Iniopterygian has 300-million-year-old brain
A few years ago, some researchers found a fossil of an iniopterygian, a really really old fish-type creature. The best part about it (in my opinion) was that when they x-rayed the fossils, they found a brain still inside- the soft brain tissue had mineralized likely due to some phosphate bacteria present before it decayed. You can read more about it in PNAS. This brain survived THREE HUNDRED MILLION YEARS!! This is seriously awesome.