卵生动物黄腹三足蛇直接产仔
One creature on this planet is changing so greatly that researchers believe they’re watching evolution in action even though they have no idea why.
This strange-looking creature is called a yellow-bellied three-toed skink(黄腹三趾蜥蜴), a species of reptile native to eastern Australia. For most of its known history on Planet Earth, this type of skink has given birth by laying eggs, but recently scientists have noticed something unusual.
Yellow-bellied skinks in the warm coastal lowlands are continuing to lay eggs, but the same species in the colder mountainous regions are starting to give birth to live young. This means that this type of skink is evolving to a new way of birth right before our very eyes. It is the first time in history that scientists have caught a reptile changing from one behavior to the other.
Baby mammals get nutrients from the placenta(胎盘), and babies incubated inside eggs get their nutrients from the yolk and shell. Without either one of these protective casings(外壳), how live skink babies are living is not known now.