Hylonomus lyelli

Overview

Hylonomus is one of the oldest true reptiles ever discovered—a tiny lizard-like creature that lived approximately 312 million years ago during the Late Carboniferous period! This small but incredibly important animal represents a major step in vertebrate evolution: the ability to live entirely on land.

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Taxonomy & Classification

• Class: Reptilia
• Family: Protorothyrididae
• Diet: Carnivorous (insects and small invertebrates)
• Type: Early reptile (amniote)

Hylonomus is one of the first known amniotes—animals that lay eggs that can survive on land.

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Physical Characteristics

Size & Build

• Length: 20-25 cm (8-10 inches)
• Weight: Unknown but very light
• Build: Small, lizard-like body

Body Features

• Long tail for balance
• Small, sharp teeth for eating insects
• Slender legs positioned slightly to the sides
• Scaly skin (probably)
• Looked like a small modern lizard

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Why Hylonomus Is So Important

The First "True" Reptiles

Hylonomus matters because:

• One of the oldest known reptiles
• Could lay amniotic eggs (eggs with shells!)
• Didn't need water to reproduce
• Freed vertebrates from living near water
• Ancestor of all reptiles, birds, and mammals!

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The Amniotic Egg Revolution

Breaking Free from Water

Before Hylonomus:

• Amphibians had to lay eggs in water
• Babies were tadpole-like and aquatic
• Animals tied to ponds and streams

With the amniotic egg:

• Eggs had protective shells
• Embryos developed in fluid inside egg
• Could be laid anywhere on land!
• Opened up entire continents to colonization

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Discovery in Hollow Trees

The Joggins Fossil Cliffs

Hylonomus was found in an amazing way:

• Discovered in Joggins, Nova Scotia, Canada in 1852
• Found inside fossilized tree stumps!
• The trees fell and became hollow traps
• Small animals fell in and couldn't escape
• Perfectly preserved for 312 million years
• Named by Sir Charles Lyell, famous geologist

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Life in the Carboniferous

A Different World

Hylonomus lived in an alien landscape:

• Giant forests of tree ferns and horsetails
• Air had more oxygen than today
• Giant insects (dragonflies with 70cm wingspans!)
• No dinosaurs yet—they wouldn't appear for 80 million years
• Warm, swampy environment

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What Did It Eat?

Insect Hunter

Hylonomus ate:

• Insects and millipedes
• Snails and other small invertebrates
• Small arthropods in the leaf litter
• Hunted among fallen logs and leaves

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Cool Facts

• Hylonomus is one of the oldest known reptiles—312 million years old!
• Its name means "forest mouse"
• Found preserved inside hollow tree trunks
• All reptiles, birds, and mammals descended from creatures like Hylonomus
• The species name "lyelli" honors Charles Lyell, the father of modern geology
• Joggins, where it was found, is now a UNESCO World Heritage Site
• Lived 80 million years before the first dinosaurs!

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Hylonomus was tiny but mighty—a little lizard whose ability to live fully on land started a revolution that would lead to dinosaurs, birds, and even us!