Respiratory Systems Of Other Cambrian Animals

Many of the animals present in the Cambrian had no specialized respiratory structures, and they generally shared a common characteristic they were covered with epithelium that allowed for the passage of water directly from the sea into the body of the animal. For them the entire body was a gill. Examples include many soft worm-like forms, such as nemerteans and the many varieties of the jellyfish-sea anemone clan, the cnidarians. The cnidarians were and are composed of but two cell layers, and...

The Permian Extinct

S the Paleozoic came to a close during the Permian Period, the continents all joined into one large landmass and then, some 250 million years ago, an enormous and devastating mass extinction swept land and sea alike. Estimates vary but a figure of 90 percent of all species on the planet is seen as a reliable estimate of the damage done to world species' diversity. The event is the Permian extinction. (It has been given a number of more flamboyant sobriquets The Great Dying, The Mother of All...

The Different Fates Of The Triassic Therapsids And Diapsids

As we saw in Chapter 7, the Permian extinction nearly annihilated land life. The therapsids were hit hard. Much less is known about the diapsids, for at the end of the Permian they were a rare and little seen group in the areas, such as the Karoo or Russia, that have yielded rich deposits with abundant dicynodont (therapsid) faunas. In the Karoo at least, only small fragments of diapsids have come from our uppermost Permian study sections, although two skulls now being prepared as I write this...

Why Chordates Evolved As They

Having looked at the respiratory structures of the most populous Cambrian animals, it is time to take a look at a small and insignificant group of fossils found at Chengjiang and later at the Burgess Shale small, fish-shaped animals that ultimately gave rise to us. The most famous of these was named Pikaia, an animal featured at length in Steven Jay Gould's book about the Burgess Shale animals called Wonderful Life. The origin of our own phylum is, of course, of intense interest and has been...