In the evolutionary history of the modern horse (Equus), what was the chronological evolutionary sequence of ancestral genera?
Answer and explanation
Correct answer: A. Eohippus (Hyracotherium) Mesohippus Merychippus Pliohippus Equus
- Step 1: The fossil phylogeny of the horse is one of the most complete paleontological records.
- Step 2: It began in the Eocene epoch with the four-toed Hyracotherium (Eohippus, dawn horse).
- Step 3: Evolutionary progression proceeded through Mesohippus (Oligocene, 3-toed) Merychippus (Miocene, grazing) Pliohippus (Pliocene, one-toed) Equus (Pleistocene to modern single-toed horse).
Answer
Eohippus (Hyracotherium) Mesohippus Merychippus Pliohippus Equus.
Why not the others: The option describing a continuous increase in digit count reverses the evolutionary timeline; The option running from Equus back to Eohippus and the option beginning with Pliohippus scramble the well-documented geological stratigraphic sequence.
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