The Geological, Isotopic, Botanical, Invertebrate, and Lower Vertebrate Surroundings of <i>Ardipithecus ramidus</i>

Sediments containing Ardipithecus ramidus were deposited 4.4 million years ago on an alluvial floodplain in Ethiopia’s western Afar rift. The Lower Aramis Member hominid-bearing unit, now exposed across a &gt;9-kilometer structural arc, is sandwiched between two volcanic tuffs that have nearly identical 40 Ar/ 39 Ar ages. Geological data presented here, along with floral, invertebrate, and vertebrate paleontological and taphonomic evidence associated with the hominids, suggest that they occupied a wooded biotope over the western three-fourths of the paleotransect. Phytoliths and oxygen and carbon stable isotopes of pedogenic carbonates provide evidence of humid cool woodlands with a grassy substrate.