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The ancient ruling archosaurs of the mesozoic were such a diverse and wildly successful group that if often seems like a shame that their reign met its end at the end of Cretaceous. Filling almost every possible niche, the archosaurs - which is the group of diapsids containing dinosaurs, pterosaurs, crocodiles, birds, and several other extinct groups - radiated into thousands of unique and fascinating morphologies and functions. They inhabited the seas, the skies, and every Mesozoic land environment until the mass extinction event at the end of the era destroyed all but a few groups of them. With a clade of such startling success and diversity, it's hard not to think about what could have been. What would time have done to these awesome creatures had they been given another 65 million years to flourish?
65 million years is a lot of time for species to go extinct just from more ordinary causes, like competition and more minor climatic changes. But some groups of dinosaurs had been immensely successful for millions of years prior, so it's easily to see how they could have stuck around for another 65. Dromaeosauridae, for instance, evolved in the middle Jurassic, meaning that the "raptor" family existed for over 100 million years. Barring a global extinction event, it's easy to see how they could have continued evolving up to the present day. What would these feathered fiends have turned into, given enough time? Would they have grown small and flighted, as their ancestors eventually did? Or, along with their cousins the Troodontidae - as the most intelligent groups of archosaurs alive at the time - would they have evolved into something... more interesting?
Which brings me to this month's discussion question: What kind of forms and functions do you imagine the dinosaurs and their cousins occupying in the present day if most of them had not been wiped out at the end of the Mesozoic?
Many people have wondered whether dinosaurs would have eventually evolved sentience as primates did. The paleontologist Dale Russell believed that Troodonts would have eventually evolved an upright stance and an enlarged braincase, mirroring the course of evolution that hominids took on their path to sentience. He called this hypothetical animal the "Dinosauroid" and collaborated with the artist Ron Sequin to create a lifelike model of this creature. While such a thing is possible, I'm hesitant to say whether I think it's actually likely - I think of the evolution of true sentience as much more of a happy accident than an evolutionary inevitability, which needs a lot of specific selection pressures in order to arise.
Other paleontologists have speculated on this on a broader scale, like Dougal Dixon in his book The New Dinosaurs. While more of an interesting thought experiment than true science, this book explores the possibilities of many new forms dinosaurs could have evolved into, from the duck-like predatory "Pouch" to the arboreal snakelike "Treewyrm." In this hypothetical future, archosaurs are still by and large the dominant animal group, with mammals still existing in the shadows of giants.
The possibilities are truly endless for what could have been. It's sad to think that such a timeline could not possibly have produced an "us" to observe them!