Page 64 - Introduction to Paleobiology and The Fossil Record

FOSSILS IN TIME AND SPACE 51

400

Number of families 300

200

100

Late
Siluro-
Cambro-
Precam- Ordovician Devonian Carbonifero- Permo- Triassic Triassic- Cretaceous Tertiary-
Permian
Jurassic
Recent
brian
Europe
NA
Pangaea I

SA India
Pangaea II Australia
Africa Antarctica
U
I Laurasia

A H Tethys
Gondwanaland
Gondwanaland
Figure 2.18 Changing familial diversity of skeletal benthos through time in relation to plate

configurations: high diversities are apparently coincident with times of greatest continental
fragmentation, for example during the Ordovician, Devonian and Cretaceous-Cenozoic. A, pre-
Appalachian-Variscan Ocean; H, Hispanic Corridor; I, Iapetus Ocean; U, pre-Uralian Ocean. (Based on
Smith, P. 1990. Geoscience Canada 15.)

example is the “Delabole butterfl y”, so called to taxonomic paleontologists; now a range of
because quarrymen in the village of Delabole, microcomputer-based graphic techniques are
in Devon (England) thought they were looking available to “unstrain” specimens. Hughes
at ancient butterflies. In fact, the wide-hinged and Jell (1992), for example, used such

fossils are spiriferide brachiopods (see p. 306), techniques to unstrain Cambrian trilobites
and they were bent and stretched in all kinds from Kashmir that had been distorted by
of ways, depending on how they were ori- earth movements during the uplift of the
ented in the rocks. The fossils are in Devonian Himalayan mountain belt (Fig. 2.19). Previ-
sediments that were bent and stretched by the ous studies had recognized seven species
Variscan Orogeny, a great phase of mountain among these trilobites; statistical and graphic
building that affected southern and central removal of the effects of tectonism revealed
Europe during the Carboniferous. By measur- only one species. The study also allowed
ing the fossils, these large-scale forces could Hughes and Jell to identify the trilobites more
be reconstructed. accurately than before and to understand how
Until fairly recently these and similarly they relate to species from India and North
deformed assemblages were of limited value China.