The earliest known reptile is Hylonomus lyelli. It is also the first animal known to have fully adapted to life on land.
Hylonomus lived about 315 million years ago, during the time we call the Late Carboniferous Period. This time period is also known as the Pennsylvanian and as the Coal Age.
Hylonomus were about 20 cm (8 in.) long, counting the tail. These lizard-like reptiles were primarily insectivores, probably feeding on millipedes, insects and land snails. (At this time, plant-eating, backboned animals had not yet appeared). Females probably deposited eggs on land in moist, sheltered areas.
The fossil bones were found in petrified stumps exposed along the sea-cliff near Joggins, Nova Scotia. Joggins fossils are mentioned in Sir Charles Darwin’s classic 1859 book on evolution, On the Origin of Species. This locale was declared a World Heritage site by the United Nations in 2008.
Hylonomus was discovered in 1852 by Sir William Dawson, a pioneering geologist and principal of McGill University from 1855 to 1893.
The genus name, Hylonomus, comes from a combination of the Greek word for "wood" and the Latin word for "forest mouse".
The species name, lyelli, is in honour of Sir Charles Lyell, Dawson’s teacher and one of the most influential geologists of the 19th century. Lyell was working at Joggins with Dawson at the time of the discovery. He is author of the landmark work Principles of Geology.
Some remains of Hylonomus were preserved inside the upright, hollow stumps of some "scale trees", which were giant club-mosses (lycopods) such as Lepidodendron or Sigillaria. These large trees attained heights of 30 m (98.5 ft.) and diameters of 1 m (3 ft.). They were common on river banks and in the coal swamps of eastern North America.
Successive forests of these scale trees were killed by the deposit of large amounts of coarse sediment when rivers flooded their banks. Over time, the trees died, toppled over, and the stumps began to rot. Hylonomus and small amphibians hunted for food or took refuge inside the hollow stumps, and when floods came again, the stumps and reptiles were buried together and subsequently fossilized.
In 2002, Hylonomus lyelli was declared the Provincial Fossil of Nova Scotia by an Act of the House of Assembly.