The journal Evolution and Education Outreach is a valuable resource to anyone interested in or teaching evolution. Fortunately, it’s just been made an open-access journal, so anyone can read it free online (link is here). While perusing the articles, I found one that I thought was really good for not only teaching students about macroevolution, but learning about one of its paradigmatic cases: the evolution of whales from their ancestors—small hoofed mammals. The article, by Thewissen et al., is called “From land to water: the origin of whales, dolphins, and porpoises“, and you can download the pdf here.
Although the article is four years old, it’s not out of date and it’s easily accessible to non-scientists. I like it because it completely destroys the ID and claim notion that although there has been “microevolution” (minor changes in form within animal or plan lineages), we don’t see any cases of “macroevolution” (major transitions between “types” of animals or plants). That notion is absolutely belied by the fossils, for we can see macroevolutionary transitions from fish to amphibians, amphibians to reptiles, reptiles to mammals, reptiles to birds, and so on. And, of course, we have the macroevolutionary transition from our early ancestors—resembling (but not apeing)—modern chimps and gorillas, to modern humans.
I’ll let you read the article yourself, for it’s one piece on macroevolution that you should have under your belt. (If you want more, there’s Don Prothero’s wonderful book, Evolution: What the Fossils Say and Why It Matters, which describes many examples of evolution in the fossil record.) But there are two figures that I want to post just because they’re cool.
The first involves a vestigial trait in cetaceans (whales, dolphins, and porpoises) that is seen only in the embryological state: whiskers. Cetaceans evolved from single whiskered common ancestor that lived on land land: an artiodactyl, or even-toed ungulates). In the course of becoming marine, though, the lineages lost their whiskers. Nevertheless, they develop briefly in the embryo and then disappear. What better evidence for common ancestry of whales and terrestrial mammals? Here’s a photo from the paper:
And here’s something close to the terrestrial ancestor of the whale, the unlikely candidate Indohyus, a small, cat-sized mammal with separate toes, each of which ended in a hoof. It’s thought to be related to the common ancestor of cetaceans because of its thickened wall in the middle ear (limited to modern whales, dolphins and porpoises), its dense bones, which would suit it for living part-time in water (heavy bones make it easier to wade), and chemical analysis of its teeth, which show an oxygen 16:18 isotope ratio characteristic of animals who live in the water:
Thewissen et al. mention a video I’ve posted before, showing how a terrestrial artiodactyl might become aquatic. It’s the African mouse deer (Hyemoscus aquaticus also called the “water chevrotain”), which, though terrestrial, stays near water and swims, fully submerged, to escape from predators. This remarkable video shows how the evolution of aquatic behavior might have started:
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Thewissen, J. G. M., L. Cooper, J. George, and S. Bajpai. 2009. From land to water: the origin of whales, dolphins, and porpoises. Evolution: Education and Outreach 2:272-288.
Great film (again). I note that the chevrotain’s coat markings resemble those of pacas and juvenile tapirs, which also live on rain forest floors.
This is very cool. The behavior of the eagle in the video is pretty interesting too: How it raises its feathers into almost a mane.
Cute little deer! And quite good under water.
I would like to plug Carl Zimmer’s book At the Water’s Edge which details both the fish-tetrapod evolution and the land mammal-whale evolution and is very nicely written.
Thanks; sounds interesting.
My plugs are yet another vote for Prothero’s book, as well as Gould’s essay “Hooking Leviathan by Its Past,” an essay on the evolution of whales, #28 in his collection “Dinosaur in a Haystack”.
So I have a question: Are pinnipeds and whales more closely related to each other than to any other mammals?
One would think so; but you could also see them as two returns to the water too.
No, the pinnipeds represent an independent return to the water, and their ancestor was a carnivore, not an artiodactyl. It’s said their ancestor was bearlike, so Darwin’s scenario about whales evolving from bears swimming on their backs might not have been wildly off after all! (Creationists always laugh ta that scenario.)
I’ll put in a plug for Don Prothero’s “Evolution: What The Fossils Say, And Why It Matters” here because he covers this very question. The upshot, though, is that, while whales evolved from hoofed animals, pinnipeds arose from bearlike ancestry.
According to TimeTree, whales and sea lions diverged 77 million years ago. Sea lions are more closely related to dogs, weasels, raccoons, and bears than to cetaceans (which, as Jerry indicated, are related to deer, pigs, and hippos).
I’m amazed at how fast evolution can be–‘only’ 10 million years to go from a long-legged raccoon to a recognizable whale? (The last picture in the article with a Pakicetid at the bottom and a Basilosaurid at the top.)
From chimp to human is 12-million evo-years, yes? (The lineages split 6 mya approx.)
Just think what we could have done instead!
Well, if you think external morphology is the most important kind of evolutionary change, then, yeah. Personally, I think going from sitting around in a forest picking ticks off each other, to dominating all other species, spreading to every corner of the planet and sending some of us to the moon, is worth at least getting the most prominent spot on your mom’s refrigerator.
(Please note that I am not necessarily saying all our accomplishments are good things, but they are worth noting.)
Oh I know. But somehow it seems harder to imagine the proto-human brain getting bigger than moving two nostrils from the front of your face to one nostril on the back of your head.
🙂
Oops. “Easier to imagine”. My brain needs to enlarge some more.
Argument noted. I think a lot of us are coming from the point of view that “if a creationist is ever going to look at the facts (not likely, I know), the ones that will affect him the most will likely be those of the Indohyus-to-whale type, that is, ones with truly spectacular changes in external morphology.”
Does the chevrotain have the same adaptation that whales and hippos do to stay underwater? Are their limb bones calcified to make them denser?
Reblogged this on Mark Solock Blog.
It’s curious how the anti-evolution lobby can lock on to some particular facet of evolutionary decent and rant on how “impossible” it really must be. Whale evolution seems to be one of their great bugbears, perhaps even more so than the bacterial flagella. My favourite evolutionary critic (if you can call him that) on this matter is Dr. David Berlinski, who produced some videos for the Discovery Institute on the “mathematical impossibility” of whale macro evolution. The quality of the “math” itself is a total and utter joke – but Berlinskis job I suppose is not to impress anyone with any mathematical skills but to sucker in the credulous. Berlinski is however a competent mathematician himself, his doctorate is in the subject. His salary from the Discovery Institute is around $60,000 a year. I have always wondered what possesses anyone of of intellect and academic accomplishment to enter such whoredom, but I suppose that must always remain one of those real mysteries of human behaviour.