/ +---------------------------------------------------+ Recent. { | Equus Caballus.{*} | \ +---------------------------------------------------+ / | | { | Equus Stenonis.{*}{**} E. Sivalensis.{*}{**} &c. | Quaternary. { | Hippidium.{**} E. Americanus.{**} &c. | { | | \ +---------------------------------------------------+ / | | { | | { | Pliohippus. | / { | | { Pliocene. { | Hipparion.{*}{**} Protohippus. | { { | | { { | | { \ | | { +---------------------------------------------------+ { / | | TERTIARY. { { | | { Miocene. { | Hypohippus. Parahippus. | { { | Miohippus. Anchitherium.{*} | { { | Merychippus. | { { | Mesohippus. | { \ | | { +---------------------------------------------------+ { / | Epihippus. | { { | Orohippus. Hyracotherium.{*} | { Eocene. { | Protorohippus. Pachynolophus.{*} | { { | Eohippus. | \ { | Phenacodus. | \ | | +---------------------------------------------------+ | | | Hippops (undiscovered). | SECONDARY. | | | No trace of Mammals except small | | Marsupials and Insectivora. |