1. an extinct reptile of the Permian period characterized by a large sail-like fin on its back
Usage: paleontology

Examples

• The pelycosaur Dimetrodon is often mistakenly called a dinosaur.
• Pelycosaurs lived millions of years before the first dinosaurs appeared.
• The distinctive sail of the pelycosaur may have helped regulate body temperature.
• Fossils of pelycosaurs have been found in Texas and other parts of North America.
• Scientists believe pelycosaurs were among the ancestors of modern mammals.
• The pelycosaur’s sail was supported by elongated spines from its vertebrae.