The French zoologist Etienne Geoffroy St-Hilaire, reading Home's anatomical works, declared that both animals should be placed in a new animal class, the Monotremata, which means "one hole" to designate that the animal has a single opening (cloaca) through which it eliminates digestive and urinary wastes and reproductive products (eggs or sperm). There were three central questions about Ornithorhyncus that emerged from the foment of the times:
First, how can we fit this strange beast into the classification and taxonomic schemes that had worked so well in the Northern Hemisphere?
Second, how does Ornithorhyncus produce its young?
Third, what relevance does this anomalous animal have for the old ideas of a perfectly created world? What is the relevance of Ornithorhyncus to the idea of evolution, which was beginning to be whispered about?
Questions
Let's consider the first question: how should we classify such an animal? Classifi cation experts like John Ray and Carl von Linneaus said that reproduction was the essential criterion for classification. Linneaus set the presence of mammary glands and the suckling of the young as the defining characteristic for the class of animals he named "Mammalia." He said that warm-blooded quadrupeds (four-legged beasts) with a four chambered heart and double circulation were viviparous and mammiferous.
Henri Marie Ducrotay de Blainville said mammals could be arranged by decreasing complexity from the primates down through the marsupials to the monotremes. He was the fi rst to note many resemblances between platypus and echidna and the marsupials. He said that regardless of the apparent absence of mammary glands, the monotremes belonged as mammals in their own distinct order, Ornithodelphia. France's scientific leader, Georges Cuvier, pronounced they were indeed mammals but put the monotremes squarely in the order Edentata that included other toothless mammals, anteaters, and sloths.
Not everyone agreed. Although the platypus was warm-blooded, had a four chambered heart, and double circulation (two diff erent sides of the heart, one pumping to the lung and the other to the rest of the body), birds had these traits too. And it had a duck-like bill! Everard Home reported in his 1802 paper that the structure of the ear and shoulder girdle combined both mammalian and reptilian features. Th e presence of a cloaca was clearly a reptilian and avian feature. Th e absence of a well-formed uterus and the apparent absence of nipples persuaded Home that the "duck-billed mole" was related to ovoviviparous reptiles. Lamarck said the platypus and echidna could not be mammals without mammary glands. He placed them in a separate vertebrate class called Prototheria.
So what is the best solution for classification for this unusual animal? If birds, reptiles, fishes, and mammals are placed in separate classes, where should an animal like Ornithoryncus be classified?
What is the best logic for predicting how the young platypus is born: viviparous, oviparous, or ovoviviparous? What seems to be the most probable reproductive method and least probable method? And once produced, how will they be fed?