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A fossilised oviraptor found on top of a clutch of eggs confirms that at least some dinosaurs sat on or near their eggs to keep them warm, as birds do. The eggs contain late-stage embryos that developed at temperatures of up to 38掳C.

There is already strong evidence that some dinosaurs brooded eggs like birds do. Several fossils of adult oviraptors 鈥� bird-like dinosaurs that were around 2 metres long, including their tails 鈥� have been found on or near clutches of eggs.

Yet not all researchers are convinced.聽Many think even small dinosaurs may have been too heavy to sit atop their eggs without damaging them. Some argue that聽the oviraptors found on nests died while laying eggs rather than during brooding or while remaining close to guard the eggs.

Now a team led by Xing Xu at the Chinese Academy of Sciences in Beijing has described and analysed a fossil found near Ganzhou in China. It consists of the partial remains of an adult oviraptor on top of at least 24 eggs, many of which have embryos inside.

Eggs with embryos have been found before, but not in association with an adult, says team member Michael Pittman at the University of Hong Kong. 鈥淭his is the first time that we have everything in one specimen.鈥�

The fact that the embryos are at a late stage shows the adult wasn鈥檛 laying eggs at the time it died.

What鈥檚 more, the team also looked at the ratios of oxygen-18 to oxygen-16 isotopes in the carbonates in the eggshells and embryo bones. These ratios reflect the temperature at the time the carbonates formed. For two eggs, the isotopic analysis suggests that the embryos developed at around body temperature 鈥� between 36掳C and 38掳C. This shows the eggs were being brooded, not just guarded, says Pittman.

For the third egg analysed, which was further from the body of the adult, the developmental temperature would have been between 30掳C and 32掳C. The phenomenon of some eggs developing at a lower temperature is seen in some modern birds too, says Pittman.

All this confirms that at least some oviraptors brooded eggs, he says. Yet聽behaviours聽probably varied in other kinds of dinosaurs. For instance, it seems unlikely that giant sauropods brooded their eggs.

The name 鈥渙viraptor鈥� is a misnomer, as it means egg thief. The first specimen to be described was also found on top of eggs, and the discoverer wrongly concluded that the animal was stealing another dinosaur鈥檚 eggs at the time it was killed.