By | August 24, 2016

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 were swimmers or floaters that drifted through the water.


Key features

■ Head shield

■ Segmented, three-lobed body

■ Many had compound eyes

■ External skeleton (exoskeleton)

When Trilobites appeared in the Cambrian Period, 526 million years ago, and disappeared at the end of the Permian Period, 250 million years ago, when the last species was wiped out.




When: 300–251 million years ago (Late Carboniferous to Late Permian)

Fossil location: N. America, Europe, Asia, W. Australia

Habitat: Seafloor

Length: 1–1.1/4 in (2.5–3 cm)

Ditomopyge lived toward the end of the trilobites’ reign, just before the age of the dinosaurs. It had a hard outer skeleton (exoskeleton) made up of overlapping plates covering its body segments. Underneath, each segment had a pair of wriggling legs.
The head was protected by a large shield with backward-pointing spines and would have sported a pair of flexible antennae (feelers) for finding the way and tasting food.




When: 465 million years ago (Middle Ordovician)

Fossil location: France, Portugal, Spain

Habitat: Seafloor

Length: Up to 1.1/2 in (4 cm)

Like many trilobites, Eodalmanitina had large eyes and good vision. Trilobites were among the first animals to evolve sophisticated eyes. These consisted of many tiny, crystalline lenses packed together in a honeycomb pattern, like the compound eyes of insects.
Eodalmanitina had distinctive beanshaped eyes. Its long body tapered toward the tail, which was tipped by a short spine.




When: 380–359 million years ago (Middle to Late Devonian)

Fossil location: Morocco

Habitat: Seafloor

Length: 2.1/2in (6.6 cm)

Ceratarges was one of many trilobites with spectacular spines and horns. These prickly weapons may have been used to ward off predators. Another theory, however, is that they evolved as a result of battles between rival trilobites fighting over mates, like the antlers of modern stag beetles.




When: 444 million years ago (Silurian)

Fossil location: Worldwide

Habitat: Seafloor

Length: Up to 2 in (5 cm)

This small trilobite had many berry-shaped bumps on the shield protecting its head. Encrinurus’s eyes were probably situated at the end of short stalks. It may have spent a lot of time hiding in the mud on the seabed, with only its eyes above the surface.




When: 380–359 million years ago (Middle to Late Devonian)

Fossil location: Worldwide

Habitat: Seafloor

Length: Up to 2.1/4 in (6 cm)

Named for its keen sense of sight, Phacops (“lens eye”), like Eodalmanitina, had bulging eyes that gave it good vision, suggesting it lived in well-lit areas such as shallow seas. One of the most common and widespread trilobites, Phacops has been found in Europe, Africa, Australia, and North America. Geologists even use its fossils as a handy way to estimate the age of a rock.
Phacops could curl up in a tight ball to protect its softer undersides when attacked, much like some modern woodlice.


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