1. An extinct jawless fish of the Paleozoic era, characterized by a bony or armored external covering.
Usage: paleontology; often used in plural form

Examples

• Ostracoderms were among the earliest vertebrates to appear in the fossil record.
• The ostracoderm's heavy armor plating provided protection in ancient seas.
• Scientists study ostracoderms to understand the evolution of early fish.
• Unlike modern fish, ostracoderms lacked true jaws for feeding.
• The discovery of ostracoderm fossils has helped paleontologists trace vertebrate ancestry.