Page 220 - Introduction to Paleobiology and The Fossil Record
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PROTISTS 207
Chromalveolates
Plantae Alveolates
Colpoderllds Aplcomplexa Dinoflageflates
Oxyrrhis
Cillates Perkinsus
Brown Algas
Piants
Charophytes
Chlorophytes
Diatoms Chromists
Red Algae
Bicosoecide
Cercozoa + Oomycetes
Glaucophytes
Opalinida
Haptophytos
Cryptomonads
Apusozoa
Hellozoa
Phytomyxids
Haplosporidia Heteroloboses
Cercozoa
Filosa Euglonids Discicristates
Foraminifera Dipionemids
Radiolaria Carpediemonas
Kinetoplastlds
Core Jakobids
Fungi
Diplomonads
Microsporidia Fungi Lobosee Archamoebae Oxymonads Retortamonads
Trichomonads
Animals Nuclcarids Ichthyospores Choanoflagelates Amoebozoa
Trimastix
Hypermastigotes
Slime Moulds
Opisthokonts Excavates
Choanoroa
Figure 9.1 Protist positions on the tree of life. In this tree, developed by Patrick Keeling, University of
British Columbia, the protozoans (foraminiferans and radiolarians) lie within the Cercozoa far divorced
from the chromists (diatoms and dinoflagellates) within the Chromalveolates. (From Keeling et al.
2005.)
(Fig. 9.1). Subdividing the diversity of protists diversity but this is not the place to go into
is equally problematic. The division into auto- the rapidly changing details of this research.
trophic protozoans and heterotrophic algae Instead, we should simply note that groups
(chromistans) is important ecologically, but with microfossil records are widely scattered
phylogenetically almost meaningless as both across the diversity of protists. Here, follow-
groups are polyphyletic. The fi rst protists ing Cavalier-Smith (2002) and others, the
were almost certainly heterotrophs, but chlo- protists are grouped into protozoans (forami-
roplasts were acquired separately in at least niferans, radiolarians, acritarchs, dinofl agel-
six lineages, producing heterotrophs, and lost lates and ciliophorans) and chromistans
secondarily even more often: for example, the (coccolithophores and diatoms); chitinozoans
classic protozoan ciliates almost certainly are difficult to classify in this scheme and are
evolved from algae. Protists are also often thus treated separately.
subdivided according to their means of loco-
motion, most simply into fl agellates and
amoebans. Again, however, these are poly- EUKARYOTES ARRIVE CENTER STAGE
phyletic groups. So simplisitic attempts at So when did the eukaryotes fi rst appear? Uni-
classifying protists do not really work and cellular eukaryotes, with nuclei and organelles,
they are perhaps better regarded as a loose represented by acritarch cysts are known from
grouping of 30 or 40 disparate phyla with rocks dated at about 1.45 Ga. Spiral ribbons
diverse combinations of trophic modes, mech- of Grypania, however, have been reported
anisms of motility, cell coverings and life from rocks as old as 1.85 Ga. One of the oldest
cycles. Modern molecular genetic and cyto- multicellular organisms is a bangiophyte red
logic research is slowly making sense of this alga (rhodophyte) preserved in silicifi ed car-