Prior to the Late Devonian, the Earth's surface was scorched everywhere by relentless sun. Moderating shade arrived with the spread of the first forests composed of the first tree Archaeopteris

A 40 cm long frond of Archaeopteris, the first tree. This specimen is on display at the Miguasha Museum and was featured on a Canadian stamp. (Photo by BDEC (c).)

Shales and sandstones of the Escuminac Formation (Late Devonian, 380 Ma) are exposed near Miguasha in the Baie des Chaleurs area of Gaspé Peninsula. These sedimentary rocks were deposited in an estuary in front of a major river draining into a very narrow Proto-Atlantic Ocean. The rocks contain not only extremely important fossil fish, but also critical fossil plants.

Some of the plant debris that swept down this river became water-logged, sank, and was fossilized along with the animals living in the estuary. The plants include spore-bearing fronds that Sir J. William Dawson, the premier paleobotanist in Canada and the Principal of McGill University, described as Archaeopteris. He thought these were fronds of a primitive fern. That assessment held until the 1960s when Charles Beck, paleobotanist at the University of Michigan, demonstrated that conifer-like wood called Callixylon was attached to fern leaflets bearing Archaeopteris foliage. Because the wood and leaflets are part of the same plant, only a single name can apply -- and that name has to be Archaeopteris because Dawson's name was published first.

Archaeopteris was more than a woody shrub -- it was the earliest known tree, and a sizeable one at that. Stumps up to one metre in diameter and trunks 30 metres tall are known. Archeopteris forests quickly became widespread across Late Devonian lowlands. The canopies of these trees would have provided protective shade and allowed for the accumulation of leaf-litter and humus on the forest floor. Such moist shaded settings had not existed on Earth previously, but these might well have been critical for the colonization of land by tetrapods. To escape the desiccating effects of the sun, the first amphibians would have sought out moist, shaded, equitable environments near water and underneath Archaeopteris trees.