Produced by the Population Genetics and Evolution class, Furman University

The Carboniferous: Protorothyrids
The protorothyrids (family Protorothyrididae) were small, lizardlike animals believed to be the earliest true reptiles (Encyclopedia Britannica 2010). Key morphological traits that establish them as the first true reptiles include specializations of the adductor chamber, cheek, and occiput leading to greater size and enhanced efficiency of the jaw musculature. Protorothyrids are also characterized by a small increase in body size, a relative increase in both the size of the skull and length of the limbs, and a fusion of the axis intercentrum to the atlas pleurocentrum (Carroll 1982). The most famous member of the protorothyrids is Hylonomus lyelli, which was first discovered in 1852 near Joggins, Nova Scotia by Sir William Dawson, who named it in honor of his teacher, the eminent geologist Sir Charles Lyell. (CMN 2009). The earliest known animal fully adapted to life on land, this 315 million-year-old primitive lizard measured about 20 cm long and featured a small skull, relatively short limbs, a short neck, a long tail, and around 40 marginal pointed teeth (Carroll 1982). Researchers believe that Hylonomus was most likely an insectivore that lived predominantly in forested areas where millipedes, insects, and land snails were plentiful, and moist, sheltered areas were available for the females to lay their eggs (CMN 2009).

Page by Robert Mazgaj
Hylonomus lyelli
Photo credit: Palaeos.com

Canadian Museum of Nature. 2009. Hylonumus: The Earliest Reptile. Accessed 3 Mar. 2010.

Carroll, Robert L. 1982. Early Evolution of Reptiles. Ann. Rev. Ecol. Syst. 13: 87-109.

Encyclopedia Britannica. 2010. Reptile fossil distribution. Accessed 3 Mar. 2010.