By looking closely at the fossil record, paleontologists are able to spot tiny clues as to how mammals, and eventually humans, may have evolved. Here are two Thrinaxodan fossils curled up together, an ancient species that marks the early transition of into mammalian traits. Looking closely at their jaw and skull, we can find tiny pits that may have housed whiskers, a sensory organ to help the animal navigate underground. Later down the line, these whiskers would evolved beyond merely a sensory tool and into hair and fur to keep early mammals warm.
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