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.
Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites). These types of fossil are called trace fossils (or ichnofossils), as opposed to body fossils.tromatolites are a major constituent of the fossil record for life's first 3.5 billion years, peaking about 1.25 billion years ago. They subsequently declined in abundance and diversity, which by the start of the Cambrian had fallen to 20% of their peak.