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Philtalic Vignettes in Prehistory-Cetacean Evolution

Recently I decided to get back into philatelic exhibiting. Twenty years ago, I started showing a thematic exhibit entitled Whales and Whaling. It rose to the gold level (with some Grand Awards) at local shows and the vermeil level at national shows. Lately I’ve been working on revising that exhibit, and this month’s column is a result of some of that research.

Biologists have long known that the animals in the Order Cetacea (whales, dolphins and porpoises) descended from four-footed land mammals. Like all mammals, whales use lungs to breathe air and they give birth to young that are sustained by milk produced by the mother. They also have five fingered hands that have developed into pectoral fins. The photograph in Figure 1 shows my daughter Emelia demonstrating that her five fingers match the five fingers of the Humpback Whale skeleton at the Louisville Science Center. (It’s an old photograph as Emelia is now 22 years old!)

Recent fossil evidence and DNA evidence indicates that the ancestor of all whales probably came from the Order Artiodactyla, the even-toed hoofed mammals, which first appeared at the beginning of the Eocene Epoch, about 55 million years ago (MYA). The Eocene Epoch lasted from 55.8 MYA to 33.9 MYA. Some of these animals returned to the sea about a million years later, evolving into the first primitive whales. These very early whales belong to the Suborder Archaeoceti, within the Order Cetacea.

One of these very primitive proto-whales is Pakicetus which is known from several finds in Pakistan. Pakicetus first appears in the fossil record in the Early-Middle Eocene, about 50 MYA. This proto-whale looked very much like a wolf with a long, thick tail. Pakicetus was hairy and walked on four hooves but was definitely aquatic and probably roamed shallow seas and rivers. Its nostrils were still located at the end of its snout, but it also possessed several distinctive features, all of which are unique to whales: an elongated skull; primitive, unspecialized, triangular teeth; and the whale’s inner ear. The structure of the whale’s inner ear allows it to hear underwater better than any other marine mammal. It also allows the whale to be an acrobatic swimmer without getting dizzy. This especially adaptive ear is unlike the ear of any other mammal in structure and position.

Two additional proto-whales have been discovered very recently in Pakistan. Ambulocetus and Remingtonocetus also lived during the Early-Middle Eocene. Both appear in deposits that are about 49 million years old. Ambulocetus was much larger, reaching a length of twelve feet, while Remingtonocetus was only about the size of an otter. Ambulocetus and Remingtonocetus show additional adaptation to marine life with webbed hands and feet. Both these discoveries are so new that they do not yet appear on any philatelic item.

   Figure 2

Protocetus, shown in Figure 2, appeared about 45 MYA, during the Middle Eocene. Protocetus had a more streamlined body than its ancestors and its nostrils were located about half way up its snout. It had also developed flukes, or horizontal bars, on its tail that aided in maneuvering in the water, as well as flippers in place of hands. In addition, it is the first proto-whale found outside Pakistan, with fossil remains known from Africa and North America as well as Asia.

One of the first prehistoric whales to be discovered was Basilosaurus, shown in Figure 3.

    Figure 3 - Comoro Islands #895g shows Basilosaurus, a whale from the late Eocene Epoch.

The first fossil remains were found in 1832. The name Basilosaurus is a result of these fossils initially being mistaken for a marine reptile. British paleontologist Richard Owen, shown in Figure 4,

   Figure 4 - Montserrat #794 shows British biologist Reichard Owens who recognized that the Basilosaurus was not a marine reptile but a marine mammal. Owens is also known as the originator of the term "dinosaur".

later examined the fossils and realized that they actually belonged to a marine mammal. He suggested the name Zeuglodon (yoked tooth) after the animal’s double-rooted molars. Unfortunately, the rules governing the naming of species gives priority to the first name even if that name is not an accurate description of the fossil remains. Basilosau-rus lived during the Late Eocene, about 38 MYA, and may have been worldwide in distribution. Extensive fossil remains have been found in the southeastern United States, Australia and Egypt.

This prehistoric whale was sixty to eighty feet long with a tail fluke and unused hind limbs. In fact, the hind limbs and the pelvis were not attached to the rest of Basilosaurus’ skeleton. Basilosau-rus lived entirely in the ocean with its thin body shape giving it the look of a sea serpent.

Another Late Eocene whale was Zygorhiza, shown in Figure 5.

   Figure 5 - Comoro Islands #895f shows Zygorhiza, another whale from the late Eocene Epoch.

Zygorhiza was much smaller than Basilosaurus at only about twenty feet long, but it had a much more robust body shape. This prehistoric whale is also known from fossil sites in the southeastern United States.

Basilosaurus and Zygorhiza were both completely recognizable whales in body type and both lived entirely in ocean environments. Excellent fossil remains of Basilosaurus and Zygorhiza have been found in Mississippi. On March 26, 1981, Concurrent Resolution #557 named Basilosaurus and Zygorhiza the State Fossils of Mississippi. This resolution is commemorated in Figure 6.

   Figure 6 - Pictorial cancel commemorates the naming of Basilosaurus and Zygorhiza as the state fossils of Mississippi.

The whales had begun their partially aquatic lives in shallow seas during the early Eocene and within 10 million years had become fully adapted to life in the open sea.

During the Oligocene Epoch (33.9 MYA to 23.03 MYA), the two modern lineages of whales began to develop from their Archaeocetes ancestors. Modern whales are divided into two suborders. The suborder Odontoceti contains all the toothed whales including dolphins, porpoises, Sperm Whales, etc. The suborder Mysti-ceti contains all the whales with baleen plates instead of teeth and includes Blue Whales, Humpback Whales, Right Whales, etc. Aetiocetus, a late Oligocene whale, first appeared about 24 MYA and is one of the ancestors of whales in the suborder Mysticeti. It had teeth but also had a loose jaw hinge like later baleen whales.

By the Miocene Epoch (23.8 to 5.3 MYA), Odontoceti and Mysticeti whales were fairly common and show up frequently in fossil deposits. One very common sight in the mid to late Miocene ocean was the long-snouted Eurhino-delphis, shown in Figure 7.

   Figure 7 - Antigua and Barbuda #2254 shows Eurhinodelphis, a long snouted dolphin from the mid to late Miocene Epoch.

This dolphin was 6-7 feet long and belonged to the suborder Odontoceti. Fossil remains have been found on both sides of the Miocene Atlantic Ocean from what are now Maryland and Virginia as well as France and Belgium.

Another member of the Suborder Odonticeti from the mid to late Miocene Epoch is Orycterocetus, shown in Figure 8.

  Figure 8 - Tristan da Cunha #619b shows Orycterocetus, a mid to late Miocene ancestor of the modern Sperm Whale.

This 10 million year old whale is morphologically similar to the modern Sperm Whale, shown in Figure 9,

   Figure 9 - Southwest Africa #440 shows the modern Sperm Whale

and has been grouped in Physeteridae, the same family which contains the Sperm Whale and Pygmy Sperm Whale.

Another Cetacean from the mid to late Miocene is Cetotherium, shown in Figure 10.

   Figure 10 - Comoro Islands #895i shows Cetotherium, a baleen whale from the mid to late Miocene Epoch.

By 15 MYA Cetotherium had made the complete transition from teeth to baleen plates, making it an early member of the suborder Mysticeti. This whale was small at only 13 feet, much smaller than most modern baleen whales.

Whales continued to evolve during the Pliocene Epoch (5.3 to 1.8 MYA). One of these Pliocene whales is Odobenoce-tops, shown in Figure 11.

   Figure 11 - A recent issue from Liberia shows Odobenocetops, a tusked whale from the Pliocene Epoch.

This rather strange creature, which lived 5 MYA, had no teeth but did have two tusks of different length. Odobenocetops also had large muscular lips that would have allowed it to suck its prey out of shells or hiding places in the coral.

Modern whales have continued to adapt. Today the order Cetacea contains over 89 species in ten different families. They dominate the world’s oceans and seas. The river dolphins even inhabit fresh water rivers such as the Amazon and Ganges. The order Cetacea also contains the largest animal that has ever lived. The Blue Whale, shown in Figure 12, reaches a length of 100 feet and weighs up to 95 tons.

  Figure 12 - Southwest Africa #442 shows the Blue Whale, the largest animal ever known.

Over the last fifteen years, we have learned more and more about the ancestors of modern whales. And there is much more to learn as new fossils are found. But we must also focus on preventing the extinction of many of the large baleen whales that are endangered due to over hunting by humans. Hopefully, as we learn more about their ancient ancestors, we can also save the current generations and protect their future.

Contact's: Dennis Carman