New Computer Models Provide Insight Into The Evolution of Harvestmen

The marvellous Eupnoi model created by computed tomography

Computer models released in the scientific journal Nature Communications have revealed remarkable new insights into the early evolution of harvestmen, better known as the 'daddy long legs.' An international team of scientists led by researchers from Imperial College, London, created 3D computer models of the basal forms of the harvestmen orders Eupnoi and Dyspnoi in order to gain fresh insight into their evolution. These ancient creatures were less than a centimetre in length and lived before the dinosaurs over 300 million years ago.

Scientists believe that harvestmen were some of the first creatures to invade the land after plants rather than scorpions and spiders which were quite primitive. The models, when compared to modern forms, show that the fossils were not very different to their descendants. They looked almost modern. This shows that harvestmen evolved very early on in their fossil record and were able to survive upon the land. They also revealed that harvestmen split away from their common ancestor around 305 million years ago.

Dr Russell Garwood, who is currently based in the computed tomography lab at the Natural History Museum in London and who carried out his research in the Department of Earth Science and Engineering at Imperial College, London, stated 'it is remarkable how little these creatures have changed in appearance since before the dinosaurs. If you went out into the garden and found one of these little creatures, it would be like holding a little bit of prehistory in your hands.'

He went on to say 'we can't yet be sure why harvestmen appear so modern when most land animals, including their cousins the scorpions, were in such a primitive form at the time. It may be because they evolved early to be good at what they do and did not need to change their bodies even further.' The models were particularly useful when it came to analysing the creatures' lifestyle as harvestmen fossils are very rare due to their delicate nature; one of the specimens used had a crushed abdomen.

The scientists were able to extract information from the fossils using the scanning and modelling techniques. Analysis of the Eupnoi fossil shows that it had a very soft and thin exoskeleton. They also believe that it would have lived in the wet and moist foliage just above the forest floor out of the reach of giant predatory amphibians and insects.

The models also revealed the presence of a hook on its legs which it would have used to grapple onto leaves and other surfaces. These traits are all found in its descendants both modern and prehistoric. A similar story is told in the Dyspnoi fossil. It has similar features to its companion. However it also had a series of spikes tougher than its exoskeleton on its back for protection against predators. Its modern American descendent Acuclavella cosmetoides has similar spikes and lives in similar environmental conditions.

Most palaeontologists analyse fossils by splitting open rocks and using a combination of careful observation, traces in the surrounding rocks and electron microscopy to extract information from specimens. This can be limited, especially with fossils that display no 3 dimensional parts such as fish. This study made use of a technique called computed tomography. The scientists took 3142 x ray scans of the fossils and, using a special computer and computer program, compiled the data into accurate, manipulatable, 3D models.

The research was a follow through from a previous study with similar techniques. Computed tomography is a powerful tool and could change the study of palaeontology, giving palaeontologists greater insight into our planet's long and illustrious history. It has become prevalent when studying well preserved, but non 3D, fossils. Fossils preserved in oil shale from the Messel Pits or the pyrite fossils of the Hunsruck slates have revealed countless, incredible secrets when subjected to such techniques.