The OLLI classes are on again, and my favorite teachers are back – this time, with a course on the Alaskan Mesozoic.

What’s that? Well, the Mesozoic is the “Middle period” of multicellular life on earth, lasting roughly from 250 million years ago to 65 million years ago. It is probably better known as the age of dinosaurs, although many of the animals of the time often looked on as dinosaurs – weren’t. And the fossils of many of these animals are indeed found in Alaska – which has led to a new look at dinosaurs.

I missed the first class of the series, on the paleogeography of Alaska, but a good deal of it was put together at the Geophysical Institute, where I used to work. I already knew that the mountain ranges that make up most of Alaska were originally island chains, carried into the state on the moving Pacific and Arctic plates and crushed against it. The north slope was actually at a higher latitude than today during the Mesozoic, and while the world (and Alaska) were a good deal warmer then, the sun was still below the horizon 24 hours a day in midwinter. Plants cannot grow without sunlight, herbivores would have a lean time of it in winter, and carnivores need herbivores to survive. It is difficult to imagine cold-blooded reptiles managing this (there are no crocodiles or snakes in mainland Alaska today) so the discovery of dinosaurs, but not fossil crocodiles, at these high latitudes has forced some reconsideration of their cold-bloodedness.

So what are dinosaurs? That was the Saturday lecture.

First, they are diapsids. That means they have two holes (other than those for eyes, nostrils and ears) in their skulls. In contrast we mammals have one on each side and are called synapsids, and turtles have none and are called anapsids. Don’t think you have one? It’s behind your cheekbone, and your jaw muscle passes through it. Feel above your cheekbone and clench your jaw, and you can feel the muscle. Well, dinosaurs, crocodiles, lizards and birds have two such holes.

In order to be a dinosaur, however, something else is required. Diapsids (think reptiles) started out sprawling. At some point some brought their hind legs under themselves – somewhat earlier than we mammals learned the trick – and began to use their forelegs as grasping hands. The first dinosaur probably looked like a large (but not too large) featherless (we think) bird.

And dinosaurs, as defined by being diapsids with upright rear legs and three-toed grasping forelegs, include birds. Furthermore, discoveries over the last ten to fifteen years have made it clear that many perfectly good, classic dinosaurs had feathers. After all, feathers make excellent insulation, as demonstrated by the down parka I wear.

So far, we’ve learned also that some creatures often lumped with dinosaurs are in fact not dinosaurs. The sail-backs often included with dinosaurs, for instance, are in fact synapsids and are our own distant relatives. Pterosaurs and marine reptiles, though flourishing at the same time as dinosaurs, were not dinosaurs, though they were diapsids.

I know there were marine reptiles in Alaska, but I’ll be fascinated to hear about pterosaurs in our long, dark winters. Did they live here, even in the summer? Did their wings allow them to migrate?

Next week we’ll focus on plants, but the final week is scheduled to cover the marine reptiles and pterosaurs. If you can’t wait, there is some information on a PBS NOVA program.

(P.S. That’s a Pterosaur skull that Pat Druckenmiller is holding.)