Evolution of spiders

Spiders have lived on Earth for a long time.

Long ago, some creatures looked like spiders. They had eight legs. But they could not make silk.

True spiders appeared much later. Early spiders lived in big forests. They used silk to hide their eggs. They also used silk to make small holes.

Later, spiders changed. They moved their silk tools to the end of their bodies. This helped them make better webs. Some spiders make round webs to catch bugs.

Today, many kinds of spiders live in the world.

Spiders have lived on Earth for a very long time. They may have existed for 380 million years.

Long ago, creatures called trigonotarbids lived on land. They had eight legs and book lungs. Book lungs are parts used for breathing. These creatures were not true spiders. They could not make silk.

True spiders appeared later. Early spiders lived in giant fern forests. They used silk to cover their eggs. They also used silk to line small holes. These early spiders had spinnerets under their middle bodies. Spinnerets are parts that make silk.

Later, spiders changed. They moved their spinnerets to the end of their bodies. This helped them make better webs. Some spiders make round webs called orb webs. These webs help them catch insects.

One fossil spider from China is the largest known fossil. Today, there are more than 45,000 known species of spiders.

Spiders are amazing hunters that have been on Earth for a very long time. They may have existed for at least 380 million years.

Most spiders belong to a group that evolved from ancestors living in water. Today, scientists have described more than 45,000 different species of spiders. There might actually be more than 120,000 species in total. These living things are organized into many different families and groups. Researchers still find and describe new species every single year.

One of the most important parts of spider history is how they use silk. Early spider-like creatures called trigonotarbids lived on land and had eight legs. They used book lungs to breathe, but they could not spin silk. Later, true spiders appeared and began to use silk in new ways. They might have used it to cover their eggs or line small holes. As plants and insects changed, spiders learned to use silk for better tools. They eventually made ground sheets and trapdoor webs to catch their food.

Scientists use a tool called a molecular clock to study spider history. This helps them see when spiders split from other creatures. They believe this happened between 375 and 328 million years ago. In the past, some fossils like Attercopus were thought to be the oldest spiders. Now, experts believe Attercopus belonged to a separate, extinct group called Uraraneida. This group could make silk but did not have true spinnerets. Spinnerets are the special body parts used to produce silk.

Many important fossils tell us about how spiders grew and changed. During the Carboniferous Period, early spiders lived in giant fern forests. These spiders often had their spinnerets under the middle of their bodies. Later, spiders moved their spinnerets to the end of their abdomen. This change helped them build more complex webs like the round orb webs.

One large fossil spider called Mongolarachne jurassica was found in China. It lived about 95 million years ago.

We can see how much spiders have changed by looking at old amber. Amber is hardened tree resin that can trap tiny things inside. One 110 million-year-old web preserved in amber shows a perfect circular orb web. This ancient web even trapped a beetle, a mite, a wasp's leg, and a fly. It shows that orb webs were already very advanced long ago. Today, many spiders belong to a group called the RTA clade. This group is very different from the spiders that lived during the time of the dinosaurs.

Spiders are highly successful predators that have inhabited Earth for at least 380 million years.

They belong to a group of animals called chelicerates, which evolved from aquatic ancestors. Today, scientists have described more than 45,000 different species of spiders. These are organized into 114 families and 3,958 genera. Researchers believe there may actually be more than 120,000 species in total. Every year, new species are identified and described by researchers in the field.

A major part of spider evolution involves the development of silk and spinnerets. Spinnerets are specialized organs used to produce and direct silk. Early spider-like creatures, known as trigonotarbids, lived on land and had eight legs. They used book lungs to breathe, which are internal organs for respiration. However, trigonotarbids were not true spiders because they lacked spinnerets and could not spin silk. They are now extinct and have no living descendants.

Scientists use a method called a molecular clock to trace spider history. This tool uses genetic data to estimate when different groups diverged from one another. By using a molecular clock calibrated with 27 chelicerate fossils, researchers found that spiders likely diverged from other chelicerates between 375 and 328 million years ago. In the past, a fossil named Attercopus was thought to be the oldest spider. Now, experts believe it belonged to an extinct order called Uraraneida. This group could produce silk but lacked true spinnerets.

The oldest reported true spiders date back to the Carboniferous Period. Most of these early fossil spiders likely belonged to a group called Mesothelae. These spiders were different from modern spiders because their spinnerets were located underneath the middle of the abdomen. They lived in giant clubmoss and fern forests as ground-dwelling predators. They probably used silk for simple tasks, such as lining retreat holes or covering eggs. They may have also built basic ground sheet webs or trapdoor constructions.

As plant and insect life diversified, spiders developed more complex ways to use silk. Spiders with spinnerets located at the end of the abdomen appeared more than 200 million years ago. This group includes the Mygalomorphae and Araneomorphae. This anatomical change likely helped them create elaborate sheet and maze webs. It also allowed for the development of the safety dragline. The oldest known mygalomorph is a fossil called Rosamygale from the Triassic of France.

By the Jurassic period, many spiders had developed sophisticated aerial webs. The famous circular orb web was already in use by orb-weaver spiders.

A 110 million-year-old web preserved in amber shows a perfect orb structure. This ancient web even contains trapped prey, including a beetle, a mite, a fly, and a wasp's leg. One of the largest known fossil spiders, Mongolarachne jurassica, lived about 95 million years ago in China.

Modern spider diversity is quite different from the species that lived during the Mesozoic era. During the Cretaceous-Cenozoic interval, there was a major turnover in spider populations. The Cretaceous was dominated by groups like Synspermiata and Palpimanoidea. The Cenozoic era is now dominated by the RTA clade and araneoid spiders. The RTA clade is a large group of modern spiders linked by a specific trait on the male pedipalp called the retrolateral tibial apophysis.