The video is very cute.
Today, let's enjoy the way a fish walks on two legs.
this is a white ray (Leucoraja erinacea), a hedgehog. This little fish is only a week old. This video is shot from the bottom up, and you can see that small fish alternately use two "legs". In nature, they "walk" on the seabed in the same way.
of course, either "walking" or "leg" here must be in quotation marks. This skate has no real legs, and the alternating "legs" we see are only part of its fins. The legs on both sides move alternately while the spine remains basically motionless, a movement pattern reminiscent of a quadruped walking.
(really cute! )
and this is not just a superficial similarity. In a recent study, scientists found that behind the "walking" movement, hedgehog white rays and land animals have very similar motor neurons and genes to control the process. The authors believe that these common features of neural control are more likely to be inherited from the common ancestors of rays and land animals.
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this is an intriguing discovery, because it may change people's understanding of the evolution of body movement. In the past, it was believed that the neural mechanism that controls the movement of land quadrupeds should be produced during the gradual evolution of the limbs when the animals landed on land (about 375 million years ago). The ancestors of rays and our terrestrial quadrupeds date back much earlier (420 million years ago). In other words, long before the fish went to land and the real legs appeared, the genes and neurons that laid the foundation for controlling land walking might have appeared. Of course, this new view is interesting, but the evidence is not sufficient so far.
PS: in the history of animals landing on land, a very important and iconic fossil evidence is the Titanic fish, which has a limb structure between fish and land animals. If you want to understand this fossil and the related evolution story, you can read the book "how did you get here: 3.5 billion years of Journey to the Human body" by Neil Shubin, the discoverer of fossils? a very good book ~
http://www.cell.com/action/showImagesData?pii=S0092-8674%2818%2930050-3