"Modern horses, in other words, are failures within a failure-about the worst possible exemplars of evolutionary progress, whatever such a term might mean," p71.
Gould is making an argument that I am having a difficult time fully grasping. I am understanding Gould's argument that evolution is about pruning a copious tree and that the evolution of modern horses cannot be looked at as progression. But to say that modern horses are a failure? True to say that horses are the last genus of a once diverse lineage, but to say that an existing species is a failure? A failure by what definition? They've had local disappearances, but the fact that horses still are around shows that they are still more successful than extant organisms. Horses are fulfilling their evolutionary role...survive long enough to reproduce. Who cares if the closest relatives are not around?
"Steady perissodactyl decline has been matched by a reciprocal rise to dominance of the contrasting artiodactyls, once a small group in the shadow of ruling perissodactyls, and now the most abundant order, by far, of large-bodied mammals, p72.
I still disagree with Gould's argument that modern horses are failures. Yes, the order might have only three surviving groups with seventeen species (horses 8 rhinos 5 and tapirs 4) and is losing ground to the artiodactyls, but they still have their niche. I doubt they could ever dominate the plains like competitors of a different order. Don't call modern horses a failure until they are extinct. I'd like to purpose a rewording for the first quote: "Modern horses, in other words, are fortunate survivors within a failing group..."
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