24 Bird or Mammal?:

Classifying animals is not always a simple process. For instance, since its discovery in the eighteenth century, the platypus has been a major problem for biologists and zoologists. This odd-looking creature seems to be part mammal and part bird at first glance, a native of Australia and Tasmania looks like a mammal, and it is in fact a mammal. But upon studying it more closely, one recognizes the bristlelike characteristics that have puzzled scientists. For instance, the platypus has webbed feet like some water birds. It also has a "leathery" bill like a duck. That's how the animal gets its name, the "duck-billed platypus." In addition, the semi-aquatic platypus lays eggs like a bird. Once the eggs are hatched, the mother nurses her young, a behavior that is secreted in the mother's stomach, however, so the baby laps it up. And even though the openings in the platypus's snout from which the milk is secreted are truly birdlike webbed feet, at the end of the webbed claws that are similar to those of a cat or raccoon.

But a mammal, not a bird. The platypus has that mammalian characteristic: it bears its young alive. But the platypus is a difficult animal to classify. Because it has mixed characteristics, the platypus is in a class by itself. After much debate, scientists have finally decided to call the platypus a mammal, just to give a classification. But it's really in a class by itself.

24 是鸟还是哺乳动物？

给动物分类并不总是一个简单的过程。例如，自从18世纪被发现以来，鸭嘴兽一直是生物学家和动物学家面临的一大难题。这种长相奇特的生物初看像是半哺乳半鸟类，它原产于澳大利亚和塔斯马尼亚，看起来像哺乳动物，实际上也确实是哺乳动物。但仔细研究后会发现，它有让科学家困惑的鬃毛状特征。比如，鸭嘴兽有像某些水鸟一样的蹼足，还有像鸭子一样的“皮革状”喙——这也是它被称为“鸭嘴兽”的原因。此外，半水生的鸭嘴兽像鸟一样产卵。卵孵化后，母兽会哺育幼崽，但乳汁是从母兽的胃部分泌的，幼崽会舔食这些乳汁。尽管鸭嘴兽口鼻处分泌乳汁的开口确实像鸟类的蹼足，但蹼爪的末端却类似于猫或浣熊的爪子。

但它是哺乳动物，不是鸟类。鸭嘴兽具有哺乳动物的特征：胎生。但鸭嘴兽是一种难以分类的动物。由于它兼具多种特征，鸭嘴兽自成一类。经过大量争论，科学家最终决定将鸭嘴兽归为哺乳动物，只是为了给它一个分类。但它实际上确实是独成一类的。