Jacob Theodor Klein was a German naturalist active in Poland during the early eighteenth century. Born in the Prussian city of Königsberg (now Kaliningrad), Klein moved to Danzig (now Gdansk) in 1713 and soon began to work in the service of the Polish king Augustus the Strong. He established a botanic garden in Danzig and made important contributions to the study of amphibians, publishing his book Tentamen Herpetologiae in 1755. This marked the first use of the term ‘herpetology’ to refer to the study of the creatures.

Klein was critical of the binomial system created by Carl Linnaeus, arguing that only distinguishing features could aid in the classification of animals, as Adam had used in Genesis. This book, his Historiae avium podromos is a classification of birds according to this belief. Klein’s classification according to characteristics, principally the number of toes a bird had, led to some odd groupings, such as chickens being listed alongside large flightless birds like the rhea.