Ancient fossil 'may prove scorpion was first land-dwelling animal'

Fossil is earliest evidence of breathing structure compatible with life on land, scientists say

Fossil experts in the US have revealed the remains of what they say is the first animal that may have set foot on land – an ancient scorpion.

The earliest animals were aquatic, but eventually transitioned on to land. While scorpions are known to be one of the first animals to have become fully land-dwelling, experts say the two new fossils add to a growing debate about when animals made the shift.

The scorpion, which is about 2.5cm in length, is thought to have lived about 437m years ago, with the fossils discovered in a quarry north of state highway 164 in Wisconsin in the 1980s.

The earliest arachnid yet discovered, the creature has been named Parioscorpio venator, meaning ancestral scorpion and hunter. The creature, like modern scorpions, had two large claws and a tail with a sting at its end.

But the team behind the discovery say it is the scorpion’s internal structure that is most exciting.

“This scorpion had the respiratory structures that indicate it was able to live on land. It is the earliest evidence we have that an animal could do this,” said Dr Andrew J Wendruff, a palaeontologist at Otterbein University, Ohio, and co-author of the research.

These structures include evidence of pulmo-pericardial sinuses that, in modern scorpions, connect the animal’s respiratory organs with its circulatory system.

Wendruff added that such structures, as well as other features of the animal’s cardiovascular system, suggested the ancient animal was, like modern scorpions, able to breathe air. The team say the features are also similar to those seen in horseshoe crabs, which live in shallow coastal waters but can venture on to land for brief spells.

“The fossil was found in a shallow water setting and so it is likely this animal lived in both environments,” said Wendruff, although he said the team cannot be sure it scuttled ashore.

Parioscorpio venator
The fossil shows evidence of pulmo-pericardial sinuses that connect the respiratory organs with its circulatory system. Photograph: Christian Wirkner and Andrew Wendruff

A move to terra firma would have offered advantages, said Wendruff.

“Throughout all of Earth’s history there is a race to utilise resources that are not being used. Land – something we take majorly for granted – was barren by todays standards,” he said.

The discovery, published in the the journal Scientific Reports, pushes back the date of the earliest known scorpion by up to three million years, with the previous record-holder a species discovered by a Victorian palaeontologist in the Pentland hills in Scotland.

Dr Jason Dunlop, curator of arachnids and myriapods at the Museum of Natural History in Berlin, who was not involved in the latest research, said the preservation of some of the scorpion’s internal structures, such as the cardiovascular system, is unusual.

“This is very rare in fossils of this age and suggests that in some aspects of their anatomy scorpions have hardly changed in almost 440m years,” he said.

However he urged caution, noting the fossil did not show whether the scorpion had lungs or gills.

“That would have been the key character, and so long as its missing I think we have to be cautious about saying whether or not it lived on land,” he said.

Dr Jesus Lozano-Fernandez, a palaeobiologist at the Institute of Evolutionary Biology of Barcelona, said it was a matter of much debate whether the earliest scorpions were indeed aquatic – a theory the new discovery piled further doubt on, he said.

“If the described fossil scorpion was indeed terrestrial, that would suggest that [other arachnids with similar breathing apparatus such as spiders], at least, or even the whole [of] arachnids would already have colonised the land by that time.”

Contributor

Nicola Davis

The GuardianTramp

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