Final answer:
Primates, including the first proto-primates, appeared around 65 million years ago and resembled squirrels and tree shrews in size and appearance.
Step-by-step explanation:
The first primate-like mammals, known as proto-primates, appeared on Earth about 65 million years ago. They were approximately the size and resembled squirrels and tree shrews. Fossils like the proto-primate Plesiadapis had some features in common with true primates, such as teeth and skeletal structure.
The earliest true primates, which resembled present-day prosimians like lemurs, lived about 55 million years ago. These early primates were found in North America, Europe, Asia, and Africa.
Overall, the first primate-like mammal appeared on Earth around 65 million years ago and resembled squirrels and tree shrews in size and appearance.