A group of researchers studying a 305 million-year-old ancient arachnid fossil stumbled across an amazing discovery. The findings, which were published in the journal Current Biology, revealed that ancient arachnids (specifically harvestmen) had two rows of eyes. According to an April 10 report from the American Museum of Natural History, the research results reveal important details of these varied and very successful arthropods, which can be found on every continent except Antarctica.
The use of X-ray imaging techniques allowed the Manchester University and the American Museum of Natural History researchers to examine the ancient arachnid fossil, which was preserved in unusually good condition. The detailed fossil characteristics they were able to discover is unprecedented.
The primitive, fossilized daddy-long-legs specimen was found in the eastern part of France. Regarding the ancient arachnids research, lead study author Russell Garwood, a paleontologist at the University of Manchester in the UK, explained that...."Although they have eight legs, harvestmen are not spiders. They are more closely related to another arachnid, the scorpion."
He also explained that ancient arachnids can have two kinds of eyes -- lateral (on the side of the body) and median (near the center of the body). Today's harvestmen lack the lateral eyes. However, the harvestmen fossil, (scientific name Hastocularis argus) had both median and lateral eyes.
These results are therefore significant steps in gaining a better understanding of this group of animals. Prashant Sharma, study co-author, said...“Terrestrial arthropods like harvestmen have a sparse fossil record because their exoskeletons don’t preserve well.As a result, some fundamental questions in the evolutionary history of these organisms remain unresolved. This exceptional fossil has given us a rare and detailed look at the anatomy of harvestmen that lived hundreds of millions of years ago.”
The arachnids are a class of arthropods that can be either terrestrial or aquatic, and they are often insectivores. This is the group that includes spiders, scorpions and mites as well as other species. They differ in their branch in that they have four pairs of legs, they do not have wings or antennae, and their eyes are simple ( ocelli ) and not compounds. Most arachnids are oviparous (animals that lay eggs) and the sexes are generally distinct morphologies.
The oldest known spider fossil was discovered in Gilboa NY. Named Attercopus fimbriunguis, it reportedly dates back about 390 million years. Without certainty about its links with existing species, this specimen is located at the origin of the group of spiders.
According to found fossils, the maximum body size of ancient arachnids does not exceed the current arachnids: the largest fossil specimen is 6 or 7 inches in length, while the difference in the size of present species is between 0.3 mm and 13 cm.
To date, the oldest known ancient arachnid fossil belongs to the order of scorpions. This fossil is about 500 million years.