 At the end of the 19th century , Georg Baur and Walter Rothschild recognised five more populations of Galápagos tortoise . In 1905 @-@ 06 , an expedition by the California Academy of Sciences , with Joseph R. Slevin in charge of reptiles , collected specimens which were studied by Academy herpetologist John Van Denburgh . He identified four additional populations , and proposed the existence of 15 species . Van Denburgh 's list still guides the taxonomy of the Galápagos tortoise , though now 10 populations are thought to have existed . 
