“LANDLUBBERS”
THE FIRST REPTILES
315 million years ago
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| Early reptile. Hylonomous, a forest-dwelling reptile from the late Carboniferous Period, about 312 million years ago. Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration is used with permission. All rights reserved. |
Amphibians are very tied to water – to lay their eggs, and often to live, at least for part of their life. Reptiles made a break from this by 315 million years ago, due to the evolution of a new kind of egg – one with an outer membrane that would protect it from drying out. This might sound trivial, but it was really, really important. Reptiles are cold-blooded, just like amphibians. But this new egg would let the evolving reptiles, living on land alongside early amphibians more than three hundred million years ago, to loosen their ties to swamps, lakes and seas, and also move into other parts of the landscape (and some also returned to the water!). This transition happened during the time when the great coal deposits of the entire world were laid – a period called the “Carboniferous,” when great swamps of impressive plants and a humid, tropical climate prevailed over most of the planet. Now reptiles inhabit virtually every continent (except Anarctica) and live in habitats ranging from tropical forests, lakes and swamps, to the driest of deserts.
The earliest definite fossil reptile is a form called Hylonomus, dating to about 312 million years ago and found in Nova Scotia in northeastern Canada. This creature, about eight inches long, had sharp teeth and probably had a diet largely of insects. The fossilized stumps of giant club moss, a dominant, tree-like form from this period, was found with Hylonomus fossils, suggesting this early reptile lived in dense forests. Footprints found in nearby New Brunswick, Canada are believed to have been made by Hylonomus.
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| Early Permian Reptile and Amphibian, about 280 million years ago. Cacops (in the foreground) is classified as an early synapsid, a mammal-like reptile, and Casea (in the background) is an amphibian from the same time period. Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration is used with permission. All rights reserved. |
HOW DO WE KNOW?
Fossils and occasional tracks of lizard-like reptiles have been found in many places. One of these early reptiles, called “Hylonomus,” left fossils and footprints in Canada around 312 million years ago. As time goes on, there is a very rich fossil record documenting the radiation and spread of reptiles around the world, including the giant forms called dinosaurs as well as ancestors of modern reptiles.
WHY SHOULD I CARE?
Although many of us may not feel we know or identify with reptiles very well – their psychology, thoughts, or feelings – we owe it to this distant reptile ancestor to have developed a new way or reproducing by making a protected egg. This new egg (an ‘amniotic egg’) unleashed us from the relatively protected environment in bodies of water – seas, lakes, and swamps. Starting from this time, reptiles started adapting to life out of the water and on the land (and finally, also in the air). Our reptilian ancestors would eventually evolve into mammals, primates, apes, and finally, humans.
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| Dimetrodon (in the foreground) was a mammal-like reptile from the early Permian around 275 million years ago. The sail-like structure on its back may have been for body temperature control. Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration is used with permission. All rights reserved. |
WEB RESOURCES
This is a national geographic video, “Prehistoric Croc Was Mammal-like.”
https://video.nationalgeographic.com/video/news/animals-news/nsf-ancient-croc-vin/
A well-presented survey of the evolution of reptiles.
https://reptileevolution.com/index.htm
An article about the oldest footprints ever found, pushing back the emergence of land animals by 18 million years to 397 million years ago.
https://www.telegraph.co.uk/science/science-news/6945194/Four-legged-animals-walked-on-earth-18-million-years-earlier-than-previously-thought.html
