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Today, despite your hosts suffering from a nasty cold, we talk about the Triassic period. During this time, the first flying reptiles appear, along with several reptiles that returned to the water. We also get the very first dinosaurs, though they were still rather small, and the very first mammals, which were even smaller rodent-sized animals.
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During the Permian, the land vertebrates grew to large sizes, the ancestors of some families of coniferous trees began to dominate the forests, and some small reptiles learned to glide from tree to tree. At the end of the period, the most devastating mass extinction event in Earth’s history happened, wiping out most of the life on land and in the oceans, and setting the stage for the next period, and the rise of the dinosaurs.
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During the Carboniferous, the sharks took over the sea. On land, a new kind of egg was invented that could be laid and hatched on land, instead of in the water. The world was covered with swampy forest, there were giant bugs, and more oxygen in the air than at any other time.
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During the Devonian, there were many firsts: the first animal to give birth to live young, the first trees, the first insects, and the first vertebrates to walk on land.
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After the cold temperatures ice sheets and drop in sea level at the end of the Ordovician, the Silurian enjoyed a warmer and more stable climate. During this time, fish developed jaws, and the first animals adapted to a life lived entirely on land appear in the fossil record.
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After the die out at the end of the Cambrian, during the beginning of the Ordovician, there was an increase in the variety of animals and plants, with many new species entering the fossil record. Chordates became fish, plants colonized the land, corals began forming reefs, and the cephalopods came into their own. At the end of the period, wild climatic shifts caused the second most severe extinction event in the history of life.
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In the Cambrian period, roughly 540 million years to 485 million years ago, most of the types of animals that are with us today got their start, even if it’s difficult to recognize them.
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Most of the history of life on our world is about single cells. Life made up of millions-billions-trillions of cells, (just for one critter!) only arrived in the last 700,000,000 years. Life in its single celled form got here 3,400,000,000 years ago. It took life nearly 3 billion years to learn the trick. Continuing the continuing story of Evolution, we look at the Precambrian, and the first multicellular life seen in the fossil record.
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Between 520 and 550 million years ago, a sudden explosion of animal types appear in the fossil record. This example of rapid evolution is known as the Cambrian explosion. Theories of how and why it occurred range from the notion that it didn’t happen at all, to a spike in oxygen levels, to the advent of the sense of vision.
Here’s an article that includes an animation of some of the oddball animals that appeared and disappeared during the Cambrian period.
Evolution: Library: The Cambrian Explosion
Here’s an article that describes the link between oxygen and predators.
What sparked the Cambrian explosion?
And here are a couple more articles with more information on the Cambrian explosion.
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In today’s rather short episode, we talk about the first creatures to have developed a centralized nervous system, though not a central nervous system as of yet. It was a simple worm like creature, with a nerve cord running along the length of its body, and an extra-large bundle of nerves toward its mouth. For worms and other invertebrate animals, like crabs, lobsters, octopuses, squid, slugs and snails, the nerve cord runs along the belly of the creature. For what would become vertebrates, including us, the main nerve cord runs along the back. Apparently, for reasons unknown, some of the worms flipped over, and decided to live their lives upside-down.
This month has included some unusually long episodes. To leave room for the upcoming Halloween special, this and the next couple of episodes are unusually short. Check back on the 31st for, “Be Afraid.: when reason can get you killed.”
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