Pairings that teach something

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Two toothed whales, two strategies

Orca vs Sperm Whale: Two Toothed Whales Compared

The largest dolphin and the largest toothed predator share every ocean but divide it by depth, diet and the way their families are organized.

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A warm-bodied fish and a patient reptile

Great White Shark vs Saltwater Crocodile: Fish, Reptile

The largest predatory fish and the largest living reptile reach nearly the same length by opposite routes, one on warm muscle and one on patience.

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A predator and its prey, known almost entirely at second hand

Sperm Whale vs Giant Squid: Predator and Prey

One of the ocean's best-known feeding relationships rests on beaks, scars and stomach contents. No encounter between the two has ever been filmed.

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A measurement problem more than a size difference

Giant Squid vs Colossal Squid: Longer or Heavier?

Two of the largest invertebrates known, separated by a measurement problem: one is much longer, the other far heavier, and both samples are tiny.

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A warm-bodied fish and a warm-blooded mammal on the same coasts

Great White Shark vs Orca: Warm Fish, Warm Mammal

A regionally warm-bodied fish and a fully warm-blooded mammal share temperate coasts, and researchers have watched one displace the other from feeding sites.

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Two Arctic animals losing the same ice for different reasons

Polar Bear vs Walrus: Two Animals on the Same Ice

Two Arctic animals that depend on the same vanishing sea ice for opposite reasons, one hunting from it and the other resting on it between dives to the seafloor.

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Two open-ocean sharks, one built for economy and one for speed

Blue Shark vs Shortfin Mako: Economy and Speed

Two oceanic sharks caught on the same longlines. One glides on long fins and breeds prolifically; the other runs on warm muscle and recovers very slowly.

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Two famous speed claims and what measurement actually supports

Shortfin Mako vs Sailfish: Measuring Speed at Sea

The two fish most often called the fastest in the ocean, and why both of their famous speed figures rest on far weaker evidence than the reputation suggests.

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Two warm-bodied fish that heat different organs

Atlantic Bluefin Tuna vs Swordfish: Heat and Depth

Two warm-bodied Atlantic predators that heat different organs and divide the ocean differently, one across latitude and the other from the surface into the deep.

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Two unrelated animals that both cross the salinity gradient

Bull Shark vs American Crocodile: Salt and Fresh Water

A shark and a reptile that both move between the sea and fresh water, using two completely unrelated solutions to the same underlying chemical problem.

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Two large Pacific cephalopods on the same short clock

Giant Pacific Octopus vs Humboldt Squid: Reef and Open Sea

Two large Pacific cephalopods that both grow fast, spawn once and die, one a solitary hunter of rocky bottoms and the other an open-ocean animal in crowds.

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One mammal that never leaves the water and one that still comes ashore

Bottlenose Dolphin vs California Sea Lion: Water, Land

Two familiar coastal mammals of American shores, one that never leaves the water and one that walks out of it, and everything that difference sets in motion.

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The widest diet of any large shark against a ray specialist

Tiger Shark vs Great Hammerhead: Generalist, Specialist

Two large sharks of the same warm coastal seas. One eats almost anything, the other concentrates on stingrays, and their conservation categories diverge sharply.

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Temperature, metabolic rate and lifespan as one connected story

Greenland Shark vs Shortfin Mako: Cold, Speed, Time

The slowest shark ever measured and one of the fastest, and how water temperature, metabolic rate and lifespan turn out to be a single connected story.

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A reptile and a bird that converged on deep diving and warm bodies

Leatherback Turtle vs Emperor Penguin: Deep and Warm

A reptile and a bird that both dive past 1,800 feet and both stay warm in freezing water, using two entirely unrelated solutions to the same two problems.