More than 66 million years ago, Earth was very different from what it is today. Back then, the Arctic was covered in palm trees, and humans didn’t exist yet. While there’s plenty of evidence about what our planet looked like during that time period—dinosaurs and all—it’s been hard to know exactly what life was like before the dinosaurs began their 200-million-year reign on Earth… Until now, that is. A new research study has revealed more about what life was like before the dinosaurs existed. Here are some of the highlights.
Impact on Humans
Our discovery shows that there was a huge extinction of marine life worldwide before dinosaurs appeared on land. However, there were some survivors in small refuges in southern continents, explained Sefako Makgoba, professor at Wits University and senior curator at SAMRC. The findings suggest that a major rise in atmospheric oxygen levels followed by massive extinction of marine species occurred about 488 million years ago. The research will be published in Palaeontologia Africana. This is very exciting because it is one of those times when geology, climate science and biology all come together to create new understanding of what happened to our planet during its early history said Professor Makgoba.
We found evidence for an ancient supercontinent called Nuna that broke up around 600-550 million years ago into fragments we now know as Australia, Antarctica and South Africa. It seems that each continent had only one or two areas where life could survive. In South Africa, it was along the margins of a large inland sea (the paleo-Tethys Sea) and in Eastern Antarctica (the paleo-Pacific Ocean). Here we found abundant fossils of multicellular organisms including sponges, worms and soft-bodied animals like jellyfish. Some of these fossils are among the earliest skeletal remains known from animal groups that survived beyond 555 million years ago. For example, they are from primitive animals such as sponges, which today live in water but have no skeletons; instead they have cells with silica skeletons that provide support. These particular fossils show how their bodies changed over time and how complex structures evolved. There’s been much debate over why animals first started appearing on land, explains researcher Dr Gavin Young. There’s also been uncertainty about when certain types of marine creatures died out and why. This study shows that at least part of it is due to environmental change – specifically a global drop in oxygen levels caused by changes in ocean circulation triggered by intense weathering of rocks on land. When dissolved oxygen concentrations drop too low, then many species cannot survive. That may explain why most of today’s land animals either evolved during a pulse of diversification just after 541 million years ago or managed to escape by moving onto land before then.
Impact on Mammals
The new evidence, presented in two papers published Thursday in Science, suggests that mammals began to thrive after dinosaurs died off. The end of the Cretaceous period was bad for dinosaurs, but it may have been just what mammals needed to get a foothold. More fossil discoveries will hopefully continue to give scientists a better picture of how life on land evolved following an asteroid strike that killed all other species about 66 million years ago. It’s clear that large animals were wiped out and small ones survived, but researchers are still working to understand why. It’s not enough to say that only small animals survived—we need to know why they did, said lead study author Steve Brusatte in a statement. And by learning more about what happened at the very end of the age of dinosaurs we can learn more about why mammals came to dominate planet Earth.
In one paper, a team led by University of Edinburgh paleontologist Stephen Brusatte analyzed fossils from North America and Asia to examine when different mammal groups first appeared. The team found that mammals emerged as early as 100 million years before non-avian dinosaurs went extinct, which is earlier than previously thought. Mammals also diversified rapidly soon after dinosaurs died out, indicating that they didn’t take long to start filling up niches left behind by their reptilian counterparts. The second paper, led by Brown University geoscientist Brian Switek, examined what conditions would have allowed mammals to spread around so quickly after dinosaurs vanished. They looked at oxygen levels during that time — since high levels of oxygen mean there is plenty of energy available for organisms — and found them to be much lower than today. That means there wasn’t a lot of energy available for larger creatures to live off of, making it easier for smaller mammals to survive. There’s still some debate over whether or not climate change or an asteroid impact caused dinosaurs to go extinct, but regardless, these findings suggest that mammals were well-positioned to fill any ecological roles vacated by those ancient reptiles.
Impact on Birds
The asteroid that wiped out most of life on Earth 66 million years ago also caused mass extinction in avian species, suggests a new study published online in Geology. Not only did it impact mammals, but birds too. The findings point to an increase in grasslands at that time. In turn, more grassland would have made it easier for mammals and birds to grow bigger and more diverse. But then came another extinction event — perhaps due to volcanic activity — that decimated bird populations and sent them into hiding for 30 million years. Only after dinosaurs went extinct were birds able to thrive once again. Today, we know some 10,000 living bird species. While scientists don’t know what kind of birds existed during the late Cretaceous period, they can make educated guesses based on related fossil evidence from North America. Fossilized remains found in New Mexico indicate that there may have been about 25 types of Cretaceous-era birds roaming around before their untimely demise around 66 million years ago. If so, it’s possible that each type of bird was present in fewer than 1,000 individuals. The diversity of modern birds is strongly influenced by ecological factors such as predation pressure or competition with other species, said James Wittke, lead author of the paper and a postdoctoral researcher at University College Cork (Ireland). However, our results suggest that ecological factors alone cannot explain why certain groups survive or go extinct.
It seems that biological interactions between species are equally important, if not more important. The fact that these birds survived several extinction events prior to when they finally went extinct 66 million years ago shows just how resilient they were, Wittke added. If these early birds had not gone extinct when they did, we probably wouldn’t be here today. Birds originated in Europe and Asia, but eventually spread across all continents except Antarctica. Some theories suggest that birds first evolved from small feathered dinosaurs called maniraptors. Other theories posit that they evolved separately from non-avian dinosaurs, much like whales evolved separately from land animals even though they share many anatomical features with their terrestrial ancestors. Regardless of where birds originated, however, it appears as though major changes to global ecosystems helped shape their evolution over time — including both climate change and biodiversity loss.
Impact on Reptiles and Fish
It’s clear that an asteroid impacted with Earth in what is now Yucatan, Mexico. However, it has remained unclear how dinosaurs reacted to these global changes and whether they outcompeted mammals or died out alongside them. Thanks to new research published in Science , scientists have been able to date a number of small mammal fossils unearthed from what’s now Mongolia’s Gobi desert. The results suggest that mammals were thriving just before and after dinosaurs went extinct. The findings also suggest that non-avian dinosaurs may have survived longer than previously thought—at least until about 200,000 years after their extinction event. Although there’s no evidence for surviving dinosaur species, there are hints of other survivors such as crocodiles, turtles and lizards—all animals known to live for hundreds of thousands of years without evolving significantly.
The big take home message here is that when you look at mammals and reptiles at very high resolution you can see very subtle things happening through time, said study author David Grossnickle, a paleontologist at University of Chicago. This allows us to ask new questions about how ecosystems functioned right before and right after [the mass extinction]. That’s something we haven’t had access to before. The fossils examined by researchers were found in early Eocene sediments (about 55 million years old) and late Eocene sediments (about 50 million years old). This is exciting because earlier attempts at dating these sediments using isotopes produced confusing results, suggesting that mammals evolved rapidly during that period instead of appearing gradually as they actually did. Grossnickle and his colleagues used argon gas analysis to determine the age of tiny fossils called molars. They looked specifically at oxygen isotope ratios within individual layers of dentine, which was once part of enamel on top of those teeth. When tooth enamel forms, some oxygen atoms in water molecules bond more strongly than others; each oxygen atom has a slightly different weight. These heavier oxygen atoms are preferentially incorporated into minerals like dentine during tooth formation; lighter ones remain behind in groundwater or rainwater. As a result, oxygen isotope ratios vary between different regions of dentine. By measuring these variations across several dozen fossilized teeth, Grossnickle and his team were able to accurately date multiple layers at once. Our ability to make these measurements really comes down to advances in technology over the last few decades, he added. We couldn’t do it 20 years ago because we didn’t have enough precision in our instruments.
