of pelvic and leg bones had been found be- 

 fore, but not enough to know whether 

 Basilosauriis bore working hind legs — the 

 crucial feature for our usual concept of a 

 satisfying intermediate form in both 

 anatomical and flinctional senses. 



In 1990, Phil Gingerich, B. H. Smith, 

 and E. L. Simons reported their excava- 

 tion and study of several hundred partial 

 skeletons of the Egyptian species B. isis. 

 which hved some five to ten million years 

 after Pakicetus. In an exciting discovery, 

 they reported the first complete hind limb 

 skeleton found in any whale — a lovely and 

 elegant structure (put together from sev- 

 eral partial specimens), including all 

 pelvic bones, all leg bones (femur, tibia, 

 fibula, and even the patella, or knee cap), 

 and nearly all foot and finger bones, right 

 down to the phalanges (the finger bones) 

 of the three preserved digits ("Hind Limbs 

 of Eocene Basilosaums: Evidence of Feet 

 in Whales," Science, vol. 249, pp. 

 154-57). 



This remarkable find might seem to 

 clinch our proof of intermediacy, but for 

 one small problem. The limbs are elegant, 

 but tiny (see accompanying figure of B. 

 isis on page 12), a mere 3 percent of the 

 animal "s total length. They are anatomi- 

 cally complete, and they did project from 

 the body wall (unlike the truly vestigial 

 hind limbs of modem whales), but they 

 could not have made any important contri- 

 bution to locomotion — the real functional 

 test of intermediacy. Gingerich and his 

 coauthors write: "Hind limbs of 

 Basilosaurus appear to have been too 

 small relative to body size to have assisted 

 in swimming, and they could not possibly 

 have supported the body on land." The au- 

 thors strive bravely to invent some poten- 



tial function for these minuscule limbs and 

 end up speculating that they may have 

 served as "guides during copulation, 

 which may otherwise have been difficult 

 in a serpentine aquatic mammal." (I regard 

 such guesswork as unnecessary, if not ill- 

 conceived. We need not justify the exis- 

 tence of a structure by inventing some pu- 

 tative Darwinian function. All bodies 

 contain vestigial features of little, if any, 

 utility. Structures of lost usefulness in ge- 

 nealogical transitions do not disappear in 

 an evolutionary overnight.) 



Verdict: Terrific and exciting, but no 

 cigar, and no bag-packer for creationists. 

 The limbs, although complete, are too 

 small to work as true intermediates must 

 (if these particular limbs worked at all) — 

 that is, for locomotion on both land and 

 sea. I intend no criticism of Basilosaurus, 

 but merely point out that this creature had 

 akeady crossed the bridge (while retaining 

 a most informative remnant of the other 

 side). We must search for an earlier inhab- 

 itant of the bridge itself. 



Case Three: Hind limb bones of appro- 

 priate size. Indocetus ramani is an early 

 whale, found in shallow-water marine de- 

 posits of India and Pakistan, and interme- 

 diate in age between the Pakicetus skull 

 and the Basilosaurus hind legs (cases one 

 and two above). In 1993, Gingerich, S. M. 

 Raza, M. Afif, M. Anwar, and X. Zhou re- 

 ported the discovery of leg bones of sub- 

 stantial size from this species ("Partial 

 Skeletons of Indocetus ramani [Mam- 

 malia, Cetacea] from the Lower Middle 

 Eocene Domanda Shale in the Sulaiman 

 Range of Punjab [Pakistan]," Contribu- 

 tions from the Museum of Paleontology of 

 the University of Michigan, vol. 28, pp. 

 393-416). 



2 Feet 



Two reconstructions show Ambulocetus, a fossil whale from Pakistan, standing, top, 

 and at the end of a swimming stroke, bottom. 



Adapted Irom Science, vol. 263. 14 January 1994 



Gingerich and colleagues found pelvic 

 bones, and the ends of both femur and 

 tibia, but no foot bones, and insufficient 

 evidence for reconstructing the full limb 

 and its articulations. The leg bones are 

 large and presumably functional on both 

 land and sea (the tibia, in particular, differs 

 little in size and complexity from that of 

 the related and fully terrestrial mesony- 

 chid Pachyaena ossifraga). The authors 

 conclude: 



The pelvis has a large and deep acetabulum 

 [the socket for articulation of the femur, or 

 thighbone], the proximal femur is robust, 

 the tibia is long.... All these features, taken 

 together, indicate the Indocetus was prob- 

 ably able to support its weight on land, and 

 it was almost certainly amphibious, as early 

 Eocene Pakicetus is interpreted to have 

 been.... We speculate that Indocetus, like 

 Pakicetus, entered the sea to feed on fish, 

 but returned to land to rest and to birth and 

 raise its young. 



Verdict: Almost there, but not quite 

 enough. We need more material. All the 

 right features are now in place — primarily 

 leg bones of sufficient size and complex- 

 ity — but we need a better sense of connec- 

 tion and function. 



Case Four: Large, complete, and func- 

 tional hind legs for land and sea — finding 

 the smoking gun. The first three cases, aU 

 discovered within ten years, surely indi- 

 cate an increasingly successful paleonto- 

 logical assault upon an old classic prob- 

 lem. Once you know where to look, and 

 once high interest spurs great attention, 

 full satisfaction often follows in short 

 order I was therefore delighted to read an 

 article by J. G. M. Thewissen, S. T. Hus- 

 sain, and M. Arif in the January 14, 1994 

 issue of Science ("Fossil Evidence for the 

 Origin of Aquatic Locomotion in Ar- 

 chaeocete Whales," vol. 263, pp. 210-12). 



In Pakistan, in sediments almost 400 

 feet above the beds that yielded Pakicetus 

 (and therefore a bit younger in age), 

 Thewissen and colleagues collected a re- 

 markable skeleton of a new whale — not 

 complete, but far better preserved than 

 anything previously found of this age, and 

 with crucial parts in place to illustrate a 

 truly transitional status between land and 

 sea. The chosen name Ambulocetus 

 natans (literally, the swimming walking- 

 whale) advertises the excitement of this 

 discovery. 



A. natans weighed some 650 pounds, 

 the size of a hefty sea Uon. The preserved 

 tail vertebra is elongated, indicating that 

 Ambulocetus still retained the long, thin 

 mammalian tail and had not yet trans- 



13 



