This story has nothing to do with
Kennewick Man or disputed sites like
Calico. We're talking before that, way before.
If you attend any journalism school, one of the the first things they tell is to get the heart of your story at the top of the page. Drop all those W's, -- who, what, when, where -- into your opening paragraph, then come back and fill in the details and background. But then, it's been a long time since I even pretended to be a journalist, so you'll have to forgive me if I write this story in reverse.
Eventually, I'm going to get to the news, but I'm going to start the story nearly 400 million years and two thousand miles from the important events. In fact, I'm going to start in my own backyard.
But if you want a hint about what's behind this story, here's the main character:
Meet the Neighbor
This ugly mug belongs to Cryptobranchus aualleganiensis, the Eastern Hellbender. This large salamander (up to 30 inches long and around five pounds) is the largest amphibian in North America and among the largest in the world. It's fairly wide spread, living from New York through the Ohio River basin and along the length of the Appalachians, but it's not particularly common anywhere in its range. Mostly that's because it's habitat -- large, clear-flowing streams with rocky bottoms -- is pretty hard to come by these days. They don't do well with the dirt and oil that runs off pavement, with fertilizer and pesticides from fields, or with the silt and mud that slides away from construction zones. That should be enough to tell you how things are going for hellbenders. Old timers will tell you that many large rivers used to hold populations of these guys. I once saw an extremely robust (and irritated) specimen dragged out of the Green River in Kentucky on a fishing line -- causing the fisherman who snagged that bad boy to nearly have a heart attack.
The hellbender is a predator, snacking down on snails, the occasional fish, and especially on crayfish (that would be 'crawdads' for those of you who grew up in my neck of the woods). It's got a mouthful of small teeth for crunching through these hard meals. However, despite the fearsome name, it's pretty hard to get a hellbender to make a move on your finger. Handle one, and you'll find it cold, wiggly, and anxious to be elsewhere.
Unlike the tiger salamanders and red efts you find lurking in the damp places of your garden, hellbenders are almost completely aquatic. They're considered more "primitive" than most salamanders, with features very close to those of their ancestors. While their stumpy legs are strong enough to move them from one pool or stream to another, they're really much better designed for kicking along a river bed, guiding the animal toward its next meal.
Okay, I'm ready to move on, but before I leave the hellbender behind, I mentioned that it had some larger relatives elsewhere in the world. Those would be the similar, but even bigger (and meaner) giant salamanders of Japan and China.
These can reach five feet long, and can deliver a nasty bite (though, like the hellbender, they are not poisonous, no matter what grandpa tells you). They're very closely related, and very similar in all but size, to the hellbender.
The Fish Next Door
To meet the next player in this drama, you have to leave my neighborhood and travel south. Keep going. Keeep going. Are in you in South America yet? Okay, stop. That's where you'll find Lepidosiren paradoxa, the South American Lungfish.
The lungfish is a good sized fish, up to four feet long, and about as big as a person's leg (assuming that person is less chunky than I). You can occasionally find them in your local aquarium shop, and they do make interesting specimens in the home tank. Not so interesting for your other fish though, as lung fish are very aggressive and will quickly make snacks of your other specimens.
The name alone is enough to key you into the oddest feature of this fish -- it breaths air. It has a neat set of paired lungs. In fact, this fish is an obligate air breather -- it has to come up for a gulp of gas now and then. It just can't make it through what it gets out of the water alone.
That may sound like a bad adaptation for a fish, but his ability to gulp air means that he can survive in nasty water conditions. Low oxygen conditions can be common in water that has a high organic content and low flow, like the sludgy backwaters of a swamp or the dwindling remnants of a wet season pool. The lungfish survives in conditions that would kill other fish, even infrequently venturing over land, where it travels more like a snake with only a little help of it's four thin, wiry fins. When the dry season comes and the last oxygen-starved pools vanish, the lungfish still doesn't die. It burrows into the mud, leaving itself a little air hole, and waits for the rain to fall again.
There are several lung fishes around the world, survivors from a group that was once more diverse and wide spread. North America has several fishes from groups as old as the lung fish, but there's something else special about this fish, something we'll see after we take a couple of more hops.
Back to the Triassic
So here we are, in the Late Triassic period, 205 million years ago. Sounds like a lot, doesn't it? But in truth we're only halfway to our destination.
During the Triassic, almost all the Earth's land mass was stuck together into a single giant supercontinent called Pangaea. At times, the drift of Pangaea through the various latitudes helped to turn the whole interior of this continent into the largest dessert ever seen on Earth. At other times, plant life was distinctly more lush.
Down along the Pangaean riverbanks, dinosaurs have only recently gotten up on their hind limbs and began the explosive period of diversification. They'll displace a group called Therapsids, a group that likely holds our own ancestors, as the dominant form of land animal for the next hundred million years.
In the waters themselves, crocodiles are a relatively recent development, but their design is already illustrating the strengths that will turn them into a long term success story. Still, crocs don't have the rivers of Pangaea all to themselves. Other animals compete with them for the title of top aquatic predator. Among these competitors is a group that is already quite old while the crocodiles are still newcomers, the Labyrithodonts.
Like the hellbender, labyrinthodonts are amphibians. They lack the scales of reptiles and must lay their eggs in the water. From what we can tell of their body structure, it appears that many members of this group of amphibians were quite similar to the hellbender and the related Asian giant salamanders. They had the same small eyes, flattened bodies, and splayed legs. They probably had a very similar lifestyle, using both tails and feet to swim through the Triassic rivers. Though the picture above makes Koolasuchus look kind of sleek, I suspect he was just as blotchy and wrinkly in real life as giant salamanders today.
Where they differed from their modern relatives was in size. Some of the labyrinthodonts grew to over fifteen feet in length, putting them in the same class as the crocs. When a Triassic animal came down to the water hole to drink, it had to watch out not only for ambush by crocodiles, but for tiny amphibian eyes lurking just below the surface.
The ancestry of hellbenders is somewhat in doubt. Some people want to group them with the more "modern" salamanders. Others think they are from separate stock, directly descended from the group that produced the labyrinthodonts.
I go with the "modern giant salamanders come from labyrinthodonts" position, both for what I think are sound cladistic reasons, and because I think it's pretty darn cool to have a survivor from before the dinosaurs crawling through the stream in my back yard.
In the swamps and pools that dot the length of the Triassic rivers, the labyrinthodonts are joined by the lungfish. The same adaptations that let these fish tolerate bad conditions today, worked just as well back then. In fact, the changing conditions of Pangaea appears to have been a hothouse of lungfish evolution, giving rise to several families in addition to those which are still with us today.
Every indication is that these fishes had a life much like those of our modern lungfish. Like them, they were capable of wriggling from one pool to another. Like them, they could probably wait out a long dry season by breathing air alone. In fact, some of these lungfish were so like those around today that their bones are almost indistinguishable and they have been given the same genus name as one of the living varieties.
Okay, jump.
The Dear Late Devonian
Here we are at the very tail end of the Devonian period, around 360 million years ago. Plants have only recently blanketed the land and the very first swamps worth the name are getting started. Insects have already colonized the ground, and a terrestrial ecosystem is developing that makes getting out of the water and chowing down on land worthwhile.
And amphibians are there. Like the crocodiles of the Triassic, they're a new deal, with only a few million years of development behind them, but already they've started to diversify in interesting ways. Some of them look remarkably like the labyrithodonts that will come later. Some are unique.
Though he's got a weird head, Diplocaulus is otherwise quite similar in shape and size to the modern hellbender. There are no crocodiles, or any other reptiles, around as yet to compete with our amphibian friends, so it's a world of salamanders gone wild. Diplocaulus, and his kin with more usually shaped heads, are common and widespread. (And okay, yeah, my "freshly caught Diplocaulus" picture is a fake, the product of a Japanese contest, but I liked it so much, I couldn't resist. You never know what you're going to find when scanning creationist sites.)
While none of these amphibians were about to get out and trot like a race horse, some of them, like Acanthostega, did seem to have a limb structure very similar to my backyard hellbender. Like the hellbender, he probably used his legs mostly for strolling along the stream bottom, but he could also have made the occasional clumsy stroll up into the new green landscape.
The lungfish are still around, too. In fact, they're also at near the peak of their variety and dominance, and again you can find specimens very like those around today. However, you can also find another kind of lungfish, ones with fins that are thicker and more supportive. These kind of fish are called "lobed-fin" fish.
Now, let's take one more hop, but compared to the last two, it's a short one.
Caught in the Middle Devonian
So, here it is about 385 million years ago in the Middle Devonian. We've seen how the giant salamanders and their kin had been around from the present to the late Devonian with remarkably little change. So, in the Middle Devonian we find... nothing. No giant salamanders. No little salamanders. No relatives with funny heads. Not an amphibian in sight.
We have just left the world of the "tetrapods" (creatures with four limbs) and gone back to a time when no backboned animal walks the land.
The lungfish are still here, though. Among them are creatures like Panderichthys,
It doesn't take much examination to see that Panderichthys is a very special fish. Its four fins are positioned in a way that's very reminiscent of more land lubberly limbs, and the bone structure that supports those fins is robust enough to suggest that Panderichthys did more with its fins than just use them for steering. Maybe it clambered along the bottoms of streams like hellbenders. Maybe it used its fins when burrowing into the mud at the end of the rainy season, or maybe they helped out when it was wriggling from one pool to another.
Whatever it did, Panderichthys was clearly on the path toward being a tetrapod. But it was just as cleary not at the end of that path.
Acanthostega, from the late Devonian, is an amphibian. It has real limbs supported by a pelvic girdle. It has a head that's distinct from the body. It has feet, not flippers. Panderichthys, in the middle Devonian, is just as clearly a fish, no matter how long it's list of odd features.
So what happened in the few million years that separate these two animals? Well that, finally, is the news.
The Go Between
When? 383 million years ago.
Where? Ellesmere Island, Canada.
Who? Tiktaalik.
What? Bridged the gap between fishes and amphibians.
Several nearly complete specimens of the fish turned up two years ago in summer digs on Canada's Ellesmere Island, above the Arctic Circle, and a formal scientific description appears in today's Nature journal. Tiktaalik means "big freshwater fish" in the language native to Canada's Nunavut Territory.
"Tiktaalik represents a transitory creature between water and land," says discovery team member Farish Jenkins Jr. of Harvard University. "Really, it's extraordinary. We found a fish with a neck."
Researchers say the find fills a gap in the fossil record, neatly matching scientific predictions of what the first land creatures were like. Tiktaalik is a "clear representative" of the Devonian age, when four-limbed creatures first left the water, says discovery team member Edward Daeschler of Philadelphia's Academy of Natural Sciences.
So, there you go. The hellbender and the lungfish live thousands of miles apart today, but in the upper Devonian, lobe-finned relatives of the modern lungfish, and the amphibian ancestors of the modern giant salamanders met in th form of Tiktaalik, an amphibian-like fish. Or... is that a fish-like amphibian? It's a wonderful example of a transitional form, that's what it is, so neatly caught in the middle space that its discoverers have tagged it a "fishapod."
In fact, Tiktaalik may be the best example of a vertebrate transitional form since the first specimen of Archeopteryx was dragged out of a quarry in 1861. Not only does it demonstrate clear internmediate features, but it's also a very good specimen. We're not talking a few bits of jawbone here, we're talking very nearly complete.
The Myth of the Missing Link
But however cool Tiktaalik may be, keep in mind that we didn't really need him to show how fish became amphibian. There were already at least half a dozen species staking out the fish to amphibian transitional space so clearly that there was no doubt about any of those w's. On the other hand, those who don't believe in evolution will never be satisfied by Tiktaalik. They demand an infinite progression of transitional forms, defining ever smaller gaps. And they'll still point to the minute differences between two species and declare it an unbridgeable void.
Even the idea of a missing link suggests that evolution works along a neat little ladder, with one species giving way to the next. It never works that way. The real deal is much messier... and much more interesting.
But in Canada, 383 million years ago, a creature took what were probably the very first movements that could be counted as "steps" onto a continent that would one day be America. How cool is that?