While I’m waiting for the battery to recharge
October 29, 2011 § 1 Comment
Some things that occurred to me recently:
The Permian extinction ended the reign of the therapsids, who were effectively the dominant terrestrial life forms before the Triassic. After the Permian, the few surviving therapsids got into an evolutionary war with archosaurs, including the emerging dinosaurs, and they lost. Despite an early strong showing following the Permian extinction event, the therapsids were forced to the fringes of the world’s surface ecosystems. They dwelled as nocturnal and subterranean entities for over 185 million years.
Now, the therapsida were hardly poorly suited to survive (just take a look at Inostrancevia here) although it’s clear that the huge blow they suffered at the end of the Permian didn’t exactly help them in competing with the archosaurs. For whatever reason, the ancestors of crocodiles, dinosaurs and birds (dinosaurs and birds themselves being so close that some paleontologists consider birds to just be a subset of dinosaurs) won, and ruled Earth for millions upon millions of years.
The therapsids were hardly wiped out, however. For instance, you’re a therapsid.
That’s right: strictly speaking, all mammals are therapsid, and there are no living therapsids left on Earth that aren’t mammals. Roughly 65 million years ago, life on Earth underwent an event similar to, but smaller than, the Permian extinction. This later extinction (known as the K-T Boundary Event) effectively reversed the results of the Permian/Triassic transition. In other words, 250 million years ago, our ancestors were pushed off the stage in favor of the archosaurs, and 65 million years ago, the archosaurs were likewise pushed off the stage for mammals. It’s as if one dynasty of large terrestrial animals was dethroned by another, which ruled for many millions of years, and then like MacDuff coming out of the Birnam Wood the therapsids rose up again.
With the help of a giant rock from space, yes, absolutely true. Then again, would the archosaurs have fared any better at the end of the Permian had the world not run riot against the therapsid rulers?
It’s interesting to imagine what would have happened had our gorgonopsid cousins not faced the Greatest Dying Ever as the Permian ended. What would the world have been like if milk producing, child rearing, egg laying almost-mammals instead of dinosaurs had been the ones in the driver’s seat for that 185 million years when the Earth’s oxygen content and climate was as favorable to large size as it ever has been? Therapsids lack the skeletal structure of birds and dinosaurs with its hollow air sacs that aid in respiration so it’s possible no therapsid could have reached the same dizzying size the dinosaurs did. While mammals did manage mammoths and indricotheres and even andrewsarchus sized terrestrial carnivores, no mammal has ever reached the size of a sauropod outside of our oceans. If therapsids had won against the archosaurs then, could they have held out against the descendants of the bunny croc Lagosuchus?
If it had been therapsids dominating the world at the end of the Cretaceous, would they have suffered the same fate as the majority of dinosaurs? Would some batlike therapsid have been the only survivor, and would our skies today be filled with flying mammal-like creatures while talking archosaurs debated what might have been?