Bossies and Blowholes 335the latest Eocene, these elephant-sized beasts sported a pair of blunt bony battering rams
on their noses, yet they evolved from beagle-sized unspecialized early Eocene ancestors
(Palaeosyops) that are difficult to distinguish from the earliest Eocene horses and tapir-rhino
ancestors. A century ago, the famous paleontologist Henry Fairfield Osborn spent years
studying them and published a huge two-volume work (Osborn 1929) that was chock-full
of bad taxonomy (even by the standards of his day). It was further confused by his unortho-
dox ideas about orthogenesis, or straight-line evolution going out of control in one direction
without the restraint of natural selection. Unfortunately, this outdated example (fig. 14.9)
continues to be published in textbooks today, even though it falsely portrays their evo-
lution as a single straight lineage. In fact, brontothere evolution was very bushy as well
(fig. 14.10), with multiple lineages coexisting in the middle and late Eocene, after which the
entire group died out. Lest the creationists attempt to misquote me, brontotheres do show
evolutionary changes in size and horn development through time, but it is in the context of many
different species branching out, not a single lineage marching to their ultimate extinction as
Osborn once thought.
Kingdom of Cloven Hooves
Nevertheless, these shall ye not eat, of them that chew the cud or of them that divide
the cloven hoof; as the camel and the hare, and the coney; for they chew the cud, butFIGURE 14.10. A modern view of brontothere evolution, showing the more branched bushy pattern of species
through time, based on the work of Mader (1989). (From Prothero 1994b)