Period: Middle Paleogene (Late Eocene, Middle Priabonian)
Date: 36,500,000 BC
Location: Faiyum Coast
The beast sleeps. It is dawn, but there is a furious storm on the horizon and the rising Sun is battling to be seen. Purple thunderheads reflected in the sea’s surface make it look like gigantic scarf of maroon silk billowing in the wind. Every so often the beast’s sinuous back breaks through. It is swimming slowly, part of its brain still alert to the need to keep moving, to rise to the surface to breathe.
The horizon lickers with lightning and the beast awakes. For a second its head rises out of the water, revealing a long snout etched with deep scars, the result of violent fights with others of its kind, evidence that this is a male. The beast is an Archaeocete Cetacean – Basilosaurus, the most fearsome Cetacean ever, on his way to a bloody massacre.
Basilosaurus is one of the Mammals’ greatest success stories. During the Eocene epoch of the Paleogene period, Mammals in general have greatly diversified into many small and large forms and inhabiting every continent – even entering the waters of the world. Certain Mammals have even taken on the roles of the now-extinct non-Avian Dinosaurs. Africa has early Proboscideans such as Palaeomastodon, and North America (as well as Asia) the advanced forms of Rhino/Hippo-like Dinoceratans. Eurasia and North America are home to the Brontotheres, giant Rhino-like Odd-Toed Ungulates such as Embolotherium, and to large carnivores such as Sarkastodon, an 800-pound Oxyaenid from Asia which resembles a Carnivoran. In the seas there are mighty Archaeocete whales such as 49 to 59 foot long Basilosaurus as well as the smaller species that it hunts.
This area will one day be the center of the future Sahara Desert, but for the moment most of North Africa is covered by a shallow continental sea, part of the once-mighty Tethys Sea, an ancient waterway running east-west between Asia and the Atlantic Ocean. The nearby coastline is thick with mangrove swamps, backed by dense rainforest filled with a lively cocktail of life: Rodents, primitive Proboscideans, Hyaenodonts, Bats, Crocodilians and Snakes. Inland lakes and swamps wear a floating clock of Water Lilies and small to large wading Birds move through or tiptoe across the flimsy leaves, some having inordinately long toes helping to spread their weight. There is no hint of the great desert that will become this place in the far future.
Just ahead of the Basilosaurus, the water shallows over a sandbank. The Basilosaurus does not quite run aground, but much of its body is forced above the surface. The front limbs are flippers, with the “fingers” enclosed in skin, a feature of all fully-aquatic Cetaceans. Other than that, Basilosaurus does not look much like a whale of the distant future. Its body is slim and sinuous, some 50-65 feet long. The reason for this sleek body is that Archaeocete Cetaceans like Basilosaurus have none of the blubber that their descended relatives will develop to keep them warm as they move into colder, even polar waters. Millions of years from now, the blubber of Bowhead Whales will be 17 to 20 inches thick. But the Archaeocetes of places like the Tethys have no need for insulation: the brackish waters and shallow seas through which they swim are tepid.
Yet as the Basilosaurus ploughs over the sandbank, its tail rises up and one glance at that immediately identifies it as a whale. A pair of large flukes held in the horizontal plane causes a tremendous splashing as the tail moves up and down, powering its owner into deeper water. This arrangement of tail flukes and their up-and-down movement are unique to strict ocean-going Cetaceans.
A spout of water vapor, some 15 feet high explodes vertically into the air. The Basilosaurus is taking a breath with a technique that is another giveaway to it being a fully aquatic Cetacean: it blows stale air out of its lungs and replaces it with fresh. The spout is visible because water droplets form when the relatively warm air expelled from the lungs comes into contact with cooler outside air. To help them take breaths at the surface more easily, the nostrils of future whales will shift back towards the top of the head and become blowholes, with special structures to seal them during a dive.
So, Bailosaurus is very much a whale, but other than its snakelike body shape how does it differ from future ones? And how is it related to them?
Part of the answer lies at the back of its body, where it has a pair of tiny, 14-inch-long legs, complete with what appear to be feet. These are testimony that its ancestors (some 20 million years back) were quadrupedal land Animals, which had begun to move into the water to hunt and feed. From this amphibious way of life some of them made the next step, immersing themselves for their wholes lives. Two lineages of these Creatures will become the dominant marine Mammals of the future – the Toothed Whales and the Baleen Whales. Basilosaurus is in fact not a member of either of these parvorders, but an aberrant branch from the common stock of origin, Archaeocetes.
To Be Continued