When did the Dinosaurs live?

On this page we’ll hope to help answer the question; “when did the dinosaurs live?” We’ll discuss the three periods which make up the Mesozoic Era, they are the Triassic, Jurassic, and Cretaceous Period. The Mesozoic Era lasted from 252 – 66 million years ago and is also referred as the “age of Reptiles”

The Triassic Period 251.9 to 201 million years ago.

Imagine a time when the earth’s surface was hot and dry, volcanic eruptions in areas, no glaciers at either poles, extreme seasonal weather from very hot in the summers to very cold winters.

Imagine Africa being attached to America and there being a period of time post a mass extinction when 90 to 95% of all life formed became extinct.

This was the Triassic period and it was in this period the earth with its life forms developed again and was the beginning of the dinosaur period. Pterosaurs (flying reptiles) also made their first appearance here as well as frogs, turtles and crocodiles. During the Late Triassic period, many small mammals also appeared.

Both the start and end of the Triassic are marked by major extinction events.

What did the Earth look like 240 million years ago

What the Earth looked like: Image source

The Triassic period was named in 1834 by Friedrich Von Alberti from the three distinct layers (Latin trias meaning triad) – red beds, capped by chalk, followed by black shales that are found throughout Germany and northwest Europe, called the ‘Trias’.

As regards the history of life on Earth, the Triassic period was significant for a number of reasons. This was a time of transition, in which many old forms of life died out, and new, and sometimes even modern, ones appeared. Bivalves, ammonoids and brachiopods all recovered from the Permian extinction to dominate the Triassic. The Triassic is usually separated into Early, Middle and Late Triassic Epochs, and the corresponding rocks are referred to as Lower, Middle or Upper Triassic.

During the Triassic, almost all the Earth’s land mass was concentrated into a single supercontinent centered more or less on the equator, called Pangea (meaning – all the land). This took the form of a giant ‘Pac-Man’ with an East-facing ‘mouth’ constituting the Tethys sea, a vast gulf that opened further westwards in the mid-Triassic, at the expense of the shrinking Paleo-Tethys Ocean, an ocean that existed during the Paleozoic. The remainder was the world-ocean known as Panthalassa (meaning – all the sea). All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates therefore very little is known of the Triassic open ocean. The supercontinent Pangaea was rifting during the Triassic, especially late in the period, but had not yet separated, the first marine sediments in the earliest rift, which separated New Jersey from Morocco, are Late Triassic in origin. Because of the limited shoreline of one super-continental mass, Triassic marine deposits are globally relatively rare, despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the West. Therefore, Triassic stratigraphy is mostly based on organisms living in lagoons and hypersaline environments, such as Estheria crustaceans.

The Triassic climate was generally hot and dry, forming typical red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole, in fact, the polar regions were apparently moist and temperate, a climate suitable for reptile-like creatures. Pangeas large size limited the moderating effect of the global ocean, its continental climate was highly seasonal, with very hot summers and cold winters.

The Earth looked much different at the beginning of the Triassic period than it does today. Mammal-Like Reptiles dominated the land and some of them grew to lengths of almost 20 feet. The first dinosaurs also appeared during this time and these included the dog-sized meat-eaters Eoraptors (‘the dawn reptile’) and Hererrasaurus. In the late Triassic period prosauropods, 20 feet long plant-eaters, also emerged. They had small heads and were able to walk on 2 or 4 legs.

The first extinction event

This happened at the end of the Permian period and therefore called the Permian-Triassic extinction.

A massive extinction paved the way for dinosaurs. The greatest known extinction event in Earths history occurred at the beginning of the Triassic. This event paved the way for dinosaurs to supplant Mammal-like Reptiles as the most dominant creatures on the planet. While not all of the mammal-like Reptiles vanished, they became vulnerable to the emerging dinosaurs. Many scientists believe that as the dinosaurs got bigger, faster and more ferocious, they killed most of the mammal-Like Reptiles, and those that survived were the smallest of these creatures. Eventually, the only ones left were the very smallest and these evolved into early mouse-sized mammals.

What happened? Well there are numerous theories out there, the first being that there was a gradual climate change or sea level change which may have been the underlying cause for extinction but this is an old hypothesis.

Some scientists believe that there was a meteorite or comet strike which was the main culprit but the most popular, and well supported theory is the start of the volcanic eruptions. These eruptions occurred over an 11 million km squared area which at the time covered North America, South America, and what is now Africa. 

These volcanic eruptions were responsible for huge amounts of carbon dioxide to be released into the atmosphere which caused global warming and changed the Oceans PH balance, causing it to become more acidic.

This also meant there were significant increases on the earth’s surface temperature and an increase in sea temperature. These conditions meant it really was a case of “only the toughest survived”. 

During the mass extinction, which was particularly severe in the oceans, the conodonts disappeared and all the marine reptiles except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods, gastropods and molluscs were severely affected. In the oceans, up to 95% of marine families and possibly about half of marine genera went missing. 

These extinctions within the Triassic and at its end allowed the dinosaurs to expand into many niches that had become unoccupied. Dinosaurs became increasingly dominant, abundant and diverse, and remained that way for the next 150 million years. The true ‘Age of Dinosaurs’ is the Jurassic and Cretaceous, rather than the Triassic.

How long did the extinction event last?

Various studies have shown scientists with different opinions over the years. Geologists and palaeontologists alike have agreed that the extinction, possibly the greatest in earth’s history, lasted over 15 million years which is hard to comprehend.

Others have claimed it happened a lot quicker over 200,000 years with most of the species being lost in the last 20,000 years.

Plants and Insects life

A lot of plant forms became extinct where the heat dried out many inland areas. Although mosses and ferns did survive and flourished in warm, moist areas where water was present.

Conifers began to flourish with trees growing to 30 meters tall, these in turn homed insects that evolved also.

For some people reading this it will come as a disappointment that some of the surviving insects were spiders and scorpions that repopulated fast. 

Sea life

As mentioned above, Scientists believe up to 95% of marine life was wiped out by extremely high carbon dioxide levels from the volcano eruptions. Few species survived the extinction, and it was a time when a group of reptiles called Ichthyosaurs (Greek for fish lizard) went back into the water and evolved by becoming pure marine species.

The Ichthyosaurs initially swam by moving side to side but as they evolved, they became slick in the water with bodies shaped like dolphins and long snouts. 

They started by breathing oxygen but by the mid Triassic period they were ruling the oceans and were well adapted to the water. One species, the Shonisaurus, grew to be 15 meters (49 foot) long and weighed up to 30 tons.    

Types of Ichthyosaurios

Nobu Tamura (http://spinops.blogspot.com), compiled by Levi bernardo, CC BY 3.0, via Wikimedia Commons

The Dinosaurs

The earth was a varied place of habitats where some areas were desert-like, and other areas were full of vegetation and life that had breed in moist wet conditions.

As the earth was reforming and evolving it was around 240 million years ago that the first dinosaurs appeared. They were small at first but these reptiles got bigger, stronger, and faster (in some cases). 

It wasn’t until the late Triassic period that dinosaurs really developed and crossed into the Jurassic period where they dominated the world for millions of years.

It was around 237 to 201 million years ago that saw the largest dinosaurs such as the sauropods evolve. The plant-eating dinosaurs, were the first ornithischians, or bird-hipped dinosaurs, and were no bigger than turkeys. Huge ferns and other primitive non-flowering trees also dominated the land. Grass never grew during the Triassic and the dinosaurs got bigger and bigger as a result of having little competition from any other forms of life on the land.

Jobaria

I, Steveoc 86, CC BY 2.5, via Wikimedia Commons

Pterosaurs

One of the most significant developments to occur during the latter part of the Triassic was that some creatures took to the air. Two families of animals began to develop at this time – flying reptiles, or Pterosaurs, and the first members of the family that became birds. By 228 million years ago the very first pterosaurs appeared, and they ruled the skies for years.

As with dinosaurs they grew in size and ended up with wingspans of over 15 meters. They were some of the biggest flying creatures that ever developed on earth.

Pteranodon

Pteranodon Image source and artist

The end of the Triassic Period

This event was a lot less devastating than the Permian-Triassic extinction and there are some similarities to the scientists’ thoughts on this mass extinction also. An increase in volcanic acidity would have caused carbon dioxide levels to increase which would have also increased acidity levels in the oceans. 

Some scientists however think that increased sea levels with lower oxygen levels and combined with climate change caused this mass extinction. 

There are also theories out there that the end Triassic extinction event was not the result of anything other than a turnover of species over a period. Therefore, some scientists believe this should not be categorised as a single event.

The Dinosaurs survived

Dinosaurs, pterosaurs, and crocodiles survived the mass extinction event. All other archosaurs did not, which meant territories were open for the surviving dinosaurs to take their place and flourish while the world went into the Jurassic period.

The Jurassic Period: 201 to 145.5 million years ago

The Jurassic Period is split into 3, Lower / Early Jurassic, Middle Jurassic, and Upper / Late Jurassic. The Jurassic begins from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the ‘Age of Reptiles’.
The start of the period is marked by the major Triassic – Jurassic extinction event. However, the end of the Jurassic Period did not witness any major extinction event. The start and end of the period are defined by carefully selected locations.
The Jurassic Period is the most famous period for dinosaurs and this is partly thanks to author Michael Crichton and Steven Spielberg’s for the book and film Jurassic Park which came out in 1993.
What did the Earth look like 150 million years ago?

What the Earth looked like: Image source

Those species that survived the Triassic period went on to flourish in the Jurassic period as the climate changed from hot and dry to subtropical and humid conditions where deserts were replaced by rainforests.
Conditions back then were possibly 5 to 10 degrees Celsius warmer than now, there were forests of plantations near where the poles are, oceans were around 8 degrees warmer, and there were warm and cold climates. With rain forests spreading, this meant life forms were evolving and so the Jurassic period was a time in the earth’s history when some of the greatest ever species lived.
You will see that the earth looked very different back then with Africa being attached to America, and even Australia being attached to India. These continents were breaking up and water was filling into the gaps which brought new coastlines and life. Of course, this was happening over millions of years.

Lower Jurassic Period – 201 -174 Million Years Ago

The Lower Jurassic is the earliest of 3 time scales of the Jurassic period. The dinosaurs have attained dominance, while most of the other Triassic species of animals have died out in two major Triassic extinctions – the mid-Carnian and the terminal Rhaetic. Apart from one or two early species, the dinosaurs seem to have been unaffected by these extinction events.

As the Jurassic Period opened, Italy, Greece, Turkey and Iran were attached to the North African portion of Gondwanaland. The supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern-supercontinent Gondwana. The climate was warmer and moister than during the Triassic. Reptiles were the dominant form of animal life and experienced a great adaptive radiation. 

In the oceans various types of ichthyosaurs and plesiosaurs evolved. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart. The Tethys Sea closed and the Neotethys basin appeared. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed.

In the air the pterosaurs began to diversify. On land many Triassic dinosaurs (prosauropod herbivores and coelophysid carnivores) continued, while a number of new forms (giant sauropods and armoured scelidosaurs) evolved. Under the feet of the dinosaurs rodent-like tritylodontid Therapsids co-existed with primitive shrew-like mammals and lizard-like sphenodont reptiles. Crocodiles also appeared, but they were mostly aquatic forms.

During the early Jurassic, evolution seems to have polarised, firstly, there were the ruling land animals, the great dinosaurs, which filled the ecological roles now taken up by medium-sized and large mammals. Secondly, the first mammals had appeared and together with the tritylodont therapsids they filled the small rodent and insectivore niche. The mammals were to remain small and individually insignificant – comparable to shrews, mice and rats of today – although doubtless very significant ecologically, for the 135 million years of the dinosaurs reign.

Middle Jurassic Period – 180-154 Million Years Ago

The Middle Jurassic, called the Dogger in the European system of classification, is the second epoch of the Jurassic Period lasting 180-154 million years ago. The second of the three divisions that make up the Mesozoic era saw warm tropical greenhouse conditions world wide, shallow continental seas, the break-up of Pangea, cosmopolitan flora and fauna, and the triumph of the majestic dinosaurs and the great sea reptiles.

MiddleJurassicMap

Paleos, CC0, via Wikimedia Commons

During the Jurassic the extent of the oceans was far more widespread then they had been in the Triassic. The Jurassic sea level rose and flooded large portions of the continents. During this time, marine life including ammonites and bivalves flourished and new types of dinosaurs evolved on land including Cetiosaurs, brachiosaurs, megalosaurs and hypsilophodonts.

Crocodiles were abundant and diverse, and included marine, semi-aquatic and even a few small lizard-like terrestrial forms. In the seas, Ichthyosaurs, although common, are reduced in diversity, while the top marine predators, the pliosaurs, grew to the size of killer whales and larger such as ferocious Liopleurodons. Modern shark groups also began to appear. The gigantic Leedsichthys, a huge, scaleless filter feeder who reached 10 or even 30 metres in length filled the same ecological role as modern baleen whales.

On land gymnosperm plants were well represented. The superficially palm-like Cycadophyta (Cycads) were so abundant and diverse that the Jurassic period could well be called ‘the Age of Cycads’. Some cycads were tall palm-like trees with rough branches marked by leaf scars, and pinnate (fern-like) leaf fronds. Other, unrelated forms, the equatorial flowering Bennettitales, were the most important group of shrubby trees, with short and stubby with squat bulbous trunks from the top of which the fronds grew. Conifers continued to be the most diverse large trees. The Middle Jurassic period was split into four sub divisions:

Aalenian – a subdivision of the Middle Jurassic epoch of the geologic timescale that extends from about 175.6 million years ago to about 171.6 million years ago.

Bajocian – this lasted from approximately 171.6 million years ago to around 167.7 million years ago.

Bathonian – this lasted from approximately 167.7 million years ago to around 164.7 million years ago.

Callovian – occurring from 164.7 to 161.2 million years ago.

It is the last stage of the Middle Jurassic. The stage takes its name from an old spelling of Kellaways Bridge, 3 kilometres north-east of Chippenham in Wiltshire in England. The name Jurassic comes from the Jura Mountains on the border of France and Switzerland, where rocks of this age were first studied. In 1795 Alexander von Humbolt described massive limestone formations of the Jura Mountains in Switzerland as the Calcaire de Jura. In 1839 Leopold von Buch formally named the rocks described by von Humbolt as the Jurassic System, the term has come into general use since.

Upper Jurassic Period – 180-154 Million Years Ago

Upper Jurassic (also known as Malm) was an epoch of the Jurassic geologic period. It lasted from 161.2 million years ago to 145.5 million years ago. It is divided into 3 ages:

Tithonian – The Tithonian is the final stage of the Late Jurassic Epoch. It spans the time between 150.8 million years ago and 145.5 million years ago. It is followed by the Berriasian stage of the Early Cretaceous Epoch. Kimmeridgian – The Kimmeridgian is a stage of the Late Jurassic Epoch. It spans the time between 155.7 million years ago and 150.8 million years ago. The stage takes its name from the town of Kimmeridge on the Dorset coast, England. The beach at Kimmeridge Bay is a good place for looking for fossils — there are specimens on the beach washed in by the tide. The Kimmeridge Clay formation is the source for about 95% of the petroleum in the North Sea. Oxfordian – The Oxfordian stage is the first stage of the Late Jurassic Epoch. It spans the time between 161.2 million years ago and 155.7 million years ago. The stage takes its name from the city of Oxford in England.

Opening_of_western_Indian_Ocean_150_Ma

Fama Clamosa, CC BY-SA 4.0, via Wikimedia Commons

Very early birds

The late Jurassic period sees the evolution of some of the greatest dinosaurs of all. The sauropods continue to flourish and to diversify, as the older Mid-Jurassic cetiosaurids are replaced by a diverse Late Jurassic fauna of Camarasaurs, Brachiosaurs and Diplodocids.

Some of these creatures attained tremendous size. The giraffe-like Brachiosaurus reached 22 metres and weighed 15 tons and more. The Seismosaurus, a more slender dinosaur, exceeded 40 metres in length. More modest sized dinosaurs appeared such as Scelidosauridae, Stegosauridae and the camptosaurid iguanodonts.

Along with the giant herbivores there were also the small fleet-footed ‘fabrosaurs’, scutellosaurs and hypsilophodontids, the ‘gazelles’ of the dinosaur world. These plant eaters were kept in check by a variety of carnivorous (theropod) dinosaurs, including small lightly built coelophysids, compsognathids and ornitholestids, and larger (from several hundred kilos to several tons in weight) dilophosaurids, Ceratosauria, Torvosauroidea and Allosauridae.

In addition there were many other types of animals around at this time: a number of different types of mammals, crocodiles, turtles, lizards, frogs, flying reptiles (Pterosaurs), marine reptiles and the first birds (Archaeopteryx).

Plants and Insects

With the influx of water coming inland brought about a change of climate going from hot and dry, to tropical and humid conditions. Conifers and ferns were among the plants that spread and dominated large areas which in turn brought more life and made new areas of the earth vibrant in life.

Large dinosaurs such as sauropods needed these plants to survive and a 10 ton / 10,000kg Diplodocus probably needed to consume 33kg of ferns and plantation to survive, which means each year it would consume well over its own body weight in food. While vegetation was fighting for space to get sunlight it meant they were growing and growing, but meanwhile so were the Sauropods.

By the end of the Jurassic Period areas would have been completely changed from the previous Triassic Period and become unrecognisable. It was over the space of 54 million years which is hard to comprehend when the average human lives for ‘just’ 72 years.

Diplodocus

Sea life

As the slow break up of the continents occurred, these warm sea filled gaps became full of diverse and abundant life. There were coral reefs growing in warm waters where snails, sponges, and many other small sea life evolved. Like every period the predators also evolved and at the very top there were Ichthyosaurs, plesiosaurs, crocodiles, sharks and rays.

Ichthyosaurs for example, were in the seas for almost the entire Mesozoic Era (251 million to 65.5 million years ago) but they were most diverse in Triassic and Jurassic periods. They were distant relatives of snakes and lizards and were well equipped aquatic reptiles which is why they survived for such a long period of time.

Plesiosaurs are another example of a sea life reptile that survived for the entire Jurassic period, and these were long necked marine reptiles that lived in seas around the world due to them being very strong swimmers.

Like Ichthyosaurs these were not dinosaurs as they just so happen to live alongside and interestingly Plesiosaur necks made up around half of their overall body.

The Dinosaurs

Dinosaurs can be split into two groups, the saurischians, and the ornithischians. This was based on their hip structure, with the saurischians being lizard-hipped, and the ornithischians being bird-hipped.

Saurischians

Sauropods were saurischians and first appeared in the early Jurassic period. By Late Jurassic they were well spread, and at their peak in regards to the number of different sauropods. Some were the biggest living animals known to have been on earth such as Brachiosaurus, and Diplodocus which was up to 24 meters / 43 feet in length and weighed up to 20 tons.

Sauropods were herbivorous dinosaurs and they evolved becoming bigger and bigger due to the lush vegetation of their surroundings. Their long necks were needed to reach areas no other dinosaurs could reach which meant they could consume vast quantities of untouched tree tops with devastating effect.

Also during Jurassic Periods the carnivorous saurischians evolved called theropods. These dinosaurs were some of the world’s fiercest ever predators and it was Mid Jurassic when they first evolved and then they became head of food chains globally.

One such example is Allosaurus which lived 155 – 145 million years ago and grew up to 13 meters / 43 feet in length. Allosaurus like many theropods was not only an active predator, hunting other dinosaurs, but it was also a scavenger and would have fed on whatever it could.

Allosaurus

Fred Wierum, CC BY-SA 4.0, via Wikimedia Commons

Ornithischians

Ornithischians such as Stegosaurus were all herbivorous dinosaurs and evolved to have heavy armour, plates, horns, and spikes.

Scientists believe this was to protect themselves from the predatory theropods that were actively hunting while both sets of dinosaurs were evolving in similar global locations. 

Minor mass extinction event

By the end of the Jurassic Period there was another mass extinction (roughly 190-183 million years ago) in which more than 80% of marine bivalve species and many other shallow-water species died out, but this was nowhere near as fatal as the one at the end of the Triassic Period.

Stegosaurus

DataBase Center for Life Science (DBCLS), CC BY 4.0, via Wikimedia Commons

Relatively little is known about this extinction as very few hypotheses have been made, but we know it severely affected ammonoids, marine reptiles, and bivalves.

The cause of this extinction is unknown, but there is some speculation that it was triggered by the release of huge methane deposits from within the Earth (these deposits formed beneath the seabed as surface algae dies and sinks to the sea floor).

Cretaceous Period: 145 to 66 million years ago

The last period in the Mesozoic Era is the Cretaceous Period which was also the longest and lasted over 79 million years. It was a period of time that lasted longer than dinosaurs have been extinct (66 million years) which demonstrates the length of time this period represents in the history of our planet.

Lower Cretaceous Period – 98-66 Million Years Ago

The Early Cretaceous or the Lower Cretaceous, is the earlier of the 2 major divisions of the Cretaceous Period. It began about 146 million years ago. During this time many new types of dinosaurs appeared or came into prominence, including the Giganotosaurus, Spinosaurs, Utahraptor and Coelurosaurs, while other survivors from the Late Jurassic continued.

By the beginning of the Cretaceous Period the earth was in two continents, North America had begun pulling away, South America had started to split from Africa. 

What the earth looked like in the Cretaceous Period.

What the Earth looked like: Image source

India, Antarctica, and Australia were also separating off and by the end of this period most of our present day continents were all separated out and the modern world was taking shape. Antarctica and Australia were still connected, and India was isolated in the Indian ocean.

The climate in the Cretaceous Period was warmer than we know the planet to be today, it was also more humid and life was rife on the polar regions and free of ice sheets. They were back then covered in forests and home to dinosaurs and other species of life. Temperatures peaked in the Mid Cretaceous but even by the end of the period it was still warmer than it is in modern times. 

Sea levels during this period were higher than at any time in the history of our planet. The percentage of land that covered the earth’s surface was around 18% and if we compare that to a modern day percentage of 28% it shows the considerable difference. In the seas, the ichthyosaurs declined and eventually died out at the start of the Late Cretaceous. Neognathous birds and angiosperms, appear for the first time. The Lower to Early Cretaceous Period was sub divided into 6 sub periods:

Berriasian – In the geologic timescale, Berriasian is a stage of the Early Cretaceous epoch. It spanned between 145.5 million years ago and 140.2 million years ago. The Berriasian stage succeeds the Tithonian stage of the Late Jurassic epoch and precedes the Valanginian stage of the Early Cretaceous epoch.

Valanginian – In the geologic timescale, Valanginian is a stage of the Early Cretaceous epoch. It spanned between 140.2 million years ago and 136.4 million years ago. The Valanginian stage succeeds the Berriasian stage of the Early Cretaceous and precedes the Hauterivian stage of the Early Cretaceous.

Hauterivian – The Hauterivian is a stage of the Early Cretaceous Epoch. It spans the time between 136.4 million years ago and 130 million years ago.

Barremian – The Barremian faunal stage was a period of geological time between 130 million years ago and 125 million years ago. It is considered to be of the early Cretaceous period.

Aptian – Aptian stage is a faunal stage of the Early Cretaceous epoch in the geologic timescale, that extends from 125 million years ago to 112 million years ago, approximately. The Aptian stage succeeds the Barremian stage and precedes the Albian stage, all in the same epoch.

Albian – Albian is a stage of the Cretaceous period. Albian is a term proposed in 1842 by A. d’Orbigny for that stage of the Cretaceous system which comes above (later) the Aptian and below (before) the Cenomanian. Approximate time range is 112.0 million years ago to 99.6 million years ago. The following representatives of the Albian stage are worthy of notice: the gaize and phosphatic beds of Argonne and Bray in France; the Flammenmergel of North Germany; the lignites of Iltrillas in Spain; the Upper Sandstones of Nubia, and the Fredericksburg beds of North America.

Upper Cretaceous Period – 146 – 66 Million Years Ago

Upper Cretaceous refers to the second half of the Cretaceous Period, named after the famous white chalk cliffs of southern England, which date from this time. Rocks deposited during the Upper Cretaceous Period are referred to as the Upper Cretaceous Series.

This was a period of great success for dinosaurs, with many new types appearing and diversifying, such as the Tyrannosaurs Rex, duck bills, Ankylosauridae and horned dinosaurs in Asia-america (Western North America and eastern Asia), and Titanosaurs and Abelisaurs in Gondwana.

Birds became increasingly common and diverse, replacing the pterosaurs which retreated to increasingly specialised ecological niches. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and giant-penguin-like polycotylid pliosaurs (3 metres long) and huge long-necked elasmosaurs (13 metres long) also diversified. These predators fed on the numerous teleost fishes, which in turn evolved into new advanced and modern forms (Neoteleostei).

Near the end of the Cretaceous Period, flowering plants diversified and didelphid marsupials and primitive placental mammals also became common. The late Cretaceous period was divided into 6 sub periods:

Cenomanian – The Cenomanian (also known as Woodbinian) is the first stage of the Late Cretaceous Epoch. It spans the time between 99.6 million years ago and 93.5 million years ago.

Turonian – The Turonian is a stage of the Late Cretaceous Epoch. It spans the time between 93.5 million years ago and 89.3 million years ago.

Coniacian – The Coniacian is a stage of the Upper Cretaceous Epoch. It spans the time between 89.3 million years ago and 85.8 million years ago.

Santonian – The Santonian is a stage of the Upper Cretaceous Epoch. It spans the time between 85.8 million years ago and 83.5 million years ago.

Campanian – The Campanian is a stage on the geologic time scale occurring from 83.5 million years ago to 70.6 million years ago.

Maastrichtian -The Maastrichtian is the last stage of the Cretaceous period, and therefore of the Mesozoic era. It spanned from 70.6 million years ago to 64.9 million years ago. The Maastrichtian is named after the Dutch city Maastricht.

Plants and insects

With the warmer and increased humid environment along with the breakup of continents and the gaps being filled by shallow seas, this period of time brought about an increase of plants and insects. Conifers and ferns were continuing to replace once harsh environments of deserted land and along with them many other plants such as angiosperms.

An important species evolved in the form of the eusocial bee which helped the evolution of the flowering plants such as angiosperms. Other insects that we know began to diversify were ants, butterflies and grasshoppers.

Sea life

The seas were warm and scientists have stated that the surface temperatures could have ranged between 27°C to 37°C.

They became full of life with modern sharks, rays, and teleosts (fish). Other marine reptiles like the long-necked plesiosaurs and ichthyosaurs also were around in this period.

Turtles emerged during the Cretaceous Period and by 120 million years ago they became very similar to the modern day turtles. The largest turtle was 4.5 meters (15 feet) in length and was one of the biggest in history. 

The Dinosaurs

During the Cretaceous Period the dominant groups changed, and many types of dinosaurs evolved. The Sauropods for example were densely populated in the Southern continents but did not migrate in mass to the North as far as we are aware.

Sauropods were some of the biggest animals there have ever been on earth, for example the Argentinosaurus was of a size that is difficult to imagine. It was over 35 meters (114 feet) in length, had a height of over 21 meters (70 feet), and weighed over 70 ton’s (70,000 kg).

Argentinosaurus

Nobu Tamura (http://spinops.blogspot.com), CC BY 3.0, via Wikimedia Commons

The amount of vegetation this herbivorous needed to consume on a daily basis to keep it well fed was staggering, studies have ranged that it needed 500 to 850kg of plantation every single day. That’s nearly a year’s food consumption of an average human, but given the difference in size that is hardly surprising.

Ornithopod dinosaurs dominated the North American landscape and during Cretaceous they became one of the most successful groups of herbivores whose members were spread to every continent back then.

An example of an Ornithopod dinosaur was the Iguanodon. This dinosaur lived between 126 and 122 million years ago and was present throughout what is now Europe.

Iguanodon

Nobu Tamura email:nobu.tamura@yahoo.com http://spinops.blogspot.com/, CC BY-SA 4.0, via Wikimedia Commons

Alpha predators of the Cretaceous Period

We can not talk about this period and not mention the alpha predators that dominated the areas they lived in.

Firstly the Tyrannosaurus Rex (T-Rex) was one of the last known members of the tyrannosaurids and lived 68 – 66 million years ago.

T-Rex was one of the most ferocious predators ever to have been on earth and was at the very top of the food chain having been one of the largest carnivores of all time. It hunted other dinosaurs at the time and armoured herbivores such as Ankylosaurs and Ceratopsians needed all the protection they had to stop the Tyrannosaurus from preying on them.

The jaws of the T-Rex were known to have been some of the most powerful ever of any terrestrial animal that has lived.

Tyrannosaurus rex

Spinosaurus was another predator that lived during the Cretaceous period and as the image shows it was even bigger than Tyrannosaurus Rex, and Giganotosaurus, and is a contender for being the largest and longest theropod dinosaur.

Fossils of Spinosaurus have been found in North Africa where it was believed to have roamed the swamps and scientists believe the Sahara desert has many Spinosaurus fossils but due to the harsh conditions, it would make them very hard to unearth.

The end of the Cretaceous Period

The breakup of the supercontinent Pangaea into separate continents was underway. The separation of Laurasia and Gondwana was complete. In the first half of the Cretaceous, temperatures were warm, seasonality was low, and global sea levels were high (no polar ice). At the end of the Cretaceous, there were severe climate changes, lowered sea levels, and high volcanic activity. The Cretaceous period ended 65 million years ago with the extinction of the dinosaurs and many, many other prehistoric life forms.

There were two theories on why this happened, the first was a volcanic eruption, the second was an asteroid strike. Click here to discover more on how dinosaurs died out.

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Last Updated on 12/07/2021 by admin