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What would dinosaurs look like today if they never went extinct? : ScienceAlert

What would dinosaurs look like today if they never went extinct?  : ScienceAlert

What would dinosaurs look like today if they never went extinct? : ScienceAlert

Sixty-six million years ago, an an asteroid hit the Earth with a force of 10 billion atomic bombs and changed the course of evolution.

The the sky darkened and plants stopped photosynthesizing. The plants died, then the animals that fed on them. The food chain has collapsed. Done 90 percent of all species disappeared. When the dust settled, everything dinosaurs except a handful of birds is extinct.

But this catastrophic event made human evolution possible. Surviving mammals flourished, including a little primeval it would evolve into us.

Imagine if the asteroid missed and the dinosaurs survived. Imagine highly evolved raptors planting their flag month. Dinosaur scientists, discovering relativity or debating a hypothetical world in which, improbably, mammals have taken over the Earth.

This might sound like bad science fiction, but it gets to some deep, philosophical questions about evolution. Is humanity here by chance or is the evolution of intelligent tool users inevitable?

Brains, tools, language and large social groups make us the planet’s dominant species. There are 8 billion of them A wise man on seven continents. By weight, there are more people than all wild animals.

We are modified half of the Earth’s landmass to feed ourselves. One could argue that they are human-like creatures bound to evolve.

In the 1980s, a paleontologist Dale Russell proposed a thought experiment in which A the carnivorous dinosaur evolved into an intelligent tool user. This “dinosauroid” had a large brain with opposable thumbs and walked upright.

Dinosaurid model. (Dale Russell & Ron Séguin/Canadian Museum of Nature via Naish & Tattersdill, Canadian Journal of Earth Sciences2021)

It’s not impossible, but it’s unlikely. The biology of an animal limits the direction of its evolution. Your starting point limits your endpoints.

If you drop out of college, you probably won’t be a brain surgeon, a lawyer, or a NASA rocket scientist. But maybe you’re an artist, actor or entrepreneur. The paths we take in life open some doors and close others. This also applies to evolution.

What would dinosaurs look like today if they never went extinct?  : ScienceAlert
Giant dinosaurs and mammals through time. (Nick Longrich)

Consider the size of the dinosaur. Beginning in the Jurassic, sauropod dinosaurs, Brontosaurus and gender evolved into 30-50 ton giants up to 30 meters long – ten times the weight of an elephant and as long as a blue whale.

This happened in several groups, including DiplodocidaeBrachiosauridae, Turiasauridae, Mamenchisauridae and Titanosauria.

This happened on different continents, at different times and in different climates, from deserts to rainforests. But other dinosaurs living in these environments did not become supergiants.

The common thread connecting these animals was that they were sauropods. A bit about sauropod anatomy – lungshollow bones with a high strength to weight ratiometabolism, or all these things – unlocked their evolutionary potential. This allowed them to grow in a way that no land animal ever has before, or since.

Likewise, carnivorous dinosaurs repeatedly evolved into huge predators of ten meters and more tons. Over 100 million years, megalosaurids, allosaurids, carcharodontosaurids, newborns, and finally tyrannosaurs evolved giant predators at their peak.

Diagram of brain size versus body mass for dinosaurs, mammals, and birds
Brain size versus body mass for dinosaurs, mammals and birds. (Nick Longrich)

Dinosaurs did big bodies well. Big brains not so much. Dinosaurs have shown a weak trend towards increasing brain size over time. Like Jurassic dinosaurs Allosaurus, stegosaurus, and Brachiosaurus had a small brain.

By the Late Cretaceous, 80 million years later, tyrannosaurs and duckbills developed larger brains. But despite its size, T. rex the brain still weighed only 400 grams. A Velociraptor the brain weighs 15 grams. The average human brain weighs 1.3 kilograms.

Dinosaurs entered new niches over time. Small herbivores became more common and birds became more diverse. Long-legged forms evolved later, suggesting an arms race between swift-footed predators and their prey.

Dinosaurs seem to have had increasingly complex social lives. They began to live what to and evolved elaborate horns for fighting and exposure. However, dinosaurs seem to repeat themselves mostly, evolving giant herbivores and small-brained carnivores.

There is little about 100 million years of dinosaur history to suggest that they would have done anything radically different had the asteroid not intervened. We’d probably still have those super-giant, long-necked herbivores and huge tyrannosaur-like predators.

They may have developed slightly larger brains, but there is little evidence that they would have evolved into geniuses. Nor is it likely that mammals would displace them. The dinosaurs monopolized their environment until the very end, when an asteroid hit.

Meanwhile, mammals had different limitations. They never developed supergiant herbivores and carnivores. But they kept developing big brains. Massive brains (as big or bigger than ours) have evolved in orcas, sperm whales, humpback whales, elephants, leopard seals, and monkeys.

Today there are several descendants of dinosaurs – birds like crows and parrots complex brains. I can use tools, talk and count. But mammals like monkeys, elephants, and dolphins have developed the largest brains and the most complex behaviors.

So, did the elimination of the dinosaurs guarantee that mammals would develop intelligence?

Well, maybe not.

Starting points can constrain endpoints, but they do not guarantee them. Steve Jobs, Bill Gates and Mark Zuckerberg they all dropped out of college. But if dropping out automatically makes you a multi-billionaire, any college dropout would be rich. Even to start in the right place, you need opportunities and luck.

The evolutionary history of primates suggests that our evolution was anything but inevitable. In Africa, primates evolved into big-brained monkeys and, almost 7 million yearsproduced modern people. But elsewhere, primate evolution followed very different paths.

When monkeys reached South America 35 million years ago they just evolved into more species of monkeys. And primates reached North America at least three separate times, 55 million years ago, 50 million years agoand 20 million years ago.

However, they did not evolve into a species that produces nuclear weapons and smartphones. Instead, for reasons we don’t understand, they died out.

In Africa, and only in Africa, primate evolution went in a unique direction. Something about African fauna, flora or geography drove the evolution of monkeys: terrestrial, large, large brain, using tools receive.

Even when the dinosaurs disappeared, our evolution needed the right combination of chance and luck.Conversation

Nicholas R. Longrichsenior lecturer in paleontology and evolutionary biology, University of Bath

This article was republished by Conversation under Creative Commons license. Read it original article.



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