Your GSI will meet you to the Botanical Garden, where you will be working in groups to solve the following problems. You will turn in your short write-ups for the following problems at the beginning of the lab mini-symposium after the Thanksgiving Holiday.
As you are strolling along in the garden, you should take an extra look at some of the plants you have studied in lecture and lab to get a sense for how they look growing in nature. These particular taxa may also be fodder for your thoughts about how ancient ecosystems might have been assembled. For each taxon listed below, write down the identification number appearing on its identification label. Checklist:
The first part of the lab concerns western North America at the end of the Cretaceous. As you recall, the early Late Cretaceous saw the explosive increase in diversity of angiosperms, which became by far the most species-rich group of plants. Previously, in the Early Cretaceous, the angiosperms were confined to low latitudes and disturbed riparian plant communities in the mid-latitudes, but were slow to develop tree/shrub habit. Meanwhile, seed plants other than angiosperms continued from the Jurassic without undergoing any major changes in relative abundance of major groups. It was not until the Maastrichtian that flowering plants attained their present range of habitats and ecologies in the mid latitudes. The proportional increase in diversity for the angiosperms was paralleled by a decrease in ferns and plants with a cycadophyte growth form (cycads and cycadeoids), while conifers maintained their relative diversity.
You should find yourself-with some help from the GSI-in a part of the Botanical Garden east of the New World Desert and west of the Australasian section. This is near the walkway known as the "Taxodiaceae Circle". Imagine that you are a gardener with the task of constructing a Late Cretaceous garden. Which of the plants that you see around you would you want to include in your planting; which would you remove; what other plants would you like to add. For example, what flowering plants were around at the end of the Cretaceous? Write down you answer as a checklist of genera.
Early Miocene Trail
The fourth part of today's lab is a walk through an Early Miocene forest, a recently rejuvenated feature in the Botanical Garden. You will follow a trail located in Mather Redwood Grove, across the road from the main entrance to the Botanical Garden. The plants along this trail are living relatives of groups that lived in the forests of western North America during the Early Miocene, 15-18 million years ago. During the Early Miocene, forests extended over much of western North America. Just as today, these forests showed great variety depending on location and climate. This trail contains only a sample of living relatives of Early Miocene plants. Your task is to identify these and try to find other plants that you know grew in an early Miocene forest.
As you know by now, forests have existed in western North America for millions of years, although the kinds of trees have changed through geologic time. In the Triassic (245-208 million years ago), forests of redwood-like trees would have covered half of our continent. By the Early Miocene, most forests were dominated by broad-leaved hardwoods
Relying on what we know about the broad correlation between leaf size and shape and climactic conditions under which plants grow (see Lab 12), Miocene leaf assemblages have been studied and interpreted. Leaves from Early Miocene forest trees generally had larger leaves than their living relatives and entire (smooth) margins were more common. This suggests that the Early Miocene climate was warmer and wetter that today's.
The leaves on display by the Miocene trail are from the Buffalo Canyon locality in central Nevada (15-18 million years ago). Do you remember under what conditions these fossils were preserved, i.e. in what environment did these plants live? What was the climate like-both according to D.I. Axelrod and your own study?
Today, the vegetation around Buffalo Canyon is very different from what it was in the Miocene. The region is cool and dry, with vegetation typical of the Great Basin: scattered Pinyon Pine (Pinus monophylla) trees and Utah Juniper (Juniperus osteosperms), and the shrubs such as Sagebrush (Artemisia tridentata) and Rabbitbrush (Chrysothamnus nauseosus).
Below the sign at the beginning of the Miocene Trail (bottom of the steps) in the Mather Redwood Grove are fossils of a number of genera from the Buffalo Canyon flora. Please answer the following questions: