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View an animation of what ocean life may have been like during the Cambrian explosion.

Post-cambrian evolution and mass extinctions

The periods that followed the Cambrian during the Paleozoic Era are marked by further animal evolution and the emergence of many new orders, families, and species. As animal phyla continued to diversify, new species adapted to new ecological niches. During the Ordovician period, which followed the Cambrian period, plant life first appeared on land. This change allowed formerly aquatic animal species to invade land, feeding directly on plants or decaying vegetation. Continual changes in temperature and moisture throughout the remainder of the Paleozoic Era due to continental plate movements encouraged the development of new adaptations to terrestrial existence in animals, such as limbed appendages in amphibians and epidermal scales in reptiles.

Changes in the environment often create new niches (living spaces) that contribute to rapid speciation and increased diversity. On the other hand, cataclysmic events, such as volcanic eruptions and meteor strikes that obliterate life, can result in devastating losses of diversity. Such periods of mass extinction    ( [link] ) have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind. The end of the Permian period (and the Paleozoic Era) was marked by the largest mass extinction event in Earth’s history, a loss of roughly 95 percent of the extant species at that time. Some of the dominant phyla in the world’s oceans, such as the trilobites, disappeared completely. On land, the disappearance of some dominant species of Permian reptiles made it possible for a new line of reptiles to emerge, the dinosaurs. The warm and stable climatic conditions of the ensuing Mesozoic Era promoted an explosive diversification of dinosaurs into every conceivable niche in land, air, and water. Plants, too, radiated into new landscapes and empty niches, creating complex communities of producers and consumers, some of which became very large on the abundant food available.

Another mass extinction event occurred at the end of the Cretaceous period, bringing the Mesozoic Era to an end. Skies darkened and temperatures fell as a large meteor impact and tons of volcanic ash blocked incoming sunlight. Plants died, herbivores and carnivores starved, and the mostly cold-blooded dinosaurs ceded their dominance of the landscape to more warm-blooded mammals. In the following Cenozoic Era, mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs, and birds, the warm-blooded offshoots of one line of the ruling reptiles, became aerial specialists. The appearance and dominance of flowering plants in the Cenozoic Era created new niches for insects, as well as for birds and mammals. Changes in animal species diversity during the late Cretaceous and early Cenozoic were also promoted by a dramatic shift in Earth’s geography, as continental plates slid over the crust into their current positions, leaving some animal groups isolated on islands and continents, or separated by mountain ranges or inland seas from other competitors. Early in the Cenozoic, new ecosystems appeared, with the evolution of grasses and coral reefs. Late in the Cenozoic, further extinctions followed by speciation occurred during ice ages that covered high latitudes with ice and then retreated, leaving new open spaces for colonization.

Watch the following video to learn more about the mass extinctions.

The chart shows percent extinction intensity versus time in millions of years before present. Extinction intensity spikes at boundaries between periods, including the end of the Ordovician, late Devonian, end of the Permian, end of the Triassic, and end of the Cretaceous periods.
Mass extinctions have occurred repeatedly over geological time.

Career connection

Paleontologist

Natural history museums contain the fossil casts of extinct animals and information about how these animals evolved, lived, and died. Paleontogists are scientists who study prehistoric life. They use fossils to observe and explain how life evolved on Earth and how species interacted with each other and with the environment. A paleontologist needs to be knowledgeable in biology, ecology, chemistry, geology, and many other scientific disciplines. A paleontologist’s work may involve field studies: searching for and studying fossils. In addition to digging for and finding fossils, paleontologists also prepare fossils for further study and analysis. Although dinosaurs are probably the first animals that come to mind when thinking about paleontology, paleontologists study everything from plant life, fungi, and fish to sea animals and birds.

An undergraduate degree in earth science or biology is a good place to start toward the career path of becoming a paleontologist. Most often, a graduate degree is necessary. Additionally, work experience in a museum or in a paleontology lab is useful.

Section summary

The most rapid diversification and evolution of animal species in all of history occurred during the Cambrian period of the Paleozoic Era, a phenomenon known as the Cambrian explosion. Until recently, scientists believed that there were only very few tiny and simplistic animal species in existence before this period. However, recent fossil discoveries have revealed that additional, larger, and more complex animals existed during the Ediacaran period, and even possibly earlier, during the Cryogenian period. Still, the Cambrian period undoubtedly witnessed the emergence of the majority of animal phyla that we know today, although many questions remain unresolved about this historical phenomenon.

The remainder of the Paleozoic Era is marked by the growing appearance of new classes, families, and species, and the early colonization of land by certain marine animals. The evolutionary history of animals is also marked by numerous major extinction events, each of which wiped out a majority of extant species. Some species of most animal phyla survived these extinctions, allowing the phyla to persist and continue to evolve into species that we see today.

Questions & Answers

what do you guys understand about evolution?
Kiana Reply
it's a process or analayzing some program
Fahamia
but am not sure if some know plz let share
Fahamia
why are diagrams not available
Evans Reply
How can nucleotide molecules of DNA be constructed?construct a six molecules of DNA?
Julia Reply
describe the breathing mechanism in the body fish.
Jackson Reply
what is genetics.
Jackson
the study of hereditary
Julia
state the importance of biodiversity of organisms in an area?
Chris Reply
what is biology
Adam Reply
Biology is the study of living things.
Patrick
what are some of the branches of biology?
Jackson
anatomy,genetics,parasitology
Evans
what is meosis
Mabatho Reply
did you mean meiosis? meiosis this is the type of cell division where one diploid parent cell produces two daughter cells that are haploid and genetically different from the parent cell.
Patrick
thankyou
Mabatho
I'm struggling to understand genetics
Mabatho
Am also struggling as well
Patrick
nothing comes on a silver platter, you need to put effort in everything you are doing not forgetting God. study as if there is no tomorrow. "Suffer now and enjoy the future"
Patrick
true bro
Patrick
exactly brother
Odhiambo
Glory to God
Patrick
Thanks Pat🙏
Mabatho
you're welcome
Patrick
what's a nervous system
tessy Reply
what's the human brain
tessy
the structure of paramecium
Charity Reply
yes
Sarah
Ho
Nevers
what is endocytosis
Stephen Reply
what is the meaning of adrenocorticotropic
Abigail Reply
adrenocorticotropic is stimulating or acting on the adrenal cortex.
Belinda
ok thanks
Abigail
What is science of biology
Thando Reply
The study 📓 of leaving things
John
how does a parasite benefit from its mode of living?
Abuk Reply
why are the images n diagrams unable to be seen?
Abuk
where are the illustrations
Simon
a parasite gets protection, food, shelter
Anguson
human being
Jackson
what is Alimentary canal?
Princess Reply
what is commenialism
jamex Reply
Do you mean commensalism?,it is a feeding relationship that has to do with two different species feeding, that is one is benefiting and the other is unaffected.
hamidat
commensalism is a feeding relationship that has to do with different species feeding, one is gaining and the other is unaffected.
hamidat

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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