Page 60 - Introduction to Paleobiology and The Fossil Record

FOSSILS IN TIME AND SPACE 47

Cambrian. At its widest in the late Cambrian,
possibly extending as much as 4000 km

0° across, only floating graptolites were similar
on both sides of the Iapetus. But as the ocean
Laurentia
closed, swimming organisms such as the
conodonts could next cross the seaway
Kalahari (McKerrow & Cock 1976), and later so could
the mobile and eventually the fi xed benthos,
Plata the trilobites and brachiopods (Fig. 2.16b). By
30°S
the late Silurian, as the Iapetus Ocean nar-
rowed to only a few hundred kilometers,

Congo benthic ostracodes scuffled their way across.
Amazonia
By the Devonian, when the ocean was almost
1 completely closed, freshwater fi shes were
similar in Europe and North America. In a
refinement to the original model, Cocks and

Fortey (1982) described the ocean in terms of
0°
a three-plate model with oceans separating
Laurentia Gondwana, Baltica and Avalonia. The smaller
Avalonia broke away from Gondwana during
the late Cambrian-earliest Ordovician and,
together with Baltica, headed north towards
Kalahari 30°S Laurentia (Fig. 2.16c, d). Neuman (1984)
placed islands within the Iapetus Ocean, small
Plata suspect terranes with peculiar faunas, not
seen elsewhere. Even more intriguing, Baltica
spun anticlockwise as it moved towards the
Congo
Amazonia equator picking up these various terranes on
2
the edge of the continent (Torsvik et al. 1991).
Both cladistic and phenetic techniques have
been used to analyze the large amount of dis-
0° tributional data from within and around the
Laurentia

Figure 2.16 (opposite and this page) Changing
ideas on the development of the Early Paleozoic
Iapetus Ocean and its faunas: (a, c, d)
paleogeographic reconstructions; (b) the mobility
30°S of organisms across a closing ocean; (e) a cluster
Kalahari analysis of the Iapetus and related Early
Plata Ordovician brachiopod faunas (tinted blocks in
descending order indicate low-latitude, high-
3 latitude, low-latitude marginal and high-latitude
marginal provinces); and (f) the possible
movement of the Precordilleran terrane in three
Cuyania terrane stages, 1–3. A dataset of early Ordovician
Brasiliano/Pan-African belts brachiopod distribution across the Iapetus
Grenvillian belts terranes is available at http://www.
Pre-Grenvillian (Transamazonian/Birmian/ blackwellpublishing.com/paleobiology/. These
Eburnian) orogenic belts data may be analyzed and manipulated using a
Pre-Grenvillian (without Transamazonian/ range of multivariate techniques including cluster
Birmian/Eburnian) orogenic belts
analysis (see also Hammer & Harper 2005).
(f) (a–d, from Harper, D.A.T. 1992. Terra Nova 4;
f, based on Finney 2007.)