The ammonite fossils.
The fossilised remains of sea creatures from up to 200 million years ago have been unearthed by builders in Lincoln.
Workmen drilling 20ft down for the foundations of The Heights housing development on the hill off Carline Road have discovered scores of ammonite fossils.
The creatures – whose closest living relatives include squid and octopi – died out with the dinosaurs but their distinctive ribbed spiral shells are clearly visible in the fossilised remains.
Although they are a very common find, the fossils clearly illustrate that even the highest parts of Lincolnshire were once covered by the ocean.
Site foreman Adrian Findley, 40, explained that the ammonites had popped up as work on Skegness-based Manorcrest Homes' complex on 19 luxury homes got underway.
"We have drilled down to six metres for the foundations and these fossils have kept popping up," he said.
"They're dead common on building sites – if you dig down far enough you will find them.
"What is quite amazing is that we are working 56 metres above modern day sea levels and we are finding things that used to be in the sea all those millions of years ago.
"The project is going to take 18 months to finish. What we don't want to find during our time on this site is a live bomb from the Second World War."
The housing development in Carline Road was opposed by residents but the City of Lincoln Council approved the scheme.
Barrie Woods, who runs The Carline Guest House, in Carline Road, said: "We sent our letter of objection originally about the trees being cut down, which will be replaced.
"The view over the city from Carline Road is the best in Lincoln and that will be lost, but then there's not much you can do about that."