Which animals are as old as dinosaurs?

By any measure, insects are the most successful animal group on Earth. There are over a million known insect species, and possibly several million more still undiscovered. Some have remained almost unchanged for hundreds of millions of years. The earliest dragonflies appeared around 320 million years ago - more than 80 million years before the first dinosaurs - and some Carboniferous dragonflies had wingspans of up to 70 cm (28 in), making them the largest insects that ever flew. Modern dragonflies are smaller, but their basic body plan has barely changed in over 300 million years.

Yes - several groups did. Lizards and snakes (collectively called squamates) were already widespread during the age of dinosaurs and survived the extinction with most of their main lineages intact. Some experts think they made it through by being small (easier to hide and find food), cold-blooded (needing less food), and able to burrow or hibernate during the worst of the post-impact cold. The tuatara, a New Zealand reptile that looks like a lizard but actually belongs to its own ancient group called Rhynchocephalia, also pulled through - and is the only surviving member of a reptile lineage that was once widespread alongside dinosaurs.

Arachnids - the group that includes spiders, scorpions, mites, and ticks - are extraordinarily ancient. Scorpions are among the oldest known arachnids, with fossils dating back about 437 million years, far older than the dinosaurs. Spiders date back at least 380 million years. There are now over 100,000 arachnid species, and all of them are predators. Most use venom to kill their prey, injecting it through fangs (spiders) or stingers (scorpions). Among the around 1,500 known scorpion species, about 25-50 produce venom strong enough to kill a human, though most scorpion stings are merely painful.

Some of the oldest are invertebrates - sea creatures without backbones. Jellyfish-like animals have lived in the oceans for around 600 million years. Sponges may be even older. Among large sea animals with backbones, sharks are the great survivors: the earliest sharks appeared around 450 million years ago - twice as old as the dinosaurs - and they have survived all five of Earth's great mass extinctions. The largest shark ever, Megalodon, lived from about 23 to 3.6 million years ago and reached up to 18 metres (60 feet) long, with teeth the size of a human hand. It is now extinct, but its smaller cousin the great white shark still patrols the oceans today.

Cockroaches are remarkably tough. They have existed in some form for about 320 million years, making them older than dinosaurs. They can survive without food for about a month, eat almost anything (including paper, glue, and soap), and can recover after being submerged in water for up to 30 minutes. They are also surprisingly radiation-resistant - capable of withstanding 6-15 times the dose of radiation that would kill a human. Cockroaches live on every continent except Antarctica. Of about 4,500 known species, only around 30 actually live near humans - most of the rest are forest insects you would never notice.

Crocodilians are a group of large, predatory reptiles that includes modern crocodiles, alligators, caimans, and gharials - 27 living species in total. They are part of the wider group archosaurs, which also included the dinosaurs - making crocodilians the closest living relatives of birds. The first crocodilians appeared around the same time as the dinosaurs, about 230 million years ago, and some early crocodile relatives even lived in the open sea (Geosaurus) or on dry land like cheetahs (Pristichampsus). Most modern crocodilians look strikingly similar to their Cretaceous ancestors - they are true "living fossils."

• Geosaurus was an aquatic crocodilian of the Jurassic Period. Instead of the heavy armour worn by most crocodilians, it had smooth, scaly skin and paddle-like limbs, making it an agile swimmer in the open ocean.
• Deinosuchus was one of the largest crocodilians ever known - up to 12 metres (39 feet) long - and could probably bring down medium-sized dinosaurs at the water's edge.
• Today's saltwater crocodile, at up to 7 metres (23 feet) long, is the largest reptile on Earth - but it is dwarfed by its prehistoric ancestors.

• The horseshoe crab has barely changed in 450 million years - it is older than trees, older than dinosaurs, and is one of the most successful body plans in Earth's history.
• Coelacanths, a fish thought to be extinct for 66 million years, were rediscovered alive off the coast of South Africa in 1938 - they had quietly survived in deep water.
• Modern turtles evolved around 220 million years ago, making them roughly as old as the first dinosaurs.
• Some bristlecone pine trees in California are over 4,800 years old - the oldest non-clonal trees on Earth, though they are nowhere near as old as dinosaurs.
• The tuatara is the only living member of an ancient reptile order called Rhynchocephalia, which was widespread during the dinosaur age but is now restricted to a few New Zealand islands.