The Saturday OLLI class was on the plants of Mesozoic Alaska – not much like today! Right now the North Slope is moist tundra, with low shrubs, sedges, grasses, lichens and ice wedges. The current latitude of the fossil locations is under 70 °N.
The Mesozoic landscape was very different. It was a forested area, with rivers draining the rising Brooks Range and flowing to an Arctic ocean that never froze, and had surface water temperatures estimated at 15° C – around 60° F. Quite a difference from the ice cover of today! The latitude at the time, inferred from sediment paleomagnetism, was 85° — a mere 5° from the pole. Yet the land was forested, with conifers, ginkgos, metasequoia, with an understory of ferns, mosses, lichens horsetails and flowering plants. No grass, though – it hadn’t evolved yet.
Most of these plants, including the conifers, dropped their leaves in the winter. After all, plants cannot photosynthesize without sunlight, and at 85° N, the winter night was over 5 months long. There would have been about 25 days in spring and another 25 in fall when the sun rose and set, but basically it was continuous daylight in the summer and continuous night in the winter. No wonder some of the predatory dinosaurs whose fossils have been found in northern Alaska had enormous eyes!
What did the herbivores eat? Most likely twigs, dormant buds, bark, possibly roots and even wood. Some may have migrated to warmer climes, but this is being debated.
The mean annual temperatures of the time can be estimated from the fraction of smooth-edged leaves versus toothed leaves. Yes I am dubious too, and no one has come up with a good explanation. But the fact remains that this measure in modern leaf litter all over the world correlates extremely well with mean annual temperature. Using this, mean annual temperatures were likely around 10°C (50°F) compared with modern mean annual temperatures well below freezing.
My suspicion is that winters were also cloudy, possibly foggy, and had at least occasional snowfalls. That warm ocean would have stayed warm – water has to lose an enormous amount of energy to cool very much. With water that warm, the cooler water would be denser and sink, and the whole depth of the ocean would have to be cooled to cool the surface. Warm water evaporates into colder air, and given a cold land breeze near the surface, and the warm, wetted air coming back inland at height, I’d certainly expect clouds, which in winter serve to keep the ground warm. Not much precipitation, but possibly a fog forest. Could fog have allowed the herbivores to hide from the predators?
Next week we’ll be looking at marine reptiles (I know some have been found in Alaska) and those that flew. For more references, check here. There’s also a DVD of the Colville dig, and a neat story about filming it.
Don’t forget the drawing!