Searching for Whale Fossils Use Whale Evolution Data Table for chart.
For many years fossils of various primitive whales between
25 and 45 million years old have been found. No fossils of modern type whales have
been found in this time frame. Examples of the early whales would include Dorudon,
Prozeuglodon, and Zygorhiza. See
fossil picture #1. The actual ages of these whales
pictured ranged from 39-36 mya. Place fossil picture
#1 at 36 mya. As more fossils have been discovered from the early Eocene
Period, we searched for a land mammal from which primitive whales most likely were
Sinonyx was a 5 feet, wolf-sized hyena-like, land-dwelling mammal with hoofs. It was from the order Condylarthra whose branches evolved into modern deer, cattle, pigs, elephants and hippos. It belonged to the Mesonychids, a group of animals that had teeth features and other skull features that were common to the earliest primitive whales. See Fossil Picture #2. Sinonyx had a large head and tiny hooves on all of its toes. They had 44 teeth, just like all primitive mammals and they had different types of teeth. The molars were very narrow shearing teeth, especially in the lower jaw, but possessed an elongated muzzle used to hunt fish like whales and dolphins. Mesonychids lived from 58-34 mya. Place fossil picture #2 at 55 mya.
This was all the information on whale evolution until 1983
when the empty gap between land animals and whales began to fill.
The first discovery was by whale specialist Philip Gingerich was Pakicetus. See fossil picture #3. In Pakistan, Gingerich found a broken skull with lots of teeth, in 50 million year old river sediment near what was once a shallow sea. Some of Pakicetus's teeth were like Sinonyx's in fossil picture #2 and some of the teeth were like those found in later primitive whales like Dorudon and Prozeuglodon in fossil picture #1. Pakicetus's skull was the same shape as late Eocene Period primitive whales like Dorudon. Pakicetus's ears were different than whale ears. They couldn't hear well in water or dive very deep. Pakicetus was 5 feet long. Place fossil picture #3 at 50 mya
In 1990, in Egypt, Gingerich and others discovered the fossilized hind limbs of Basilosaurus, a large serpentine primitive whale that lived from 39 to 36 million years ago. See fossil picture #4. The hind legs were very tiny. Basilosaurus's foot and the lower leg only measured 35 cm. These legs would have been to small to support the animals movement on land. But they are better devloped than the legs found embedded in the hip region of some modern whales today. This animal had a large single nostril that had migrated to the top of its head. It was 50 feet long and had 67 vertebrate. Place Fossil Picture #4 at 37 mya
In 1994, in the middle Eocene (46-7 million years ago), Gingerich found the remains of Rodhocetus with well-developed hip bones. See Fossil Picture #5. By looking at its skeleton scientists have decided that the back legs could be used, but Rodhocetus probably could not get around as well on land as its predecessors. The backbone shows it had powerful tail muscles and probably swam like a whale does today. The Rodhocetus may also have had whale-like tail flukes. Rodhocetus's skull showed the whale like characteristic of the nostrils being in a blow hole position. The Rodhocetus also had enlarged ear capsule bones like modern whales. It was a good 10 foot long tail-swimmer with a reduced ability to walk on land. Place Fossil Picture #5 at 46 mya
In late 1994, Hans Thewissen (one of Gingerich's students) discovered what he called Ambulocetus natans , "the walking whale that swims". Ambulocetus was a complete fossil, found in 48 million year old sediment, See Fossil Picture #6. Ambulocetus was as large as a sea lion. It had a long and slender tail that showed no use for swimming. It had short, strong hind legs, with huge feet. Each toe had a tiny mesonychid (See Fossil Picture #2)-type hoof. The head had a long snout and it didn't have a blow hole. It probably walked on land like a sea lion. Ambulocetus had teeth similar to Sinonyx's and early whales and ate fish. It probably swam with an up and down motion from its hind quarters like a sea otter. It used its feet like paddles. It was a 4-legged 10 foot long cetacean (water mammal). Place Fossil Picture #6 at 48 mya
Recent DNA work and examination of of early whale ankles has suggested that Mesonychids might not be the land ancestors of whales. These studies suggest that hippos may be the closet living "cousins" to whales. But there is no fossil evidence to prove this.