Researchers believe Invictibellatrix would have been three to four metres long and just over a metre and a half in height – about as tall as a human.
It would likely have had feathers and its claws might have been about 10cm to 20cm long.
It would have eaten small dinosaurs, lizards and mammals – occupying a similar role in the food chain to the hyena today.
Megaraptors are regarded as the most mysterious of the large, meat-eating dinosaurs, as few megaraptor fossils have been found.
Until now no megaraptorans had been found in Europe.
Lead author Dr Cassius Morrison (UCL Earth Sciences) said: “It is a real mystery that this fossil was overlooked for so long, sitting in a drawer for nearly 100 years.
“Lots of bones are found on the Isle of Wight – who knows what else is waiting to be discovered.”
The researchers undertook a CT scan of the fossil, creating a 3D model of this part of the skull.
They compared the fossil with skulls and brain cases from tyrannosaurs, spinosaurs, raptors and other two-legged meat-eating dinosaurs.