Triassic and Jurassic

The Mesozoic began with Pangea fully assembled and with low sea levels. During Triassic time, the Tethys Sea formed between the single northern continent, Laurasia, and Gondwanaland, but it remained narrow in places; there may have been intermittent contacts between the northern and southern continents during much of the Mesozoic. By the Middle Jurassic, sea level had risen and shallow continental seas separated North America—Greenland from Europe and South America from Africa, at least intermittently. Also during the Jurassic, India-Madagascar may have already broken away from Africa.

Glossopteris survived through the Triassic but died out early in the Jurassic, ending one pteridosperm lineage. Two other now extinct orders possibly derived from the pteridosperms, namely the Caytoniales and the Bennettitales, arose during the Triassic. The Caytoniales had a fleshy tissue partly enclosing the seed that suggests animal dispersal. One genus of Caytoniales, Lepidopteris , had a remarkable range across Laurasia and Gondwanaland in paleolatitudes from 60°N to 60°S. The Bennettitales, which superficially resemble cycads, had spectacular reproductive structures that suggest adaptation for animal pollination.

The two Paleozoic gymnosperm orders that survive today, Cycadales and Ginkgoales, spread widely through both Laurasia and Gondwanaland in the Mesozoic, increasing greatly in abundance and diversity. Some Jurassic Ginkgo leaves are indistinguishable from those of the living G. biloba, and some of the cycads were already similar to living genera.

Two other living orders of gymnosperms, Coniferales and Taxales, arose in the Mesozoic not long before the Voltziales, their probable progenitors, became extinct. Five important modern conifer families had evidently already diverged by the Early Jurassic: Pinaceae in Laurasia, Podocarpaceae in Gondwanaland, and Araucariaceae, Cupressaceae, and Taxodiaceae on both

Figure 13. Late Paleozoic Range of Glossopteris , a Dominant Seedfern on the Supercontinent of Gondwanaland.
Gondwanaland broke up into several continents, outlined by dashed lines. Fossils of Glossopteris were then
displaced to widely separated parts of the globe. Since the genus evidently was not adapted for transoceanic
dispersal, its fossil distribution appears inexplicable on an earth with fixed continents. This was noted as evidence
for the hypothesis of continental drift long before the modern theory of seafloor spreading was developed.

continents. During the Jurassic, the Taxales, precursors of the living yew, entered the fossil record in Laurasia.