Page 113 - Introduction to Paleobiology and The Fossil Record

100 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Sepkoski’s (1981) robust division of Phanero- for their lack of science. They are, however,
zoic life into his Cambrian (trilobites, based on real case histories and numerical data
non-articulated brachiopods, primitive echi- are now available for many of these recon-
noderms and mollusks), Paleozoic (suspen- structions. For example, two spectacular depos-
sion feeders such as the articulated brachiopods, its, the Newark Supergroup and the Posidonia
bryozoans, corals and crinoids) and the Shales, provide important windows on life in
Modern faunas (detritus feeders such as the continental and marine environments, respec-
echinoids, gastropods and bivalves together tively, during the early part of the Jurassic.

with crustaceans, bony fishes and sharks) has Major new finds in the Newark Supergroup
acted as template for much paleoecological and equivalent strata in eastern North America,
research (see p. 538). have painted a vivid picture of life on Late
Triassic and Early Jurassic arid to humid land-
Communities and habitats through time scapes of Laurentia swept by occasional mon-
soons. Olsen and his colleagues (1978, 1987)
Most paleoecological studies attempt to recre- have described diverse dinosaur communities
ate the dynamism and reality of past communi- of both large and small carnivorous thero-
ties from environments ranging from mountain pods, at the top of the food chain, together
lakes (see p. 90) to the strange chemosynthetic with large herbivorous sauropods and some
environments of the deep sea (Box 4.4). Despite early armored forms. Most of the terrestrial

the significant loss of information through tetrapods are preserved in volcaniclastic
taphonomic processes, realistic reconstructions deposits, but adjacent fl uviatile facies contain
are possible, depicting the main components, crocodiles. Lake facies have preserved diverse

their relationships to each other and the sur- floras of conifers, cycads, ferns and lycopods.
rounding environment. During most of geo- Fast-swimming holostean fi shes patrolled the
logical time, microbial organisms were the sole lakes and abundant insects of modern aspect,
inhabitants of Earth. The Ediacara biota representing seven orders, populated the
appeared at the base of the Ediacaran System, forests and shores or may have swum in the
some 630 Ma, but most members had disap- shallows together with crustaceans.
peared by the start of the Cambrian. McKer- The Posidonia Shales crop out near the
row (1978) was first to summarize, in broad village of Holzmaden in the Swabian Alps,

terms, the development of communities Germany. The shales are bituminous or tar-
throughout the Phanerozoic (see also Chapter like, packed with fossils, generally with echi-
20). These tableaux were necessarily qualita- noderms and vertebrates towards the base
tive but now there are a growing number of and cephalopods at the top. Seilacher (1985)
more quantitative approaches providing more and his colleagues showed how this rock unit
accurate reconstructions of community change with exceptionally preserved fossils, or Lager-

through time. One of the first seascape recon- stätte, was a stagnation deposit (see p. 60)
structions, Sir Henry de la Beche’s watercolor where fossils accumulated in almost com-
of Duria antiquior (1830), depicted life in an pletely anoxic seabed conditions, and so were
early Jurassic sea. It was an iconic painting but hardly damaged by decomposers. Benthos is
nevertheless scientific, illustrating, graphically, rare, and encrusting and recumbent brachio-

the relationships between predators and prey pods, bivalves, crinoids and serpulids that
in the Modern evolutionary fauna. Today we could not live on the stagnant seabed attached
know much more about the range of environ- themselves to driftwood, ammonite shells and
ments that existed during the Jurassic Period. other floating or swimming organisms to

pursue a so-called psedoplanktonic life mode.
Jurassic Park and deep-sea worlds The dominant animals were nektonic ammo-
nites and coleoids together with the superbly
Jurassic environments provide a wide range of preserved ichthyosaurs and plesiosaurs, now
communities and habitats showing the early displayed in many European museums. Some
stages of development of post-Paleozoic faunas. horizons are characterized by monotypic
A selection demonstrating environments, life assemblages of small taxa such as diademoid
modes and trophic strategies are illustrated echinoids and byssate bivalves, like Posidonia
(Fig. 4.20). Such tableaux have been criticized itself. These benthic colonizations may have