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The Tale of the Whale
The Winter 1996 issue of Pacific Discovery, published by the California Academy of Sciences, was devoted to whales. Among the nice articles and beautiful pictures is a particularly interesting article about the origins and early evolution of whales by Elizabeth Culotta, a writer for Science who covers evolution and ecology. Culotta is collaborating on a book on whale origins with Hans Thewissen, one of the scientists intimately involved in studying whale evolution. Her interviews with noted specialists underscore what tremendous progress in understanding whale origins has occurred just in the last few years. At least three new forms — Pakicetus, Ambulocetus, and Rodhocetus — have been found to fill in some of the gaps between the whales we know and their terrestrial ancestors, a group of mesonychid carnivores that lived in the Eocene epoch, some 60 million years ago. Along the way, paleontologists have learned a lot more about the evolution and relative timing of the adaptation of skulls, ears, jaws, backbones, and limbs for life in the open sea.
The problem of the origin of whales, of course, has long been one in which anti-evolutionists have been particularly interested. "Creation scientist" and former biochemist Dr Duane Gish liked to mock the traditional paleontological assertion that whales evolved from an ungulate ancestor. In his lectures, Gish would explain to his audiences that an ungulate was a hoofed mammal, like a cow. Then he would show a cartoon of Jersey cows with bells around their necks and mermaid-like tails, asking his audience if they thought such an evolutionary transition were possible. No paleontologist, of course, suggested that whales evolved from cows, but this seemed to make little difference to Gish.
Culotta’s article points out that the fossil relatives of living whale groups are recognized not primarily by the great size and specialized swimming adaptations that generally describe today’s whales, but instead by features of their skulls and teeth that are shared only with living whales. However, what interests most people is how whales came to take up an aquatic existence.
The first steps in whale evolution included a reduction of the pelvis and hindlimbs even while these structures still remained fully functional for locomotion and bearing weight. By the evolutionary stage represented by Ambulocetus, we find elongated hands and feet, a longer skull, and larger teeth. But the tail is still long and lacks a fluke, and the toes still end in little hooves.Thewissen and his co-workers suggest that this animal swam by vertical undulations and was amphibious (lived both on land and in water).
Rodhocetus, which occurs a bit later in time, has a shortened neck and more reduced hindlimbs. It appears to have been a more open-water swimmer, while still retaining many terrestrial features. These animals are still in the 5- to 8-foot range and lived about 50 million years ago. However, Basilosaurus shows that by 40 million years ago, whales had become much larger and more like the living groups.
As its name suggests, Basilosaurus was thought to be a dinosaur or marine reptile when it was first discovered in the early 19th century, but its mammalian affinities were soon recognized. NCSE Reports reported that Duane Gish dismissed it as a reptile (Anonymous, 1990), however, to my knowledge he has not published a peer-reviewed scientific paper documenting his evidence. Meanwhile, the rest of us may find interesting some recent scientific efforts on early whales, many of which are summarized in a couple of nice (and short) pieces by Dr Michael Novacek, a pre-eminent mammalian paleontologist and Vice President of the American Museum of Natural History in New York (Nature 1993, 361:298-299; and 1994, 368:807; Other relatively accessible pieces are listed at the end of this article.)
A more recent creationist postscript to the whale saga began not long after the recent "Firing Line" television program on evolution. Science teacher Larry Flammer wrote to law professor and self-proclaimed Darwin expert Philip Johnson, asking about his comment that a "recent article in Science" refuted what biologist Dr Ken Miller said on the show about whale evolution. Johnson referred Flammer to microbiologist Dr Michael Behe, who responded by citing a single sentence in Novacek’s 1994 article (listed above): "Ambulocetus, Rodhocetus and other more aquatically specialized archaeocetes cannot be strung in procession from ancestor to descendant in a scala naturae." Flammer checked with NCSE as to whether Johnson’s interpretation was an accurate statement of Novacek’s views.
The excerpted sentence, which begins the last paragraph of a nearly full-page commentary, is classically taken out of context. Novacek spends the entire article explaining the traditional problem of the lack of fossil intermediates between land mammals and whales, then shows how recent discoveries are morphologically, functionally, and stratigraphically intermediate. Novacek’s quoted sentence means only to say that we do not regard these things as successive direct ancestors. This is because Ambulocetus, Rodhocetus, Pakicetus, and other forms each have their own "autapomorphies" or distinguishing characteristics, which they would have to lose in order to be considered direct ancestors of other known forms. (For general information, modem evolutionary biologists do not search for ancestors, but for relationships among organisms based on the new appearances of heritable features, which are represented in the form of cladograms.)
Here’s the important part. Any modern paleontologist or evolutionary biologist knows that the chances of finding an actual lineal ancestor to a later form are very small. Imagine your own chances if you returned to where you think your 6th-century ancestors are buried and started to dig looking for them. Even if you found a graveyard from that period, what are the chances that any of the bones would belong to your direct ancestors? A distant cousin, maybe. But couldn’t you tell a lot about those people and how they lived, the stage of cultural development in their society, their possessions and features? Would it be unreasonable to suppose that your direct lineal ancestors had the same features and lived in more or less the same ways?
This is exactly the approach that Novacek is taking to the whale fossils. He is clearly saying that these fossils show progressive specialization of features common to whales today, even if they are not the direct lineal ancestors of whale species that survive in modern oceans. This is what he means when he writes: "Nonetheless, these fossils are real data on the early evolutionary experiments of whales." In previous paragraphs he pointed out that archaic whales first evolved cetacean features of the middle ear, muzzle, skull roof and teeth; then an amphibious habit with front-to-back flexion of the body for providing locomotion in the water aided by paddle-like hind feet (Ambulocetus); then shorter neck vertebrae, unfused hip vertebrae, and the reduced femur (Rodhocetus); and so on. Finally, Novacek writes, "They powerfully demonstrate transitions beyond the reach of data, whether molecular or morphological, derived from living organisms alone."
Readers may judge for themselves, based on what Novacek actually said, but in my view it is not responsible scholarship, nor accurate representation, to tell someone that Novacek’s article refuted what Miller said about whale evolution. Novacek, Gingerich, Thewissen, and other scientists are understandably upset about the distortion of their work and publications, but it seems to make little difference. Sadly, as long as creationists can pretend to hold scientists to a semantically strict and epistemologically unreasonable definition of ancestry, they will continue to try to fool the public. Readers who are not professional scientists might be interested to know, however, that if someone tried this sort of misrepresentation in the scientific literature, they would be sat down hard by reviewers and by the authors themselves. Understanding what someone actually said and meant in his work is the first precept of scholarship.
ReferencesAnonymous. Gish reclassifies Basilosaurus as a mososaur? NCSE Reports Sept-Oct 1990; 10(5): 11.
Berta A. 1994. What is a whale? Science 1994 Jan 14; 263:180-1.
Gingerich PD, Raza SM, Arif M, Anwar M, Zhou X. New whale from the Eocene of Pakistan and the origin of cetacean swimming. Nature 1994; 368:844-7.
Gingerich PD, Smith BH, Simons EL. Hind limbs of Eocene Basilosaurus: Evidence of feet in whales. Science 1990; 249:154-7.
Thewissen JGM. Madar SI, Hussain S. Ambulocetus natans, an Eocene cetacean (Mammalia) from Pakistan. Courier Forschungsinstitut Senckenberg 1996 Jun 28; 191:1-86.
Thewissen JGM, Hussain ST, Arif M. Fossil evidence for the origin of aquatic locomotion in Archacocete whales. Science 1994 Jan 14; 263:210-2.
Thewissen JGM. Phylogenetic aspects of cetacean origins:A morphological perspective. Journal of Mammalian Evolution 1994; 2: 157-84.