Here we are, back 4.5 billion years ago. Our planet is then a massive lava, gas and vapour ball. With time, it's going to grow cold and slowly become solid. The lighter matter will stay on surface to become the earth's crust. The vapour from water with colder temperatures becomes rain, creating the first seas. At this time there is only one continent. Of course to arrive where we are, we had had a lot of patience. With this new climate, new landscape, life appears eventually…. That was 3.5 billion years ago.

This life appears in the seas (still shallow) and will see, in 3 billion years, more than a 1000 species developed (all from the marine environment). Life on firm ground is non-existent because there is no vegetation. The first vertebrates appear (500 million years (MY) ago). They have a shell and are not very adapted to under water life, like the first fish.

From Silurian to Devonian, which is between -425 MY and -345 MY, major changes for us happen. The fish evolve and become true hunter. It's a very important period for marine evolution as it sees 2 kinds of fish developing; those with radian fins and those with muscular fins (i.e. the COELACANTHE that still exists). The RHIPIDISTIAN, from the second category (muscular based fin), will experience for some of them a terrestrial migration. Indeed, plants are slowly appearing on the ground (they were only living in the water until now). By improving their independence, they conquer barren areas.
Vegetation becomes lush. Now the first insects appear, followed by their natural predators. These will have to adapt to the terrestrial way of life whilst evolving in water (their original environment). The end of the Devonian period sees the appearance of the first amphibian vertebrates (descended from a primitive fish family) from which will develop the terrestrial vertebrates. All vertebrates have a remote aquatic origin.

Our killer whale, as we know it, is still far away, but its ancestor is roaming…
Between 365MY and 245MY, a major transformation is going to happen. At this time, the land is divided in 2 parts. The Gondwanaland in the South and the Laurasia in the North. The rest is ocean. It is a period of species proliferation everywhere on the planet, under water as well as on the land. But here is the arrival of the dinosaurs during the Triassic (between 230 and 180 MY). If the Jurassic period (180 to 135 MY) is associated with these dangerous carnivores, it is more important to note, as far as we are concerned, that it's the period of the advent of the birds, the mammals and the large marine reptiles (including our ichtyosaure, which will be the first reptile with a fish appearance). The beginning of the cetacean era, which goes from 135MY to 65MY, will announce a truly immense planetary change, which is going to lead to the end of the dinosaurs, the supremacy of the mammals and the emergence of the dolphins and whales.

Indeed, 135MY ago, the Gondwanaland is going to break up to form Africa, South America, Antarctica and India. The Laurasia is going to form North America and Eurasia. This is going to create a climatic alteration that is going to cool the planet, slowly beginning the end of the dinosaurs. But another event, as brutal as it is spectacular, is going to accelerate this decline…

Now we are, 65MY ago. The dinosaurs reign supreme on the planet. The small size mammals live amongst the carnivores. Under water, large reptiles have become the masters of the oceans, amongst the fish and the mollusc…. Nothing can stop the evolution of this world, nothing except…a meteorite.

It is indeed a meteorite, hundreds of meter of diameter, speeding towards Earth and hitting it (current Yucatán penisular). The force of the impact is such that the earth's crust is going to shake and open, creating intense volcanic activity.
Massive fires start, generating an opaque smoke that is soon going to cover all of the planet. This smoke is so thick that the sun cannot penetrate, creating an everlasting night. The impact also created such a shockwave that a huge tidal wave, about 100m high sweep everything on its way, especially the large marine animals.
In fact, these two accumulated effects are going to exterminate the dinosaurs. They have cold blood and need the sun to warm them up (unlike the mammals with warm blood and a thermoregulation system).
Without this solar heat, it's certain death for these giants, without light, vegetation is going to wither. Consequently these huge herbivores will not have enough food to feed themselves and will disappear. And with them, their predators, the large carnivores.

Thus, 65 millions years ago, 80% of animal species disappear.
In the oceans, the large marine reptiles, too slow, are killed by the ground swell or the cold. Fish, are going to adapt better and conquer new, previously uninhabited areas, just like the cephalopods.

It's therefore natural that the mammals are going to impose themselves like the dinosaurs did before them. The main difference is that they are going to do it on distant continents. They are going to diversify even more. Never before have animal species adapted so well to their new environment.

For some, life on firm ground is difficult (following the cataclysm). By strategy, some ungulates, ancestors to ichtyosaures, will prefer to seek more abundant food closer to the shores. They are going to adapt themselves and evolve incredibly well, so much so that they are going to adopt an aquatic way of life and develop accordingly.

The body, originally terrestrial, is going to evolve, to adapt to the marine environment. Consequently, the anterior limbs are going to profile themselves for swimming, covering themselves with an envelope to form the fin. The posterior limbs are going to atrophy and then disappear (or stay in a vestigial state). The tail is going to slowly evolve to become a fin.

Some particularly show the transition period between terrestrial and aquatic.

Amongst them, the MESONYX, a kind of large dog with long hair, which had 5 fingered paws, not with claws, but strong nails. Its behaviour resembled our modern otter.

PAKICETUS, kind of large seal about the size of a human being, (of which remnants have been found at the foot of the Himalayas), lived in Tethys. It had an eardrum bubble whose aim was to isolate sounds in the aquatic environment. It was much better adapted to the marine environment.
It is the proof that cetaceans come from terrestrial mammals, and more precisely from the ungulates. The mystery of the cetaceans' origin is often debated. For the paleontologist, this origin can be found in the Mesonychids family, which are carnivorous ungulates. But for the molecular biologists, it is in the Artiodactyles family; the herbivorous ungulates. Actually, our cetaceans are coming directly from the CETARTIODACTYLES family (that includes the Artiodactyles). These are the results of the research of J.G.M. Thewissen and his team from the Ohio University, USA. It is thanks to the Pakicetus, ancient cetacean of the tertiary era that they reached this conclusion. They noticed that a specific bone from the ankle, the astragal, had 2 pulleys allowing an important flexibility. Until now, it had only been observed in the Artiodactyles family, these herbivorous ungulates from which come the hippopotamus (see now why we had to go so far back in the evolution…). Another study led by Philipp D. Gingerich (Michigan University) arrives at the same conclusion. PAKICETUS and the Artiodactyles have indirect links between each other, but they are from the same group, the Cetartiodactyles. Furthermore, the studies from the two teams prove that cetaceans and Mesonychids have no link between them.

It is important to emphasize two things; firstly, apart from the same ancestral group, hippopotamus and Pakicetus have no link. Secondly, Pakicetus was not a marine animal (despite what was thought for a long time). The drawings showing him a good swimmer (and sometimes with webbed legs) and having an aquatic life are therefore incorrect. It is none the less the ancestor of dolphins and whales.

AMBULOCETUS: "The amphibian cetacean" Its posteriors limbs of large size allow efficient propulsion in the water by beating of the tail (the tail is still short). The anterior limbs, short and not mobile, are perhaps used as a rudder. Ambulocetus had a cetacean skull, fur and webbed legs. It was able to live totally emerged or immersed. Reminding of a sea lion, it was about 80 cm long.

Called Basilosaurus in the past (king of lizard), the ZEUGLODON measured 15 to 20 metres and weighted about 5 tonnes. It had a typical terrestrial dentition (molars, canines, incisors), not adapted to the marine life (fish slip on classical teeth). It hunted in shallow water and reproduced on the ground. Its vertebrae were not attached to each other (unlike the killer whales') and therefore gave a better mobility but meant that the animal had to sneak around similar to our current eels. Too much energy was spent for limited movement; Zeuglodon was not adapted to the marine world.

The Eocene, from -58 to -36 MY ago, will see the coming of the Basilosaurids, Protocetids and Dorudontines (these last ones have a similar appearance of our modern dolphins). But 40 MY ago, the earth moves again, changing again the temperatures and the direction of the marine currents. Most of the archeocetes will not survive this brutal change. The last archeocete (comes from ARKHIOS ; old et KETOS ; fish) dies 30 MY ago. But our famous Dorudontines will give birth to a large family. 35 MY ago, the Agorophiidae, ancestors to the Odontoceti, are very well adapted to the marine life. . They will disappear 20 MY ago, leaving the place, 5 MY earlier to the Kentriodontids.

An important event took place 25 MY ago: The family divides into the ODONTOCETI (with teeth) and the MYSTICETI (with baleen).

The odontoceti develop an echolocation system, which is a very effective biologic sonar. Their teeth are identical and cone shaped to better grab their prey. The mysticeti, in the other hand, will lose their teeth to develop a hair-fringed plate called baleen, which are used to filter plankton.

We are now in the Miocene period (-25 to -13 MY), also called the cetaceans Era. It is truly a time for species development in the oceans. The Kentriodontides will give birth to the DELPHINIDAE (here we are), the PHOCOENIDAE (porpoises), the MONODONT (beluga, narwhal) as well as the Albireonides (they will disappear before -2 MY). It is a very marine period.

The Pliocene (-13 to -2 MY), which ends the tertiary, will be the mammals' era as there will be a new species development on earth.

The Quaternary, which starts -2 MY ago, confirms the achievement of the marine species, our Killer whale is there. They will only evolve slightly. They actually have the forms and characteristics of dolphins and whales that we currently know. The main evolution will happen on earth (evolution or cataclysm, it's up to you). An animal, a primate, will evolve as well, becoming Homo Habilis. It will conquer the lands, decide on the species fate and even decide on its peers' fate. It is so confident and arrogant that, sometimes, Mother Nature makes it understand that She will decide on Mans' fate and not the other way round…

Some animals, living during the Eocene, have lived until today. Their evolution has been slow because their way of life has not been radically changed. It's the case of the HYDRODAMALIS (meaning 'young woman from water') that lived for 57 million years and was only discovered in 1741, in the Baring Straight. Man exterminated them in less than 30 years. Nice example of what human stupidity can do…
Today, Man is the main cause of the disappearance of the animal and plant species.