that taxon, which was about 13 m long.

Classification
In a phylogenetic analyses, Vasuki is recovered as a member of the extinct snake clade Madtsoiidae as the sister taxon to the clade formed by Madtsoia pisdurensis (Late Cretaceous India) and Gigantophis garstini (Late Eocene North Africa). It is a member of a lineage of medium–large bodied madtsoiids, which is in turn the sister taxon to a clade of smaller madtsoiids. The results are displayed in the cladogram below:

Paleoenvironment
Unlike other large-bodied snakes like Titanoboa, Vasuki was probably not an aquatic animal. Its vertebral morphology instead suggests a terrestrial (or possibly semi-aquatic) lifestyle when compared to related madtsoiids and modern pythonoids. The Vasuki fossils were deposited in a backswamp marsh. Large extant pythonids are found in similar habitats.

Vasuki is known from the Naredi Formation, which dates to the Middle Eocene. Fossils of catfish, turtles, crocodilians, and early cetaceans are also known from this formation, any of which may have been the prey of Vasuki. At this time, India was largely isolated from Asia.