Respiratory effects [edit]. The PRG antagonizes the apneustic center, cyclically inhibiting inhalation. The PRG limits the burst of action potentials in the phrenic nerve, effectively decreasing the tidal volume and regulating the respiratory rate.espiratory effects [edit]. The PRG antagonizes the apneustic center, cyclically inhibiting inhalation. The PRG limits the burst of action potentials in the phrenic nerve, effectively decreasing the tidal volume and regulating the respiratory rate.
Because the ones at the bottom, the animals would have died first and soil would have covered them building a cliff and the fossils up top would have died later. 3 people found this useful.
The Chondrichthyes are considered the oldest existing jawed-vertebrates related to bony vertebrates (Osteichthyes) [2][4]. The earliest dated Chondricthyes fossils are from the Silurian period (444-416 mya).