Fossil plant specimens at Miguasha are dominated by at most five species. Other Upper Devonian areas have revealed much more diverse assemblages. Compared, for example, with flora from the beginning of the Frasnian Age in the state of New York, the Escuminac Formation at Miguasha lacks typical groups like the aneurophyte progymnosperms, cladoxylopsids, iridopterids and lycophytes.

Even so, fossil spores in the rocks reveal that the Miguasha habitat was not nearly as species-poor as the fossil record might indicate. It seems that the apparent lack of plant diversity is the result of the small size of the fossiliferous outcrop available for sampling, or the effect of selective sorting of species while being transported by a current before fossilization.

Plant fossils of the Escuminac Formation are divided into two assemblages: Protobarinophyton and Archaeopteris. The assemblage in the layer containing Protobarinophyton, a plant that lived on the banks of the ancient estuary, suggests it underwent a short transport distance compared to the assemblage containing Archaeopteris, a tree that preferred to establish itself some distance from the bank where the soil wa Read More
Fossil plant specimens at Miguasha are dominated by at most five species. Other Upper Devonian areas have revealed much more diverse assemblages. Compared, for example, with flora from the beginning of the Frasnian Age in the state of New York, the Escuminac Formation at Miguasha lacks typical groups like the aneurophyte progymnosperms, cladoxylopsids, iridopterids and lycophytes.

Even so, fossil spores in the rocks reveal that the Miguasha habitat was not nearly as species-poor as the fossil record might indicate. It seems that the apparent lack of plant diversity is the result of the small size of the fossiliferous outcrop available for sampling, or the effect of selective sorting of species while being transported by a current before fossilization.

Plant fossils of the Escuminac Formation are divided into two assemblages: Protobarinophyton and Archaeopteris. The assemblage in the layer containing Protobarinophyton, a plant that lived on the banks of the ancient estuary, suggests it underwent a short transport distance compared to the assemblage containing Archaeopteris, a tree that preferred to establish itself some distance from the bank where the soil was more stable. Desiccation cracks in sediment layers containing Protobarinophyton are evidence of an environment that was sporadically exposed to air. In contrast, sedimentary structures associated with the best Archaeopteris-bearing layers suggest strong currents.

The case of paleoflora (ancient plants) is an excellent example of how paleontologists must deal with natural “filters” that come between the original ancient environment and the researcher who attempts to interpret it. Miguasha illustrates this point well: only plants that died in the waves of the estuary, or whose remains were washed into it, could eventually become fossilized, and the fossil record thus excludes any species that lived too far from the water’s edge. Even then, the sediments in which the plants fell must have survived as sedimentary rock or their precious information would be lost forever.

© Miguasha National Park 2007

A Layer of Archaeopteris Fossils

The fossil plant Archaeopteris is abundant in several layers of the Escuminac Formation. This example contains both species found at Miguasha. The one with the larger leaves is Archaeopteris obtusa and the other A. halliana.

Miguasha National Park

© Miguasha National Park 2007


A small, unobtrusive leafless plant grew quietly on the edges of the ancient Miguasha estuary. Its fossils are rare and often incomplete, such that paleobotanists assign it with hesitation to the genus Protobarinophyton. It is only found in a thin layer within the lower part of the Escuminac Formation.

Protobarinophyton was a member of the barinophytes, a group whose phylogenetic position is still a matter of debate. It may have been something of an evolutionary experiment because its fertile branches resemble nothing seen in any other plant group. Its sporangia, arranged in two lateral rows on each side of a thin stem, formed small clusters called strobili. Barinophytes were heterosporic, meaning that they produced both male and female spores. Strangely, both spore types are contained in the same sporangia, unlike other heterosporic plants – including progymnosperms, lycopsids and ferns – which contain the two spores in separate sporangia.
A small, unobtrusive leafless plant grew quietly on the edges of the ancient Miguasha estuary. Its fossils are rare and often incomplete, such that paleobotanists assign it with hesitation to the genus Protobarinophyton. It is only found in a thin layer within the lower part of the Escuminac Formation.

Protobarinophyton was a member of the barinophytes, a group whose phylogenetic position is still a matter of debate. It may have been something of an evolutionary experiment because its fertile branches resemble nothing seen in any other plant group. Its sporangia, arranged in two lateral rows on each side of a thin stem, formed small clusters called strobili. Barinophytes were heterosporic, meaning that they produced both male and female spores. Strangely, both spore types are contained in the same sporangia, unlike other heterosporic plants – including progymnosperms, lycopsids and ferns – which contain the two spores in separate sporangia.

© Miguasha National Park 2007

<i>Protobarinophyton</i>

Sporangia of a barinophyte from the lower part of the Escuminac Formation.

Miguasha National Park
2007
© Miguasha National Park 2007


Archaeopteris is the best known plant in the Escuminac Formation, where it occurs in abundance. Its discovery at Miguasha dates back to the end of the 19th century, when the famed paleontologist J. William Dawson of McGill University wrote the first description of Miguasha flora. Spreading around the world during Upper Devonian time, Archaeopteris became the main constituent of Earth’s first forests.

Archaeopteris existed for only a few tens of million of years, but is well known to paleontologists and is recognized as the first plant truly worthy of the name “tree”. Reaching up to seven metres tall, its trunk was made of lignin and cellulose, and its structure was very similar to that of today’s conifers. It was topped by branches supporting fronds reminiscent of ferns, and these extended horizontally to capture sunlight. The plant is placed in the class of progymnosperms, a group that is regarded as ancestral to true gymnosperms, which include conifers.

Two different species, A. Read More
Archaeopteris is the best known plant in the Escuminac Formation, where it occurs in abundance. Its discovery at Miguasha dates back to the end of the 19th century, when the famed paleontologist J. William Dawson of McGill University wrote the first description of Miguasha flora. Spreading around the world during Upper Devonian time, Archaeopteris became the main constituent of Earth’s first forests.

Archaeopteris existed for only a few tens of million of years, but is well known to paleontologists and is recognized as the first plant truly worthy of the name “tree”. Reaching up to seven metres tall, its trunk was made of lignin and cellulose, and its structure was very similar to that of today’s conifers. It was topped by branches supporting fronds reminiscent of ferns, and these extended horizontally to capture sunlight. The plant is placed in the class of progymnosperms, a group that is regarded as ancestral to true gymnosperms, which include conifers.

Two different species, A. halliana and A. obtusa, grew in the Devonian Miguasha estuary region. A. obtusa is distinguished by its larger leaves. These species possessed both ordinary vegetative branches as well as fertile branches. The latter looked different and displayed clusters of sporangia bearing microspores and macrospores, meaning that Archaeopteris produced both male and female spores. This is therefore an example of heterospory, much like the pollen-producing plants of today. At Miguasha, the great fronds – well preserved in many levels in many layers of the Escuminac Formation – are plentiful, as are pieces of carbonized trunk. Petrified trunks of Archaeopteris are also known by the name Callixylon.

© Miguasha National Park 2007

<i>Archaeopteris halliana</i>

A large frond from Archaeopteris halliana in the Escuminac Formation.

Miguasha National Park

© Miguasha National Park 2007


<i>Archaeopteris</i>

Archaeopteris figure parmi les arbres les plus anciens de la planète, c’est le principal constituant des premières forêts. Sa taille atteignait environ 7 mètres.

Miguasha National Park

© Miguasha National Park 2007


Video

Interview with Patricia G. Gensel

Patricia G. Gensel talks about the fossil in her hands that she found along the Miguasha bank.

Reporter

So Mrs. Gensel you discovered that this morning ?

Patricia G. Gensel

Actually one of the other people did and showed it to me. This is a specimen of archeatris showing several of the branches with its typical for bully shape leaves and little ginko leaves.

Reporter

What’s the importance of that kind of fossil or plant fossil ?

Patricia G. Gensel

Well this one is actually a reprentative of one of the first trees that ever existed and also one of the first plants to have obvious laminate leaves of this type. Most of the plants before this time had stamps which branch many many times but did not have laminated photosynthetic structures.

And that is how it all began!

Miguasha National Park

© Miguasha National Park 2007


The advent of the seed as a means of reproduction was a revolution in the world of plants. The origin of seeds probably goes back to Middle Devonian time.The oldest known seed-producing plant was found in Belgium in rocks from the Famennian Age. After the Devonian, seed plants (spermatophytes) gradually became one of the most important groups of organisms on Earth, a group that includes the modern conifers (gymnosperms) and flowering plants (angiosperms) we encounter every day.

In their quest for the origin of seed plants, a tiny Miguasha fossil has held the attention of paleobotanists for forty years. The fossil is that of a megaspore – a spore large enough to be visible to the naked eye – that goes by the name of Spermasporites devonicus. It shows all the characteristics of the primitive seeds that later became widespread in the Carboniferous Period.

When a modern plant produces ovules, macrospores in the fertile part (either a flower or a cone) undergo meiosis: two successive cellular divisions of one macrospore that produces four ovules. These four ovules form what we call a tetrad, which awaits fertilization by male pollen before becoming a s Read More
The advent of the seed as a means of reproduction was a revolution in the world of plants. The origin of seeds probably goes back to Middle Devonian time.The oldest known seed-producing plant was found in Belgium in rocks from the Famennian Age. After the Devonian, seed plants (spermatophytes) gradually became one of the most important groups of organisms on Earth, a group that includes the modern conifers (gymnosperms) and flowering plants (angiosperms) we encounter every day.

In their quest for the origin of seed plants, a tiny Miguasha fossil has held the attention of paleobotanists for forty years. The fossil is that of a megaspore – a spore large enough to be visible to the naked eye – that goes by the name of Spermasporites devonicus. It shows all the characteristics of the primitive seeds that later became widespread in the Carboniferous Period.

When a modern plant produces ovules, macrospores in the fertile part (either a flower or a cone) undergo meiosis: two successive cellular divisions of one macrospore that produces four ovules. These four ovules form what we call a tetrad, which awaits fertilization by male pollen before becoming a seed – in other words, a plant embryo. Spermasporites “microfossils” have exactly the same tetrad arrangement as that of the first seed plants.

The search for the mysterious plant that produced this famous megaspore continues in various locations around the world, with particular attention given to a new Spermasporites site in eastern Greenland.

© Miguasha National Park 2007

Spermasporites devonicus

The megaspore Spermasporites devonicus of the Escuminac Formation. Taken from Chalowner and Pettit, 1964.

Chalowner and Pettit, 1964

© Chalowner and Pettit, 1964


Plants evolved rapidly during the Devonian Period, but most species were restricted in their distribution in time. Plant spores disperse by wind or water and were omnipresent in ancient sediments. Thanks to their resistant walls that facilitate preservation, rocks often contain millions of fossil spores. These tiny grains are indispensable tools for fixing the ages of the subdivisions in the Devonian time scale. At Miguasha, fossil spores helped establish that the Escuminac Formation is the same age as the Upper Devonian reference section in the Frasne region of Belgium, after which the Frasnian Age is named. Fossils that can be used to date rocks are called index fossils.

More than fifty species of spores have been identified in the Escuminac Formation, demonstrating that plant diversity in the area was much larger than is implied by the limited number of fossilized macro-flora species. There are undoubtedly affinities between the spore assemblages of the Escuminac Formation and those of the “Old Red Sandstone” in Europe because the North American plate (Laurentia) was attached to the European plate (Baltica) in the ancient continent Euramerica during the U Read More
Plants evolved rapidly during the Devonian Period, but most species were restricted in their distribution in time. Plant spores disperse by wind or water and were omnipresent in ancient sediments. Thanks to their resistant walls that facilitate preservation, rocks often contain millions of fossil spores. These tiny grains are indispensable tools for fixing the ages of the subdivisions in the Devonian time scale. At Miguasha, fossil spores helped establish that the Escuminac Formation is the same age as the Upper Devonian reference section in the Frasne region of Belgium, after which the Frasnian Age is named. Fossils that can be used to date rocks are called index fossils.

More than fifty species of spores have been identified in the Escuminac Formation, demonstrating that plant diversity in the area was much larger than is implied by the limited number of fossilized macro-flora species. There are undoubtedly affinities between the spore assemblages of the Escuminac Formation and those of the “Old Red Sandstone” in Europe because the North American plate (Laurentia) was attached to the European plate (Baltica) in the ancient continent Euramerica during the Upper Devonian. At that time, there was no more than 1,500 kilometres separating the Frasne and Miguasha regions!

Palynology is the study of microfossils with resistant organic walls, such as fossil spores and pollen seeds of continental origin, and acritarchs and chitinozoans of marine origin. The presence of acritarchs in the palynological assemblage at Miguasha indicates that the environment was subjected to both freshwater and marine influences, thus supporting the hypothesis that Miguasha was once the site of an ancient estuary.

© Miguasha National Park 2007

<i>Auroraspora</i>

Auroraspora, one of the numerous spores in the Escuminac Formation.

Miguasha National Park
2003
© Miguasha National Park


<i>Corystisporites</i>

Corystisporites, another spore in the palynological assemblages of the Escuminac Formation

Not Available
2003
© Miguasha National Park 2007


Learning Objectives

The learner will:
  • identify and classify different types of fossils;
  • explain the stages of fossilization and the best conditions to create and preserve fossils;
  • make assumptions about the evolution of living beings;
  • make assumptions as to the explanation of the disappearance of some species.

Teachers' Centre Home Page | Find Learning Resources & Lesson Plans