Unique anatomy sets giraffe apart in the animal kingdom

A circulatory system that beats gravity. Spots that dissipate heat. This giant is purpose-built for its size and surroundings.

This story appears in the October 2019 issue of National Geographic magazine.

At 14 to 19 feet tall, giraffes tower over the entire animal kingdom. But their iconic height, which evolved over seven million years, requires unique features to regulate blood flow, mitigate the effects of gravity on muscles and bones, and heat and cool their massive bodies.

Heat regulation

Bones

Vascular system

RETICULATED GIRAFFE

Giraffa reticulata

MALE

FEMALE

Life span

Weight

2,600 lbs

25 years

1,750 lbs

Height

17 ft

14 ft

An agile, thick tongue that can be up to 20 inches long, grasps leaves while tough skin in the mouth protects against thorns. The tip of the tongue is black, possibly for sun protection.

ANGLING FOR

ADVANTAGE

A joint at the base of the skull allows the head to lift into a line nearly vertical with the neck.

Scientists theorize

that clusters of blood

vessels and sweat

glands under each

brown patch

release heat.

Arteries

Scapula

Vertebrae

Esophagus

Heart

Humerus

Metacarpal

THE POWER BASE

As giraffes grow, their leg bones thicken,

narrowing the marrow cavity and support

ing increasing weight. Bones are especially

long and straight in the lower legs.

ARTERIES AND GRAVITY

Arteries above the heart are muscular and elastic to pump blood against gravity to the brain. Lower arteries are narrower with thick walls to bear higher pressures and to prevent blood from pooling.

Neck

artery

Leg

artery

MULTITASKING HEART

The left ventricle has thick muscular walls to pump blood up to the head and then around the body. The thinner right ventricle pumps blood a short distance to the lungs.

Right

ventricle

wall

Left ventricle

wall

ADJUSTING FOR PRESSURE

A network of elastic vessels expands when the head is lowered, to prevent blood from flooding the brain, and constricts when the head is raised, to prevent quick depletion

Brain

Elastic

vessels

Open

valve

Closed

valve

When the head is lowered, valves in the veins close to prevent backflow of blood.

WHY THE LONG NECK?

The reason for the giraffe’s six-foot neck remains

a mystery. It may have evolved to reach high

branches, above competitors. Other theories

suggest it improved vigilance or that longer

necks provided an advantage to males fighting

to win a mate.

Feeding

Surveying

Fighting

FERNANDO G. BAPTISTA, TAYLOR MAGGIACOMO, EVE CONANT, AND SOREN WALLJASPER, NGM STAFF; LAWSON PARKER; SHIZUKA AOKI; QINGYANG CHEN; TANIA VELIN

SOURCES: SARA FERGUSON AND JULIAN FENNESSY, GIRAFFE CONSERVATION FOUNDATION; MARYLAND ZOO

Heat regulation

Bones

Vascular system

RETICULATED

GIRAFFE

Giraffa reticulata

WHY THE

LONG NECK?

The reason for the giraffe’s

six-foot neck remains a mys-

tery. It may have evolved to

reach high branches, above

competitors. Other theories

suggest it improved vigi-

lance or that longer necks

provided an advantage to

males fighting to win a mate.

MALE

FEMALE

Weight

2,600 lbs

1,750 lbs

Tongue can be

20 inches long.

Height

17 ft

An agile, thick tongue grasps leaves while tough skin in the mouth protects against thorns. The tip of the tongue is black, possibly for sun protection.

14 ft

Life span

25 years

Ossicones, made of bone, are thicker in males, for sparring.

Feeding

1

KEEPING A COOL HEAD

A large nasal cavity likely helps cool both blood and the brain.

2

ANGLING FOR ADVANTAGE

A joint at the base of the skull allows the head to lift into a line nearly vertical with the neck.

Surveying

3

SUPER FLEXIBLE

Like okapis and humans, giraffes have seven neck vertebrae, but ball-and-socket connections, similar to human shoulders, allow them to rub their noses on their lower backs.

A powerful elastic ligament structure in the neck reduces the muscle effort required to support the head and neck.

4

Fighting

ARTERIES AND GRAVITY

Arteries above the heart are muscular and elastic to pump blood against gravity to the brain. Lower arteries are narrower with thick walls to bear higher pressures and to prevent blood from pooling.

5

COOLING PATCHWORK

Scientists theorize that these unique color patterns provide more than just camouflage. Clusters of blood vessels and sweat glands under each brown patch act as thermal windows that release heat from the body.

6

Esophagus

Esophagus

7

Scapula

MULTITASKING HEART

The left ventricle has thick muscular walls to pump blood up to the head and then around the body. The thinner right ventricle pumps blood a short distance to the lungs.

Blood vessels

Blood vessels

OKAPI

Okapia johnstoni

MALE

FEMALE

24

pounds

Weight

395 to

575 lbs

530 to

785 lbs

60-90 beats per minute

Stomach

chambers

Intestine

Height

4.5 - 5.1 ft

(shoulder)

4.7 - 5.2 ft

ADJUSTING FOR PRESSURE

A network of elastic vessels expands when the head is lowered, to prevent blood from flooding the brain, and constricts when the head is raised, to prevent quick depletion

Humerus

Life span

20-30 years

The okapi is the giraffe’s

closest living relative.

Ulna

Brain

Brain

Radius

Radius

Elastic

vessels

Elastic

vessels

Humerus

Humerus

Like a cow, a giraffe has four stomach chambers.

0.7

pound

60-100

beats per minute

Humerus

6-7

pounds

Radius

Ulna

80-100 beats per minute

Ulna

Ulna

THE POWER BASE

As giraffes grow, their leg bones thicken, narrowing the marrow cavity and supporting increasing weight. Bones are especially long and straight in the lower legs.

Metacarpal

When the head is lowered, valves in the veins close to prevent backflow of blood.

Radius

Radius

Like compression socks, tight skin aids circulation by squeezing blood vessels and helping regulate blood pressure.

Metacarpal

Okapi

Giraffe

Okapia johnstoni

SMALL FAMILY TREE

Early giraffes coexisted with two other subfamilies: the massive sivatheres (now extinct) and the ungulate group that includes the okapi. Scientists first became aware of the okapi, which has a long tongue and legs proportioned like those of a giraffe, at the turn of the 20th century.

G. camelopardalis (one million years ago)

No known

changes

Six ancestors

Palaeotragus

primaevus

Sivatheriinae

Palaeotraginae (2 mya)

Okapia

Sivatherium

gigantium

Palaeomerycinae

(approximately 18 mya)

MEASUREMENTS ARE AVERAGES.

FERNANDO G. BAPTISTA, TAYLOR MAGGIACOMO, EVE CONANT, AND SOREN WALLJASPER NGM STAFF; LAWSON PARKER; SHIZUKA AOKI; QINGYANG CHEN; TANIA VELIN

SOURCES: SARA FERGUSON AND JULIAN FENNESSY, GIRAFFE CONSERVATION FOUNDATION; MARYLAND ZOO