Unformatted text preview: ? 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? The First Question
How should we classify this animal? The French zoologist Etienne Geoffroy StHilaire, 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). Classification experts like 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." Fourlegged beasts with a four chambered heart and double circulation are viviparous and mammiferous. And that's it. But where are its mammary glands-- its nipples? Now what? Lamarck said the platypus and echidna could not be mammals without mammary glands. He placed them in a separate vertebrate class called Prototheria. AND Although the platypus was warmblooded, had a four chambered heart, and double circulation (two different 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 ducklike bill! Everard Home reported in his 1802 paper that the structure of the ear and shoulder girdle combined both mammalian and reptilian features. The presence of a cloaca was clearly a reptilian and avian feature. The absence of a wellformed uterus and the apparent absence of nipples persuaded Home that the "duck billed mole" was related to ovoviviparous reptiles. Henri Marie Ducrotoy de Blainville said mammals could be arranged by decreasing complexity from the primates down through the marsupials to the monotremes. He was the first 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. Then there was Cuvier France's scientific leader, Georges Cuvier, pronounced that indeed they were mammals and placed them as a separate genus in the order, Edentata that included other toothless mammals, anteaters, and sloths. 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? Class Pices Class Aves Class Reptilia Class Mammalia A) B) C) D) E) How should the platypus be classified? A separate class (Prototheria or Monotremata) equivalent to other classes like birds, reptiles & mammals. (Lamarck, St. Hilaire) A separate order of mammals, Ornithodelphia. (Blainville) A separate genus in t...
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- Spring '07
- Evolution, mammary glands, th th rr, th ke th, Thomas Bewick, ou th Wa