Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Testudines, also known as turtles and tortoises, are an order of reptiles characterized by a bony or cartilaginous shell developed from their ribs. They are one of the oldest reptile groups, having existed for over 200 million years.
5 Must Know Facts For Your Next Test
Turtles and tortoises belong to the order Testudines.
Testudines have a unique shell composed of a carapace (top) and plastron (bottom) which is fused to their ribs and spine.
Members of Testudines can be found in various habitats including aquatic, semi-aquatic, and terrestrial environments.
Testudines exhibit oviparous reproduction, laying eggs on land even if they live in water.
The metabolic rate of Testudines is generally slow, contributing to their long lifespan.
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Related terms
Carapace: The dorsal (top) part of the shell in turtles and tortoises.
Plastron: The ventral (bottom) part of the shell in turtles and tortoises.
Oviparous: A mode of reproduction where animals lay eggs that hatch outside the mother's body.