Somali Sengi (Somali elephant shrew)
This little fella was considered "lost to science" until just last August, with its last recorded sighting dating all the way back to 1968. As it turns out, there is a pretty significant population currently thriving across three countries in the Horn of Africa.
For my part, as someone who is regularly late enough to be considered "lost to science" myself, I identify closely with the Somali Sengi. They're not "lost," just... Fashionably late (since 1968).