Sharks have survived 450 million years by ditching bones for cartilage
In short: Imagine a predator that predates both trees and dinosaurs. Sharks have navigated the ocean's evolution for nearly half a billion years. By trading heavy bone skeletons for flexible cartilage and developing unique physiological traits, they have become one of the planet's most enduring and successful biological designs.
Sharks are members of the subclass Elasmobranchii, a group that also includes skates and rays. Their primary anatomical distinction is a skeleton made entirely of cartilage rather than bone. This structural choice, combined with bodies covered in tooth-like scales called dermal denticles, allows for a distinct form of movement and durability. Additionally, while most fish possess a single gill opening, sharks typically feature between five and seven gill openings to facilitate respiration.
The group is diverse, with approximately 500 species currently inhabiting the world's oceans. They are categorized into nine key orders based on size, diet, and habitat. For instance, the order Lamniformes contains about 15 species of mackerel sharks. These sharks are notable for being partially warm-blooded, a physiological adaptation that enables them to regulate their body temperature and remain highly active in frigid waters where other fish might struggle to function.
The evolutionary success of these predators is evident in their specialized hunting strategies. The great white shark, a member of the mackerel shark group, uses a torpedo-shaped body and powerful tail for ambush attacks from below. In contrast, the basking shark—the second largest living fish, reaching up to 12 metres in length—uses a completely different method, swimming with its mouth wide open to filter plankton using specialized gill rakers. This diversity highlights how different lineages within the same subclass have adapted to occupy vastly different ecological niches.
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Sources
- Summary by Intellect · source: Sharks & Manta Rays: The Hidden World Beneath the Ocean | Wildlife Documentary
- Also: Meet the nine types of sharks in the ocean | Natural History Museum
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