What it is
A house sparrow, standing in for all birds in the cave-mummy chapter, in a row beside a reptile and a mammal.
Why it is there
In 2026, scientists looked inside a 289-million-year-old Captorhinus mummy from Oklahoma and found a rib cage with its cartilage, built to breathe by moving the ribs. They propose that this was the starting point for the rib-powered breathing of living reptiles, birds and mammals.