living fossil
Refers to a species that has remained unchanged for millions of years and resembles fossils of ancient organisms. Used both in biology and figuratively for something outdated.
The coelacanth is called a living fossil.
His way of thinking is a living fossil.
Compound of 生きている (living) + 化石 (fossil). A calque of English 'living fossil', coined by Charles Darwin in 'On the Origin of Species'.