A few years ago, ex-teen heartthrob Kirk Cameron went on Fox News as a pitchman for young-Earth creationism. Claiming there were no transitional fossils, he ridiculed evolution saying that, if it were true, we would have duck-crocodile hybrids. Ha, ha—oh, wait, scientists found a dinosaur that's half duck, half croc.

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Cameron appeared as an "expert" on Fox News prior to the airing of an ABC Nightline segment, featuring footage of Cameron participating in a debate on the existence of God.

As Cameron explained:

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"Nothing becoming something, blowing up in becoming an organized everything, just doesn't fit logic to me. Plus, Darwin said, in order to prove evolution, which is the number one alternative to God, you've got to be able to prove transitional forms—one animal transitioning into another—and all through the fossil record, we don't find one of these [holds up photoshopped photo], a crocoduck."

Cameron and fellow young-Earth creationist Ray Comfort went on to film this "mockumentary," featuring biologist "Richard Attensquirrel" in search of the elusive crocoduck in the "Swamps of Gopolapus."

But, while the YEC crowd was having fun with their new poster creature, crocoduck became a popular meme to highlight misconceptions about evolution. Richard Dawkins, who began sporting a crocoduck necktie, even devoted a segment of his book, The Greatest Show On Earth: The Evidence for Evolution, to the mythical chimera:

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'Why doesn't the fossil record contain a fronkey?' Well, of course, monkeys are not descended from frogs. No sane evolutionist ever said they were, or that ducks are descended from crocodiles or vice versa. Monkeys and frogs share an ancestor, which certainly looked nothing like a frog and nothing like a monkey. Maybe it looked a bit like a salamander, and we do indeed have salamander-like fossils dating from the right time. But that is not the point. Every one of the millions of species of animals shares an ancestor with every other one. If your understanding of evolution is so warped that you think we should expect to see a fronkey and a crocoduck, you should also wax sarcastic about the absence of a doggypotamus and an elephanzee. Indeed, why limit yourself to mammals? Why not a kangaroach (intermediate between kangaroo and cockroach), or an octopard (intermediate between octopus and leopard)? There's an infinite number of animal names you can string together in that way.

Of course hippopotamuses are not descended from dogs, or vice versa. Chimpanzees are not descended from elephants or vice versa, just as monkeys are not descended from frogs. No modern species is descended from any other modern species (if we leave out very recent splits). Just as you can find fossils that approximate to the c ommon ancestor of a frog and a monkey, so you can find fossils that approximate to the common ancestor of elephants and chimpanzees.

But now, science has bestowed upon us the real-life equivalent of a crocoduck—a magnificent specimen that illustrates how evolution actually works.

"It was a chimera"

The real creature was a 50-foot dinosaur called Spinosaurus.

As an article in Smithsonian magazine explains:

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What really makes Spinosaurus special are its unique adaptations that may have allowed the dinosaur to hunt underwater. Like crocodiles, Spinosaurus had a long narrow snout with nostrils mid-skull, perfect for submerging. It also had a second pair of openings, likely neurovascular slits that are also found in crocodiles. Spinosaurus had a long neck, like a heron or a stork… Its big feet had flat claws, a structure that may have been useful for paddling. Loosely connected tail bones could have allowed the animal to propel itself forward in water just like a fish, and its densely packed bones resemble those of a penguin.

"It was a chimera: half duck, half crocodile. We don't have anything alive that looks like this today," says study co-author Paul Sereno, a vertebrate paleontologist at the University of Chicago.

Sereno, of course, doesn't mean that Spinosaurus was, literally, a duck-crocodile hybrid. He's speaking descriptively—referring, for instance, to the flat-bottomed foot claws that it used for moving in the water, and an anatomy adapted for buoyancy.

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The article also notes that Spinosaurus's pelvis was small but attached to powerful, short legs, similar to the ancient ancestors of whales. Indeed, like whales, these dinosaurs probably evolved from land-dwelling ancestors to become semi-aquatic.

In fact, if Kirk Cameron and other YECs want to see several specimens of what a real transitional fossil looks like, they could visit Egypt, where a parched valley is home to whale skeletons dating back 37 million years, when the region was covered by a shallow, tropical sea:

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The prehistoric specimens in the sand would offer clues to one of evolution's most nagging questions: how whales became whales in the first place. For these long-dead whales had feet.

"We had sometimes joked about walking whales," says Philip Gingerich, a University of Michigan paleontologist who discovered the dainty little appendages, complete with tiny toes, when working in Wadi Hitan ("The Valley of the Whales") in 1989. "When we found what we did in Egypt, we thought, 'That's not a joke anymore.'"

Scientists had long suspected that whales were terrestrial mammals that had eased into the ocean over millions of years, gradually losing their four legs. Modern whales, after all, have vestigial hind leg bones. But little in the fossil record illustrated the transition—until Gingerich began excavating Wadi Hitan's hundreds of whale fossils, finding legs and knees.

Gingerich speculates that whales' landlubber ancestors were deer- or pig-like scavengers living near the sea. About 55 million years ago, they started spending more time in the water, first eating dead fish along the shore, and then chasing prey in the shallows, and then wading deeper. As they did, some evolved traits that facilitated hunting in water. Over time—since they no longer had to bear their full body weight at sea—they got bigger, their backbones elongating and their rib cages broadening.

Back here in the 21st century, science bloggers are enjoying the irony that Kirk Cameron chose to ridicule evolution with the idea of a crocoduck. As James McGrath, a theologian who studies the intersection of religion and science put it, "And so I will admit it. I was wrong about the crocoduck – just as Kirk Cameron was wrong about evolution."