Eophrynus prestivicii (left) and Cryptomartus hindi are species of spiders that lived about 300 million years ago. Discovering the details of their biology from fossils isn't easy, especially since these arachnids were only about an inch long. So scientists from England and Germany took more than 3000 X-ray images of each fossilized spider with a CT scanning device and created 3-D computer models of the ancient arachnids.
The models revealed details that couldn't be seen from gazing at the fossils: E. prestivicii (first video below), which had long legs that could have enabled it to run and chase its prey, had defensive spikes on its back. The scientists say the spikes might have helped protect the spider from amphibian predators.
The way in which the two sets of front legs of C. hindi angle toward the front has led the scientists to think that this species might have been an ambush predator. C. hindi also had mouth appendages called pedipalps, which are present in some rare species of modern spiders and help them to manipulate prey.
All images courtesy of the Natural History Museum and Imperial College London.