FIGURE 8.5. Evolutionary sequences in some of the planktonic foraminifera. (A) In the Pliocene and Pleistocene,
the fingerlike projections of Globigerinoides fistulosus evolved from the smooth-shelled Globigerinoides sacculifer.
(B) The evolution of Praemurica (top) to the keeled Morozovella (bottom) that occurred between 63 and
59 million years ago. (C) The evolution of Globoconella in the early Miocene (20–18 million years ago), from the
unkeeled forms at the top to the keeled Globoconella conoidea at the bottom, which vanished about 6 million
years ago. (D) A similar trend in the genus Fohsella, from the ancestral unkeeled forms at the top to the highly
keeled species at the bottom. (Photos in (A) courtesy J. Kennett; (B–D) courtesy R. Norris)
FIGURE 8.6. Evolutionary patterns in the radiolarian Pterocanium from the late Cenozoic. Solid bars show
the time distribution of the main lineages, while gray zones show intervals of intergradation and possible
hybridization of lineages. Time scale along left indicates millions of years before present (Ma). Scale bars
= 10 micrometers. 1, Pterocanium korotnevi; 2, Pterocanium praetextum; 3 1 , Pterocanium charybdeum allium;
32 , Pterocanium charybdeum charybdeum; 3 3 , Pterocanium charybdeum trilobum; 4, Pterocanium prismatium; 5,
Pterocanium audax. (From Lazarus et al. 1985: fig. 21; used by permission of the Paleontological Society)
AGE
(Ma)
0 1 2 3 4 5 6 71 2 3345(^32)
(^31)
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