Since you are so interested, Police came and picked me up to look for the jawbone but we could not find it anymore. Workers threw new piles of dirt on that place and I wasn't sure the exact location so we didn't exactly dig for it.
The building site is quite big, it's a promenade they've been working on since 2016. Sometimes in the evenings, I take a stroll where I saw this along with, no doubt, many other people but only I reported it.
One police officer talked to the guys at the construction site and they said how it was probably in the dirt they got shipped from, apparently, unknown locations.
They also got annoyed I didn't report it the same moment I discovered it, but I was not sure it was human. It's one of those moments where you don't believe your eyes.