Dinosaurs The Last Day

[Barb Frison]

Ateam of scientists has discovered the youngest dinosaur preserved in the fossil record before the catastrophic meteor impact 65 million years ago. The finding indicates that dinosaurs did not go extinct prior to the impact and provides further evidence as to whether the impact was in fact the cause of their extinction.

The team is now examining other fossil specimens that appear to be buried close to the K-T boundary and expect to find more, Lyson said. He suspects that other fossils discovered in the past may have been closer to the boundary than originally thought and that the so-called three-meter gap never existed.

Other authors of the paper include Eric Sargis and Stephen Chester (Yale University); Antoine Bercovici (China University of Geosciences); Dean Pearson (Pioneer Trails Regional Museum) and Walter Joyce (University of Tbingen).

Come chill with us and some cool scientists on our last day with these dinosaurs! Meet current researchers that study polar environments to learn more about microbial ecosystems, its use in drug discovery and even how to grow plants in space!

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An artist's impression of what an asteroid colliding with Earth might look like. Sixty-six million years ago an event like this, although on a much smaller scale, caused 75% of all animals to die out. Image: Don Davis Via NASA Image and Video Library

In 1980, Nobel Prize-winning physicist Luis Walter Alvarez and his geologist son Walter published a theory that a historic layer of iridium-rich clay was caused by a large asteroid colliding with Earth.

Luis Walter Alvarez (left) and his son Walter (right) are known for their theory that an asteroid collided with our planet 66 million years ago and caused all non-bird dinosaurs and many other animals to die out. Image: Lawrence Berkeley Laboratory/ Wikimedia Commons

Paul says, 'An asteroid impact is supported by really good evidence because we've identified the crater. It's now largely buried on the seafloor off the coast of Mexico. It is exactly the same age as the extinction of the non-bird dinosaurs, which can be tracked in the rock record all around the world.'

The asteroid is thought to have been between 10 and 15 kilometres wide, but the velocity of its collision caused the creation of a much larger crater, 150 kilometres in diameter. It's the second-largest crater on the planet.

Iridium is one of the rarest metals found on Earth. It is usually associated with extraterrestrial impacts, as the element occurs more abundantly in meteorites. Hi-Res Images of Chemical Elements/ Wikimedia Commons (CC BY 3.0)

The dinosaur-killing crash threw huge amounts of debris into the air and caused massive tidal waves to wash over parts of the American continents. There is also evidence of substantial fires from that point in history.

Paul explains, 'The asteroid hit at high velocity and effectively vaporised. It made a huge crater, so in the immediate area there was total devastation. A huge blast wave and heatwave went out and it threw vast amounts of material up into the atmosphere.

Like dominos, this trailed up the food chain, causing the ecosystem to collapse. The reduction in plant life had a huge impact on herbivores' ability to survive, which in turn meant that carnivores would also have suffered from having less food available.

'There is a lot of discussion over the actual kill mechanism and how long that period lasted. There are still a lot of unknowns. But it was a massive event affecting all life on Earth, from microorganisms all the way through to dinosaurs,' says Paul.

In what is now central India, there was substantial volcanic activity that, although unrelated to the asteroid impact, was causing problems of its own. The resulting lava outcrop is now known as the Deccan Traps.

'There were also longer-term changes. The continents were drifting around and splitting apart from each other, creating bigger oceans, which changed ocean and atmosphere patterns around the world. This also had a strong effect on climate and vegetation.'

During the Cretaceous extinction event, plants were less affected than animals because their seeds and pollen can survive harsh periods for longer. After the dinosaurs' extinction, flowering plants dominated Earth, continuing a process that had started in the Cretaceous, and continue to do so today. But all land animals weighing over 25 kilogrammes died out.

'What we're left with are basically the seeds of what we have today. Many of the major animal groups that are alive today were in place before the asteroid impact and they all suffered some level of extinction - but the lines that led to modern animals got through,' says Paul.

'It was only around 15 million years after the non-bird dinosaurs disappear, during what's termed the Oligocene Epoch, that we started to get really big mammals. This is when rhino-sized animals start to reappear. But up until that point it's a world filled with small animals, especially in comparison with the dinosaurs that came before them. It took a while for body size to catch up.'

There is research to suggest that if the impact had occurred elsewhere on the planet, the fate of life on Earth could have been very different. If it had fallen just minutes later the asteroid would have landed in deeper water, causing less rock to vaporise and rise to block out the Sun's light and warmth. This would have lowered the chances of a mass extinction.

'I suspect some of them would still be around. We don't know a lot about the last 10 million years of their reign and what we do know is based on only one area in the world, western North America. There is a really good record of those classic last non-bird dinosaurs like Tyrannosaurus and Triceratops.

'From that part of the world it looks like dinosaurs are thriving in terms of numbers, but the number of different types of dinosaurs is reduced. We don't know if that pattern held elsewhere - it's still a big mystery.'

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Writing in the journal Science Advances last month, a team of researchers looked at a newly discovered fossil skull from a cousin of modern birds, a bird called Ichthyornis, which went extinct with the rest of the non-avian dinosaurs. Their logic was that if the brain of Ichthyornis was different from modern birds, that difference might explain why Ichthyornis died with the dinosaurs, while the ancestors of modern birds survived.

CHRISTIE TAYLOR: It was a really long time ago, but it was also a really big deal, right? The climate changed really drastically thanks to all the dust in the air, and we can think that event for the loss of 85% of species on Earth at the time.

So Dr. Julia Clarke is a professor of vertebrate paleontology at the Jackson School of Geosciences at the University of Texas, and Doctor Chris Torres is a postdoctoral researcher in bird paleontology at Ohio University. And I should note that we talked to them in front of a live studio audience on Zoom. I started by asking Julia to help us set up the murder scene a little bit better. Why is it so mysterious that the ancestors of modern birds survived while a lot of other species did not?

So if you look at the brains of early birds, their brain is vaguely linear. You get one structure, the cerebrum, out front, the optic lobes, or the midbrain, in the middle as might be expected by its name, and then the cerebellum is at the back. But in living birds, that is totally shifted so that what was formerly the midbrain is now totally underneath what is formerly the forebrain. And so the changing shape is so fundamental that even those words are not very descriptive anymore. So we see this general reshaping that happens as a consequence of this relative expansion of the cerebral hemispheres.

And if we can turn to modern neuroscience and look at bird brain researchers, looking at the actual functions of birdbrains and comparing those to the brains in other reptiles, we start to get an idea of what those functions may have been. And we can start to hypothesize or at least speculate as to what the links would have been.

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