Maybe a repeat, search was too difficult. I was readiing biography of Georg Bauer, aka Agricola,
and it mentioned he wrote a book De Re Focillium. The first meani;ng of "fossil" is anything dug
out of a "fossa" - get it? Restriction ot ancient bones etc, came much later.

fossa

Thanks, Doc! That's somethin' I never knew all these fossiliferous years of paleontologisizing!

from the AHD:

fossa

SYLLABICATION: fos·sa
PRONUNCIATION: fs
NOUN: Inflected forms: pl. fos·sae (fs)
Anatomy A small cavity or depression, as in a bone.
ETYMOLOGY: Latin, ditch, from feminine past participle of fodere, to dig.
OTHER FORMS: fossate (fst) —ADJECTIVE

You're in the army now,
You're not behind a plow;
You'll never get rich,
Diggin a ditch
You son-of-a-bitch,
You're in the army now

And "foss" = "fossa" = ditch, trench!

fosse or foss
n.
5ME < OFr < L fossa < fossa (terra), dug (earth) < fossus: see FOSSIL6 a ditch or moat, esp. one used in fortifications