How do you think we could trace back the evolution of organs within our body by hundreds of millions of years – from our reptile ancestors – by examining coevolution patterns and fitness landscapes?

How do you think we could trace back the evolution of organs within our body by hundreds of millions of years – from our reptile ancestors – by examining coevolution patterns and fitness landscapes?
Discuss, for instance, the “missing link,” Tiktaalik, that has made headlines around the world (see “Your Inner Fish” by Neil Shubin).
What kind of selection pressures could have been at work here, based on species adaptations, climate changes, and shifting landmasses?