Thunder Lizards of the North Slope
I can't pass some things by. Book sales always stop me. So do articles about dinosaurs, especially when they have some relevance to Alaska and the north. And, like any dinosaur-besotted child, I can't resist passing on what I learn.
What entangled me in the pages of a recent issue of the American Association for the Advancement of Science publication Science had to do---yet again---with the dinosaurs' demise. More is found daily about the catastrophe that marked the boundary between the Cretaceous and Tertiary eras of geologic time. The asteroid that struck Earth then was perhaps even bigger than first thought, and could have created even more damage.
But was it the right kind of damage to kill off the dinosaurs? The standard scenario has dust hurled skyward from the impact blocking the sun's light and heat, leading to a planetary deep-frozen darkness lasting for months at least, years at most. According to this scenario, the dinosaurs froze to death in the dark. This seems logical, because dinosaurs are reptiles, and today's reptiles can't cope with long periods of unbroken cold. Alaska's native fauna shows that; we live in a virtually snake-free state, and the only lizards alive here are someone's pets.
But dinosaurs may not have been so much like modern reptiles in that regard. Evidence from the North Slope shows that not only did dinosaurs live there, they hung out year-round through the darkness and comparative cold. Researchers had tried to explain away the arctic dinosaur fossils by postulating that the animals had migrated away to avoid winters above the Arctic Circle, sort of like construction workers nowadays. Others had speculated that even if the far north did have three-month nights, they weren't severely cold.
Disputing both views now are researchers from the University of California, Berkeley. William A. Clemens and L. Gayle Nelms have reviewed the North Slope evidence, and they believe the dinosaurs were resident in a far northern environment that was too chilly for modern reptiles.
They base their assertions about temperature partly on plant fossils. The flora of the North Slope is of a sort that thrives in cold temperatures. The plants indicate that the slope endured annual temperatures averaging 2 or 3 degrees centigrade---about the same as the annual temperature of Anchorage nowadays. That might not be what we consider a truly arctic clime, but it is evidently too cold for other sorts of reptiles.
As evidence against the migration theory, Clemens and Nelms turn to fossils of the dinosaurs themselves. They think they have evidence that at least one of the big meat- eating dinosaurs overwintered beyond the circle, which would mean that prey species should also be present. Their prime evidence comes from a collection of teeth from young specimens of a light-boned and light-footed kind of dinosaur known as hypsilophodonts. The adults were not very big---at about two meters height, a full-grown hypsilophodont would not stand taller than a typical high-school basketball player---and naturally the youngsters were smaller. If they hatched in the Arctic, they would have been too small too migrate thousands of miles southward. (Consider that impressively migratory caribou don't have to leave the climate, just the pastures, and you get some idea of the distances that would be involved and the stresses imposed on a little land-bound animal.)
As further evidence that the arctic darkness in the Cretaceous was also cold is what isn't found among the North Slope fossils: any remains of nondinosaur reptiles or amphibians. Then as now, apparently, those animals couldn't deal with the long cold.
So Alaska's long-gone dinosaurs argue against the popular theories of what killed off all dinosaurs---but they have nothing to tell us of what did cause the great extinction. At least, they have nothing to tell us yet. People even more fanatically devoted to dinosaurs than I am are going to keep looking, and looking, and looking---perhaps until they find satisfactory answers, or until humankind too has gone the way of the dinosaurs.
