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 Earth with the force of 10 billion atomic bombs and changed the course of evolution.

The the skies darkened and plants stop photosynthesizing. The plants died and then the animals that fed on them. The food chain collapsed. Above 90 percent of all species disappeared. When the dust settled, everything dinosaurs except a handful of birds had disappeared.

But this catastrophic event made human evolution possible. Surviving mammals thrive, including a few protoprimates which will evolve in us.

Imagine the asteroid missed and the dinosaurs survived. Imagine highly evolved birds of prey planting their flag The moon. dinosaur scientists discovering relativity or discussing a hypothetical world in which, improbably, mammals have taken over the Earth.

This may sound like bad science fiction, but it touches on some deep, philosophical questions about evolution. Is humanity here by accident or is the evolution of intelligent tool users inevitable?

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

We have changed half the earth’s land to eat One can argue about creatures like humans bound to develop.

In the 1980s, a paleontologist Dale Russell propose 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.

Dinosaur 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. An animal’s biology limits the direction of its evolution. Your starting point limits your ending points.

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

Giant dinosaurs and mammals through time chart
Giant Dinosaurs and Mammals Through Time. (Nick Longrich)

Consider the size of dinosaurs. Beginning in the Jurassic period, the sauropod dinosaurs, brontosaurus and born 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 multiple groups, including DiplodocidaeBrachiosauridae, Turiasauridae, Mamenchisauridae and Titanosaurus.

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. Something about sauropod anatomy – lungshollow bones with a high strength to weight ratiometabolism, or all these things – unlocked their evolutionary potential. It allowed them to grow large in a way that no land animal had before or since.

Similarly, carnivorous dinosaurs repeatedly evolved into huge, ten-meter, multi-ton predators. Over 100 million years, megalosaurids, allosaurids, carcharodontosaurids, neovenatorids, and finally tyrannosaurs evolved giant apex predators.

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

Dinosaurs did well with large bodies. Big brains not so much. Dinosaurs show a slight trend of increasing brain size over time. Jurassic dinosaurs like Allosaurus, stegosaurus, and Brachiosaurus had small brains.

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

Over time, dinosaurs entered new niches. Small herbivores became more common and birds diversified. 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 started living in herds and evolve complex horns for fight and show. Yet dinosaurs seem to have mostly repeated themselves, evolving into giant herbivores and carnivores with small brains.

There is little in the 100 million years or so of dinosaur history to suggest that they would have done anything radically different had the asteroid not intervened. We would probably still have those super-giant herbivores with long necks and huge tyrannosaur-like predators.

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

Mammals, meanwhile, had different limitations. They never evolved supergiant herbivores and carnivores. But they have repeatedly developed large brains. Massive brains (as big or bigger than ours) have evolved in killer whales, sperm whales, baleen whales, elephants, leopard seals, and monkeys.

Today, several descendants of dinosaurs—birds such as crows and parrots—have complex brains. They can use tools, speak and count. But mammals such as monkeys, elephants, and dolphins are the ones that have developed the largest brains and the most complex behaviors.

Did the elimination of the dinosaurs guarantee that mammals would develop intelligence?

Well, maybe not.

The start points may constrain the end points, but they also do not guarantee them. Steve Jobs, Bill Gates and Mark Zuckerberg all dropped out of college. But if dropping out automatically made you a multi-billionaire, every college dropout would be rich. Even if you 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 did evolve into big-brained and limbed apes 7 million yearsproduced modern people. But elsewhere, primate evolution took very different paths.

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

Yet they haven’t evolved into a species that makes nuclear weapons and smartphones. Instead, for reasons we don’t understand, they disappeared.

In Africa, and only in Africa, primate evolution took a unique direction. Something about the fauna, flora or geography of Africa set in motion the evolution of apes: terrestrial, large, big brain, using tools primates.

Even after the extinction of the dinosaurs, our evolution needed the right combination of opportunity and luck.The conversation

Nicholas R. LongrichSenior Lecturer in Paleontology and Evolutionary Biology, University of Bath

This article was republished by The conversation under a Creative Commons license. Read on original article.

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