Category Archives: Invertebrates


Possibly the largest insect that has ever lived, Meganeura looked like a gigantic dragonfly. Its wingspan was 2. ft (75 cm)—12 times greater than that of common dragonflies today. This monster insect used its giant wings to hunt other insects in midair. Insects and other invertebrates grew to a great size in the lush forests… Read More »


Ammonite fossils are unmistakeable, thanks to their beautiful coiled shapes. These sea creatures were close relatives of today’s octopuses and squids but lived inside a shell, which they enlarged with new chambers as they grew, forming a spiral. They lived throughout the seas and swam by squirting water, the hollow inner chambers of their shells… Read More »

Fossil Gems

Ammonite fossils can be as beautiful as jewels. Some look like glass ornaments when they are cut open and polished, their once-hollow shells having filled up with crystalline minerals over millions of years. Others have a pearly surface that shimmers with color, forming one of the world’s most precious gemstones. Ammonites grew in a spiral… Read More »

Fossil Seashells

The seashells on this gallery might look like a collection found on a beach, but these are all fossil shells and are millions of years old, some dating back to before the dinosaurs. Seashells fossilize well because they are so hard. They are among the easiest fossils to find. Most are shells of mollusks—soft-bodied invertebrates… Read More »

Brittle Stars

Look at any part of the seabed and you are likely to find star-shaped creatures with long, slender arms wriggling across the bottom. These are not fish, but invertebrates called brittle stars, and they are relatives of starfish and sea urchins. They are also known as snake stars because of the way they move their… Read More »


For more than 250 million years, the ancient seas teemed with trilobites prehistoric animals related to today’s insects, woodlice, and crabs. There were more than 17,000 different types of trilobite, ranging from the flea-sized to monsters twice the size of this book. Most crawled along the ocean floor in search of food, but a few… Read More »

Cambrian Explosion

About 530 million years ago, a huge range of new animals appeared in the seas, including the first creatures with clear legs, heads, sense organs, skeletons, and shells. All the main categories of invertebrates (animals without backbones) known today seem to have evolved almost at once, as well as some weird creatures quite unlike anything… Read More »