Based on this excellent piece of speculative fiction.
5.33 million years ago, the TARDIS lands in the middle of a vast salt desert, shining like a perfectly-polished mirror in the harsh sun: the bottom of the Mediterranean Sea. At this time, sea levels and tectonic movements conspired to close the Strait of Gibraltar, causing it to evaporate in a time known as the Messinian Salinity Crisis. The Doctor and their companion are surprised to find a pre-human civilization of elephants living in this harsh environment, but find the identity of their pets even more surprising; domesticated, upright-walking apes, to do all the delicate work the behemoths canât with their trunks. There would be a great deal of political intrigue and perhaps some indication that the ape-servants arenât as animalistic as they seem, ending in the Doctor and co. inciting what paleontologists call the Zanclean Flood: the day the Straits of Gibraltar and Sicily opened back up and massive amounts of water came pouring in, drowning the great elephantine cities and burying them forever. A group of apes manages to escape into the wilds of Africa to the south, and the rest is history. Their descendants will never know where they really came from.