Spineless Wonders of Evolution 199and in fossil manipulation, and the establishment of a progressively refined timescale
contribute to a present-day palaeontology offering the strongest support, the demon-
strative “proof,” of the fact and the process of evolution in terms wholly concordant
with the essence of Darwinian theory.
—T. George Neville, “Fossils in Evolutionary Perspective,” 1960When you point out the examples that we just discussed to the creationists, they weasel out
of the problem by arguing that these changes are all within the “created kinds” as described
in the Bible. As we pointed out in chapter 5, however, the concept of “kind” has absolutely
no biological meaning, but creationists use it as a convenient dodge to allow changes on the
microevolutionary scale (whatever evolves is within one kind) but to deny that major mac-
roevolutionary changes could occur. Of course, this concedes that a heck of a lot of evolution
is taking place, because nearly every group in the fossil record shows some evolution, and
they can’t all be created kinds—and they couldn’t even all fit on Noah’s ark, as we already
mentioned in chapter 3. But let’s play by their absurd rules and look at some radical changes
in body form and ecology that are clearly macroevolutionary.
How about sand dollars? These cute little flat shells that are so popular with tourists
and beachcombers are actually related to sea urchins and heart urchins and their kin. They
are members of the phylum Echinodermata that also includes sea star, brittle stars, and sea
cucumbers as well as many extinct groups. Living sand dollars are very flat and spend much
of their time just below the sea bottom, buried with a light coating of sand. When they are
feeding, however, they maneuver themselves with their short fuzzy spines and tube feet so
that they stick out diagonally from the seafloor like a set of shingles (fig. 8.13A). Their mouth
are on their undersides and face into the current, allowing them to trap food particles. Look-
ing at a sand dollar, it seems nothing like any other “kind” on the seafloor, and it seems hard
to imagine that it could evolve from something else—but it did! As documented by Porter
Kier (1975, 1982), sand dollars evolved rapidly in the late Paleocene and early Eocene from
the biscuit-shaped urchins known as cassiduloids to the slightly flatter oligopygoids to an
even more flattened transitional fossil known as Togocyamus from the late Paleocene of Togo,
West Africa (fig. 8.13B). In addition to getting flatter and flatter, sand dollars also show a
progressive reduction in the size but an increase in the number of spines and bumps on the
shell, so they go from rough and spiny to almost “furry” with tiny spines and bumps (which
makes burrowing easier). The mouth, which had been on the leading edge of the bottom of
the shell, shifts to the middle of the base of the shell, and the anus, which had been on the
top side of the shell in primitive forms, shifts to the back edge of the bottom surface. Later in
their evolution, they developed little holes and notches on the edge of the shell, which help
modify the water flow around the shell as they lie buried. All of these transformations are
well documented in specimens from the Paleocene and early Eocene (65–40 million years
ago), starting in the central West African region, and eventually spreading worldwide.
Or how about a classic “living fossil,” the horseshoe “crab”? They are familiar to anyone
who has combed the beaches of the Atlantic Coast of the United States, since they wash up
frequently. During particularly high tides once a year, hundreds of them crawl up on the
beach, mate, and lay their eggs in the sand in an orgy straight out of prehistory. Yet horse-
shoe “crabs” are not true crabs but instead are members of the group known as the Che-
licerata that includes spiders and scorpions. (True crabs are a family within the Crustacea,
a different group entirely.) Surely, they don’t look like any other group of arthropods, and