50 Fun Facts About Vertebrates

Nearly all mammals, even giraffes, have seven neck vertebrae; which tree-dwellers are a rare exception?

Sloths break the mammal rule: two-toed kinds have five or six neck vertebrae and three-toed kinds have nine. The only other known exception is the manatee, with six.

Which Australian mammal lays eggs, has webbed feet and a duck-like bill, and carries venomous ankle spurs if male?

The platypus is one of only five living monotremes, the mammals that lay eggs; the other four are echidnas. A male's venom is strong enough to cause people severe pain.

Which sluggish fish can live for at least 270 years, longer than any other known vertebrate?

The Greenland shark is aged by radiocarbon dating the lenses of its eyes, and the oldest one measured was put at roughly 390 years. It may not be ready to breed until about 150.

Which mammals, about a fifth of all mammal species, are the only ones capable of sustained flight rather than gliding?

Bats fly on a thin membrane stretched across long, spread-out fingers, which makes them more agile in the air than most birds. At least 1,500 species are known.

Which sea mammal, weighing up to about 190 tonnes, is the largest animal known ever to have existed?

The blue whale reaches about 30 metres in length, yet it feeds almost entirely on krill. It lunges at a swarm with its mouth wide open, then strains the water out through baleen plates.

Which living reptiles are the closest relatives of birds, the two groups being the only surviving archosaurs?

Crocodilians also parent more like birds than lizards: they are unusual among reptiles in how much care they give their young after the eggs hatch.

Which Mexican salamander keeps its external gills for life and never leaves the water to live on land?

The axolotl can regrow lost limbs, gills and even parts of its brain without scarring. In the wild it is now limited to Lake Xochimilco, a remnant of canals hemmed in by Mexico City.

Which bird of prey is widely called the fastest animal on Earth because of its steep hunting dive, the stoop?

The peregrine falcon is often credited with dives of over 320 km/h, though the highest speed reliably tracked by radar is 184 km/h. It soars to a great height, then drops steeply onto its prey.

Dolphins and porpoises evolved from land mammals; which pig-like living animal is their closest relative?

The hippopotamus and the cetaceans share an ancestor from which they split about 55 million years ago. Blood proteins, DNA and fossils all point to the same family tie.

Which birds can swivel their heads about 270 degrees, helped by having 14 neck vertebrae, twice as many as humans?

Owls have eyes fixed in bony tubes, so they cannot glance sideways and must turn the whole head instead. Extra-wide channels in the neck bones keep blood flowing to the brain as it twists.

Which flightless bird, the largest alive, lays the biggest eggs of any living bird and can sprint at about 70 km/h?

The ostrich is also the fastest animal on two legs, covering up to five metres in a single stride. Only extinct giants such as Madagascar's elephant bird laid bigger eggs.

Which Indonesian reptile, growing up to three metres long, is the largest living species of lizard?

The Komodo dragon lives wild on only a handful of Indonesian islands, among them Komodo, Rinca and Flores. The biggest males can weigh as much as 150 kg.

Which nectar-feeding birds of the Americas can hover and fly in any direction on wings beating up to 99 times a second?

Hummingbirds include the bee hummingbird, the world's smallest bird at about 2 grams. The hum that gives the family its name is the sound of those rapidly beating wings.

Which bird breeds during the Antarctic winter, the male balancing a single egg on his feet for about two months?

The emperor penguin male eats nothing while he guards the egg and loses around 12 kg before it hatches. The female spends those weeks feeding at sea.

Kangaroos, koalas and opossums belong to which mammal group, whose tiny newborns usually finish growing in a pouch?

Marsupials are not only Australian: about 30 percent of the species live in the Americas, though the Virginia opossum is the only one found north of Mexico.

Which order of gnawing mammals, from tiny mice to the capybara, makes up about 40 percent of all mammal species?

Rodents are set apart by pairs of sharp incisors that never stop growing, which they use to gnaw food, dig burrows and defend themselves. Most species weigh less than 100 grams.

Which process, driven by the hormone thyroxin, turns a legless tadpole into a four-legged adult frog?

Metamorphosis does not shed the tadpole's tail: the tail is absorbed back into the body through programmed cell death. Lungs for breathing air develop along the way.

Skates and stingrays have boneless skeletons made of which tough, elastic tissue that also shapes the human nose?

Cartilage is the main skeletal tissue of every vertebrate early in development, and in most it is later largely replaced by bone. Skates and their kin simply never make the switch.

Which bundle of nerves, about 45 cm long in adult humans, is protected by a canal running through the vertebrae?

The spinal cord does more than relay messages: it contains reflex arcs that can control some reflexes independently, without waiting for the brain.

Which organ has two chambers in fish, three in amphibians and four in birds and mammals?

The heart of a fish is a single pump that sends blood once through the gills and straight on to the body. Birds and mammals have two pumps in one, with four chambers in total.

Birds are the only living members of which group of reptiles, long believed to have died out 66 million years ago?

Dinosaurs live on as birds, which evolved from the two-legged theropods. The mass extinction that ended every other branch also killed off the flying pterosaurs.

Which reptiles have backbones of 200 to 400 vertebrae or more, far outnumbering the 33 found in a human?

Snakes have ribs along almost the whole body, because nearly every vertebra in front of the short tail is built like a chest vertebra. Only a few neck bones go without.

Which reptiles have ribs that grow sideways into broad bony plates, leaving the shoulder blades inside the rib cage?

Turtles can never leave their shells, because the upper shell, or carapace, is fused to the ribs and backbone. Even the hip bones sit inside it.

Which fish hatch in fresh water, grow up at sea, then return to the stream of their birth to spawn?

Salmon find their home stream so reliably that tracking studies have shown the old folklore to be mostly true, though a share of every run strays to spawn elsewhere.

Which South American river fish, a knifefish despite its common name, can stun prey with shocks of up to 860 volts?

The electric eel must also rise to the surface to breathe air, which lets it live in water low in oxygen. Its main organ alone can discharge at least 600 volts.

Which fish, thought extinct for over 60 million years, turned up alive off South Africa in 1938?

The coelacanth has fleshy, lobed fins and is more closely related to four-legged land animals than to most other fish. Its return made it the best-known Lazarus taxon, a lineage that reappears after vanishing from the fossil record.

Which jawless fish, the only living animals with a skull but no vertebral column, fend off predators with slime?

Hagfish slime clogs an attacker's gills, and the hagfish then cleans itself by tying its body into a knot and sliding the knot from head to tail.

Which forked bone, usually formed from two fused collarbones, braces a bird's chest against the strain of flight?

The wishbone also works like a spring, flexing between the shoulders in flight, as films of flying starlings have shown. Its formal name, furcula, is Latin for little fork.

Birds have no teeth, so which thick-walled, muscular part of the stomach grinds their food, often with swallowed grit?

The gizzard does the chewing that a toothless bird cannot, crushing food against swallowed stones. It can also pass a meal back to the true stomach and take it in again.

Lungless salamanders, the largest family of salamanders, have no lungs and take in oxygen mainly through which organ?

Skin is a major breathing surface in every amphibian that has been measured, not only the lungless ones. Oxygen passes straight through it into the blood.

Which organ, expelled after birth, passes food and oxygen from a mother's blood to the unborn young of most mammals?

The placenta evolved around 150 million years ago and was a key factor in the rapid spread of the mammals that carry their young this way. It also makes hormones that steer the pregnancy.

Which tough protein builds bird feathers, reptile scales and the claws, horns and hooves of mammals?

Keratin also forms human hair and fingernails. Hair is rich in the sulfur-bearing amino acid cysteine, which is why it gives off such a pungent smell when it burns.

What term describes cold-blooded animals such as lizards and frogs, which rely on sunlight and other outside heat?

Ectotherms run on little fuel: because they do not burn food to keep warm, they get by on far less of it than a bird or mammal of similar size.

Amphibians, reptiles, birds and mammals all descend from fish that crawled onto land, forming which group?

Tetrapods are named for their four limbs, but the group includes every descendant of those four-limbed ancestors, even legless lizards and two-limbed manatees.

Which single rear opening serves the digestive, urinary and reproductive tracts of all birds, reptiles and amphibians?

Cloaca is the Latin word for a sewer or drain. A few mammals have one as well, among them the egg-laying monotremes.

Which rod supports the early vertebrate embryo, then survives only as the soft core of the discs between vertebrae?

The notochord is also a signalling centre: it releases a protein named sonic hedgehog that helps direct how the nervous system and other organs take shape.

Which gas-filled organ lets most bony fish hold a chosen depth without having to keep moving?

The swim bladder shares its origin with the lungs of land animals: both arose from pouches off the gut that let early fish gulp air in oxygen-poor water.

Which sense organ lets a fish detect movement, vibration and pressure changes in the water around it?

The lateral line helps schooling fish hold their formation, and it lets predators home in on the vibrations made by their prey.

Over half of all living vertebrate species are fish of which kind, named for fins webbed over thin bony spines?

Ray-finned fish outnumber all the amphibians, reptiles, birds and mammals put together. Their lobe-finned cousins have bulkier, fleshy fins instead.

Mammals alone have three tiny bones, two of them evolved from ancestral jaw bones, in which part of the body?

The middle ear of a mammal holds the malleus, incus and stapes, a chain that amplifies faint airborne sounds. Reptiles make do with a single bone there, the columella.

Which small bone at the base of the human backbone, made of three to five vertebrae, is the remnant of a tail?

The coccyx is the final segment of the backbone in humans and in all the other apes, none of which has a tail. Its everyday name, the tailbone, says as much.

Which vertebra is the topmost in the backbone, the one that supports the head?

The atlas carries the head much as its mythical namesake bore the weight of the heavens. Together with the vertebra below it, the axis, it lets the head nod and turn.

A bird's wing, a horse's foreleg and a human arm share one ancestral bone pattern, making them which kind of structures?

Homologous was first used in this sense by the anatomist Richard Owen in 1843, who contrasted it with analogous parts that share a job but not an origin.

In many egg-laying reptiles, which condition during incubation decides whether a hatchling becomes male or female?

Nest temperature works within a narrow window: in some species a shift of as little as one or two degrees switches a clutch from mostly male to mostly female.

Which branch of zoology, named from the Greek for creeping animal, studies both reptiles and amphibians?

Herpetology pairs two very different classes because, strictly defined, it is the study of the cold-blooded four-limbed vertebrates. Fish fall to a separate field, ichthyology.

Which naturalist coined the name Mammalia for mammals and gave humans the scientific name Homo sapiens?

Carl Linnaeus introduced both names in the tenth edition of his Systema Naturae. His campaigning for mothers to breast-feed their own babies is thought to have influenced the choice of Mammalia.

Which New Zealand reptile looks like a lizard but is the last survivor of an order that flourished in the Mesozoic era?

The tuatara has a third eye on top of its head, visible only in hatchlings as a translucent patch at the centre of the skull. Some lizards have one too.

Which limbless, burrowing amphibians have tiny or missing eyes and a name that comes from the Latin for blind ones?

Caecilians mostly live hidden in soil or streambeds, which makes them some of the least familiar amphibians. They find prey with a pair of sensory tentacles set between the eyes and nostrils.

Which 375-million-year-old fossil fish from Canada, the earliest known with a neck, links fish to four-legged animals?

Tiktaalik takes its name from an Inuktitut word for a large freshwater fish, suggested by Inuit elders of Nunavut, where the fossils were found in 2004. It had scales and gills but a flat head.

Which French naturalist, founder of vertebrate paleontology, proved from fossil bones that animals can go extinct?

Georges Cuvier showed that mammoth and mastodon bones belonged to vanished species rather than to living elephants. Until then many of his peers treated extinction as mere speculation.