Victorian scientists believed the creature was a giraffe with a trunk and a "missing link" between mammals.
Digital reconstructions of the bones show that while the giraffe was gigantic, the theory that it was as big as an elephant was not true.
The findings, published in Biology Letters, shed new light on the work of 19th Century fossil hunters.
The first fossil specimen was found by the Scottish geologist Hugh Falconer and the English engineer Proby Thomas Cautley on an expedition to the Siwalik hills in India in the 1830s.
In a paper published in 1836, the two men outlined their discovery of an animal with a skull the size of an elephant which they believed had a trunk.
Palaeontologists envisaged it as an elephant sized, moose-like creature - a view that has prevailed.
Christopher Basu of the Royal Veterinary College in Hertfordshire, co-researcher of the study, said the fossil hunters did a "beautiful job at describing it and taking measurements", although it turns out the body mass calculation was "educated guesswork". Read more on bbc.