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They found that the dinosaur group directly related to birds shrank rapidly from about 200 million years ago.

Theropods shrunk 12 times from 163kg (25st 9lb) to 0.8kg (1.8lb), before becoming modern birds.

The researchers found theropods were the only dinosaurs to get continuously smaller.

From this analysis they produced a detailed family tree mapping out the transformation of theropods to their bird descendants.

It traces evolving adaptations and changing body size over time and across dinosaur branches.

The researchers concluded that the evolution of the branch of dinosaurs leading to birds was more innovative than other dinosaur lineages.

this sustained shrinking and accelerated evolution of smaller and smaller body size allowed the ancestors of birds to develop traits which helped them to cope much better than their less evolved dinosaur relatives.

The researchers believe that miniaturisation and the development of bird-like traits had a joint influence on the evolution of the dinosaurs into today's birds. Professor Michael Benton, from the University of Bristol's school of earth sciences, said: "This study means we can't see the origin of birds as a sudden or dramatic event, with a dinosaur becoming a powered flyer overnight. "The functions of each special feature of birds changed over time - feathers first for insulation, and later co-opted for flight; early reductions in body size perhaps for other reasons, and later they were small enough for powered flight; improvements in sense of sight and enlargement of brain - even a small improvement in these is advantageous. "So perhaps it's a long-term trend associated with deputation to a new set of habitats, in the trees, to avoid predation, and to exploit new food resources."

"Birds evolved through a unique phase of sustained miniaturisation in dinosaurs," Mr Lee said.

The sleep terror or sleepwalking may last a few minutes to an hour.

With sleepwalking, the behavior seems purposeful. The child could be sitting up or getting out of bed, eating or dressing. A sleepwalker often has a blank expression and is difficult to awaken. Sleepwalking is more common in males and is often linked with bedwetting.  About 15% of children 5 to12 years of age walk in their sleep. As with sleep terrors they don’t remember sleepwalking or the behavior the next morning.

relational bullying, involves hurting someone’s reputation or relationships. Social bullying includes:

Physical bullying involves hurting a person’s body or possessions.