Parts of the site have been cordoned-off following the discovery yesterday.
Nottinghamshire Police said: “Bones have been found underground by workers constructing a tram line in Dunkirk, Nottingham.
“The discovery was made at around 5.15pm on Tuesday 4 March in Poplars Court in Lenton Lane.
“Bones, including a skull, were found underground, though it is not yet known how old they are or whether they are human or animal.
“The bones, which remain partially uncovered in the ground, will be examined by forensic experts in daylight hours tomorrow.
“A cordon will remain at the scene until then.”