An eagle-eyed shopper first spotted the snail-shaped fossils, measuring up to 12cm across, dotted along a 400m stretch of pavement by the Siam Square shopping centre in a major tourist district.

Palaeontologists from the natural resources and environment ministry investigated and found 77 ammonite fossils.

Ammonites are marine creatures believed to have died out 66 million years ago, Preecha Saithong, director of the ministry’s fossil protection division, told AFP today.

“The ammonites are real,” he said, adding that the fossils differed from ones usually found in Thailand.

Local media reported that the footpath was repaired two years ago and the shells may have been inserted into the concrete as decoration by sub-contractors.

The fossilised ocean-dwelling molluscs, which lived during the Jurassic and Cretaceous periods, are sold as souvenirs in several popular tourist destinations including Madagascar and Morocco.