Geoscience Reference
In-Depth Information
The early reptiles that emerged in the Late Carboniferous were small, slender animals. The one that Lyell
and Dawson found preserved inside a fossilized tree trunk, Hylonomus lyelli, was a mere 20 centimeters (8
inches) from head to tip of tail. One hundred million years later, these diminutive creatures gave rise to the
great dinosaurs. Again, some of the oldest fossils of these “terrible lizards” are found along the shores of the
Bay of Fundy.
The Dawn of the Dinosaurs and Birth of the Atlantic
Following the Carboniferous, in Permian times (290 to 248 million years ago), the continents continued to
press closer together. The area of the contemporary east coast of North America was in the region of the trop-
ics but was also continental—that is, stuck in the interior of the supercontinent Pangaea. The coming together
of Pangaea caused profound climate change—“a great drying”—and the wetlands that had fostered the luxuri-
ant growth of the Coal Age forests began to disappear. The year was now divided between a dry season, which
was followed by so-called megamonsoons in regular sequence. Because of the prolonged dry spells, the
moisture-loving giant club mosses and horsetails were replaced by conifers, which had previously been restric-
ted to the highlands, as well as by gymnosperms like cycads, ginkgoes, and seed ferns.
The great tides of the Bay of Fundy continue to erode its fossil-rich cliffs, opening a window in time.
The dominant land animals were mammal-like reptiles such as the pely-cosaurs, or sail-reptiles, which have
been found in the redbeds of Prince Edward Island. They sported a distinctive fanlike sail on their backs,
formed by elongated neural spines of the vertebrae covered by skin. Richly supplied with blood vessels, this
sail could be deployed to gather heat or to dissipate it, depending on how the animal oriented itself to the sun.
The fusion of the continents created huge deserts in the interior of Pangaea, which have been invoked to
partially explain the “great dying” that brought the Permian to a resounding close, 245 million years ago, when
nearly 75 percent of all amphibian and reptile families and fully half of all marine families were wiped out.
Where mountains formed as the continental plates jammed together, cold temperatures, accompanied by gla-
cial activity, may have prevailed. The productive shallow coastal seas were also reduced by the coming togeth-
er of the continents. Chemical changes to the atmosphere seem to have occurred around the Permian-Triassic
