Earth Science 13.4 Cenozoic Era : Age of Mammals Cenozoic Era : The Age of Mammals The Age of Mammals The Age of Mammals: (65 m – present) If the Mesozoic was the “Age of reptiles” the Cenozoic can be called the “Age of Mammals”. During the Mesozoic, mammals were mainly small scavengers and plant eaters. After the Cretaceous extinction, mammals began to adapt to environments and expand in their diversity. Mammals of the Cenozoic The Age of Mammals The Age of Mammals: Mammals succeeded during the Cenozoic because of adaptations that enabled them to out compete the surviving reptiles. For example, because mammals are warm-blooded, they can live in cold environments and search for food any time of day or time of year. Other adaptations include more efficient hearts and lungs than reptiles, and the development of insulating body hair or fur. These adaptations allowed mammals to lead more active lives than reptiles. Mammals of the Cenozoic The Age of Mammals The Tertiary Period: During the Tertiary period (65 – 1.5 million), mountain building and climate changes accompanied the breakup of Pangaea. Mammals became widespread and diverse worldwide. Major fragments of Pangaea became separate continents during the Tertiary. Seas separated North America from South America and Europe from Africa. Plate movements led to major mountain building activity in western North America (the Rockies), Europe (the Alps) and India (the Himalayas). The Age of Mammals The Tertiary Period: Generally, climates during the Tertiary period were cooler than those of the Cretaceous. The mid-Tertiary had temperate dry climates. Later in the period, Earth’s climates cooled leading to the development of large continental glaciers in Antarctica about 10 million years ago. The Age of Mammals Tertiary Life: The Tertiary saw the development of many new species, from songbirds to snakes. The major development of the Tertiary was the evolution of many new types of mammals. Mammals evolved specialized limbs and teeth for particular environments. For example, meat-eaters evolved sharp teeth for cutting and tearing. Rodents developed selfsharpening teeth for gnawing. Plant eaters developed flat molars for chewing. The Age of Mammals Tertiary Life: Some animals evolved to take advantage of a rich new food source; grass. As the climate became cooler and drier, vast grasslands developed. Many types of grazing animals, including the ancestors of cattle and horses, evolved during the Tertiary. The Age of Mammals Quaternary Period: (5.3 – 0) Two factors have greatly affected life on Earth during the Quaternary period : The advance and retreat of continental glaciers (which have formed and melted about 30 times in the last 3 million years) And the migration of homo sapiens (humans) to every corner of the Earth The Age of Mammals Quaternary Period: (5.3 – 0) A map showing the physical features of Earth 2 million years ago would look much the same today. But beginning in the late tertiary, a series of ice ages covered large parts of the northeast hemisphere with continental glaciers. The Age of Mammals Quaternary Period: (5.3 – 0) Because Earth is a complex system, many factors determine whether Earth’s climate becomes cold enough for an ice age. These factors include ocean currents, the size of the ice covered areas, and the affects of living things on the atmosphere. The Age of Mammals Quaternary Period: (5.3 – 0) In the 1940’s, astronomer Milutin Milankovitch proposed that three different cycles, related to Earth’s movements, were the main cause of ice ages. These cycles are called the Milankovitch cycles. The Age of Mammals Quaternary Period: (5.3 – 0) For example, there is a 100,000 year cycle related to changes in the shape of the Earth’s orbit. Earth receives more or less energy from the sun depending on it’s position within each of these cycles. The Age of Mammals Quaternary Period: (5.3 – 0) Milankovitch thought that ice ages occur when solar energy reaching Earth is at a minimum. Scientists today think that Milankovitch cycles provide a “partial” explanation for recent ice ages. The Age of Mammals Quaternary Life: (5.3 – 0) One trend in evolution during both the Tertiary and Quaternary periods was that some mammals became very large. During the ice ages, many large mammals lived in the cold grasslands, or steppe, that bordered the ice covered regions of North America. The Age of Mammals Quaternary Life: (5.3 – 0) These animals included mastodons and mammoths, which were both huge ancestors of the elephant. In North America, there were also giant beavers, ground sloths, wolves. bears, sabre-tooth cats and bison. All these animals became extinct about 10,000 years ago, at the end of the last ice age. The Age of Mammals Quaternary Life: (5.3 – 0) How can the extinction at the end of this last ice age have occurred? Scientists have multiple theories. No single explanation provides a complete answer. The Age of Mammals Quaternary Life: (5.3 – 0) Some scientists suggest disease or climate change played an important role in their demise. Still other scientists suggest that humans hunted large animals down to the point of extinction. Other skeptics question whether small groups of humans could have caused so many different species to all go extinct all at once. The Age of Mammals Quaternary Life: (5.3 – 0) Modern Homo sapiens evolved from ancestors in Africa more than 100,000 years ago. The fossil record shows that about 50,000 years ago early humans began to migrate out of Africa. Soon, the range of early humans extended from Europe, Africa, and Asia to Australia. The Age of Mammals Quaternary Life: (5.3 – 0) Than, as sea level fell during the last ice age, a land bridge formed that connected Asia with North America. Scientists think this land bridge enabled humans to migrate to the Americas about 14,000 years ago. The Age of Mammals Quaternary Life: (5.3 – 0) Today, Homo sapiens - humans inhabit every continent. Our species has become the most powerful factor in changing Earth’s environment; for the better or worse. This in turn affects the other species with whom we share the planet.