Are reptiles faster than mammals

How reptiles became mammals

Zurich - Echidna and platypus are the most original mammal families still in existence today. During the Cretaceous Period, over 100 million years ago, their ancestors were among the first mammals to walk on earth. Scientists at the University of Zurich have now been able to gain an insight into the development of the earliest ancestors of mammals - and thus also of us humans - based on the embryonic development of these monotons.

Two achievements have made it possible for mammals to populate the whole world: embryos mature in the womb and the young are suckled by the mother. This protection in early development ensured that the probability of survival increased sharply. One of the big differences between monotons and other mammals is the fact that they lay eggs. The suckling itself also works differently: the females have no teats, the young lick the milk from a field of mammary glands on the mother's belly.

Ingmar Werneburg and Marcel Sánchez from the Paleontological Institute at the University of Zurich have now examined the anthers' embryos. Using over 100 characteristics, they compared the development of the Echidna embryos with that of 23 species of salamanders, turtles, birds, crocodiles and lizards.

"Mosaic-like" transition

Like the researchers in the specialist magazine Acta Zoologica report that the transition from reptiles to mammals was "like a mosaic". The young of the monotremes still have some things in common with those of the reptiles. In this way they form an egg tooth that they use to slit open the egg in which they develop. However, their eyes and ears develop rather slowly, as with other mammals - and in contrast to reptiles. On the other hand, the jaw and throat apparatus form much faster in mammals. In guinea pigs, for example, the eyes are closed long after they are born.

The researchers explain this by the fact that mammals can delay the development of the sense organs because they are protected by the mother. The organs for suckling food, on the other hand, are vital for them.

Reptiles, on the other hand, have to protect themselves from predators shortly after hatching and find food themselves. To do this, they need good eyes and ears. Their feeding mechanism, on the other hand, is simpler than in mammals, which is why the neck and tongue muscles develop later. (red / APA / sda)