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Everything You Know About Lizards Could Be Wrong By JOE EATON Special to the Planet

Tuesday December 06, 2005

Anyone else remember the Firesign Theater’s record “Everything You Know is Wrong”? You get that feeling if you follow science at all closely. One day the earth is solid and stable; the next, the continents are whizzing around the mantle like bumper cars. You learn that the dinosaurs went extinct 65 million years ago, and then it turns out you just had one for Thanksgiving dinner. It’s what the historian of science Thomas Kuhn called the paradigm shift, and it just keeps happening. 

Case in point: A couple of years back I wrote a magazine article about the Bay Area in the Miocene Epoch, 10 million years ago, based on fossil discoveries at the Blackhawk Ranch site in Contra Costa County. One of the major themes of the piece was the rise of the grasslands as the global climate became cooler and drier, and how this drove the evolution of herbivorous mammals. Unspecialized leaf-browsers died out, and lineages that evolved teeth capable of processing the tiny bits of silica in the grass blades—horses, for one—throve. That was the conventional wisdom at the time, laid down by botanists like the late G. Ledyard Stebbins. Everybody believed grasses were a Miocene innovation. 

But no. As recently reported, a botanist named Caroline Stromberg at the Swedish Natural History Museum has found the telltale silica crystals—phytoliths—in coprolites dated around 70 million years old. Coprolites are fossilized dung: dinosaur dung in this instance, from enormous sauropods that inhabited India about the time it was docking with Asia. The fact that Stromberg identified five types of phytoliths suggests that grasses had had plenty of time to diversify before this slice of time.  

So the whole scenario about the Miocene triumph of the grasses has to be rethought. And then there’s the business of the lizard venom. I couldn’t tell you how many times I’ve explained that although a lot of snakes are venomous, most lizards are not, the only exceptions being the oddball Gila monster and beaded lizard. This happened with some regularity when I lived in Georgia, where there was an ingrained folk belief that skinks—small lizards with, at some point in their life cycle, bright blue tails—were deadly poisonous.  

It appears now that although I was right about the skinks, I was wrong about many of the rest of the lizards. We owe this knowledge to University of Melbourne biologist Bryan Fry, who studies the evolution of snake venom. Snakes, of course, are just highly specialized lizards, having shared a relatively recent common ancestor with the Komodo dragon and other members of the monitor family. And venom glands are a widely shared, although not universal, trait among snakes. The sophistication of the apparatus varies, from the hypodermics of the cobras and vipers to the rear-fanged snakes in which venom flows from modified salivary glands down channels in the back teeth. A whole bunch of species, like the little ring-necked snakes that show up in our flower beds, are mildly venomous. Not to the point of being dangerous to us, fortunately—a ringneck would have to chew on your finger for a long time before the stuff had any effect—but potent enough to immobilize the snakes’ prey so they can get it down. 

The exceptions to the venom trend are mostly constrictors like the boas and pythons, who squeeze the life out of their victims. Because of anatomical features like vestigial hindlegs, they’re considered to be primitive among snakes. So it made sense to see venom and its delivery system as characteristics that more progressive snakes evolved. 

Except that Fry took the trouble to look at lizards, sampling their mouth secretions and analyzing them for the venom genes previously identified in snakes—not just Gila monsters, but all kinds of lizards: skinks, geckos, iguanas. “We isolated some rattlesnake toxins from the bearded dragons and started getting really excited,” he told the New York Times’ Carl Zimmer. I’ll bet they did. As it happens, I know a bearded dragon reasonably well; I’ve let her sit on my shoulder, even given her a bath. Her species is one of the East Bay Vivarium’s recommended starter lizards. And all the time she was venomous, like the common ancestor of all snakes and a good many lizards. 

The geckos and skinks are clean, Fry says. But the “venom clade” includes the iguanians (of which chameleons are a subset), the anguids (legless and alligator lizards), and the monitors. The venom produced by the Australian lace monitor causes a sudden relaxation of the aorta. The damage done by the bite of the Komodo dragon now seems attributable to venom, not, as once believed, the septic conditions in its mouth. I haven’t seen a complete list of Fry’s subjects, but it’s reasonable to assume that our own ubiquitous western fence lizard would now have to be considered venomous, as would the northern and southern alligator lizards.  

No need to panic, though; as with ring-necked snakes, we’re talking about small doses of what to us would be very mild poison. But it may be enough to slow down a fence lizard’s insect prey. Fry’s research raises all kinds of questions: have vegetarian species like the green iguana and its Galapagos relatives lost the ability to manufacture venom? Then there are the potential medical applications. Fry says the molecules in lizard venom are smaller than those in snake venom, thus less likely to trigger an immune system reaction. “I’ll reckon we’ll be able to get something useful our of them,” he says. 

So there goes another paradigm. And that’s fine; that’s the way science is supposed to work, what distinguishes science from theology. Any scientific theory is potentially falsifiable. Someone once asked JBS Haldane what he would consider as clenching disproof of evolution. “Fossil rabbits in the Precambrian”, he replied. Fair enough; if those 600 million-year-old rabbits ever turn up, science will have some explaining to do. But no rabbit, fossil or otherwise, is ever going to convince the acolytes of faith-based pseudoscience that their belief in intelligent design is misplaced.