Sharks are ancient aquatic predators that have navigated the world’s oceans for hundreds of millions of years, evolving specialized biological features that allow them to thrive in diverse marine environments. Their existence is marked by surprising adaptations. We will explore five remarkable aspects of their biology and behavior.
The Sixth Sense: Detecting Electric Fields
Sharks possess a unique sensory apparatus known as the Ampullae of Lorenzini, a network of specialized electroreceptors concentrated around their snout and head. These organs consist of small pores that open into jelly-filled canals, which lead to sensory bulbs. The highly conductive gel allows the shark to detect minute electrical potential differences in the surrounding water. This system is sensitive enough to detect electrical fields generated by the muscle contractions of nearby prey.
This ability acts as a short-range hunting tool, especially when vision is obscured. It allows them to locate prey buried under the sand, a common behavior for bottom-dwelling rays. The Ampullae of Lorenzini also aid in navigation, potentially allowing the shark to orient itself by sensing the Earth’s magnetic field.
Lifespans that Dwarf Humans: The Deep-Sea Elders
Certain shark species exhibit extraordinary longevity, far surpassing that of most other vertebrates. The Greenland Shark, a slow-moving resident of the Arctic and North Atlantic, holds the record for the longest-living vertebrate known to science. Scientists estimate its lifespan to be at least 272 years, with some individuals potentially reaching ages exceeding 500 years.
This age is attributed to the shark’s extremely slow metabolism, an adaptation suited to the frigid, deep-sea waters it inhabits. Age estimation is achieved through radiocarbon dating of proteins found in the center of the eye lens. The Greenland Shark’s slow rate of growth, less than one centimeter per year, underscores its lengthy existence and delayed maturity, which is estimated to occur around 150 years of age.
Birthing Strategies: The Diverse Ways Sharks Reproduce
Shark reproduction utilizes internal fertilization and three distinct methods of gestation and birth.
The oviparous strategy involves the female laying eggs encased in a tough, leathery shell, often called a “mermaid’s purse.” Species like the Horn Shark and Catshark deposit these eggs externally, where the embryo develops, nourished entirely by the yolk sac.
The ovoviviparous method is the most common. The eggs hatch internally, and the young are retained within the mother’s uterus without forming a true placental connection. Embryos rely initially on a yolk sac. In species like the Sand Tiger Shark, the first pup to hatch consumes its developing siblings and unfertilized eggs for nutrients, a behavior called intrauterine cannibalism.
Finally, viviparity involves the development of a yolk-sac placenta. This connects the embryo directly to the mother’s bloodstream for nourishment, resulting in a live birth similar to mammals, as seen in the Bull Shark and Hammerhead Shark.
The Endless Supply: Replacing Thousands of Teeth
Sharks are classified as polyphyodonts, meaning they continuously replace their teeth throughout their lifespan. Unlike human teeth, which are deeply rooted, a shark’s teeth are embedded in the soft tissue of the gums and arranged in multiple rows that function like a conveyor belt.
As functional teeth at the front of the jaw are lost or damaged, the teeth in the row behind move forward to take their place. This replacement process is fast, occurring over days or weeks depending on the species. A single shark can shed and replace tens of thousands of teeth over its lifetime, ensuring a sharp, functional set for hunting.
Skin Like Sandpaper: Nature’s Hydrodynamic Armor
The skin of a shark is covered in millions of tiny, V-shaped structures called dermal denticles, which translates to “skin teeth.” These denticles are structurally similar to teeth, composed of dentine and an enamel-like coating, making the skin feel rough like sandpaper.
The primary function of the denticles is hydrodynamic. Their microscopic ridges and grooves reduce drag and turbulence as the shark moves through the water, allowing for highly efficient swimming. This natural design has inspired biomimicry, with the structure being studied to create specialized coatings for ship hulls and competitive swimwear to improve speed.