THE auction trade works on Darwinian principles. A gap in Bonhams calendar last September (to have been filled by Lord McAlpine's cabinet of curiosities, which went elsewhere) mutated into the now-famous sale of dinosaur eggs and similar age- old relics.

A clutch of 10 fossilised eggs fetched pounds 46,200 and set telephone lines humming between custodians of dinosaur eggs worldwide. As a result, next Friday's 311-lot sale (2pm) of 'Fine Natural History' has evolved: Bonhams has cornered the market in things fossilised.

This time there are at least 16 sauropod eggs arranged in an 'aesthetic cluster' (damned fastidious, those dinosaurs) and estimated pounds 15,000- pounds 20,000. An immaculate fossil of a small European pterosaur, with a 46in wingspan, appears to have fossilised vegetation in its beak: pounds 20,000- pounds 30,000. The largest egg ever laid - by a Madagascan great elephant bird - is 1ft high, with the capacity of 180 hens' eggs. One of only 30 known, it is estimated pounds 30,000- pounds 50,000, more than enough to have saved the bird from extinction a century or more ago.

A severed hand with a 'fine glossy brown patina', said to have been bought in 1947 from 'a cash-strapped Aleister Crowley', is est pounds 200- pounds 250 with a 17th- century church casket.

Few auctions over Easter, but Christie's South Kensington offers Oriental ceramics and artworks, Thursday (10.30am), and travel, topographical and natural history books, atlases and maps, Friday (11am). Great Britain postage stamps at Phillips, Thursday (11am).