As described by Dennis Dean in his book Gideon Mantell and the Discovery of Dinosaurs Mantell (Cambridge University Press; 1999) by November 1821 Mantell was in possession of at least six iguanodon teeth found in the locality of Lewes where he lived.
Mantell had been exploring and logging what he found in the local geology around him in Sussex since childhood and published his description of them in 1822 entitled The Fossils of South Downs, or Illustrations of the Geology of Sussex. His books contains plates from drawings by his wife Mary Ann Mantell including “ the teeth, vertebrae, bones, and other remains of an animal of the lizard tribe, of enormous magnitude, are perhaps the most interesting fossils that have been discovered in the county of Sussex.”
In 1825 Mantell was publishing his paper on the description of a newly discovered animal he called iguanodon and has described the original teeth as having been found by his wife in deposits at the side of the road used by road builders in the summer of 1822. She picked up what looked different from the other stones in the pile and showed it to her husband who tracked the stones back to a quarry in Cuckfield. The quarry at Whitemans Green is where other parts of the ancient animal were uncovered allowing him to make his assessment of the size and form of the large lizard or reptile like animal. There is a plaque in Cuckfield showing the location and items in their museum describing the find.
The paper entitled Notice on the Iguanodon a newly discovered fossil reptile from the sandstone of Tilgate Forest in Sussex was presented on February 10th 1825.