A paedomorphic dwarf species, Gauthieria pumilio sp. nov. (Echinoidea: Phymosomatidae), from the Campanian (Late Cretaceous) of Hannover, Germany

A new phymosomatoid species, Gauthieria pumilio sp. nov., from lower Campanian (Late Cretaceous) deposits in the vicinity of Hannover, Germany, is described. This species is very close in its overall appearance (i.e. tuberculation and ambulacral plating pattern) to a few other species: Gauthieria radiata and the juvenile stages of the Santonian Gauthieria spatulifera and the Maastrichtian Gauthieria princeps, with which Gauthieria pumilio sp. nov. is accordingly closely related. However, it deviates from its relatives by a significantly smaller test diameter. Accordingly it is deviating from the general increase in size during the evolutionary lineage leading from the Turonian G. radiata via G. spatulifera to the Maastrichtian G. princeps. This lineage exemplified Cope's Rule through increasing test size. However, G. pumilio sp. nov. challenges this pattern with its dwarfing phenomenon, exhibiting a test diameter < 18 mm. It shares the ambulacral plating pattern with G. radiata and the juvenile stages of G. spatulifera and G. princeps, providing further  insights into the genus's evolutionary history.