Many people would argue that no one species was on the Earth before another species. These people believe in creationism.
dinosaurs
The early bacterias. Hominids
Zoegrass
The human species that appeared first on Earth is Homo habilis, followed by Homo erectus, then Homo sapiens (modern humans).
Coelophysis,Pterosaure and Technosaures.
Oxygen was discovered by the very first species on planet Earth.
Porpoises are not actually dolphins, they are both different branches of sea mammals known as ceteceans but they are not the same so in answer to your question porpoises were not the first dolphin species on earth because they are not a dolphin.
about 18,492,002 species consists on earth
The dinosaurs are one of the species that has disappeared from the earth.
It was celophysys a small dinosaur that hunted in groups and ate fish.
God made Man !st (Adam0 Then made woman(eve).
There really isn't a date the Earth was discovered, as humans have known of the existence of the planet since the species was first capable of symbolic thought.