[SOUND] [MUSIC] If you ever been on a boat at night and came upon another boat, the boats are gliding through the calm still waters of the evening, and hopefully not colliding, but if you're cruising past each other, there's just the quiet splash of the water against the hulls. And the two boats are passing each other in the middle of the night. There's these large, very significant structures called ships and they have people on them but they're moving quietly through the water, and they pass each other going opposite directions. So we use this analogy actually for looking at the history of the rise of the synapse of reptiles, and the diapse of reptiles. In essence, there two major ships that have passed through the night, not once but actually twice. And this is important metaphor for us to think about because as we look at the evolution of Biology as it runs from the Paleozoic through the Mesozoic into the Cenozoic, we see that these two great lineage of the reptiles they rise and they fall out of phase, out of concert with each other. And as one rises, the other falls, and as the other falls, the other rises, and vice versa. So this is kind of the stage that we want to think about in the history of evolution on our planet of the synapsid and the diapsid reptiles. So let's dial back a little bit. We're in the Pennsylvania. It's the rise of the three great lineages, the synapsids, the turtles, the diapses eventually, dinosaurs and birds, and the synapses eventually the mammals. All three lineages arise at the same time in the late Pennsylvania. But right off the block, our lineage, the synapses are the ones that did really well. The diapses, the lineage of the dinosaurs, did very poorly. So going from the late Pennsylvanian into the Permian, it was a landscape completely dominated, in terms of predation. Big meat eaters, that would be the big beefy guys and girls that ruled the landscape and preyed on whatever they wanted to, because they were the best predators in town at that time. They were part of the lineage of the synapses. Remember our friend Dimetrodon, which is part of the Pelycosaurs, the first lineates of the synapsids? They rose to dominate the landscape by 70%. And in that time period, in the Permian that was completely dominated by the synapses, the diapses, the lineage drawing eventually to the dinosaurs later on in the Mesozoic, they were very small. They were in the background and they were preyed upon. So the end of the Paleozoic is a story of dominance by the synapses. Well, one of the underlining driving forces of the structure of geological time are meteor impacts. And at about 251 million years before present, we had an impact hit the earth, and one of the result's was to cause 85% of what was living on planet earth at that time to go extinct. It defines what we call the Permian–Triassic boundary. It's the boundary between the Paleozoic and the Mesozoic. One of the results of that was to reset the entire stage of this dominance of the synapse of lineage. So at the impact and just after the impact, all three lineages of the reptiles got through the impact. Some of them did survive. 85% is a lot to go extinct. But not everything went extinct. Well, we passed through the impact event, and early in the Triassic we still had synapsid predators. The Therapsids, the big reptiles that were very strong in the front, had smaller legs in the back, they were still predators. They were still dominating the landscape, but it didn't last long. And the triassic [COUGH] is the story of these two ships for the first time called the diapsids and the synapsids passing each other in the night. In other words, the previous dominant synapsid reptiles, after through the Permian-Triassic boundary impact event, they did very poorly, and they were out competed, and they were replaced by the diapsids. And in fact, the diapsids did so well and started radiating and diversifying to a point where they ruled the landscape. And by the late triassic, we had our first true dinosaurs. So the reptiles that were diapsids they invaded the ocean again. They invaded the land environment, and they rose to be the dominant predators. They ruled the entire landscape. So the Permian-Triassic boundary and going into the early Triassic is the first example of the synapsid ship going down, the diapsid ship going up and the two of them passing silently through these transitions to the point where we lived on a diapsid ruled planet. And the rule of the diapsids and the eventual manifestation of that in the age of the dinosaurs, lasted throughout the Mesozoic. Nothing can last forever. So we get to a world dominated by the dinosaurs in the Cretaceous. And we have another major meteor impact. This one was at the Cretaceous-Tertiary boundary about 65.5 million years before present. That impact, it served to be a really bad day for the dinosaurs. There are a lot of theories that suggest that perhaps the dinosaurs were already starting to fade and that the meteor impact added to this, and was the nail in the coffin, so to speak. But the meteor impact event defines the moment when the dinosaurs went extinct. Now, not quite so silently, we had another meteor impact. But this time again, we had the two ships of the diapses and the synapses pass each other in the night. And as a result of the KT impact, the Cretaceous Tertiary impact event. The synapses rose in the landscape. Right after the Cretaceous event. And the diapses, the dinosaurs became extinct, and only one really strong lineage of those dinosaurs survived to this day, which are the birds. So it's a story of dominance in both the marine and the terrestrial landscape, it's the story of resetting the stage by having a catastrophic, cataclysmic event, called a meteor impact hit the planet, reset the rules of the game. Now, Darwin laid out the idea that organisms are the result of survival of the fittest. But that's not such a good way to describe this necessarily. Actually, a better way to think about it is that, these ships passing in the night are a great example of the survival of those who are fit the best to the environment, and one of the things that linear impacts do is to change drastically the environment at a very, very quick pace. In other words, it happened instantaneously and these rapid catastrophic events end up changing the environment dramatically for a very long period of time. And because your organisms aren't evolved to a point where they are fit best to that new environment, then they're the ones who go extinct. So two ships passing in the night, the synapsids and diapsids, first, the rise of the synapsids, and secondary place in history that the diapsids took took at the end of the Paleozoic. Boom, meteor impact! The rise of diapsids, the secondary place into the synapsids. End of the Mesozoic. Boom, another meteor impact! Rise of the synapsids, drop of the diapsids. The natural next step in this process of synapsesboat passing diapsidboat is that the modern day environment on earth is ruled by us, the mammals and we are part of that synapse lineage. But if history repeats itself to any degree, one way to look at the future is we're waiting for that next great meteor impact to hit and we know it will. And when that happens, then perhaps the next manifestation is that the diapses ship will once again pass the synapses ship and the era of the reign of the mammals will be over. And the next phase of the reign of the reptilian lineages that are derived from the diapsids, that's their time to take over the planet. [MUSIC]
