Morphological review describes unique shell anatomy and passive defense mechanisms in chelonians, highlighting evolutionary adaptations that preserve biodiversity.
Chelonians (turtles and tortoises) are among the oldest and most fascinating biological groups on Earth. As a unique branch of reptiles, they play a crucial role in maintaining ecosystem health and biodiversity. Their most remarkable feature lies in their distinctive anatomy: a dorsal carapace and a ventral plastron, composed of bony plates connected by a bony bridge to form a relatively rigid, box-like structure. Their vertebrae and ribs are fused to these bony plates, which are covered on the outside by a layer of keratinous scutes or leathery skin. Together with a neck that can retract to varying degrees, toothless jaws covered by a keratinous beak, and limbs adapted to different lifestyles, this set of features gives chelonians their distinctive body form. These specialized structures provide an effective passive defence mechanism that sets chelonians apart from other vertebrates. Though such features might seem clumsy at first glance, they have proven highly effective over evolutionary time.
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Binbin Zhan (2026) studied this question.
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