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2. The Cretaceous: A Time of Change The sun rose and set over 29 billion times during the Cretaceous. Each succeeding dawn and nightfall saw the birth and death of billions of organisms, and in every passing millennium , species arose or became extinct. Dramatic physical and biological changes molded the evolution of insects, plants, and dinosaurs during that period in the planet’s history. Differences in insect taxa are evident in the amber fossils found in Lebanon in the Early, Burma in the mid, and Canada in the Late Cretaceous. Other fossil deposits tell us that similar changes also occurred in dinosaurs and plants. Geographic and Climatic Changes In the 25–30 million years separating each amber site, continents drifted hundreds of miles, mountains formed, sea levels changed, volcanoes erupted and died, climates shifted, and earthquakes fractured the land. All of these physical transformations in the earth’s architecture were the consequences of what is known as plate tectonics. Geologists have made great strides deciphering the mysteries of the planet’s history with the study of plate tectonics. They have established that the earth’s surface is composed of a complex of continental and oceanic plates that are being continuously pushed apart in some areas and forced together in others, so that they are constantly slipping and sliding over, under, or against each other. Even today the earth continues to shift and in the most active areas of plate movement, earthquakes and volca- noes are a daily reminder of its restlessness. Although this movement does not appear to have been uniform over geological time, and long periods of near-stasis have been interspersed with periods of rather intense activity, the end result was that the geography of the Early, mid and Late Cretaceous worlds was significantly different. When we are presented with a map of 130 to 135 million years ago, the most obvious difference from one of today would be the very close association of continents situated in the Southern and Northern Hemispheres.9 The landmasses joined in the supercontinent Gondwanaland (Africa, South America, Antarctica, Australia , and India) were beginning to separate from each other. Africa and South America were still contiguous and remained in contact with the other southern continents via land bridges and island chains (fig. 6). In the northern regions the continents forming the Laurasian complex (North America, Greenland, and Eurasia) were also still closely interconnected. The flora and fauna were free to migrate over the entire conjoined landmasses, thus potentially allowing for the distribution of a specific genus or species of insect, plant, or dinosaur to become quite extensive. Moving forward to 97 to 105 million years ago, another map would show that as the continents separated, a rise in sea levels had placed the interior of Burma and its amber-forming forest close to the water’s edge (fig. 7). While the rising sea level inundated the interior of North America with a vast epicontinental ocean and reduced much of Europe to large islands, it also further opened the Tethys Seaway between the northern and southern continents. Antarctica had almost reached the position it occupies today at the South Pole. By the time the Canadian amber was being formed some 77–79 million years ago, western and eastern North America were still separated by that large interior sea (fig. 8). The continents had continued moving and now resided close to their present locations . Such an extended period of geological isolation would have resulted in endemic species occurring on the eastern and western sides of continental North America. 18 – CHAPTER TWO We are left with the knowledge that geological changes over the course of the Cretaceous created an increasingly smaller terrestrial world as continents separated and sea levels rose. A team of scientists has estimated that from the beginning to near the end of the Cretaceous, there was a net loss of approximately 14% of non-marine areas on the globe so that at 80 million years ago, the world had the least amount of exposed land seen over the last 245 million years and an astonishing 28% less then it had 5 mya.9 THE CRETACEOUS: A TIME OF CHANGE – 19 Warm Subtropical Subtropical Tropical 0° Figure 6. This map illustrates the putative positions of the continents when amber was being deposited in Lebanon (asterisk) during the Early Cretaceous. The probable extent of the land masses are in white, oceans are in light gray, epicontinental seas are in dark gray, and black...

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