Using Fossil Leaves to Calculate Ancient Mean Annual Temperature (MAT) Knowlton, F.H. (1917) Geology and paleontology of Raton Mesa: USGS Professional Paper 101. Instructions Carefully examine each of the following leaves collected from the Late Cretaceous Vermejo Formation in southern Colorado and northern New Mexico. Decide whether the leaf margins are entire (smooth) or not (toothed). Calculate the percentage of smooth leaves in order to find the MAT for southern Colorado near the end of the age of dinosaurs. Source: Smithsonian Education