Spineless Wonders of Evolution 189oblong bubbles clustered together in a spiral arrangement (fig. 8.5A). Through the many
cores that sample the Pliocene oceans we can find more and more specimens that develop
these long slender fingerlike extensions all over the final few chambers. As you move up the
cores, these little “fingers” become longer and more common. These creatures are so distinct
from the ancestral lineage that they branched away from that they are given their own spe-
cies: Globigerinoides fistulosus (they do indeed look like little fists). Another common trend is
the gradual evolution of foraminifera with flatter chambers and keels along the edges from
species with more primitive bubble-shaped chambers. These trends can be seen in the evolu-
tion of keeled Morozovella from Praemurica in the late Paleocene (fig. 8.5B), in keeled forms
of Globoconella in the early Miocene (fig. 8.5C), and in keeled Fohsella, also during the early
Miocene (fig. 8.5D).
Let us look at the other amoeba-like group, the radiolarians. As we mentioned already,
this group is much like the forams, only their skeletons are made of opaline silica (fig. 8.2B).
Unlike forams, which are both benthic and planktonic, all radiolaria are planktonic, so their
evolution and ecology closely mirrors the change in water temperature and chemistry where
they live and grow. Most of the time, they flourish only in places where nutrients are brought
up from the deep ocean to the surface. To the radiolarian, the scarcest and most important
nutrient is silica itself, which is depleted in normal surface seawater. When silica is carried
up from the deep by upwelling ocean currents, radiolaria and diatoms bloom in enormous
numbers and consume almost all of it immediately. After they die, their delicate skeletons
rain down on the ocean floor by the millions, so any ocean sediment in areas of upwelling
(typically in the boundary currents between water masses) is full of siliceous plankton such
as radiolaria and diatoms.
When I was a graduate student at Columbia University and at the American Museum of
Natural History in the late 1970s and early 1980s, I decided to learn about micropaleontology
to balance out my education in fossil vertebrates and invertebrates. Affiliated with Columbia
is Lamont-Doherty Geological Observatory (now Lamont-Doherty Earth Observatory), one
of the foremost geologic research institutions in the world. Lamont was the place that led
the revolution in geology known as plate tectonics in the 1960s. I rode the shuttle bus up the
Hudson River to Lamont so that I could take classes from the giants of plate tectonics, paleo-
magnetism, and seismology. Lamont has long been one of the pioneers in oceanography
and marine geology, with a collection of deep-sea cores from the oceans of the world that is
second to none. While at Lamont, I spent most of my time in the core laboratory, where I got
to examine microfossils by the thousands and learned about foraminifera from Tsunemasa
Saito, radiolaria from Jim Hays, and diatoms from Lloyd Burckle. Soon I was working on a
research project with my fellow graduate student Dave Lazarus, counting and measuring
hundreds of specimens on slides and trying to decipher the evolutionary patterns in a group
of radiolaria known as Pterocanium (Lazarus et al. 1985). These cute little “Christmas orna-
ments” were shaped like a lacy bell (the thorax) with a knob (the cephalis) and a spike on top,
and three long spines sprouting out from the open base (fig. 8.6). From the ancestral form
Pterocanium charybdeum allium (so named by Dave because the thorax was shaped like a clove
of garlic, allium in Latin) that lived 7 million years ago, we documented a complex pattern
of divergence among different shapes. Some developed larger pores and more robust spines
that flared out from the base and lost the distinct “knob” of the cephalis at the top (Pteroca-
nium audax). Another lineage developed a more cylindrical, boxy shape with distinct “shoul-
ders” (Pterocanium prismatium, an important index fossil for the Pliocene). Another lineage
developed huge flaring spines and shrank the size of the thorax to a little ball (Pterocanium