Fuligo septica is highly likely but this looks to be late in the mobile stage so there is still a chance it might be something else. Would you be able to find it again in a day or two to see id it has changed into the spring stage? If you can, a follow-up photo would be a nice addition.
It started forming a brown crust (photo 3) a couple of hours after the first two photos 27 Feb. By the next day the brown crust was hard and the mould was shrinking. After three days it was quite hard and brittle: the last photo shows the inside underneath on 2 March. There did not seem to be spores.
In slime moulds, the development from mobile to sporing may sometimes abort and perhaps that is the case here. Still, the additional photos support the ID as Fuliogo septica.