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Unformatted text preview: ts time in the uterus. Its flexible shell is stretched as nutrients are absorbed from the uterus. Question: Do these discoveries change your view about how to classify the platypus? A) B) C) D) Once again: How should the platypus be classified? A separate class equivalent to other classes like birds, reptiles & mammals. A separate order of mammals. A separate genus in the same order as other toothless mammals, the Edentata (sloths & anteaters). None of the above. Here's how the experts do it today: Class Mammalia
Subclass Protheria (Egg laying mammals)
Order Monotremata (Platypus & Echidna) Subclass Theria (Mammals bearing live young)
Infraclass Metatheria Order Marsupialia (Pouched mammals) Infraclass Eutheria (Placental mammals) Metatheria Theria Mammalia Eutheria Marsupialia Placentalia Monotremata Protheria AN ANTIPODAL MYSTERY
Part V: "The Big Picture" Aristotle's view of a ladder of nature (Scala Naturae, or Great Chain of Being) suggested that species were fixed in a position on an ascending ladder leading toward humans at the top. How does platypus fit into the doctrine of "Creation?" This may have made sense a couple of thousand years ago when only 500 species of animals were known, but as new species were discovered, with more and more intermediate or hybrid characteristics, this static view of the world seemed less and less tenable. For example, in 1803 French expeditions returned from Australia with 100,000 animal specimens; 2,500 were species new to science. Georges Cuvier, said they had collected: "more new Robert Brown, who traveled extensively around creatures than all traveling naturalists of recent times put together." Australia's coasts, collected 465 genera and 2,000 species of plants in 1811, all new to science. Classification schemes that had been created for Europe were completely inadequate for the Southern Hemisphere. The platypus was only one of a thousand new riddles, albeit the most spectacular. How do all of these new species fit into the Scala Naturae? How do all of these new species fit into the Scala Naturae? There seem to be all sorts of new intermediates. Some of them like kangaroos were really spectacular. The Bible said nothing about any of them. It appeared that the Bible focused only on a small part of the world Another problem was emerging: fossils were being discovered everywhere. Many were of animals no longer alive. This suggested that some species had gone extinct. If extinction occurred, then what had happened to the ladder of life? Are there missing steps? And what about the pefection argument of Paley? Were all of these fossils imperfect? How should scientists solve this problem? Throw out the Scala Naturae concept altogether? Cuvier did. He argued physical catastrophes periodically occur and destroy organisms. They were replaced after each disaster by successive creations of new and more complex species. Revise it? Lamarck did. He believed there was a linear order of living organisms from simple to complex, and that organisms could move upward on the ladder via evolution--rather like an escalator. He thought extinction was impossible. Question: When Charles Darwin came into the picture, he had his own view of the Scala Naturae. What do you think it was? Today we have DNA evidence & traditional taxonomic analysis. Draw a phylogenic tree showing the evolutionary relationships among Monotremes Placental mammals Marsupials Reptiles Birds Early Mammallike animal Hadrocodium from China 195 MYA Monotremes This is a story of how science works
An unknown animal is discovered 2) Scientists try to categorize it by comparing it to known organisms. 3) It defies easy categorization. It isn't a mammal--no mammary glands It isn't a bird--no feathers It isn't a reptile--no scales
1) 4. New information: platypus has * mammary glands but no nipples * cloaca reproductive tract like a bird or reptile * lays leathery eggs * shoulder girdle & ear like reptile Conclusion: Platypus is a transitional species between reptiles & mammals 5. Broad conclusions: Platypus is only one example of thousands of transition species not known to ancients & not in Bible & not in the Linnaeus' system of classification. & the millions of extinct species throw Creationism into question Transition species are expected Extinction is expected The transition species Evolution can explain both: Knowledge is always being refined Science is selfcorrecting...
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- Spring '07