# The bone that proved whales used to walk > For a century the argument was about which land animal whales came from. Two skeletons dug out of Pakistan settled it, and the deciding evidence was an ankle. - **Publisher:** VOTVS (Fair coverage for everyone) — https://votvs.com - **Author:** VOTVS - **Published:** 2026-09-09 - **Language:** en - **Topic:** Deep Time - **Canonical URL:** https://votvs.com/en/articles/whales-walked-ankle-bone - **Tags:** evolution, fossils, whales, deep time - **Facts last verified:** 9 September 2026 --- A blue whale has no legs, no hips you would notice, and no reason to be on land. It also has, buried in the wall of its body, the remains of a pelvis. That is not a curiosity. It is a receipt. ## The sequence, with dates The fossils come mostly from what is now Pakistan, India and Egypt — Eocene coastline, then as now the right place to be buried in fine sediment. The Smithsonian dates the sequence like this: **Figure (StatRow):** Four steps out of the water and back into it — Dates from the Smithsonian National Museum of Natural History, Evolution of Whales. Eleven million years, start to finish. It is a short walk for something that ends in a blue whale. ## What actually changed Four things, in roughly this order, according to Berkeley's summary of the fossil series. **The ear went first.** Pakicetus was a land animal that would have looked something like a long-snouted dog, but its skull already resembles a whale in the inner ear region. Hearing adapted to water before the body did. **Then the nostrils walked backwards.** In the early forms they sit at the front of the snout, as they do on a dog. Across the sequence they migrate up and back until, in a modern whale, they are a blowhole on top of the head, above the eyes. **Then the limbs swapped jobs.** The forelimbs stopped carrying weight and became steering surfaces. The hind limbs shrank — Berkeley describes them becoming almost nonexistent, then tiny, then vestiges inside the body wall. The 1990 paper in *Science* that described what was left of them in *Basilosaurus* is titled "Evidence of Feet in Whales." **Then the tail took over.** It got longer and more muscular and grew horizontal flukes. Horizontal, not vertical like a fish — because the animal inherited a spine that bends up and down, the way a running mammal's does. A whale swims by galloping. ## The argument that would not close For most of the twentieth century the fossils showed *that* whales came from land mammals but not *which* ones. The favoured answer was the mesonychians, an extinct group of hoofed carnivores. It was a reasonable guess and it was wrong. Molecular work on living animals kept pointing somewhere else — at the artiodactyls, the even-toed hoofed mammals: deer, camels, pigs, hippos. That answer had a problem. The fossils did not obviously agree, and the two lines of evidence sat there contradicting each other. ## The ankle In September 2001, Thewissen, Williams, Roe and Hussain published skeletons of early Eocene pakicetids in *Nature*. The skeletons included the astragalus — the ankle bone. The artiodactyl astragalus has a shape found in no other group of mammals: a pulley at both ends, so the joint rolls in two places instead of one. Berkeley's description of the later basilosaurid version is worth reading twice: a pulley and a hooked knob pointing up towards the leg bones, as in artiodactyls. It was there, in the whales. The paper concluded that cetaceans are more closely related to artiodactyls than to any mesonychian, and the disagreement between the molecules and the bones closed. The whale's closest living relative is the hippopotamus. ## Why this one is worth knowing Not because it is strange, though it is. Because of the shape of the argument. Two independent methods — reading DNA in living animals, and digging up bones from 48 million years ago — were asked the same question and gave different answers. Nobody split the difference. People went and found more ankles. That is the part worth carrying around. A disagreement between two good sources is not a problem to be smoothed over; it is an instruction about where to dig next. ## Questions people ask ### Did whales really walk on land? Their ancestors did. The Smithsonian dates Pakicetus, a four-legged animal whose skull already shows the whale inner ear, to about 48 million years ago, and Ambulocetus, which was more aquatic with paddle-like hands and feet, to about 47 million years ago. ### What is a whale's closest living relative? The hippopotamus. Whales sit inside the artiodactyls, the even-toed hoofed mammals, alongside hippos, deer, camels and pigs. ### Why is an ankle bone such strong evidence? Because the artiodactyl astragalus has a distinctive double-pulley shape found in no other group. When that exact shape turned up in early whale skeletons, it placed whales inside the artiodactyls rather than with the mesonychians, the group they had previously been assigned to. ### Do whales still have leg bones? Reduced ones. Berkeley's summary of the fossil sequence describes hindlimbs becoming tiny and eventually surviving as vestiges inside the body wall. A 1990 paper in Science on Basilosaurus is titled, plainly, Evidence of Feet in Whales. ## Sources - Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls — Thewissen, Williams, Roe and Hussain, Nature, volume 413, 20 September 2001. https://www.nature.com/articles/35095005 - The evolution of whales — Understanding Evolution, University of California Museum of Paleontology, Berkeley. https://evolution.berkeley.edu/what-are-evograms/the-evolution-of-whales/ - Evolution of Whales Animation — Smithsonian National Museum of Natural History. https://naturalhistory.si.edu/education/teaching-resources/life-science/evolution-whales-animation - Hind Limbs of Eocene Basilosaurus: Evidence of Feet in Whales — Gingerich and colleagues, Science, volume 249, page 154, 1990. https://www.science.org/doi/10.1126/science.249.4965.154 --- Published by VOTVS. Free to quote with attribution and a link to https://votvs.com/en/articles/whales-walked-ankle-bone.