"Comparison of ancestral and existing horse"
The lower figure is a model of a full-sized Eohippus, placed beneath the skull of a modern horse, to show that the skull of the modern horse is larger than the entire body of its ancestor.
Despite being one of the most commonly cited “facts” in basic paleontology (as found in many elementary school science texts), this size comparison is actually incorrect. Geologist Henry Fairfield Osborn distributed (largely correct, aside from this point) educational pamphlets citing the size of Eohippus to be comparable to a “small fox terrier” to schoolhouses, to promote the science of paleontology, around the turn of the century.
His pamphlets reached so far and wide that the “fact” still persists to this day in many textbooks. Eohippus was about twice the size of a fox terrier, which is about 2.5 times the size of a modern horse skull.
Origin and History of the Horse. Address before the New York Farmers Metropolitan Club, 1905.