Page 229 - Introduction to Paleobiology and The Fossil Record

216 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Classification Micro- Porcel- Hyaline
Agglutinates granular aneous Benthic Plank-
tonic
Families of Foraminifera Ammodiscidae

Stratigraphy Lituolidae Orbitolinidae Endothyridae Fusilinidae Miliolidae Alveolinidae Nodosariidae Buliminidae Discorbidae Rotaliidae Nummulitidae Orbitoididae Miogypsinidae Globigerinidae
Ceno- zoic Tertiary

Cretaceous
Paleozoic Mesozoic Jurassic

Triassic
Permian

Carboniferous

Devonian
Silurian
Ordovician

Cambrian

Figure 9.8 Stratigraphic ranges of the main foraminiferan groups. (Based on various sources.)

apical horn
spine cortical shell
cephalis
pore
medullary joint
shells
chambered
bar lattice shell

tripod

Spumellaria Nassellaria

Figure 9.9 Descriptive morphology of the radiolarians.

mental work on the group by Alfred Eisenack
Acritarchs
(1891–1982) initially suggested that these tiny
The acritarchs are a mixed bag of entirely fossils were the eggs of planktonic inverte-
fossil, hollow, organic-walled microfossils that brates; however, later he considered the group
are impossible to classify. The acritarchs are to be fossil members of the phytoplankton,
probably polyphyletic; they include a wide plants rather than animals. William Evitt of
range of forms, probably representing the cyst Stanford University, in establishing the scope
stages or resting phases in the life cycles of of the group in the early 1960s, noted that his
various groups of planktonic algae. Funda- term “acritarch” (meaning “uncertain origin”)