Platypus – Fossils Advance Understanding

Modern Platypus in WaterPlatypuses are certainly the cause of a lot of confusion, mostly concerning how they came to look the way that they do, and why evolution would lead them here. They are monotremes, a mammal who lays eggs. The only other monotreme is the echidna. They have teeth when they are younger but lose them as they grow up, and instead develop a spiky ridge along their bill. Their back claws also produce venom during mating season, probably to compete with other males. They seem just like a mashup of a variety of other animals, the duck, beaver, and otter for the bill, tail, and feet respectively. But if we look into their evolutionary history, a few of these questions might be cleared up.


Monotremes are thought to have separated from mammals who give live birth at a very early stage in the evolutionary tree, and platypuses and echidnas separated roughly 20 to 50 million years ago. The modern platypus first is seen in the fossil record 100,000 years ago. While modern platypuses don’t have teeth into adulthood, their ancestors did. Steropodon galmani, for example, is the oldest example we have of mammals in Australia, dating back to 110 million years ago. The discovery of Steropodon indicates that teeth in adulthood was in only an earlier stage of the one line to modern day platypuses, but rather that the two evolved in separate branches.


Platypus FossilThe discovery of Obdurodon tharalkooschild in recent years has solidified this theory. The fossil discovery of an adult tooth is only 15 million years old at the olest, concretely pointing to teeth being a recent loss. This new find is also the largest platypus we know about to date, being about a yard long.

The fossils of prehistoric platypuses have also been discovered in South America. Monotrematum sudamericanum, found in Argentina, proves that monotremes lived all throughout Gondwanaland, the supercontinent of South America, Australia, and Antarctica. Gondawana existed until about 167 million years ago, making the Argentinian discovery older than Steropodon. The separated continent of South America was not suitable for these monotremes, however, or else they went extinct at teh joining of both American continents, which is why none exist in South America today.



Large Extinct PlatypusThe part about platypuses being a combination of other animals isn’t true in reality, but as scientists have studied their genome, there may be some truth in that idea in a metaphorical sense. Platypuses have both mammalian and reptilian genes for egg fertilization. They have five sets of sex chromosomes, as opposed to the one that humans have. Some of these genes are similar to the Z chromosome that birds, some fish, some snakes, and some lizards have. A study published in 2008 showed that the platypus also have genes unique to only birds, amphibians, and fish. They are the only known mammals to have these specific gene sequences.


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