Mammalian Explosion 307to construct ancestor-descendant sequences. Because the hard enamel on teeth is often the
most durable part of the skeleton, the teeth and jaws are usually the only parts to survive the
beating caused by scavengers and river currents and trampling. Basing our understanding
of mammals largely on their teeth may seem inadequate, but fortunately teeth are the most
diagnostic part of most mammals, even when we do have the luxury of fossilization of the
rest of the skeleton. Teeth not only preserve patterns of their ancestry in the intricate details
of their cusps and crests, but they also reflect (to varying degrees) the diet of the animal as
well. Thus, if we had to choose only one part of the animal skeleton to be preserved, we are
lucky that the most useful part happens to be what fossilizes. Some vertebrate paleontolo-
gists joked (after seeing one talk after another on the protocones, paracones, metacones, and
other cusps on mammalian teeth) that we “protoconologists” seem to think that one tooth
gave rise to another tooth ad infinitum. But this is not by choice, but by necessity. By con-
trast, a fish or reptile paleontologist usually cannot do much with teeth or other fragments
and typically only works with nearly complete specimens. This is one of the reasons that the
mammalian fossil record is the most complete and detailed and densely fossiliferous of all
vertebrate groups. We can do many things with fossil mammals that cannot be done with
any other group of vertebrates.
When I was an undergraduate, my final project in my vertebrate paleontology class
was to identify a collection of early Eocene mammal teeth from the Bighorn Basin of Wyo-
ming and then try to research their origins in the scientific literature. I did my best on the
project using what was published at the time. But when I came to the American Museum
of Natural History in 1976 to begin graduate school at Columbia University, I was in for
a shock. Here were the very best minds in the business working with the best fossils
of every group of mammals. They were all feverishly studying specimens and drawing
cladograms, using this new approach to decipher the century-long puzzle of the rela-
tionships of the major groups of fossil and living mammals. I gave a copy of my humble
undergraduate thesis to my friend, Earl Manning, the collections manager and a former
graduate student, and he tore it to shreds because the new cladistic approach (plus his
better knowledge of the actual specimens) gave him a perspective that I could never have
obtained as an undergrad reading older published literature. (This is a lesson for creation-
ists: you can’t do research by reading other people’s work in the literature. Until you
do the research with the real specimens yourself, you have no right to talk about these
things). Soon, I was discovering for myself the groundbreaking new thinking about mam-
malian relationships, and the century-old problem of the relationships of the orders of
mammals was soon to be solved.
Just a year before I arrived in New York, my graduate advisor Malcolm McKenna pub-
lished the first cladistic analysis of fossil mammals. At the time he did it, it caused howls of
shock and outrage. Cladistics was already second nature to entomologists and ichthyologists
by then, but vertebrate paleontologists and mammalogists tended to be more conservative.
Although many had heard of cladistics, and some had tried it out on their own group of
organisms, none had ever used it to decipher the higher-order relationships of mammals
before. But it was just the tool that was needed to address this complex problem that had
eluded solution for over a century. Instead of trying to find more primitive ancestral teeth
in earlier beds, paleontologists could now use cladistics to take advantage of the anatomy
of the entire organism, not just the teeth. This worked especially well for living groups that