![Geological Survey of Canada Geological Survey of Canada](/web/20061103055950im_/http://www.gsc.nrcan.gc.ca/esst_images/gsc_e.jpeg) Natural Resources Canada > Earth Sciences Sector > Geological Survey of Canada > Past lives: Chronicles of Canadian Paleontology
Past lives: Chronicles of Canadian Paleontology Under the shade of the Archaeopteris tree
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).) 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).)](/web/20061103055950im_/http://www.gsc.nrcan.gc.ca/paleochron/images/archaeo1.jpg) 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.
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