You might know the Cretaceous Period for big animals such as Tyrannosaurus rex and Triceratops, or for being the end of the age of dinosaurs.
But what was the world like in the millions of years leading up to this this mass extinction?
Our dinosaur expert Dr Susie Maidment and fossil plant expert Dr Paul Kenrick explore what the world was like back then and the animals and plants that called our planet home.
When was the Cretaceous Period?
The Cretaceous is a geological period that began 145 million years ago and ended 66 million years ago. It is the last period in the Mesozoic Era. It comes after the Jurassic Period and before the Paleogene - the first period of the Cenozoic Era, our current era.
It lasted a long time, nearly 80 million years, making it the longest geological period of the Phanerozoic Eon, which began some 539 million years ago.
The Cretaceous is split into two smaller time periods called epochs. The Early Cretaceous Epoch lasted from 145 million years ago to 100.5 million years ago and the Late Cretaceous Epoch lasted from 100.5 million years ago to 66 million years ago.
The Cretaceous climate and continents
Our planet's continents were once joined together into one supercontinent called Pangea. It formed about 335 million years ago, but by the end of the Jurassic, this single landmass had begun to break apart. This continued throughout the Cretaceous and by the end of the period the continents had moved almost into the positions they are in today.
Back then Earth was a lot warmer than it is today and there was little or no ice at the North Pole or South Pole. Sea levels fluctuated but were in the most part high. In fact, at times sea levels were 170 metres higher than today.
Shallow seas formed, dividing some continents. In the Late Cretaceous, for example, the Western Interior Seaway split North America into two landmasses. At its largest this sea was more than 3,000 kilometres long, almost 1,000 kilometres wide and 760 metres deep.
Plants in the Cretaceous Period
The plant life of the Cretaceous was quite different to that of today. For example, temperate rainforest grew close to the poles, which back then were ice free.
'We have evidence from West Antarctica of polar forests that would have been dominated mainly by conifers, things like podocarps, araucarias, and probably gingko trees as well, with understories of ferns and cycads,' explains prehistoric plant expert Dr Paul Kenrick.
Unlike the temperate rainforests that exist today in North America's Pacific Northwest, including in Oregon and Washington, each winter the Cretaceous polar forests would have had to survive four months of the year living in the total darkness of polar night. A very long period without Sun for plants to survive!
Today, about 90% of plants are flowering plants, also known as angiosperms. While the origin of flowering plants may go back as far as the Triassic Period, we don't see much evidence of them in the fossil record at the start of the Cretaceous. However, by the end of the Cretaceous, angiosperms made up a much more prominent part of the planet's plant life.
'In flowering plants today, something like 70% are insect pollinated,'explains Paul.
'Insect pollination happens earlier on in the Jurassic with gymnosperms [a group of seed-producing plants], but it becomes much bigger with the flowering plants.'
'So, there is this big evolutionary story going on between plants and animals.'
Cretaceous Period animals
'Everything that lived on land that was larger than a metre in size in the Cretaceous was a dinosaur,' says palaeontologist Dr Susie Maidment.
'There were small, furry mammals running around at the feet of the dinosaurs, but they were a relatively minor component of the ecosystem.'
'Birds had evolved and were in the skies, as well as pterosaurs. In the seas, there were mosasaurs, which are big marine reptiles, and there were groups of plesiosaurs and ichthyosaurs,' explains Susie.
When it comes to Cretaceous dinosaurs, we often think of Triceratopsand T. rex,though these dinosaurs only lived at the end of the period, around 68-66 million years ago.
'The Cretaceous is 80 million years long, so there's a lot of turnover in that time,' says Susie.
'The Jurassic, which ended 145 million years ago, was the time when we have really big dinosaurs in the northern hemisphere. Things like Diplodocus and Stegosaurus. Those seem to go extinct or at least decline in the Early Cretaceous and they're replaced by iguanodontians and ceratopsids.'
In the Early Cretaceous, iguanodontians were some of the first dinosaurs to evolve complex chewing mechanisms rather than just gulping down food like other reptiles.
In the Late Cretaceous, hadrosaurs - the duck-billed dinosaurs - did similar, using their hundreds of tiny teeth to grind up vast amounts of plant matter. Susie calls them 'the cows of the Cretaceous'.
While the northern hemisphere's biggest dinosaurs lived during the Jurassic, it was in the Cretaceous that the southern hemisphere saw its largest reptiles. In fact, during this period, some of the biggest land animals to have ever existed appeared. The largest of all belong to a group of sauropod dinosaurs called titanosaurs.
Patagotitan, a 37.5-metre-long titanosaur from Argentina in South America, might be the largest found so far. But it's possible that one day we'll find even bigger dinosaurs.
'I think before Patagotitan we would have said dinosaurs were on the edge of what is physically possible, and then you find something bigger,' notes Susie.
It's not clear why some dinosaurs and pterosaurs, such as Quetzalcoatlus, got so large during the Cretaceous Period. Some think it could be related to what gases were in the atmosphere, while others suggest that an evolutionary arms race between prey and predators may have been responsible.
'Big dinosaurs couldn't really run so they had to protect themselves in other ways. So, the prey animals got bigger and then the predators got bigger and so on,' explains Susie.
How did giant dinosaurs affect their environment?
Sauropods might have lived and travelled in big herds. But how could the Cretaceous environment have supported so many giant herbivores?
'We have such a mammal-centric view of the world, but sauropods were so different to mammals. I suspect they had a very different metabolism and probably didn't need to eat as much food. They could also probably survive on lower-quality plant matter,' says Susie.
'They hatched out of eggs a bit smaller than a football and could grow into these 60-tonne animals. We can see that they deposited bone tissue very rapidly, so they were growing very fast, and they probably had to eat a lot to fuel their growth.'
'It's been suggested that their metabolism changed as they grew. So early on they had a really fast metabolism and as they got big their growth slowed and they actually had a much slower metabolism.'
Giant sauropods would have stripped cellulose-rich leaves off conifers and these may have taken a long time to process in their digestive systems. They might have also eaten the cones from these trees.
'The cones contain the seeds. They're different to the leaves because they contain starches rather than just cellulose, so you get more for your bucks by eating them,' says Paul.
Herbivorous - plant-eating - dinosaurs might also have been ecosystem engineers, meaning they changed the places where they lived through their behaviour. When these dinosaurs ate plant seeds, they may have passed through their guts and out in their poo, which helped to spread the seeds across the animal's habitat as they moved around.
'If you think about the analogies in the modern world, such as elephants, then seed dispersal may have been an important function of big dinosaurs,' notes Paul.
But was there any way Cretaceous plants could prevent themselves from becoming a dinosaur's dinner? Paul points out a few groups of plants that might have done just that!
Of the around 370 species of cycads alive today, almost all of them are toxic to most mammals, with only a few primates able to stomach them. If cycads were this toxic during the Jurassic and Cretaceous, it's possible this could have been enough to put dinosaurs off eating them.
Bennettitales are an extinct group of plants that looked a lot like cycads.
'Cycads have cones that are produced at the top of the plant, whereas in many Bennettitales, cone-like structures were embedded in the trunk,' Paul explains.
'It might be that these plants were protecting their reproductive parts by encasing them in an armour-like trunk rather than allowing them to be exposed and being easy to predate by dinosaurs.'
Some plants might have survived by being robust. The monkey puzzle tree, Araucaria araucana, for example, looks almost armour plated, covered in thick, scale-like leaves with sharp edges. The group this plant belongs to was at its most diverse during the Jurassic and Cretaceous.
Cretaceous Britain
The name Cretaceous comes from the Latin 'creta' which means chalk. It's named for the large quantities of chalk rock laid down at this time in Western Europe. The UK's famous White Cliffs of Dover are just one of many Late Cretaceous chalk deposits.
Chalk is laid down in marine environments, and the fossils within it can tell us about the creatures that lived in the ocean. But it also means scientists have less of an understanding of the plants and land animals that lived in Britain at the end of the Cretaceous Period.
We have a much better idea of what lived on land here in the Early Cretaceous, particularly thanks to rocks near Bournemouth in southern England known as the Wealden Group. This area is well known for the discovery of Iguanodon. In fact, the UK is particularly well known for iguanodontians, with 12 genera having been found here from the Early Cretaceous.
We know from the fossil record that rather than dense deciduous woodlands, back in the Cretaceous Britain's landscapes would have featured conifers with an understory of ferns and cycad-like plants.
These landscapes would have been relatively open. Today, big areas dominated by grasses and with sparse tree cover are known as savannahs and prairies. In the Cretaceous, open landscapes like these would have been dominated by ferns rather than grass.
'We think of ferns as being these little delicate things that like wet places, but back then you had ferns that were quite robust and lived in semi-arid environments,' says Paul.
How did the Cretaceous Period end?
The Cretaceous-Palaeogene extinction 66 million years ago is possibly the most famous mass extinction event. It was caused by a large asteroid crash-landing off the coast of Mexico, which changed the climate of the planet dramatically.
'It vapourised carbonate and sulphate rocks, which caused acid rain, and threw lots of ash, dust and dirt into the atmosphere, blocking out the Sun. This caused a global collapse of the food chain,' explains Susie.
'There also would have been a thermal heat pulse that caused wildfires - that's evidenced by charcoal in the rock record - and huge tsunamis washed across the ocean basins.'
Adding to the chaos was the formation of the Deccan Traps, one of the planet's largest volcanic features. The vast quantities of sulphur released would have cooled the atmosphere.
The Cretaceous extinction wiped out about 65% of all species.
Plants were affected, though not in quite the same way as animals.
'With animals, whole groups disappeared. Whereas with plants, you see a lot of extinction, but you don't tend to see whole groups of plants disappear,' explains Paul.
'In many respects, plants are more robust than animals, more resilient to physical disturbance.'
Paul likens this to cutting the grass. Even after cutting a plant in half with a lawnmower, it can regenerate, something that is impossible for animals to do. In catastrophic circumstances, plants can regrow from rooting systems, buds and other parts.
Plants also have the advantage of creating vast quantities of seeds that, in some types of plants, can survive in the soil for decades until conditions are right for them to begin to grow.
Ecological variation within groups also helps in the face of catastrophe.
'You see plants that produce big trees and small shrub-like things. You might have families that have annuals and long-lived perennials. You might have groups that are adapted to hot and cold climates in the same family.'
'The family level of plants may be more diverse than animals, so that's why you don't get the massive losses of these big groups, because some element of them finds a way to survive extinction.'
What came after the Cretaceous Period?
When the Cretaceous Period and Mesozoic Era ended 66 million years ago, the Palaeogene Period and the Cenozoic Era began.
In the Palaeogene, the continents drifted even closer to their present-day positions, and during the following Neogene Period the world was cooler and the effects of seasonality were more widely felt.
Many modern plants evolved in this period and grasses began to spread.
In place of pterosaurs, birds became the dominant animals in the skies and the extinction of the non-avian dinosaurs allowed mammals to rapidly diversify and grow.
While it would still be many millions of years before ancient human relatives would appear, evidence of some of the earliest primate-like mammals comes from the Palaeogene.
FAQs
What was the Cretaceous Period like? ›
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites, and rudists, while dinosaurs continued to dominate on land.
What was life like in the Cretaceous Period? ›The climate was generally warmer and more humid than today, probably because of very active volcanism associated with unusually high rates of seafloor spreading. The polar regions were free of continental ice sheets, their land instead covered by forest. Dinosaurs roamed Antarctica, even with its long winter night.
What was the Cretaceous Period known for? ›During the Cretaceous, accelerated plate collision caused mountains to build along the western margin of North America. As these mountains were rising, the Gulf of Mexico basin subsided, and seawater began to spread northward into the expanding western interior. Marine water also began to flood from the Arctic region.
What are the key 2 facts of the Cretaceous Period? ›The Cretaceous Period started around 145.5 million years ago and ended around 65.5 million years ago. During this period, land on Earth was breaking up into separate continents the way it is today. Flowering plants appeared for the first time, and dinosaurs lived all over the Earth.
Why was it so hot during the Cretaceous Period? ›During the Cretaceous Thermal Maximum (CTM), atmospheric carbon dioxide levels rose to over 1,000 parts per million (ppm) compared to the pre-industrial average of 280 ppm. Rising carbon dioxide resulted in a significant increase in the greenhouse effect, leading to elevated global temperatures.
How hot was it in the Cretaceous Period? ›The Cretaceous period is an archetypal example of a greenhouse climate. Atmospheric pCO2 levels reached as high as about 2,000 ppmv, average temperatures were roughly 5°C–10°C higher than today, and sea levels were 50–100 meters higher [O'Brien et al., 2017; Tierney et al., 2020].
Was there snow in the Cretaceous period? ›And while the Cretaceous world was a bit warmer, with no polar icecaps, winter could still be harsh. “There would have been ice and snow in the three-month-long, dark winters,” Rich says.
What species went extinct in the Cretaceous period? ›In addition to the non-avian dinosaurs, vertebrates that were lost at the end of the Cretaceous include the flying pterosaurs, and the mosasaurs, plesiosaurs and ichthyosaurs of the oceans.
What went extinct in the Cretaceous extinction? › Was the Cretaceous Period hot or cold? ›The Cretaceous, which occurred approximately 145 million to 66 million years ago, was one of the warmest periods in the history of Earth. The poles were devoid of ice and average temperatures of up to 35 degrees Celsius prevailed in the oceans.
How long did the Cretaceous era last? ›
It lasted a long time, nearly 80 million years, making it the longest geological period of the Phanerozoic Eon, which began some 539 million years ago. The Cretaceous is split into two smaller time periods called epochs.
What are 5 living things from the Cretaceous Period? ›The dinosaurs of the last 10 million years of the Cretaceous in North America are some of the best known in the world. They include tyrannosaurs such as Tyrannosaurus, diverse small theropods, ankylosaurs, bone-headed pachycephalosaurs, horned and frilled ceratopsians such as Triceratops, and “duckbilled” hadrosaurs.
What was the smartest dinosaur in the Cretaceous Period? ›By studying the brain size in comparison to the actual size of the dinosaur and examining some of its physical attributes to determine how it might have behaved, scientists now think Troodon formosus, a relatively small dinosaur from the Late Cretaceous, was the smartest dinosaur ever.
What survived the Cretaceous Period? ›Birds: Birds are the only dinosaurs to survive the mass extinction event 65 million years ago. Frogs & Salamanders: These seemingly delicate amphibians survived the extinction that wiped out larger animals. Lizards: These reptiles, distant relatives of dinosaurs, survived the extinction.
What plants were alive during the Cretaceous Period? ›The land plants of the Early Cretaceous were similar to those of the Jurassic. They included the cycads, ginkgoes, conifers, and ferns.
Did it rain in the Cretaceous Period? ›It likely rained more in the Cretaceous Period overall than it does on Earth today, a reflection of several different climate factors. For starters, the Cretaceous era was warmer than the modern era by an average of several degrees, meaning that more ocean water evaporated and formed precipitation in the atmosphere.
Could humans survive 65 million years ago? ›For this reason, it would be difficult for a modern-day human to survive and thrive on Earth at this time. Even if the die-off hadn't occurred, it would still be very hard for a modern-day human to live during that time period. There would have been massive predators such as dinosaurs that would hunt a human.
Was the Earth warmer 12000 years ago than today? ›The planetary change that accompanied that warming is mind-boggling: 12,000 years ago, most of North America was 36 degrees colder than it is today, largely because of the retreating ice sheets.
Was Earth warmer when dinosaurs lived? ›When dinosaurs were having their heyday in the late Cretaceous Period roughly 78 million years ago, Earth's climate was both warmer and more varied than what we have known before.
Was there more oxygen during the dinosaurs? ›This result has very interesting implications about the era of the dinosaurs. The dinosaurs apparently breathed air that was much richer in oxygen than our air and lived in forests and grasslands that were far more combustible than ours.
Could humans breathe in the Cretaceous? ›
How would a person fare living during the late Cretaceous? From what I was taught, O2 levels were quite high, but research has shown that oxygen levels during the Triassic was 15-19%. OSHA defines oxygen deficiency as O2 being 19.5 % or less. So humans would have a hard time breathing.
Could dinosaurs be brought back? ›It is therefore entirely possible for prehistoric genetic material to survive for up to one million years. But the big dinosaurs departed this life some 66 million years ago. So the prospect of finding enough viable DNA material in what remains of them today is therefore vanishingly remote.
Did dinosaurs live with humans? ›No! After the dinosaurs died out, nearly 65 million years passed before people appeared on Earth. However, small mammals (including shrew-sized primates) were alive at the time of the dinosaurs.
Could dinosaurs survive in today's atmosphere? ›The beginning of the age of dinosaurs, about 215 million years ago, corresponded with an increase in atmospheric oxygen from 15 percent to 19 percent. The current atmosphere has about 21 percent oxygen so some of those early dinosaurs from the Triassic would likely be plenty comfortable running around today.
How many times has life been wiped out on Earth? ›The planet has experienced five previous mass extinction events, the last one occurring 65.5 million years ago which wiped out the dinosaurs from existence. Experts now believe we're in the midst of a sixth mass extinction.
What was the largest predator of the Cretaceous period? ›Tyrannosaurus rex arose during the Cretaceous period about 85 million years ago, and thrived as a top land predator until the dinosaurs went extinct 20 million years later...
Are we in a mass extinction? ›The Holocene extinction continues into the 21st century, with human population growth, increasing per capita consumption (especially by the super-affluent), and meat production and consumption, among others, being the primary drivers of mass extinction.
When did humans almost go extinct? ›How Human Beings Almost Vanished From Earth In 70,000 B.C. : Krulwich Wonders... By some counts of human history, the number of humans on Earth may have skidded so sharply that we were down to just 1,000 reproductive adults. And a supervolcano might have been to blame.
How long was Earth uninhabitable after the asteroid? ›Darkness caused by dino-killing asteroid snuffed out life on Earth in 9 months. As sunlight dimmed, plants and animals died.
How many species have humans made extinct? ›At least 680 vertebrate species had been driven to extinction since the 16th century and more than 9% of all domesticated breeds of mammals used for food and agriculture had become extinct by 2016, with at least 1,000 more breeds still threatened.
Has the Earth been hotter than it is now? ›
Highlights. Earth's temperature has risen by an average of 0.14° Fahrenheit (0.08° Celsius) per decade since 1880, or about 2° F in total. The rate of warming since 1981 is more than twice as fast: 0.32° F (0.18° C) per decade.
What's the hottest Earth's ever been? ›The current official highest registered air temperature on Earth is 56.7 °C (134.1 °F), recorded on 10 July 1913 at Furnace Creek Ranch, in Death Valley in the United States.
What was the hottest period on Earth? ›One of the warmest times was during the geologic period known as the Neoproterozoic, between 600 and 800 million years ago. Conditions were also frequently sweltering between 500 million and 250 million years ago.
What did the Earth look like before dinosaurs? ›At that time, Earth was covered in hot, humid swamps and rainforests. These places were home to many large amphibians. One of the bizarre creatures that lived in those swamps was Diploceraspis.
What came before dinosaurs? ›Before the dinosaurs, the dominant forms of life on land and sea were the synapsids — a group also known as “proto-mammals.” Learn about some of the strangest and most ferocious synapsids and how these unusual creatures evolved into mammals like us.
What ended the Jurassic Period? ›This era includes the Triassic, Jurassic, and Cretaceous Periods, names that may be familiar to you. It ended with a massive meteorite impact that caused a mass extinction, wiping out the dinosaurs and up to 80% of life on Earth.
What killed the dinosaurs? ›Sixty-six million years ago, dinosaurs had the ultimate bad day. With a devastating asteroid impact, a reign that had lasted 180 million years was abruptly ended. Prof Paul Barrett, a dinosaur researcher at the Museum, explains what is thought to have happened the day the dinosaurs died.
How did dinosaurs become extinct? ›Evidence suggests an asteroid impact was the main culprit. Volcanic eruptions that caused large-scale climate change may also have been involved, together with more gradual changes to Earth's climate that happened over millions of years.
What could humans eat in the Cretaceous period? ›- edible parts of plants.
- meat of early mammals.
- fish (Sturgeon, Coelcanth, Lancetfish etc.)
- eggs.
The Least Intelligent Dinosaurs:
The primitive dinosaurs belonging to the group sauropodomorpha (which included Massospondylus, Riojasaurus, and others) were among the least intelligent of the dinosaurs, with an EQ of about 0.05 (Hopson, 1980).
What is the IQ of at Rex? ›
The largest tyrannosaurs like T. rex had an EQ in the range of 2.0 to 2.4. By comparison, our EQ is about 7.5, dolphins come in around 4.0 to 4.5, chimps at about 2.2 to 2.5, dogs and cats are in the 1.0 to 1.2 range, and mice and rats languish around 0.5.
Why did crocodiles survive but not dinosaurs? ›There are two main reasons. First, crocodiles can live for a very long time without food. Second, they lived in places that were the least affected when the asteroid hit Earth.
When did God make dinosaurs? ›According to the Bible, dinosaurs must have been created by God on the sixth day of creation. Genesis 1:24 says, “And God said, Let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the earth after his kind: and it was so.”
What happened at the end of the Cretaceous Period? ›At the end of the Cretaceous Period, 65 million years ago, an asteroid hit Earth in the Yucatan Peninsula, Mexico, forming what is today called the Chicxulub impact crater.
What dinosaur rammed its head? ›The thick skull domes of Pachycephalosaurus and related genera gave rise to the hypothesis that pachycephalosaurs used their skulls in intra-species combat.
What percent of life was killed in the Cretaceous Period? ›Dawn of a New Age
The extinction that occurred 65 million years ago wiped out some 50 percent of plants and animals. The event is so striking that it signals a major turning point in Earth's history, marking the end of the geologic period known as the Cretaceous and the beginning of the Tertiary period.
Birds: Birds are the only dinosaurs to survive the mass extinction event 65 million years ago. Frogs & Salamanders: These seemingly delicate amphibians survived the extinction that wiped out larger animals. Lizards: These reptiles, distant relatives of dinosaurs, survived the extinction.
How many times has humanity been wiped out? ›There have been five mass extinctions in Earth's history - Our World in Data.
Why did no dinosaurs survive? ›Evidence suggests an asteroid impact was the main culprit. Volcanic eruptions that caused large-scale climate change may also have been involved, together with more gradual changes to Earth's climate that happened over millions of years.
How long did the Cretaceous extinction last? ›For example, radiometric dating of volcanic ashbeds in Montana and Haiti located near geological evidence of the asteroid impact that killed the dinosaurs at the end of the Cretaceous period suggests that mass extinction only took about 32,000 years.
How big was the asteroid that killed the dinosaurs? ›
When the 6-mile-wide asteroid that led to dinosaur extinction hit Earth 66 million years ago, the impact also triggered a “mega-earthquake” that lasted weeks to months, new evidence suggests.
Did humans live with dinosaurs? ›No! After the dinosaurs died out, nearly 65 million years passed before people appeared on Earth. However, small mammals (including shrew-sized primates) were alive at the time of the dinosaurs.
What if the asteroid didn't hit the earth? ›According to new research, dinosaurs would have lived on Earth for many more years, if a huge asteroid hadn't smashed into the planet and wiped them out. At the time of the asteroid impact, 66 million years ago, dinosaurs were the dominant land animals living across the globe.
What species went extinct in the Cretaceous Period? ›In addition to the non-avian dinosaurs, vertebrates that were lost at the end of the Cretaceous include the flying pterosaurs, and the mosasaurs, plesiosaurs and ichthyosaurs of the oceans.
What happens at the end of the Cretaceous? ›Mass extinctions
Best known for killing off the dinosaurs, the end-Cretaceous mass extinction also caused many other casualties. Ammonoids (marine mollusks), pterosaurs (gliding reptiles), mosasaurs (swimming reptiles), and a host of other plants and animals died out completely or suffered heavy losses.