In the case of mesonychids, the relationship to archaeocetes is based on the most general of similarities. As Van Valen acknowledged in the original article proposing mesonychid ancestry:
[M]any features of the skull of Protocetus [an early archaeocete - AC] are not similar to those of either the Hyaenodontidae or the Mesonychidae (or to any other terrestrial mammal known to me) and probably represent to a considerable extent a reorganization of the skull, the chain of effects resulting from adaptation to hearing, feeding, locomotion, and other functions in an aquatic existence.[11] This point was later echoed by Edwin Colbert: “In general this [archaeocete] skull appears as if it might have been derived from a mesonychid type, but there is little beyond certain general resemblances to support such a relationship.”[12] Others have likewise noted that the cited similarities in skull and dental characters “are not all clear-cut.”[13] One need only compare the reconstructed skull of the late Paleocene Sinonyx jiashanensis to that of an early archaeocete to appreciate these remarks.[14 ]
Ayden Turner
>Amphibious Archaeocete to Fully Marine Archaeocete
The second claim in the evolutionists’ explanation of the origin of whales is that an amphibious archaeocete evolved into a fully marine archaeocete. It is believed that this transformation is documented by a sequence of intermediate forms, what one writer called the “sweetest series of transitional fossils an evolutionist could ever hope to find.”[15] This series, which spans 10-12 million years of the Eocene, includes Pakicetus inachus, Ambulocetus natans, Rodhocetus kasrani, Indocetus ramani, Protocetus atavus, and Basilosaurus isis.[16] It is important to understand that, in calling these creatures a “series of transitional fossils,” the evolutionist does not mean that they form an actual lineage of ancestors and descendants. On the contrary, they readily acknowledge that these archaeocetes “cannot be strung in procession from ancestor to descendant in a scala naturae.”[17 ] What they mean is that these fossils show a progressive development within Archaeoceti of certain features found in the later, fully marine forms such as Basilosaurus. (The specific features relate mainly to the middle ear and the appendicular skeleton.) This progression of features is believed to correspond to changes that were occurring in the actual basilosaurid lineage.
Gavin Ward
Whether the early archaeocetes form a series or sequence of intermediate forms depends, of course, on their morphology and their stratigraphic position. The claim is that, for each of these fossils, the degree of evolutionary advancement corresponds to the stratigraphic position. In other words, the older the fossil the less advanced its features; the younger the fossil the more advanced its features. It is this correspondence of form and position (age) that provides the impression of directional transformation through time.
The generally accepted order of the archaeocete species, in terms of both morphological (primitive to advanced) and stratigraphical (lower/older to higher/younger) criteria, is Pakicetus, Ambulocetus, Rodhocetus, Indocetus, Protocetus, and Basilosaurus (see note 16). One problem for this tidy picture is that the stratigraphical relationships of most of these fossils are uncertain.
In the standard scheme, Pakicetus inachus is dated to the late Ypresian, but several experts acknowledge that it may date to the early Lutetian.[18] If the younger date (early Lutetian) is accepted, then Pakicetus is nearly, if not actually, contemporaneous with Rodhocetus, an early Lutetian fossil from another formation in Pakistan.[19] Moreover, the date of Ambulocetus, which was found in the same formation as Pakicetus but 120 meters higher, would have to be adjusted upward the same amount as Pakicetus.[20] This would make Ambulocetus younger than Rodhocetus and possibly younger than Indocetus and even Protocetus.[21]
Jace Mitchell
In the standard scheme, Protocetus is dated to the middle Lutetian, but some experts have dated it in the early Lutetian.[22] If the older date (early Lutetian) is accepted, then Protocetus is contemporaneous with Rodhocetus and Indocetus. In that case, what is believed to have been a fully marine archaeocete was already on the scene at or near the time archaeocetes first appear in the fossil record.[23]
Given the significance evolutionists have attributed to these fossils in their battle with creationists, one cannot help but wonder whether their stratigraphical arrangement in the standard scheme has been influenced by their morphology. One committed to evolution would tend to be less critical of dates that placed these fossils in a morphological sequence and more critical of dates that disrupted that sequence.[24] As the diversity and shifts of expert opinion indicate, stratigraphical correlation is more an art than is commonly appreciated.
Samuel Torres
Based on the foregoing, it is reasonable to believe, even from within an evolutionist framework, that all the early archaeocetes were essentially contemporaries. Basilosaurus isis, on the other hand, was a gigantic marine archaeocete dating to the early Bartonian.[25] Evolutionists suspect that basilosaurids descended from the earlier Protocetidae (which includes the archaeocetes discussed above), but specialists admit there is a “lack of clear ancestor to descendant relationships.”[26] Indeed, the tremendous size difference between Basilosaurinae and protocetids casts doubt on that hypothesis. All protocetids were less than ten feet long, whereas Basilosaurus cetoides was over 80 feet in length, and Basilosaurus isis was over 50 feet.[27] It has been calculated that, even in a rapidly evolving line, changes in size are usually on the order of only 1-10% per million years.[28]
Lacking a cogent argument that Basilosaurus isis actually descended from protocetids, evolutionists claim it is transitional in the sense that it exhibits features between the earlier protocetids and the later cetaceans. If Protocetus was fully marine, as some experts now believe, it is questionable whether and to what extent the features of Basilosaurus can be characterized as more “advanced.” But more importantly, if Basilosaurus did not descend from protocetids and was not ancestral to cetaceans (see below), what does the presence of intermediate features in Basilosaurus establish? It seems the most one could say is that it indirectly supports the claim of descent with modification by showing a creature similar to the creature hypothesized to be in the actual lineage. Creationists find this too weak to carry the extraordinary claim of cetacean evolution.
Carter Brown
>Archaeocetes to Modern Cetaceans
The third claim in the evolutionists’ chain of events is that archaeocetes gave rise to modern cetaceans. This is sometimes asserted as a fact, but the relationship between these suborders has long been debated. There are major differences between the archaeocetes and cetaceans (e.g., body shape, thoracic fin structure, and skull arrangement) which have led many experts to deny that archaeocetes gave rise to odontocetes or mysticetes.[29] As George Gaylord Simpson concluded:
Thus the Archaeoceti, middle Eocene to early Miocene, are definitely the most primitive of cetaceans, but they can hardly have given rise to the other suborders. The Odontoceti, late Eocene to Recent, are on a higher grade than the Archaeoceti and, on the average, lower than the Mysticeti, middle Oligocene to Recent, but apparently were not derived from the former and did not give rise to the latter.[30]
Kayden Gonzalez
The point was reiterated two decades later by A. V. Yablokov, who wrote, “It is now obvious to most investigators that the Archaeoceti cannot be regarded as direct ancestral forms of the modern cetaceans.”[31] This was the consensus opinion until relatively recently.[32] The current leaders in the field believe that archaeocetes were ancestral to modern whales, but there is no agreement on which family of archaeocetes was involved. In fact, all three families (Protocetidae, Remingtonocetidae, and Basilosauridae) have been proposed.[33] This is particularly revealing when one considers how radically different Remingtonocetidae is from the other archaeocetes.[34]
In addition, no chain of descent from archaeocetes to modern whales has been identified. The phylogenetic relationships among major lineages within the Cetacea continue to be “very poorly understood,” which is why recent phylogenies are dominated by dead ends, broken lines, and question marks.[35] As for Basilosaurus isis, it is generally recognized that Basilosaurinae was an isolated subfamily that had nothing to do with the origin of modern whales.[36]
Hunter Hall
>Endnotes
[1] E.g., Stephen Jay Gould, “Hooking Leviathan By Its Past,” Natural History (April 1994): 12; Carl Zimmer, “Back to the Sea,” Discover (January 1995): 83; Elizabeth Culotta, “It’s A Long Way From Ambulocetus,” Pacific Discovery (Winter 1996): 16. Szalay and Gould divided Mesonychidae into three subfamilies: Mesonychinae, Hapalodectinae, and Andrewsarchinae. Frederick S. Szalay and Stephen Jay Gould, “Asiatic Mesonychidae (Mammalia, Condylarthra),” Bulletin of the American Museum of Natural History 132 (1966): 156. However, “mesonychids are now often given ordinal rank as either Mesonychia or Acreodi.” Maureen A. O’Leary and Kenneth D. Rose, “Postcranial Skeleton of the Early Eocene Mesonychid Pachyaena (Mammalia: Mesonychia),” Journal of Vertebrate Paleontology 15, no. 2 (1995): 402. Current thinking is that Hapalodectinae should be placed in its own family. Xiaoyuan Zhou, Renjie Zhai, Philip D. Gingerich, and Liezu Chen, “Skull of New Mesonychid (Mammalia, Mesonychia) From the Late Paleocene of China,” Journal of Vertebrate Paleontology 15, no. 2 (1995): 387, 396-98.
Ayden Adams
[2] The scenario is sketched in Keith Banister and Andrew Campbell, eds., The Encyclopedia of Aquatic Life (New York: Facts on File Publications, 1985), 294-296. See also Culotta, 16. The order Cetacea includes the whales, porpoises, and dolphins. The 75 to 77 living species are divided into 13 or 14 families and two suborders: Mysticeti (baleen whales) and Odontoceti (toothed whales, dolphins, and porpoises). The extinct suborder Archaeoceti is a wastebasket group that includes all ancient toothed Cetacea that lack the cranial features of Odontoceti and Mysticeti. It is comprised of three extinct families: Protocetidae, Remingtonocetidae, and Basilosauridae. The family Protocetidae includes the extinct subfamily Pakicetinae. The family Basilosauridae is comprised of two extinct subfamilies: Dorudontinae and Basilosaurinae. See, R. Ewan Fordyce and Lawrence G. Barnes, “The Evolutionary History of Whales and Dolphins,” Annual Review of Earth and Planetary Science, 22 (1994): 419, 427-31.
[3] Zimmer, 84.
[4] Leigh Van Valen, “Deltatheridia, A New Order of Mammals,” Bulletin of the American Museum of Natural History 132 (1966): 92.
[5] Frederick S. Szalay, “The Hapalodectinae and a Phylogeny of the Mesonychidae (Mammalia, Condylarthra),” American Museum Novitates 2361 (1969): 25; for application of statement to archaeocetes, see figure 19, p. 24.
Parker Walker
[6] Szalay and Gould, 169-170 lists Dissacus as the only middle Paleocene mesonychid known at the time. Dissacus sensu Szalay and Gould was later divided into Dissacus and Ankalagon (type species being Dissacus saurognathus, which is Dissacus carnifex of Osborn and Earle). Leigh Van Valen, “Ankalagon, New Name (Mammalia: Condylarthra),” Journal of Paleontology 54, no. 1 (1980): 266. Microclaendon, which was not listed by Szalay and Gould, is now generally classified with triisodontines rather than mesonychids. Philip D. Gingerich, “Radiation of Early Cenozoic Didymoconidae (Condylarthra, Mesonychia) in Asia, With a New Genus From Early Eocene of Western North America,” Journal of Mammalogy 62, no. 3 (1981): 535. It is noteworthy that the skull of neither Dissacus nor Ankalagon has been recovered. These genera are known from jaws, teeth, and rather limited postcrania.
[7] Discoveries of Dissacusium and Hukoutherium were first published in 1973; discovery of Yangtanglestes was first published in 1976. Li Chuan Luei and Ting Su-Yin, “The Paleogene Mammals of China,” Bulletin of Carnegie Museum of Natural History 21 (1983): 1-93. Dissacus and Ankalagon are the only Paleocene mesonychids for which postcrania have been described. O’Leary and Rose, 401.
