Detectives searched a Network Rail construction site in Sharnbrook, Bedforshire where it is believed the remains came from.
The Network Rail site is run by Murphy who are working on a viaduct strengthening scheme.
It is understood the head was transported by skip from the site as part of a landfill consignment for the quarry.
Detective Inspector Jerry Waite, from the Beds, Cambs and Herts Major Crime Unit (MCU), said: “We are conducting enquiries both locally and across the county borders, and would urge anyone with information about the finding to contact us.
“At this stage we do not know if the head is male or female, however we have got officers carrying out searches at a site in Mill Road, Sharnbrook, Bedfordshire, as we believe this is where the remains may have come from.”