So, what vertebrates have been the most successful throughout the history of the world? Was it dinosaurs? No. They were around for about 250 million years before they went extinct 65 million years ago. I'd say insects but I don't think they count. LOL! I think it's perhaps the mammals that are the most successful. Why? Because they ruled the land twice. It started in the Permian period. I used to look at mammals as evolutionary losers. Especially after Jurassic Park and what I learned about dinosaurs after becoming fascinated by them in the movie. It was actually reading Dougal Dixon's book that made me a believer in the age of mammals.
In the Permian, we had synapsids. We cannot call them "mammal-like reptiles" anymore, but they were reptiles with mammal-like characteristics. Most people today refer to them as "mammaliformes". Which is a name I originally was going to assign to the mammals of tomorrow because there are a few distinct differences between them and the mammals we are familiar with today. But during the Permian to the late Triassic, these synapsids ruled the Earth. But then the Jurassic came along, and created a hole in the mammals' take over. That was when the dinosaurs became dominant. The mammals had by then become true mammaliformes, like we are familiar with today. But they also got smaller, and stayed more out of the way of the dinosaurs. They still evolved though.
Some changes were made to mammals when the dinosaurs dominated. For one thing, the lifespan of mammals is believed to have gotten shorter due to dinosaurs. I saw an article about this the other day. It's called the Longevity Bottleneck Hypothesis, and you can read about it here The 'longevity bottleneck' hypothesis: Research suggests that dinosaurs may have influenced how human beings age (phys.org) This theory describes how mammals have such short lifespans whereas similar-sized birds (like parrots) live much longer. Those of us who have aging dogs can see plainly how upsetting it is that their lifespan is so short.
Well, since the extinction of dinosaurs, mammals have evolved to fill all niches open in the ecosystem. It may have been slow to start, but it eventually got there. It took 30 million years for mammals to get to the point we are familiar with today. But one thing that all mammals today have in common, they are all living synapsids. The synapsids first dominated in the Permian, took a break during the Mesozoic, and now are back again, more advanced. So, this is why I now say mammals are the most successful vertebrates in the world. They are so good, they ruled the world twice! And I don't think they will be going extinct any time soon. Not even in geological timescale. This is why I created the Metazoic era. The animals that we see as pests today, are just successful enough to survive and create an era of their own.
