Squirrels' Evolution Biological & Biomedical Sciences Essay

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Squirrels' Evolution
Squirrels belong to the family Sciuridae, which consists of small and medium-sized rodents. The most common types of squirrels are tree squirrels, chipmunks, ground squirrels, marmots (like woodchucks), prairie dogs and flying squirrels. These living things are mostly found in the United States, Africa, Eurasia, and Australia. It is believed that the earliest fossilized squirrels belonged to the Eocene period and were related to the mountain beaver. These 56-million-year old squirrel fossils were discovered in North America. It is said that a lot of chemical changes took place in their bodies along with drastic environmental changes, both of these changes eventually led the earliest squirrels to vanish from the face of the Earth.
Nearly 50 million years ago, the climate was quite cool, and a lot of extinctions in squirrels and other animals took place. The very first European evidence for squirrels dates to 30 million years ago, but experts are still not sure how these living organisms reached there since they were native to Africa, America, and Eurasia. Some of them, especially flying squirrels, were brought to Australia by human beings. According to the fossil records, the first squirrel arrived in Africa nearly 18 million years ago. At that time, the continent collided with Eurasia and caused a lot of problems for both animal and plant species. Their populations were affected to a great extent, and DNA evidence reveals that the first branching in the lineages of modern tree squirrels and flying squirrels date to a...