Where did dinosaurs lay eggs
How the dinosaurs laid eggs and what kind of eggs they were
The pores of the shells show that the soil was placed on the ground (as in birds) and not in it (as in crocodiles).
The Archosauria appeared 245 million years ago, they looked like crocodiles - they became crocodiles too - they were animals with four legs and a long tail. This is what the second ones that developed from the Archosauria, the dinosaurs, looked like at first. But they soon rose on two legs and ran like that until an asteroid killed them 65 million years ago. Their heirs, the birds, had long since been there; they survived the catastrophe as well as the crocodiles.
But in one thing they are very different from their ancestors and the crocodiles: All three lay eggs, but dinosaurs and crocodiles did / do that with two ovaries. The birds put one of them to rest or put them down - presumably to save weight for flying - they did this early, as evidence from China shows, they are around 125 million years old: Both ovaries are still there, but one is inoperable (Nature, March 17).
And what kind of eggs do they or the crocodiles and dinosaurs lay? The eggshell provides information about this: crocodiles and other reptiles lay in the ground in damp terrain, the eggshells let a lot of water through. Birds lay in the open air - and then sit on the clutch - these eggs have to hold their fluid well, but at the same time ensure a good exchange of air. And at least one species of dinosaur did the same, Troodon. They grew three meters high and looked like birds. They also laid the eggs in a similar way, a little in the ground, but most of them were exposed to the air, Darla Zelenisky (Montana State University) has shown it (Paleobiology, 39, p.278). How? In comparison the pores of the egg shells, which regulate the exchange of water and air.
Wings brought the two-legged walk
The troodon and other dinosaurs also walked like birds, on two legs, and with a body held almost horizontally, which must be well balanced. Until now it was assumed that this type of movement was only possible or necessary when the long tail shortened (the crocodiles still have it). But elaborate dinosaur reconstructions by John Hutchinson (Royal Veterinary College) have now shown that this two-leggedness came less from the rear part of the body and more from the front (Nature, April 24th): The front legs - in the case of birds: the wings - were already at bird-like dinosaurs so powerful that their weight had to be balanced. jl
("Die Presse", print edition, April 26, 2013)
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