The Forest horse also known as the Warmblood subspecies or Diluvial Horse, now extinct, is a postulate of the Four Foundations theory that argues that there were between four and seven primitive subtypes that preceded the development of the domestic horse, each adapted to a given ecosystem. This subtype is thought to have evolved into the warmblood horses of northern Europe, as well as being an ancestor of some of the older breeds of "heavy horses" such as the Ardennes. It was a large-boned, slow-moving, heavy horse with broad hooves, which enabled it to live in the widespread swampy areas of Europe, and a thick and wiry coat which may have been dappled for camouflage.
Proponents of the four foundations theory have labeled this subtype Equus ferus silvaticus and Equus ferus germanicus, though modern taxonomy disputes this classification.
Bennett, Deb (1998). Conquerors: The Roots of New World Horsemanship (First ed.). Solvang, CA: Amigo Publications, Inc.. ISBN 0-9658533-0-6. OCLC 39709067. pp 6-8