Paleontica Community

HI. Is there anyone able to determine what it might be?
Found close to a brook, approx. 1-2m deep, a nest of stones/fossils of similar shapes.
Diameter 50-70cm.
Lokal. Ukraine

https://iv.pl/image/GISqRSI
https://iv.pl/image/GISqC34
https://iv.pl/image/GISqnN2
https://iv.pl/image/GISqhBY
https://iv.pl/image/GISqE0D

the links do not work ..

graag een slotje hierop zetten want er komt geen enkele reactie..