8. What trait is shared by frogs, humans, hares, caimans, and parrots

They are all tetrapoda.

Tetrapods are animals (group of vertebrates) with four limbs including amphibians (frogs), reptiles (caimans), birds (parrots) and mammals (hares, humans). Even though the subgroups within Tetrapods differ a lot, they all have various adaptations of the skeleton and muscles that enable them movement on land, adaptations of cranium (for head stability), tissues that reduce water loss (because of living outside the water) ... Except amphibians all other tetrapoda are amniotes (have amnion layer around embryo)