Page 75 - Global Tectonics

62 CHAPTER 3

Areas of tropical coal forests at 300 Ma which
some 50 Ma later became vast hot deserts
Areas of glaciation between 300 and 250 Ma
with arrows indicating known directions of ice movement
Figure 3.9 Use of paleoclimatic data to control and confirm continental reconstructions (redrawn from Tarling &

Tarling, 1971).

their dispersal (Hallam, 1972). An obvious example of Oceans can also represent dispersal barriers to
this would be the growth of an ocean between two certain animals which are adapted to live in relatively
fragments of a supercontinent which prevented migra- shallow marine environments. The widespread disper-
tion between them by terrestrial life-forms. The sal of marine invertebrates can only occur in their larval
past distribution of tetrapods implies that there must stages when they form part of the plankton (Hallam,
have been easy communication between all parts of 1973b). For most species the larval stage is too short-
Gondwana and Laurasia. Remains of the early Permian lived to exist for the duration of the crossing of a large
reptile Mesosaurus are found in Brazil and southern ocean. Consequently, ancient faunal province boundar-
Africa. Although adapted to swimming, it is believed ies frequently correlate with sutures, which represent
that Mesosaurus was incapable of travelling large dis- the join lines between ancient continents brought into
tances and could not have crossed the 5000 km of ocean juxtaposition by the consumption of an intervening
now present between these two localities. ocean. The distribution of Cambrian trilobites strongly