Event 14

525 million years ago

Dunkleosteus and Cladoselache
Giant vertebrate fish. Artist’s reconstruction of Dunkleosteus, an enormous armored fish from the Devonian period (380 million years ago), about to attack a shark. Dunkleosteus was up to 33 meters long.
Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration is used with permission. All rights reserved.

Although vertebrates make up only about 5% of animals alive today, most of the animals we are familiar with today – that we see on a regular basis both domestic and wild – are vertebrates. We are vertebrates, along with fish, birds, amphibians, reptiles, and all of the other mammals. All vertebrates are based on the basic chordate body plan that emerged slightly earlier, but have the important addition of a spinal column or backbone along with a brain case (such a brain case is only found in some early chordates, the “craniates”). Vertebrates have a definite “front end” – with sensory organs such as eyes and a concentration of nervous tissue, burgeoning early brains in the early forms. Early vertebrates appear fairly early in the Cambrian, 525 million years ago, about 5 million years after the Cambrian ‘explosion’ began.

Haikouichthys is an extinct genus of jawless fish, believed to have lived about 530 million years ago, during the Cambrian explosion. Haikouichthys had a defined skull and other characteristics that have led paleontologists to label it a true craniate, and possibly one of the first fish.
Credit: Photo by Vertebres Fossiles <https://vertebresfossiles.free.fr/>

These did not look like modern vertebrates, but show the early development of this type of body plan – by this time early animals had managed to get a backbone and get a head. Although not technically fish, the early jawless fishes develop out of these early vertebrates during the next 100 million years. Plants also started getting more complex, with green algae apparently developing into forms that finally colonized the land, included types of early liverworts and fungi.


Fossils from some early Cambrian localities at Chengjiang, China, show early, developing vertebrate features – including eyes, rudimentary vertebrae, and a brain. The very earliest fossils not true “fish” and show many differences from the fish that emerge later, the closest living animals that these resemble are the fish. Fish emerged from such early vertebrates by 510 million years ago. These early fish had no jaws and lived in fresh, not salt water. Fish fossils become widespread over the next 100 million years, fish with jaws emerge by around 400 million years ago, and marine fish by about 300 million years ago.


Although vertebrates are numerically a minority on the earth, they have had a significant impact on the earth and on our lives. They made a significant advance for the evolution of animals – organizing body parts to take on different functions, the building of more complex, protected neural networks and significant neural processing center centers (CPU’s) in the brain. Early vertebrates laid the groundwork for the evolution of complexity in animals. A similar evolution of complexity took off in land plants soon afterwards, gradually developing larger plants with more and more complex organs and tissues. If vertebrates had not emerged, we humans would not be here, as we are descended from these ancient vertebrates. Most of the animals we rely on from day to day – our pets, our other domestic animals, most of our common animal foods – are vertebrates. And these animals are important in the food chains of the more ‘invisible’ invertebrates that really dominate our planet in terms of species.





An informative 15-minute YouTube video about vertebrate phylogeny and diversity.

This site gives the basics of vertebrate evolution.

This is a site for kids about the origins and characteristics of vertebrates.

A kid-friendly web-site about the different kinds of vertebrates.

Relationship found between ancient climate change and Earth’s second largest mass extinction.



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