Je was op zoek naar: fossilized (Engels - Japans)

fossilized
化石

it's a fossilized worm.
- 化石化した虫だよ

the bones are fossilized but this formation seems to be perfectly preserved.
骨の化石かな だが、それにしては 形が残っている

it is certainly easier to detect anomalies on new bones than on fossilized ones.
化石化したものよりも わかりやすいな