蛇类的祖先长什么样

The original snake ancestor was a nocturnal, stealth-hunting predator¹ that had tiny hindlimbs with ankles and toes, according to research published in the open access journal BMC Evolutionary² Biology. The study, led by Yale University, USA, analyzed³ fossils, genes⁴, and anatomy⁵ from 73 snake and lizard⁶ species, and suggests that snakes first evolved on land, not in the sea, which contributes to a longstanding debate. They most likely originated in the warm, forested ecosystems⁷ of the Southern Hemisphere around 128 million years ago.   Snakes show incredible diversity, with over 3,400 living species found in a wide range of habitats, such as land, water and in trees. But little is known about where and when they evolved, and how their original ancestor looked and behaved.   Lead author Allison Hsiang said: "While snake origins have been debated for a long time, this is the first time these hypotheses have been tested thoroughly⁸ using cutting-edge methods. By analyzing⁹ the genes, fossils and anatomy of 73 different snake and lizard species, both living and extinct, we've managed to generate the first comprehensive reconstruction¹⁰ of what the ancestral snake was like."   By identifying similarities and differences between species, the team constructed a large family tree and illustrated¹¹ the major characteristics that have played out throughout snake evolutionary history.   Their results suggest that snakes originated on land, rather than in water, during the middle Early Cretaceous period (around 128.5 million years ago), and most likely came from the ancient supercontinent of Laurasia. This period coincides with the rapid appearance of many species of mammals and birds on Earth.