Gideon Mantell and the Ammonites

Castle Place in Lewes High Street was once the home of Dr Gideon Mantell - geologist and pioneer palaeontologist who discovered the Iguanadon fossils. The porch of the house has standard Ionic columns with spiral volutes but the fluted pilasters on the upper facade are topped with .... ammonites. There is apparently an unsolved chicken or egg question here - were the ammonites added for Mantell or was he attracted to the property because of the ammonites?