Fossil Footprints Reveal Oldest Elephant Herd   Live Science - February 22, 2012
The world's oldest elephant tracks have now been revealed, 7-million-year-old footprints in the Arabian Desert, researchers say. These prehistoric footsteps, likely the work of some 13 four-tusked elephant ancestors, are the earliest direct evidence of how the ancestors of modern elephants interacted socially, and the oldest evidence of an elephant herd.

Rabbit-Size Elephant Ancestor Found -- Oldest Known   National Geographic - June 23, 2009
Oldest Elephant Relative Found   Live Science - June 23, 2009

Elephant 'had aquatic ancestor' BBC - April 15, 2008

Ancient Elephant Ancestor Lived in Water, Study Finds National Geographic - April 14, 2008

Elephants