Illustration of 'Horn of the Iguanodon' (3) and 'The Claw or unguical bone of an Iguanodon' (1) with, for comparison 'The Nail and the bone which it covered of a recent Iguana' (2, 3). Drawn and lithographed by F. Pollard, printed by Graf & Soret. From 'The Geology of the South East of England' by Gideon Mantell, 1833, published by Longman, Rees, Orme and Brown of Paternoster Row. One of the most celebrated but understandable mistakes in Palaeontology was the placing of the thumb-spike of the Iguanodon on the nose of the animal as a horn in early reconstructions such as those at the Crystal Palace at Sydenham. The mistake perpetuated itself for many decades until in 1878 (Berrissart, Belgium) more complete specimens indicated the 'horn' was actually a modified thumb, perhaps used for defense.