because its remains are rarer. This effect—known as the Signor-Lipps
effect, after the scientists who first identified it—tends to “smear out”
sudden extinction events, making them look like long, drawn-out affairs.
Following the K-T extinction, it took millions of years for life to
recover its former level of diversity. In the meantime, many surviving
taxa seem to have shrunk. This phenomenon, which can be seen in the
very tiny forams that show up above the iridium layer at Gubbio, is called
the Lilliput effect.
LANDMAN, Garb, and the graduate students chipped away at the creek
bed all morning. Although we were in the middle of the country’s most
densely populated state, not a single person passed by to wonder at what
we were doing. As the day grew warmer and more humid, it was pleasant
to stand ankle-deep in the water (though I did wonder about the reddish
slime). Someone had brought along an empty cardboard box, and, since I
didn’t have a pickax, I helped out by gathering up the fossils the others
had found and arranging them in the box. Several more bits of
Discoscaphites iris turned up, as well as pieces of an ammonite, Eubaculites
carinatus, which, instead of having a spiral shell, had one that was long
and slender and shaped like a spear. (One theory of the ammonites’
demise, popular in the early part of the twentieth century, was that the
uncoiled shells of species like Eubaculites carinatus indicated that the
group had exhausted its practical possibilities and entered some sort of
decadent, Lady Gaga-ish phase.) At one point, Garb rushed over in a flurry
of excitement. He was carrying a fist-sized chunk of the creek bed and
pointed out to me, along one edge, what looked like a tiny fingernail. This,
he explained, was a piece of an ammonite’s jaw. Ammonite jaws are more
common than other body parts but still extremely rare.