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What Was There Before Dinosaurs? Details Explained!

People of all ages have been fascinated by dinosaurs. The enormous, frightening creatures capture imaginations and have probably haunted some nightmares. But have you ever pondered what came before the dinosaurs? When the sun rose in those long-gone years, were there other animals that roamed the earth?  If so, what was their appearance like, what kind of animal were they, and what happened to them? 

In the time before dinosaurs, there were organisms like bacteria, algae, and amoeba. There were fish, sharks, horseshoe crabs, lobsters, duck-billed platypus, and echidna that developed before dinosaurs. Therapsids (a form of mammals) dominated a portion of the period before the dinosaurs. 

In this article, we will explore the age before dinosaurs. We’ll look at what was happening on the earth and what creatures were living and roaming our planet before dinosaurs came along…

The History Of The Earth

To understand what came before dinosaurs, we need to understand the history of the earth. The earth’s history can be divided into different periods, and there were differing life forms on earth during those periods. Some people ask how scientists can ascertain the age of an item or know the age of fossils because there is no written history to indicate what earth was like in these times. 

A technique called radiocarbon dating is used by scientists to determine the age of items. It can be used on wood, fabrics, paper, charcoal, fossils, and shells. Radiocarbon dating measures the quantity of carbon-14 and nitrogen-14 isotopes in materials. Radioactive carbon-14 decays to form nitrogen-14.

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Determining the ratio between the number of carbon-14 isotopes and nitrogen-14 isotopes gives an estimate of the material’s age. Potassium-40 decays to form argon-40, which scientists may also use in calculations of the age of an item.

Many of the theories regarding the early history of the earth are educated guesses. They cannot explain everything in exact detail, but there is enough evidence to allow for speculation. 

The Time Periods Of Earth

The time periods of the earth are given names. They are measured in millions of years, with a unit of time called megaanni. Let’s take a deeper dive into what they were so we can get a good picture of the history of the Earth…

Hadean Eon

The Hadean Eon is also known as the Precambrian Supereon or the Cryptic Era. During this time, scientists postulate that the protoplanet earth collided with another protoplanet which scientists have named Theia. The resulting dust and rocks were thrown into the orbit of the earth and formed rings around the earth similar to Saturn’s rings.

After a few million years (nobody is sure exactly how long), the dust and rocks merged to form the moon, which orbited the earth. During this time, the world was covered with an ocean of magma. There was still a lot of dust and gas in the atmosphere due to the interplanetary collision. A solar wind developed, which blew away the dust and gas debris from the earth and the moon.

Eoarchian Era

The Eoarchian era is marked by the development of tectonic plates in the earth’s crust. Mountains and metamorphic rock were formed during this time.

Paleoarchian Era

Mountains and minerals continued forming during the Paleoarchian era. At this stage, it was believed the only life on earth was bacteria. During this time, it was thought that the earth was still being bombarded by asteroids. The atmosphere’s oxygen content began to increase slowly, and bacteria that could not cope with the high levels of oxygen began to die off.

During the Paleoarchian era, the moon was still very close to the earth and caused huge tides of one thousand feet (three hundred and five meters) high. Hurricane-force winds blasted through the world, and evolutionary processes began. 

Neoarchean Era.

During the Neoarchian era, geological formations continued to form on earth—the first known super-volcano developed around present-day Ontario and Quebec.  Reefs were created in the oceans, and oxygen increased substantially in the earth’s atmosphere. 

Paleoproterozoic Era

The Paleoproterozoic era is divided into four different periods, but we will not delve into them for ease of understanding. During the early years of the Paleoproterozoic era, the Great Oxygenation Event occurred, and the earth’s atmosphere mainly became oxygen.

Anoxic (cannot live in the presence of oxygen) bacteria became extinct, and scientists feel this was the first extinction event on earth. This era saw a lot of tectonic plate shifting and the development of geological structures in the earth’s crust. 

Mesoproterozoic Era

Blue-green algae was developed during the Mesoproterozoic Era

The Mesoproterozoic Era was characterized by the deposition of metals such as silver, copper, and zinc. Eukaryotes (single or multiple cell life forms that contain DNA enclosed in a nucleus) and blue-green algae developed during this era. Meiosis and sexual reproduction occurred in eukaryotes for the first time. 

Neoproterozoic Era

Protozoans like Paramecium, Amoebas, and Melanocyrillium evolved during this time. The first animal cells differentiated from plants, and the animal cells began feeding on plants – this was the development of the first herbivores. During this era, the earth froze over at least three times, and this stunted evolutionary development. It is thought that fungi, worms, and small bilaterally symmetrical animals developed during this time. 

Paleozoic Era.

Complex life forms began developing during the Paleozoic era. These included fish, arthropods, mollusks, and echinoderms. During this period, plants and animals began living on the land for the first time, and so the first air-breathing animals were seen. Sharks, horseshoe crabs, and starfish evolved in the oceans during this period.

This era is divided into several periods, but the first two will not be commented on here. The third period is the Silurian period. During this period, ray-finned fish were seen in the ocean, and scorpions developed on land. Fish with teeth and nautiloids evolved. Nautiloids are marine mollusks such as octopus, squids, snails, and slugs.

Devonian Period

At the beginning of the Devonian period, insects began developing. A jawless fish with bony armor known as the Cephalaspis was seen in freshwater systems. Crabs and ferns became common, and large sharks, hagfish, and ratfish evolved. 

Carboniferous Period

The climate during this period was thought to be tropical, with minor divisions between seasons. Meganeura (giant dragonflies) with wingspans of twenty-five to twenty-seven inches could be seen in the skies during the Carboniferous period.

During this time, amphibians began to diversify, and reptiles evolved into a more modern lizard-type body plan with a backbone, allowing them to live and move on land. You can click here to see a picture of reptiles from that time. For the first time, reptiles began to lay amniotic eggs on land. Animal life diverged into three groups: 

  • Synapsids: which had one hole in the skull and evolved into mammals and mammal-like reptiles. These animals are now referred to as stem mammals or protomammals. Synapsids were vertebrates that lived on land. Synapsids did not evolve into reptiles but rather all developed in mammals. Some common synapsids were Archeothyris and Clepsydrops.
  • Anapsids: which had no holes in their skulls and died out. Some scientists argue that turtles are representatives of anapsids, but this point is contentious in the scientific world.
  • Diapsids: had two holes in their skulls and evolved to form primitive reptiles, which then experienced further evolution and were divided into two subgroups: birds and dinosaurs. 

During this period, coal was first formed

Permian Period

During the Permian period, approximately 360 million years ago, all the continents existed as one large landmass known as Pangea. Plants began to diversify, and the first cycads evolved.  Synapsids underwent changes and became therapsids. 

Therapsids were classed as amniotes – their young were encased in amniotic membranes filled with amniotic fluid. They still resembled what we would think of as reptiles today, with small heads, four limbs situated under the body, and a hole on each side of the skull behind the eyes. Some of the therapsids had some fur, but this did not cover their whole bodies. 

One of the most important characteristics of therapsids was the appearance of earbuds. The complex multiple-boned jaws moved further back in their positioning on the head, and some of the bones in the jaws gave rise to three bones that formed the middle ear. Reptiles were always characterized by having only one bone in their ears.  

The Dimetrodon was a therapsid that was about five meters long and had a large sailor fin-like structure on its back. It is thought that the sail was used for thermoregulation as therapsids were not fully warm-blooded yet. During the Permian period, the mammals were increasing in dominance.

The largest of these was the Gorgonopsians, giant bear-like creatures characterized by heterodontics – different teeth specialized for various functions.  Therapsids were either herbivores or carnivores and could weigh less than a kilogram or more than a ton. A type of therapsid known as Cynodonts (dog-like teeth) showed social behavior. There is evidence that they hunted in packs. 

In the oceans, fish with a true bony skeleton developed. Sharks and rays continued to flourish, as did sponges and coral. On land, insects with adapted mouthparts developed. These included mouthparts for sucking and piercing. Other insects such as beetles, cockroaches, and cicadas developed.

Diapsids developed further into Sauropsids that diversified, giving rise to dinosaurs and birds. The dinosaurs during this period were few in number, small and insignificant.

The climate during the Permian period was similar to the variations seen in climates in the world today. The interior of Pangea was dry and arid, while coastal regions had high rainfall and abundant vegetation. The weather allowed for rapid evolutionary change, and animals began to occupy niches in the ecosystem, adapting to function optimally in that niche. An example of a niche may be insectivorous mammals that lived in trees. 

The Great Dying

Two hundred and fifty two million years ago the Permian era was brough to an end by a cataclysmic event causing mass extinction. This event divided the Paleozoic era from the Mesozoic era. Scientists are uncertain of the precise cause of this disaster but have several theories:

  • There is a possibility that earth was struck by a giant, unknown asteroid.
  • There is some evidence to suggest that current-day Siberia and China experienced massive volcanic eruptions with resulting extensive dust and ash clouds. The volcanic clouds would have caused an enormous drop in temperatures across the earth, resulting in glaciation in vast areas, known as a nuclear winter. Plants would have been unable to photosynthesize, which would have depleted food sources. The lack of food, together with high carbon dioxide levels in the ocean, caused ecosystems on both land and sea to collapse. 
  • Some scientists postulate that the ocean released vast amounts of methane which altered the atmosphere, making it difficult for life to survive. 
  • Another theory is that sea-level changed dramatically.
  • There was an increase in aridity. 

Recent scientific researchers feel that it was a combination of the above. Whatever the trigger was, the results were devastating for life on earth. Ninety-five percent of all marine species and seventy percent of land animals were obliterated. This is considered to have been the most severe and devastating mass extinction to have ever occurred on earth. 

Mesozoic Era

The Mesozoic era is sometimes described as the age of reptiles. The era is divided into periods that showed differing evolution of species. 

Triassic Period.

The Triassic period occurred between 252 – 201 million years ago. The Triassic period is an interesting period of the earth’s history as two mass extinction events bookended it. After the Great Dying, there was a period of a few million years where there were no coal stores laid down. Coal is formed when plant matter decays in peat. There were no plants to form coal due to the mass destruction of almost all plant species during the Great Dying.  

As the earth entered the Triassic period, ecosystems had to be re-established. Scientists estimate that it took the world about ten million years to recover after the Great Dying. The Triassic period was much drier than the Permian period, and plants and animals had to adapt to these new conditions.

The climate changed overtime during the Triassic period as the earth settled again after the cataclysmic Great Dying events. The interior of Pangea was still arid, but the coastal regions had monsoon-type rainy seasons. It was thought that the general temperature of the earth was much warmer, and there were no polar ice caps. 

Plants began to recover, and soon there were vast conifer forests populated with trees of up to thirty meters tall. The environment started to dry out, and the forests gave way to immense fern prairies. 

There were very few types of fish left in the ocean after the Great Dying. A sub-group of reptiles developed known as Icthyosauria that specialized in ocean living. Initially, they were lizard-like with four limbs, and they swam by moving their bodies from side to side. Later in the Triassic period, the Ichthyosaurs became more streamlined, and the forelimbs adapted to become fins.

At the same time, the hind legs diminished and became nothing more than vestigial limbs. The Ichthyosaurs snout lengthened and grew teeth to resemble modern-day dolphins, using their muscular tails to propel them through the water. Evidence indicates that they breathed air and gave birth to live young. Ichthyosaurs became the most dominant marine species, with some specimens reaching immense sizes. The Shonisaurus was one such giant, measuring approximately fifty feet (15 m) and weighing thirty tons. 


Although the Triassic period is known as the Age of Reptiles, the early Triassic period was dominated by the therapsids. Of note is one genus known as Lystrosaurs that seemed to have survived the Great Dying. The Lystrosaurs resembled heavy set pigs and had beaks with large tusk-like teeth. They were equipped with powerful forelimbs that were used for burrowing. Fossil evidence proposes that they were the most common terrestrial therapsids. As the Triassic age progressed, the therapsids became smaller, looking more like shrews, some with long necks.

The Gorgonops were therapsids that developed during the Triassic period. They are from the order Gorgonopsia that became the dominant land predators of their time. Some of them grew up to three meters in length. Gorgonops were medium-sized Gorgonopsia with two large sharp canines that could easily penetrate the hides of other animals.

They were also faster than their prey because their legs were placed under their bodies, allowing them to lift themselves off the land and run. Most of their prey had legs that came out the sides, which caused them to slither, making them much slower than the Gorgonops.  

The First True Mammals

By the mid to late Triassic period, some therapsids had developed into true mammals. Scientists think that the earliest mammals were Monotremes, similar to the duck-billed platypus and echidna. These mammals lay eggs and do not have nipples. They produce milk by sweating it out of their chests. Urination, defecation, and reproduction occur through the same orifice, hence the name monotreme. 


The Archosaurs were a class of reptiles that developed. They grew in dominance and soon became apex land predators. Their fossils are characterized by two openings on either side of the skull and teeth that are firmly fixed in the jawbones.  They are closely related to crocodiles, but their legs were fixed underneath them, giving them a more upright posture and movement than crocodiles. 

Amphibians dominated many geographical regions. Lissamphibians evolved -examples are frogs, salamanders, and caecilians. There were large amphibians such as the Temnospondyls that resembled our current-day crocodiles. They grew to about four meters in length. 


There were unusual animals that developed known as drepanosaurs. These reptiles were not lizards or dinosaurs. They had grasping hands similar to chameleons with a second finger that ended in a deadly claw. They had arched backs with thick muscular tails. Adam Pritchard from Yale University describes them as chameleon- anteater hybrids. The current thought is that the claw was used to pull open insect nests to feed on the insects and possibly their larvae. 

For pictures of some of the animals that existed during the Permian and Triassic eras, click here

Another Mass Extinction

Two hundred and one million years ago there were massive volcanic eruptions, earthquakes, and tectonic plate movement that brought about the end of the Triassic period. Pangea broke up into smaller continents. The volcanic activity resulted in the release of carbon dioxide and sulfur dioxide.

This caused acid rain that allowed the oceans to become acidic and oxygen in the atmosphere to become much reduced. This upheaval of the earth caused another mass extinction. More than three-quarters of all life on the planet was completely obliterated. Smaller, less specialized species were the only ones that survived. 

The Jurassic Period

The Jurassic period ushered in the era of the dinosaurs. Dinosaurs survived the mass extinction because they were small and had no specialized needs. After the mass extinction, the ecology was open ground for the development of species that had survived.

Dinosaurs were able to evolve quickly ( a process known as adaptive radiation) and become the dominant life form. Dinosaurs were able to fill many ecological niches and developed adaptations to assist them with this. So some became herbivores, some omnivores and some carnivores. They dominated the land, water, and skies during the Jurassic period. 


Much of what we know of the earth’s history is speculation on the part of scientists. We cannot know everything about the life forms that existed in those times, and all we have to go on are fossils that sometimes are not even complete. One thing is certain; many life forms existed before dinosaurs. The different life forms were not as clearly delineated as they are now, and there were strange mixes of creatures. The past lost in the mists of time will probably continue to surprise us when new fossil discoveries are made. 

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