CHINA 42 million years old fossils of long tailed furry primates as big as your thumb add evidence of rich evolutionary history of Asian primates, questioning long-held views that humans originated in Africa. Oldest human fossils found are 2 - 4 million years old, from east Africa. Early primates appeared 66 million years ago. Anthropoids evolved 40 - 50 million years ago.
Fossils of 4-ounce Eosimias (dawn monkey) and the 2 tiny species were found in a limestone quarry at Shanghuang, 100 miles W of Shanghai. More Eosimias fossils were found in central Chinese province Shanxi. Close examination of tiny ankle and foot bones, some as big as grains of rice, established Eosimias as an extremely primitive anthropoid, the oldest known, a transitional. This first unambiguous evidence bridges anatomical gaps between lower and higher primates when lower primates, prosimians, went separate ways, evolving into today's lemurs, lorises, bush babies and tarsiers. Higher primates, anthropoids, evolved into monkeys, great apes and man. The second primate and Eosimias are anthropoids with prosimian characteristics. All 3 animals could help bridge the transitional gap between the 2 great primate branches.
The smallest animal, weighing 1/3 ounce, was identified from a single heel bone examined under a microscope. Bone shape and joint structure showed he walked on 4 legs in trees, like today's monkeys. He's somewhat like today's prosimians, mostly tarsiers, a rat-like tree dweller thought to occupy the intermediate stage between lower primates and anthropoids, probably an advanced prosimian. Connections between this primate and tarsiers is not strong. Lower primates aren't built to be quadrupedal walkers. They leap through and cling to trees. Accumulated fossils reveal many evolutionary steps leading to the emergence of humans in Africa over 100,000 years ago. Genetic analysis shows the human line split off from the one leading to chimpanzees and apes 5 - 7 million years ago. Scattered fossils point to the earliest primates of any kind appearing 55 million years ago, mainly in Asia, when the 2 primate lines seemed lost in wide fossil record gaps.
Tiny size, express train metabolism and jackhammer heartbeats, they burned calories too fast to eat grass. They ate insects, fruit and nectar. Unlike most primates they had no time to socialize. They had to be loners and night hunters, leaping from tree to tree, vulnerable to nocturnal predators. These fossils are much younger geologically than the soft Shanghuang limestone they were found in. The stone is threaded with fissures and small caverns carved by millions of years of rainwater. Mud containing bones of tiny animals washed into interstices and solidified. Absence of whole skeletons suggests they were eaten by owls and regurgitated as owl pellets carried away by rain.
Most of the bones are broken and had to be tediously examined and sorted under a microscope. Also found were remains of rodents, lizards, birds, frogs, rabbits and other small creatures. One puzzle is the site's almost total lack of large animal bones. 42 million years ago the quarry was a tropical forest, a habitat ordinarily not supporting many species of small animals. There's maybe 12 - 16 primate species. It's unheard of to find many animals the same size competing against each other. They're not found in Amazon, Indonesia, Wyoming forests. Transition to anthropoids was assumed made by animals larger than prosimians. Chinese collections include what may be several distinct Eosimias species. One specimen weighed 1/2 ounce. Others weighed up to 4 ounces. You'd expect early anthropoids to be small, but smaller than the smallest known living prosimians? Minute size and other primitive characteristics is close to the transition between low and high primates, further evidence that although more immediate human forebears arose in Africa their earliest primate ancestors migrated from Asia to Africa. Madagascar's 1-ounce mouse lemurs, today's smallest living primates, are eaten like popcorn.
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