Platypus

The platypus is one of the most unusual creatures. It’s a mammal, but neither placental nor marsupial. Instead it’s a monotreme, an unusual line of mammals that diverged from other mammals very early on. It evolved on its own confined to the Australian continent.

Interesting facts about the Platypus:

  • The plural of platypus is platypuses, platypus, or platypoda. Platypi is actually wrong but is used so often colloquially that it’s now acceptable.
  • The duck-billed platypus is obviously named after its unusual snout. Interestingly, there are no other varieties of platypi.
  • Platypi are often incorrectly identified as the only mammals that lay eggs. Actually all monotremes lay eggs. However, the only other extant monotremes are the echidnas (including the spiny anteater).
  • Platypi have a single orifice that combines reproductive functions, and solid and liquid waste disposal. (This is the definition of a monotreme.)
  • The platypus has mammary glands but NO nipples! The mother’s pink milk oozes out of pores and collects on a fold of skin where the babies lap it up. It’s the only mammal without teats.
  • Platypi have TEN sex chromosomes. We, like most mammals, have only two (XY).
  • The platypus is one of only five venomous mammals. The male has a poisonous claw on its hind legs that administers a toxin that is not lethal to grown humans, but is extremely painful. The pain can last weeks or months.
  • The platypus is carnivorous, primarily feeding on insects and worms it catches in the water. However, it does not open its eyes under water. Instead, it is the only mammal that uses electrolocation.
  • It’s ears are located at the ends of its snout.
  • It’s the only mammal that swims with an alternate rowing motion of its front feet. The back feet are webbed, but for unknown reason are not used for swimming.
  • Females have two ovaries, but only the left one is functional – another conundrum for the Intelligent Design guys.

Update May, 2008 – Platypus Genome Mapped!

On May 8, 2008 Nature published the research of a group of international scientists that sequenced the DNA of the platypus for the first time, funded in part by the U.S. National Human Genome Research Institute (NHGRI). Its genome contained roughly 18,500 genes. The scientists compared the platypus genome with human, mouse, dog, chicken, andopossum genomes and found that the platypus shares 82 percent of its genes with these animals. A central goal was to determine which platypus features were inherited from reptilian ancestors and which evolved independently. Platypus DNA was found to include a number of genes not found in other mammals, such as genes for egg yolk proteins shared only with reptiles and fish.

The new information confirms that platypus egg-laying is truly a holdover from its primitive reptile ancestors as commonly assumed. On the other hand, mammal genes for lactation (milk production) were also found in the platypus genome. While milk production and giving birth to live young would seem to go hand in hand, the platypus genome shows that the two common mammalian traits evolved at very different times. “The presence of the full repertoire of milk genes confirms that lactation evolved at least 166 million years ago, way before live-bearing,” said project co-leader Jennifer Graves, of the Australian National University in Canberra.

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