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QUESTION Did some types of dinosaur have the equivalent of a brain in their backsides?

THE stegosaurus, whose name means 'roofed lizard' because the plates on its back look like roof tiles, had a sizable enlargement in its spinal chord at the point where it passed through the pelvis.

This creature had a famously small brain, about the size of a golf ball, and this enlargement was about 20 times that size, leading earlier scientists to hypothesise that the area contained another brain.

Sadly, modern experts dispute this theory. The supposed 'after-brain' is now thought to have been a neural junction where many nerves enter the spinal chord.

This bundle of nerves probably helped the stegosaur to walk and to swing its spiky tail. Such nerve junctions are found in many lizards, as well as in the ostrich.

Graham Dicks, Bethnal Green, London.

QUESTION Five times in the past three months I have woken in the night and my bedside digital clock has read either 2.22, 3.33, 4.44 or 5.55. Can anyone explain why?

WE ALL wake up during the night, look at the clock, and if, for example, it's 3.25am, think 'Good, I can sleep for another four hours', before going back to sleep. We just don't remember doing it for the most part.

If the time is palindromic (the same in reverse) we notice it (as we notice pattern, rhyme etc) and are more likely to remember it the next day.

Judging by the number of times this has happened to the questioner, he is probably of higher than average mathematical inclination or musical ability.

It probably isn't statistically significant.

Garry Grant, Ilford, Essex.

QUESTION Is it possible through DNA testing to determine if someone has Celtic, Roman or Anglo-Saxon ancestry?

THIS level of accuracy has not been determined by DNA testing, but there are two general methods of tracking your ancestry.

One is by looking at blood type groupings - most people have blood of type O or A. In England, south and east of a line running from North Yorkshire to the Mersey and Severn estuaries, and also in Pembrokeshire, up to 40pc of the population has group A.

Similar proportions occur in European countries from which Anglo-Saxons and Vikings originate.

Elsewhere in Britain, the percentage with blood group A decreases to the west and north. …