Shark

Older than dinosaurs

Sharks first appeared in the fossil record over 400 million years ago — predating dinosaurs by 200 million years and surviving all five mass extinction events that have shaped life on Earth. Their basic body plan (cartilaginous skeleton, multiple gill slits, ventral mouth) hasn’t changed dramatically in 200+ million years.

The ancient shark Megalodon (extinct ~3.6 million years ago) reached 20+ meters in length and was likely the largest predator the oceans ever saw — vastly bigger than any modern shark.

500+ species, dramatic range

Sharks range across all ocean habitats:

• Dwarf lanternshark (Etmopterus perryi) — 18 cm, the smallest shark.
• Whale shark (Rhincodon typus) — 18 m, largest fish in the sea, plankton feeder.
• Greenland shark (Somniosus microcephalus) — Arctic, can live 400+ years (the longest-lived vertebrate).
• Bull shark (Carcharhinus leucas) — capable of swimming up rivers; one was found 4,000 km up the Mississippi.
• Hammerhead shark — distinctive head shape, eye placement gives it 360° vertical vision.
• Goblin shark — deep-sea, projectile-extending jaws.

The bite issue

Sharks are involved in roughly 80 unprovoked human bites globally per year, with about 5–10 fatalities. Statistically, vending machines kill more Americans than sharks (about 10/year). The Australian saltwater crocodile, hippopotamus, and falling coconuts each cause more deaths than sharks worldwide.

Shark “attacks” are usually mistaken-identity bites — the shark grabs once, recognizes that humans don’t taste like seal or fish, and lets go. The damage from a single bite of a large shark, however, can still be severe.

Conservation crisis

Despite their reputation as fearsome predators, sharks are far more endangered by humans than vice versa:

• Shark fin soup drives massive Asian-market demand; an estimated 100 million sharks are killed annually for fins alone.
• Bycatch in commercial fishing (especially longline tuna fisheries) kills millions more.
• Overfishing has driven many shark populations to 80–99% declines from historical numbers.

Many large shark species (great hammerhead, oceanic whitetip, scalloped hammerhead) are Critically Endangered. The ecological impact of removing apex predators from marine food webs is significant and ongoing.

Cartilage, not bone

Sharks have cartilaginous skeletons — flexible, lightweight, and don’t preserve well as fossils (most “shark fossils” are just teeth, since cartilage decays). Modern sharks share this feature with rays, skates, and chimaeras (collectively, Chondrichthyes).