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The latest archaeological study finds that 65,000,000 years ago, the earliest primate species are tree dwelling mammals similar to squirrels. They eat fruit and insects.
Paleontologists obtained conclusions of this study through the analysis of the ankle fossil from Northeast Montana 0.65 million years ago. The most primitive primate specie was named "Purgatorius". It is now extinct and a branch of the monkey shape taxa. Monkey was first appeared in the fossil record after the extinction of the non-flying dinosaurs.
Many researchers have long speculated that the monkey species are terrestrial species, and they climb up tress afterwards. Such theory still exists in the biological anthropology textbook.  Stephen Chester, from the the City University of New York, said: "in the textbook of biological anthropology, there are pictures showing terrestrial lives of monkeys. The latest research is expected to change the understanding of the earliest evolution, and helpful to learn that monkeys are species of tree dwelling creatures."
So far, the ancient biologists have only examined the teeth and jaw of the species. The main characteristics and the behaviors of the species are still mysteries. Where finding the monkey ankle fossil teeth, the scientists also found the fossil teeth so as to enable researchers to better understand how the monkeys live.
Chester pointed out that the ankle fossil we found has the characteristics of mobility which exists only in primates and their close relatives. These unique features make the monkeys climb the trees, rotate and adjust their feet. In contrast, ground dwelling mammals lack those characteristics, and they can better adapt to the vertical moving forward.
That study provides the most ancient fossil evidence, which confirms that the special structure of the limb skeleton plays an important role in the evolution of primate species. It means the evolution of primates from other mammals is not a dramatic event.
Primates changed subtly in the evolution so that they could move more easily to get food on the trees. The latest research shows that the first 10000000 years of the evolution of primates is the early stage of flowering plants. They evolve to climb the trees in the early stages, and can gather fruits and other foods.
Monkey lives in the Paleocene after a period of time dinosaur species become extinct. The end of the dinosaur era comes the reign of mammalian, which promotes the rapid evolution of humanity's earliest ancestor species. At present, scientists said monkey is weighed about 36 grams (1.3 ounces), equivalent to the smallest primate specie now in the world—Madagascar lemur.
From: Creative Animodel
Reference:
https://en.wikipedia.org/wiki/Primate