As life evolved on Earth, worldwide catastrophes periodically decimated entire ecosystems and wiped out scores of living creatures. In fact, the appearance and disappearance of various species and entire groups of animals define many of the divisions in the geologic record. It is estimated that present-day biodiversity represents only 1% of the total number of species that ever lived on the planet, which means that 99% of species have disappeared at one time or another.

The Phanerozoic Era, which began around 540 million years ago, left us a bountiful fossil record. The evidence in this record reveals that Phanerozoic time was marked by many extinction phenomena, with five of those events each affecting more than 60% of existing species. These events also represent the best documented extinctions.

The first coincided with a severe ice age at the end of the Ordovician Period. Examples of afflicted contemporary animals are found in the Percé region of Quebec, and the rock sequence on Anticosti Island in the Gulf of Saint Lawrence is one the best in the world for documenting the recovery of animals at the beginning of the Silurian, just after the extinction. Read More
As life evolved on Earth, worldwide catastrophes periodically decimated entire ecosystems and wiped out scores of living creatures. In fact, the appearance and disappearance of various species and entire groups of animals define many of the divisions in the geologic record. It is estimated that present-day biodiversity represents only 1% of the total number of species that ever lived on the planet, which means that 99% of species have disappeared at one time or another.

The Phanerozoic Era, which began around 540 million years ago, left us a bountiful fossil record. The evidence in this record reveals that Phanerozoic time was marked by many extinction phenomena, with five of those events each affecting more than 60% of existing species. These events also represent the best documented extinctions.

The first coincided with a severe ice age at the end of the Ordovician Period. Examples of afflicted contemporary animals are found in the Percé region of Quebec, and the rock sequence on Anticosti Island in the Gulf of Saint Lawrence is one the best in the world for documenting the recovery of animals at the beginning of the Silurian, just after the extinction.

The second event occurred during the Upper Devonian, shortly after the creation of Miguasha, and its effects were particularly harsh on aquatic life. Reefal communities disappeared, including brachiopods and trilobites, and many fish groups were also affected.

The ichtyofauna represented at Miguasha offers a remarkable view of the diversity achieved by vertebrates just before this second great extinction, which lasted several million years at the beginning of the Famennian Age.

The end of the Permian Period marked the third of these events and the greatest crisis in the history of life on Earth when 95% of the planet’s species rapidly disappeared.

Forty million years later, at the end of the Triassic Period, the fourth event was characterized by the disappearance of many members of the dinosaur group, whereas in the sea, animals like ammonites and nautiluses were particularly affected.

The extinction that led to the disappearance of the dinosaurs in a general slaughter at the end of the Cretaceous is the most famous of the five extinctions because it was caused by the impact of a giant meteorite, a phenomenon that readily captures the imagination of the general public. The planet was essentially set afire and then surrounded by a veil of ashes that blocked out sunlight, provoking extreme changes to the climate accompanied by corrosive acid rain! Along with dinosaurs, almost all shallow-water marine life, a large portion of terrestrial plants, and all large animals disappeared.

Small mammals, protected by their burrows, were able to survive and profited from the newly vacated ecological niches, rapidly evolving in different directions to eventually attain their present day diversity.

Great catastrophes are often cited to explain great extinctions. Those that occurred at the end of the Ordovician and Cretaceous are the best understood. The Triassic extinction, like the Cretaceous event, was possibly caused by a meteorite impact, whereas the substantial increase in volcanic activity at the end of the Permian was likely a source of that crisis. But the causes of extinctions are multiple and not yet well understood. The upheavals that affected communities at the end of the Devonian are an excellent example of the complexities involved.

Changes to the climate and large-scale biotopes have become increasingly noticeable during these early years of the 21st century, and some say that they will lead to the next episode of severe extinctions. Nevertheless, the Earth’s fossil record has taught us that life is stubborn and has readjusted time and time again when faced with major upheavals.

© Miguasha National Park 2007

The Ordovician-Silurian boundary at Anticosti

The Anticosti rock sequence in the Gulf of Saint-Lawrence displays a continuous series of sedimentary rocks that overlap the Ordovician-Silurian time boundary, indicated here by an arrow. The ice age at the end of the Ordovician Period had a harsh impact on the fauna living at that time.

Miguasha National Park
2002
© Miguasha National Park 2007


Massive extinctions

Five massive extinctions of life are thoroughly documented in the history of earth. The fauna of Miguasha offers a window into the world of vertebrates just before the extinction at the end of the Devonian.

François Bienvenue
2007
© Miguasha National Park


Towards the end of the Devonian, at the boundary between the Frasnian and Famennian ages (about 375 million years ago), a great extinction turned the living world upside-down. It was the second mass extinction to hit the planet, the first being at the end of the Ordovician. This time, it was not a single, abrupt event, but instead a series of extinctions spread out over a relatively short period of two to four million years.

At that time, the colonization of land by terrestrial plants, invertebrates and the first tetrapods was still in its early days. Animal groups already adapted to land were less affected by the crisis because paleontologists find their populations “intact” in the Carboniferous Period that immediately followed. Marine species, on the other hand, were very hard hit.

Large underwater reef ecosystems, constructed mainly by rugose and tabulate corals and by stromatoporoids, dramatically vanished. They would not return until 145 million years later in the Triassic Period, built that time by scleractinian corals and calcisponges.

It is estimated that 75% of all fish families disappeared during this Upper Devonian extinction Read More
Towards the end of the Devonian, at the boundary between the Frasnian and Famennian ages (about 375 million years ago), a great extinction turned the living world upside-down. It was the second mass extinction to hit the planet, the first being at the end of the Ordovician. This time, it was not a single, abrupt event, but instead a series of extinctions spread out over a relatively short period of two to four million years.

At that time, the colonization of land by terrestrial plants, invertebrates and the first tetrapods was still in its early days. Animal groups already adapted to land were less affected by the crisis because paleontologists find their populations “intact” in the Carboniferous Period that immediately followed. Marine species, on the other hand, were very hard hit.

Large underwater reef ecosystems, constructed mainly by rugose and tabulate corals and by stromatoporoids, dramatically vanished. They would not return until 145 million years later in the Triassic Period, built that time by scleractinian corals and calcisponges.

It is estimated that 75% of all fish families disappeared during this Upper Devonian extinction. Although freshwater fish were barely affected, marine animals were much more so. Placoderms, for example, did not survive, acanthodians were decimated, and almost all agnathans vanished. Numerous brachiopods became extinct, conodonts all but disappeared, and only one family of trilobites survived. In total, over 70% of species living in the Devonian no longer existed in the Carboniferous Period.

Marine hypoxia? Global cooling? A drop in sea level? Meteorites? Many hypotheses have been advanced to explain the Devonian mass extinction. The cause remains poorly understood, and perhaps the difficulty lies in that there were multiple causes! But whatever the reason, as is always the case following major extinctions, life reorganized itself within the oceans, and tetrapods and plants continued their conquest of the land.

The plants and animals represented by Miguasha’s fossils lived a few million years before this crisis. They therefore offer us a glimpse of life on Earth immediately before these events, particularly with respect to vertebrate diversity.

© Miguasha National Park 2007

Location of Meteorite or Fossil Craters in Québec

The impact of bolides is often suggested to explain certain events leading up to the sudden disappearance of a large proportion of living species in Earth’s history. The meteorite crater in Charlevoix dates back to the Upper Devonian, but it is unlikely that the mass extinction at the end of the Devonian is linked to the impact of this meteorite.

François Bienvenue
2007
© Miguasha National Park


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.

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