Warm and cold blood

Reptiles are cold-blooded, which means that they depend on conditions outside their body, such as the Sun's heat, for temperature control. Warm-blooded animals, such as mammals, produce heat from food energy, have hair for warmth, and sweat to cool down. Although dinosaurs were reptiles, much of their behavior, such as agile running, has more in common with

Blood vessels Cross-section of mammal bone

Blood and bones Dinosaurs had bones more like mammals than reptiles. Mammal bones contain

Blood vessels mammals. scientists are therefore puzzled over whether dinosaurs were warm- or cold-blooded.

Blood vessels Cross-section of mammal bone

Blood vessels

Blood and bones Dinosaurs had bones more like mammals than reptiles. Mammal bones contain

Side view: blood vessels passed through holes in the bony plate

Cross-section: hole for blood vessel

Cross-section: hole for blood vessel

Side view: blood vessels passed through holes in the bony plate

Back plates

Stegosaurus used its back plates for warming up and cooling down. To warm up, Stegosaurus stood with its side to the sun to heat the blood as it flowed through the plates. To cool down, it stood in the shade and lost heat through the plates.

Cold-blooded sunbather A typical cold-blooded creature, such as a lizard, spends hours sunbathing to raise the body's temperature to a level where it can work effectively. To avoid overheating, the lizard can cool off in the shade. When it is cold at night, or in the winter, reptiles are inactive.

Lizard sunbathing

Lizard sunbathing

High blood pressure was needed to reach brain 50 ft (15 m) above the ground.

High blood pressure was needed to reach brain 50 ft (15 m) above the ground.

Good example Dromaeosaurus is one of the best arguments for dinosaurs being warm-blooded animals. Fast-moving and agile, Dromaeosaurus had a lifestyle better suited to warm-blooded killers like wolves rather than reptiles like lizards.

Blood pressure Tall dinosaurs needed high blood pressure to pump blood to their brain. But down at the level of their lungs, such high pressure would be fatal. Warm-blooded animals have a twin pressure system. Perhaps dinosaurs had a similar system.

Brachiosaurus

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