Its fossil, holotype BMNH 42997 (now NHM R 42997), a part of a right femur, 312 mm long, was found in the Netherlands near Maastricht, and originally described as a new species of Megalosaurus in 1883 by Harry Seeley: M. bredai, honouring the late Dutch biologist and geologist Jacob Gijsbertus Samuël van Breda, a director of the Teylers Museum, who had collected the fossil at some time between 1820 and 1860 from the chalkstone quarry at the St Pietersberg.

Only the top part of the femur has been conserved; of the distal end about eight centimetres are missing as the bone was cleanly cut in two when the chalk block containing it was sawed out.

[1] A re-evaluation of the fossil by Friedrich von Huene in 1926, however, showed that it came from a genus distinct from Megalosaurus — which in the nineteenth and early twentieth century was a "wastebin taxon" where many unrelated carnivorous dinosaurs were lumped together.

In 1972 Dale Russell confirmed Von Huene's opinion that Betasuchus was an ornithomimosaurid, but also considered the name a nomen vanum: a failed emendation.

Jean le Loeuff and Eric Buffetaut in 1991 concluded it was a small abelisaurid, close to Tarascosaurus and that it was distinct enough not to consider it a nomen dubium: they mentioned a more narrow femoral neck, a lack of orientation of the femoral head towards the front, the lack of an opening, or foramen, under the lesser trochanter and that the anterior face is narrower.