Extinct Animals: Facts & Causes

Instructor: Taormina Lepore

Taormina has taught advanced high school biology, is a science museum educator, and has a Master's degree in museum paleontology.

In the course of Earth's history, many animals have become extinct. In this lesson we'll learn about a few major examples of extinct animals, and the causes for their extinction.

The End Of The Road

Earth is a pretty volatile place. Animals and other organisms fight a daily battle to survive, both individually and as whole populations. Sometimes they just don't win that battle, and when an entire group or species of organisms completely dies out, we say that they have become extinct.

Extinction has thrown a wrench in animal evolution many times over the course of Earth's history, but it makes sense! If no species had ever gone extinct, we would have a very crowded planet with no room for expansion and adaptation. In the battle to survive, some animal species find ways to adapt and this helps them gain an evolutionary edge and avoid extinction.

But other animals are not so lucky. Thanks in part to natural extinction and the folly of humankind, many fascinating and unique animals have been eradicated from the planet altogether. Let's take a look at some examples of extinct animals, discuss a few facts about them, and review the causes of their demise.

Natural Extinctions

Natural extinction is a sad but inevitable fact, and one that sometimes plays out dramatically. Natural extinctions have happened throughout Earth's history--sometimes via a natural catastrophe that wipes out whole groups of organisms (think dinosaurs). Other natural extinctions happen very slowly, as natural selection favors survivors with helpful adaptations. Natural selection is the selective process that leads to species developing new physical or behavioral traits that can give them the edge to survive.

Here we'll look at two of the most famous examples of natural extinction: the trilobites and the dinosaurs.


The trident-headed trilobite Walliserops trifurcatus

If you've ever seen a spider or a horseshoe crab, you've observed a distant cousin to one of the most diverse and successful animal groups ever to have lived: the trilobites. Trilobites got their name from having three (tri-) lobes, and although they look like insects, they're a group all on their own.

Trilobites were aquatic animals with a tough, protective exoskeleton, or exterior shell, surrounding their soft insides. They scuttled around the ancient oceans from 521 million years ago to the end of the Permian Period, just before the age of dinosaurs, about 250 million years ago. While many trilobites came and went throughout their long history, all of the trilobites became extinct at the end of the Permian. We call it the 'great dying' --and it really was catastrophic. The Earth's most devastating bout of climate change decimated almost all life on Earth. It's no wonder the last of these little guys kicked the bucket.


The feathered dinosaur Microraptor gui
microraptor gui

Who doesn't love dinosaurs? These hugely diverse and successful reptilian animals enjoyed a reign of almost 200 million years, across almost all of the Mesozoic Era, 230 to 66 million years ago. Most readers will be familiar with the extinction event at the end of the Cretaceous Period, around 66 million years ago, which killed off almost all of the dinosaurs. Humans and dinosaurs are therefore separated by more than 60 million years.

The current consensus is that an asteroid or meteorite struck the Earth, and the resulting cloud of dust and debris enveloped the atmosphere in a sunlight-blocking shroud. Several other animals became extinct at this period, which we call the K-Pg or K-T boundary, short for Cretaceous-Paleogene or Cretaceous-Tertiary. Of course, many avian dinosaurs still live on in the form of birds.

Human-Caused Extinctions

Even more cringe-worthy than the loss of animal species by natural causes are the extinctions that humans have caused. These animals were once abundant but were killed off by humans for food, from fear, or simply because of a lack of understanding. By learning about more about the motivations behind human-driven extinctions, we can learn how to protect the animal species we have today.

Dodo Birds

The skeleton and a reconstruction of the dodo

The dodo was a large bird related to the pigeon and it lived on the island of Mauritius in the Indian Ocean. Unfortunately when European sailors reached Mauritius in the late 1500s and early 1600s, they saw the dodo as a slow and easily caught food source. The introduction of foreign animals to Mauritius and destruction of habitat were huge detriments to the dodo.

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