The bones of prehistoric horses have been found in chamber tombs dating from Vere Gordon Childe's period III - IV in southern Britain. This would date the bones at the transition from a hunter-gatherer society to an agricultural society (the Neolithic Revolution) around 3500 BC; the bones are probably from wild horses, but domestication may have begun by that date. Archeological investigation from the 1970s has shown that domesticated ponies were to be found on Dartmoor as early as 1500 BC. The first written record, dated to AD 1012, refers to wild horses at Ashburton, and early records from Dartmoor manors refer to ponies being branded and earmarked.