Vasuki

Vasuki indicus is a giant madtsoiid snake described in 2024 from the early Middle Eocene of western India. Its holotype is a series of 27 associated precloacal vertebrae recovered from the Naredi Formation at the Panandhro Lignite Mine in Gujarat. Some bones remained articulated, and their size and anatomy distinguish the animal from other known madtsoiids. The often repeated estimate of roughly 11–15 metres is calculated from comparative models; no complete skeleton was found, and the skull, ribs and tail are unknown. Vasuki is included in the ancient lizard and snake catalogue.

Quick facts

A vertebral series from Kutch

Debajit Datta and Sunil Bajpai named Vasuki indicus in 2024 after studying fossils from the Panandhro Lignite Mine in the Kutch region of Gujarat. The type specimen is IITR/VPL/SB 3102-1-21, held in the vertebrate palaeontology collection at the Indian Institute of Technology Roorkee. The material was recovered from lignite-bearing sediments assigned to the Naredi Formation and dated to the early Lutetian, about 47 million years ago.

The holotype consists of 27 associated vertebrae from the part of the spine in front of the cloaca. Twenty-two were identified as trunk vertebrae. A few adjacent elements were preserved in articulation, helping establish that the bones belong to one individual rather than a mixed accumulation. The series is substantial for a fossil snake, yet it remains a partial spine: it does not include the skull, ribs, pelvis, cloacal region or tail.

The genus name refers to Vasuki, the serpent in Hindu tradition, while indicus refers to India. The name does not itself establish an evolutionary origin in the modern political region. That broader biogeographic claim comes from comparisons of the fossil with other madtsoiids and remains an inference from an incomplete record.

Why the vertebrae matter

The centra of the preserved vertebrae range from 37.5 to 62.7 millimetres long. Their prezygapophyseal width ranges from 62.4 to 111.4 millimetres. The broad, massive bones carry a combination of features used in the diagnosis, including the form of the neural spine and haemal keel and the arrangement of the zygosphene and zygantrum, paired joints that help stiffen the snake’s vertebral column.

Vertebral anatomy is particularly important for madtsoiids because many members of this extinct snake family are known mainly from isolated spinal bones. A similar-looking vertebra can be misleading if taken alone, so taxonomists compare several characters across multiple positions along the column. In Vasuki, the large dimensions are striking, but the diagnosis also depends on shape and joint details rather than size by itself.

The authors interpreted closed neurocentral sutures as evidence that the individual was skeletally mature. This supports treating the large bones as belonging to a grown animal, although maturity does not remove the uncertainty in estimating the full length. A fossil can document the size of its preserved bones directly while leaving the animal’s total dimensions unmeasured.

How a length range is calculated

Datta and Bajpai estimated body length using regressions that relate vertebral dimensions to total length in living snakes. Different measurements and comparative sets produce estimates from about 10.9 to 15.2 metres. The spread is meaningful: it records how the result changes when the model and anatomical assumptions change, rather than a known minimum and maximum measured from the fossil itself.

The number and positions of Vasuki’s vertebrae along the whole spine are unknown. Snakes also have vertebrae that vary in size from the front of the trunk toward the tail. If a preserved large vertebra is compared with the wrong position or with animals of different proportions, the extrapolated length changes. For that reason, a single headline figure should always be accompanied by the fact that only part of the spinal column is known.

The estimate supports describing Vasuki as a very large snake, among the largest known madtsoiids. It does not establish that the animal exceeded Madtsoia in length: its upper estimate is model-dependent, and direct specimen completeness differs. Comparisons are most useful when they distinguish measured bone dimensions from calculated body size.

Climate, relatives and unanswered ecology

The fossil-bearing interval represents a warm phase of the Eocene. The study cites a regional average-temperature estimate near 28 degrees Celsius. That climate is relevant context for a large ectothermic reptile, but the presence of one giant snake cannot establish that warmth alone caused its size. Body size evolves through interacting ecological and evolutionary factors that the vertebrae do not preserve.

The authors’ phylogenetic analysis grouped Vasuki with the Indian madtsoiid Madtsoia pisdurensis and the North African Gigantophis garstini. They proposed that madtsoiids had a Gondwanan history and later dispersed between landmasses as India approached Asia. The inferred branch and dispersal scenario depend on the taxa included and on how fragmentary vertebral characters are coded; they are not directly observed migration routes.

No stomach contents, associated prey, bite marks or skull are known for Vasuki. Its diet, prey size and method of killing are therefore unconfirmed. A heavy body might be compatible with ambush hunting, but that is a functional suggestion, not preserved behaviour. The evidence securely shows a mature, exceptionally large madtsoiid represented by associated trunk vertebrae. Its head shape, colour, exact body length and ecological role remain beyond the fossil record currently available.