mesohippus vs Equus caballus

mesohippus and Equus caballus both are nouns.

Word	Noun	Adjective	Verb	Adverb
mesohippus	Yes	No	No	No
Equus caballus	Yes	No	No	No

As nouns, Equus caballus is a hypernym of mesohippus; that is, Equus caballus is a word with a broader meaning than mesohippus:

mesohippus: North American three-toed Oligocene animal; probably not directly ancestral to modern horses
Equus caballus: solid-hoofed herbivorous quadruped domesticated since prehistoric times

Other hypernyms of mesohippus include horse.

mesohippus (noun)	Equus caballus (noun)
North American three-toed Oligocene animal; probably not directly ancestral to modern horses	solid-hoofed herbivorous quadruped domesticated since prehistoric times