Skip to 0 minutes and 11 seconds Hi everyone. Welcome to week three of extinctions past and present. The focus of today’s lecture will be on the radiation of the reptiles and how they became so successful and dominant on our planet. We will talk about the end of the Permian Mass Extinction event and we will see how this event changed the floral and faunal components of terrestrial eco-systems. But let’s begin at the beginning. Reptiles are vertebrates,that is they are animals with backbones. We’ve seen in the fossil record that vertebrate history extends to about 525 million years. Soon after the beginning of vertebrates we see the development of jawless fishes and thereafter we see the evolution of fishes with jaws. Then we see the radiation of the cartilaginous fish.
Skip to 1 minute and 4 seconds And then we get the bony fish. From these bony fish we see the rise of the lobe-finned fishes which become the ancestors of the tetrapods. After the end of the Devonian Mass Extinction event about 375 million years ago one of the most important developments occurs in vertebrate history. We see the tetrapods begin to colonise land. Amphibians were the very first vertebrates to move onto land, but they were still restricted to living close to water because they needed to return to water to reproduce. Amongst the amphibians there were many well-adapted forms. Some of them could move about on land very easily but there were still others that were largely aquatic at that time. By this time, on land, plants were flourishing.
Skip to 2 minutes and 0 seconds We know that arthropods, that is insects, scorpions, millipedes, also moved onto land soon after the plants. And by this time they were also well established. We know that in most of these carboniferous times amphibians dominated the ecosystems. But we see that once reptiles develop, we see that they become the dominant terrestrial animals. The most significant step in the development of reptiles and the one that makes them far superior to amphibians, is the fact that they become independent of water. And the one thing that allows them this independence of water is the development of the amniotic or cleidoic egg. This egg is very special. It creates an environment where the young develop in their own private pond.
Skip to 3 minutes and 1 second The egg is protected by a semi-permeable egg shell and this insulates it from the environment and also protects the young within the egg. Within the egg there is also amniotic fluid that creates a moist environment and very importantly there is yolk within the egg that provides nutrition for the young to develop. Very importantly, we see that once the egg hatches the young reptile that emerges from the egg is a miniature of the adult. There’s no need for metamorphosis. So this little tiny individual is fully capable of living on land. Thus the amniotic egg allows reptiles to be completely independent of water and is regarded as a major advancement in the evolution of vertebrates.
Before and After the End Permian Extinction Event
The End Permian extinction event that we are looking at this week happened 252 million years ago. This was the third and largest mass extinction event, and almost wiped out life on earth. After the extinction event, recovery led to further reptile diversifications, which among others eventually give rise to the ancestors of mammals, pterosaurs, and dinosaurs (the latter later give rise to birds). This talk begins by describing how the development of the cleidoic (or amniotic) egg (the type of egg which reptiles and birds lay), was absolutely critical in facilitating the dominance of reptiles during the Permian.
In this week I will chat with postdoctoral researcher, Michael Day about the Guadalupian extinction event, which predated the End Permian extinction event by 8 million years. After this, I will talk with palaeontologist/geologist Roger Smith, about the extraordinary mammal-like reptiles from South Africa, and how they were affected by the End Permian extinction event. Lastly, palaeobotanist, John Anderson, will talk to us about his research into the plant (and insect) biodiversity that straddles the Permian-Triassic boundary.
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