How Long Ago Were Dinosaurs Alive? Amazing Facts & Figures

Uncover the age of dinosaurs and their tenure on Earth…

When Did Dinosaurs Exist?

The first dinosaurs emerged approximately 245 million years ago, and they dominated the Earth until their extinction about 66 million years ago. This period, spanning 179 million years, is vastly longer than the time humans have inhabited the Earth. Dinosaurs have been extinct for over 200 times the entire length of human existence.

Humanity made its first appearance about 315,000 years ago. This implies that dinosaurs had already been extinct for roughly 65.685 million years when the first humans showed up.

The onset of human existence occurred about 244.685 million years after the first dinosaurs made their appearance.

Continue below for more fascinating facts about dinosaurs…

Did Dinosaurs Truly Go Extinct?

Suchomimus Dinosaurs

In modern scientific understanding, birds are considered descendants of dinosaurs, suggesting that dinosaurs, in a sense, are still with us, contradicting their supposed extinction 66 million years ago.

For the purpose of this page, our references to dinosaurs are specifically about “non-avian dinosaurs”, those dinosaurs that did not evolve into birds.

How Triumphantly Did Dinosaurs Survive?

Dinosaurs were an incredibly prosperous group of animals, having existed from around 245 million years ago until now.

Contrary to what many believe, dinosaurs were not evolutionary failures. Despite the non-avian dinosaurs becoming extinct about 66 million years ago, they dominated the land for about 179 million years. In this span, they evolved into a wide variety of roles, from apex predators like the T. Rex to herbivores like the Parasaurolophus.

Indeed, the total duration dinosaurs (excluding birds) were alive is about 568 times longer than humans have been in existence (so far).

Had it not been for a colossal asteroid strike around 66 million years ago, dinosaurs might still be with us, and humans might never have evolved!

Despite this, dinosaurs continue to exist (as birds), signifying that they have a longer history than mammals.

Hence, rather than being evolutionary failures, dinosaurs are an emblem of evolutionary success!

The Mesozoic Era: The Reign Of Reptiles

The Mesozoic Era, during which dinosaurs existed, is part of the geologic timescale – the tool used by geologists to chronicle Earth’s history.

(The geologic timescale is constructed based on layers of rock formed at specific points in Earth’s history. More information can be found here: Geologic Timescale Facts)

Throughout the Mesozoic Era, reptiles, including dinosaurs, were the principal vertebrate animals on land, in the air, and in the sea. Consequently, the Mesozoic Era is also called the “Age of Reptiles”.

The Mesozoic Era is divided into three periods: Triassic, Jurassic, and Cretaceous. The lengths of each of these periods can be seen in the following table:

  • The Mesozoic Era as a whole started 251.902 million years ago and ended 66 million years ago. Total duration: 185.9 million years.
  • The Triassic Period started 251.902 million years ago and ended 201.3 million years ago. Total duration: 50.6 million years.
  • The Jurassic Period started 201.3 million years ago and ended 145 million years ago. Total duration: 56.3 million years.
  • The Cretaceous Period started 145.0 million years ago and ended 66 million years ago. Total duration: 79 million years.

What Was Happening On Earth During The Age Of Dinosaurs?

The time when dinosaurs roamed the Earth was marked by considerable transformation.

Initially, a supercontinent known as Pangaea ruled the planet.

The world was remarkably different back then compared to today. The sound of birdsong was absent, mammals had yet to emerge, grasslands were nonexistent, and flowers had yet to bloom. These organisms were all awaiting their evolutionary debut.

Fast forward approximately 185 million years, just before the extinction of dinosaurs, and you would find the Earth somewhat more recognizable. By this time, Pangaea had split into the continents we recognize today. Birds had evolved, small mammals were darting about, grass covered the land, and flowers were in bloom, being pollinated by bees.

However, even with this more familiar setting, the presence of dinosaurs on land, pterosaurs in the sky, and mosasaurs and plesiosaurs in the seas would still render Earth unrecognizable to human observers.

Catastrophic Extinction Events

Earth has been through five significant extinction events. The most well-known is the Cretaceous-Paleogene Extinction Event (also known as the ‘K/T extinction event’) that caused the demise of the dinosaurs (along with many other animals and plants) 66 million years ago.

Interestingly, the Cretaceous-Paleogene Extinction Event wasn’t the most severe mass extinction Earth has ever experienced.

The title of the most catastrophic extinction event goes to the Permian-Triassic Extinction Event, often referred to as the “Great Dying”. During this cataclysmic period, an estimated 90% of all life on Earth was eradicated.

The Triassic Period: The Struggle for Dominance

At the dawn of the Triassic Period, well before dinosaurs came to be, the Earth was recovering from the Permian-Triassic Extinction Event.

With the extinction of most land animals, the remaining animal groups battled for supremacy in the vacant niches.

The primary groups of terrestrial vertebrates were the therapsids and archosaurs.

Therapsids included the precursors of mammals, while the archosaurs were a group of reptiles that included the progenitors of dinosaurs.

The archosaurs then split into two main branches: Pseudosuchia and Dinosauria (dinosaurs).

During the Triassic Period, the dominant land predators were not dinosaurs but pseudosuchians.

Large carnivorous pseudosuchians, such as the 13ft. / 4 m long Postosuchus, were the apex predators of the Late Triassic Period.

The Triassic-Jurassic Extinction Event and The Ascendance of Dinosaurs

Around 50 million years after the Permian-Triassic Extinction Event, Earth was struck by another mass extinction.

The Triassic-Jurassic extinction event, which occurred about 201.3 million years ago, also known as the ‘Tr-J extinction event’ or the ‘end-Triassic Extinction’, led to the extinction of most of the pseudosuchians.

With their chief rivals eliminated, dinosaurs ascended to become the dominant land animals during the Jurassic Period.

What became of the pseudosuchians? Some survived, but the group would never reclaim the prominence they had during the Triassic Period.

Today, the only extant pseudosuchians are the crocodilians: creatures such as crocodiles, alligators, and caimans.

The probable cause of the Triassic-Jurassic Extinction Event was sustained volcanic activity in what we now know as the Central Atlantic magmatic province (CAMP).

An alternative cause could have been an asteroid impact similar to the one that led to the Cretaceous – Paleogene Extinction Event and the extinction of the dinosaurs.

Regardless of the cause, the Jurassic landscape was primed for a new ruling group of animals: the dinosaurs!

The dinosaurs would proceed to reign as the dominant land creatures throughout the Jurassic and Cretaceous Periods.

The Cretaceous-Paleocene Extinction Event

The protracted dominance of dinosaurs was ultimately brought to an abrupt halt by the Cretaceous-Paleocene Extinction Event. However, their legacy lived on in the form of birds, a group of animals that continues to flourish today, across every continent on Earth!

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