Primeval spiders in three dimensions

3D model reveals features and way of life of two spider ancestors

Eophrynus prestivicii: Long Legs and Spines © Imperial College London
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When the first amphibians conquered the country about 300 million years ago, the members living there had to adapt to the new danger. An indication of their strategies are now two

three-dimensional models of early spider ancestors. They show the characteristics of the animals in never before visible detail.

Around 359 to 299 million years ago, life had just begun to spread across the country. The first rainforests were created on the land masses near the equator. They also had two types of arthropods, distant ancestors of today's spiders. About as large as a one-cent coin were Cryptomartus hindi and Eophrynus prestivicii, which show preserved fossils. Unfortunately, scientists from the relics have been able to read little more than that the animals had four pairs of legs and resemble today's spiders.

3D model gives insight into lifestyle

Now, scientists at Imperial College London have used computer tomography to gain new insights into the anatomy of these primeval spider ancestors. From around 3, 000 individual images of CT, a software developed by them constructed an accurate 3D model of each fossil animal. The models revealed some of the physical traits that enabled the two species to successfully prey and escape predators.

Lurker Cryptomartus hindi © Imperial College London

Cryptomartus: Lauerjäger with holding claws

Thus, the images show that the foremost pair of legs of Cryptomartus hindi was turned forward - an adaptation to the hunt, which made it easier for them to catch their prey. According to the researchers, this indicates that the animal may have been a Lauer hunter. It may have lived in pieces of wood or litter, waiting there hidden for passing insects. A similar behavior is still observed in their modern offspring, the crab spiders, which, well camouflaged by their color, sitting on flowers and hunt nectar-collecting insects. display

The spider ancestors' mouthparts were also adapted to his youthful way of life: his pedipalps had tiny foot claws at their ends, which helped to manipulate the prey after grasping it. Hood spiders (Ricinulei) still have similar claws today. Rather primitive features, however, were the ball-like bulges at the base of the extremities, the so-called coxalendites. They are relics that probably come from the last common ancestor of crabs and arachnids. Some cancers today use such thickening to crush their food before pushing it into their mouth.

Eophrynus: Quick legs and back spines

The second prehistoric species, Eophrynus prestivicii, was no lure-fighter, as the 3D model shows. Instead, his long legs suggest that the spider was chasing their prey, running on the open forest floor. For the first time, pal ontologists were also able to discover that this species bore defensive spines on their back bumper. Perhaps they should protect Eophrynus from becoming a prey to amphibians who had just conquered the land at that time.

"Our models bring these primeval creatures back to life and it's really exciting to be able to look into their richness of detail, " explains Russell Garwood, principal author of the study. Our work helps us to understand what happened in this period of the early history of rural life. We suspect that one of the two species responded to the increased threat from the amphibians by their back spines grew. The other, on the other hand, became a Lauerj ger and lived in hiding.

According to the scientist, her new method could also be used to reexamine other fossils and thus gain a clearer picture of past life worlds.

(Imperial College London, 05.08.2009 - NPO)