What's Older Than A Dinosaur?

Long before any backboned creatures - whether amphibian or reptile - set foor on land, invertebrates (animals without backbones) crept across the Earth. Among the first were arthropods, animals with a hard outer body casing (made chiefly of the strong protien chitin) and joint limbs (formed by tough tubular sections with muscles on the inside).
Arthropods included centipedes, millipedes, mites, ticks, scorpions, and insects.
With a 400-million year history, land arthropods far oulived the dinosaurs, and still survive in incredible numbers. They evolved from the Devonian Period, and at first didn't have wings. But during the Carboniferous Period, winged insects became common.
By the time of the Dinosaurs, there were grasshoppers, bettles, termites, and flies. Bees and other insects became important in the pollination of flowering plants.
Today, these small scurriers are sometimes called "mini-beasts." But some mini-beasts reached maxi-sizes - one centipede was longer than your leg!

Arthropods breathe by a system of air tubes known as trachea, that form from a branching network through the body. The tubes open at rows of holes, spiracles, along the creature's body. Their microsopic branches carry oxygen directly to the muscles, nerves, guts, and body fluids. Body and muscle movements keep the aair on the move.

Centipedes make up the group Chilopoda. Centipede means "a hundred legs", but only a few of the 3,000 living species have exactly this number.
They first crawled up the land 250 million years ago. Today these creatures grow to about 10 inches (20 centimeters) long, but their ancient cousins reached over three feet (one meter) in length.
Inside a centipede are several networks of ladder-like tubes. One network contains pale blood pumped by the heart. The tracheral network carries oxygen. Nerve cords, linked by clusters of nerve cells called ganglia, transmit nerve signals to and from the two-part brain.
Centipedes usually hide during the day, then chase their victims - worms, snails, wood lice, and insects - at night. The centipede seizes its struggling meal in its first pair of legs, which resebmle massive fangs, and delivers a paralyzing poisonous bite.

Dragnflies and the smaller damselflies make up the insect group Odonata. Meganeura, a crow-sized dragonfly from 300 million years ago, had a wingspan of 32 inches (80 centimeters), making it the hugest insect ever. Today's dragonfly wingspans are only 8 inches (20 centimeters).
Two pairs of meshlike wings attached to the dragonfly's thorax are held in an outstretched position when the insect lands.
A dragonfly eye is a honeycomb of 25,000 seperate lenses, known as ommatidia. Each focuses light rays to form an image of a small part of the scene. These images are somehow combined in the inset's brain.

These "bugs" from the insect group Blattodea have changed little over 300 million years. The biggest roaches were hand-sized, but tiday none grows longer than three inches (8 centimeters).
Much of the cockroaches' success is due to their versatile mouthparts. The mandibles or jaws are simple but strong chewers, which can deal with a variety of foods, from meat fibers to bread crumbs, leather paper - even solid wood.

Today, more than 4,000 kinds of roach live almost everywhere, except in seas and polar regions. Most dwell outdoors, tucked under rocks or logs. But indoors, roaches are considered pests. They love warmth, garbage, and food scraps, and their flattened profiles make it easy for them to slide - and hide - in narrow crevices and cracks.

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