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Scientists have discovered an incredibly rare fossil suspended in 16 million-year-old amber: a never-before-seen tardigrade species, a chubby aquatic creature that rarely appears in the fossil record.
Modern tardigrades, also known as water bears or moss piglets, can be found in just about any environment with liquid water, from ocean depths to thin films of water that cover terrestrial mosses. The tiny creatures are famous for their survival skills; by expelling most of the water from their bodies and drastically slowing their metabolism, tardigrades enter a suspended animation-like state in which they can withstand extreme temperatures, pressures, and radiation.
But although tardigrade fossils are nearly impossible to destroy when alive, their small size and lack of hard tissue means that very few tardigrade fossils have ever been discovered – only three, to be exact. The species of two of these fossils, found in Canada and New Jersey, have been officially named; the other, found in Western Siberia, remains unnamed.
Related: 8 reasons why we love tardigrades
But now, in a new study published Tuesday (October 5) in the journal Proceedings of the Royal Society B: Biological Sciences, scientists introduced a new species of tardigrade they discovered in amber from the Dominican Republic. The fossil dates from the Miocene era (23 million to 5.3 million years ago) and is so well preserved that the team were able to place the new water bear, named Paradoryphoribius chronocaribbeus, in the tardigrade “tree of life”.
“There are really only two clear tardigrades in the fossil record,” referring to the two fossils whose species are known, “so it’s really exciting to find a third,” said Frank Smith, biologist at the evolutionary development and assistant professor at the University of the North. Florida who was not involved in the new study. And thanks to the quality of the fossil, the researchers were able to apply the same techniques used to identify living tardigrades, which helped the team determine the connection between the new species and modern water bears, said Smith.
The tardigrade is less than 0.02 inch (0.6 millimeter) long, so how did the researchers spot it? It was really a matter of luck, first author Marc Mapalo, a doctoral student in the Department of Organic and Evolutionary Biology at Harvard University, told Live Science.
Mapalo collaborators at the New Jersey Institute of Technology first acquired the amber to search for ants captured in the material; the team, led by evolutionary biologist Phillip Barden, is studying the evolution social insects such as ants and termites.
“They had amber for months, but they only looked at ants,” Mapalo said. But at one point, a keen-eyed lab member noticed a stocky caterpillar-like shape with tiny clawed legs protruding from its underside. Lo and behold, they had found a tardigrade floating in amber, alongside three ants, a beetle, and a flower.
“It was luckier they saw it… because it’s not something they are looking for,” Mapalo said. Upon learning of the fossil’s existence, Mapalo said he was “really surprised” because the chances of finding a tardigrade fossil are so slim. Like someone who loves water wears so much that he once wrote a song about them, he was eager to examine one of the few known late fossils.
In addition to finding the fossil, the team were lucky because the tardigrade sat quite close to the surface of the amber, meaning that light from their microscopes could easily reach the sample. Using techniques called transmitted light and confocal fluorescence microscopy, the researchers examined both the external anatomy, such as the tardigrade’s claws, and some of the internal morphology, including various hard structures found in the intestine. anterior of the creature – roughly similar to its “throat”.
Related: Ancient footprints of tiny “vampires”: 8 rare and unusual fossils
“This is the first tardigrade fossil whose internal morphology we have been able to visualize,” Mapalo said.
Based on the shape and location of the tardigrade’s claws, researchers identified the water bear as part of the superfamily Isohypsibioidea, a diverse group of modern tardigrades. This makes P. chronocaribbeus the oldest known member of the superfamily.
However, there are aspects of the water bear’s internal anatomy that distinguish it from related tardigrades. In particular, a hard structure located between the mouth and the esophagus, called the macroplacoid, had a unique shape; while other members of Isohypsibioidea have two to three thick macroplacoids, the new tardigrade fossil had only one thin, marked with a crest.
“For this reason, it does not match any gender that exists within this superfamily,” Mapalo said. And for this reason, the team created a whole new genus and species to accommodate P. chronocaribbeus.
At its peak, P. chronocaribbeus likely lived in conditions similar to modern water bears, hanging out on moss cushions and sucking fluid from plant cells, Smith said. “If we went back 16 million years to this place, we would probably find this species everywhere.” And in theory, more tardigrade fossils could be lurking in Dominican amber from the same region, as well as other amber deposits around the world, he said.
Right now, very few people are looking for tardigrade fossils in amber, so if more scientists joined in the hunt, more tardigrade fossils could be found, Mapalo said.
To the naked eye, “I don’t even know if that would look like a speck of dust, you probably wouldn’t see it at all,” Smith said. So, to spot plump sea creatures, scientists should carefully inspect all of their amber samples under a microscope. But generally speaking, “if you find amber, it is more than likely that there were tardigrades living somewhere near the tree that produced that amber … So it is worth looking for tardigrades in n ‘any sample of amber,’ he said.
Until more tardigrade fossils are found, Mapalo plans to study the genetic and molecular mechanisms that stimulate the growth and development of living tardigrade. Currently he is visiting Smith’s laboratory in Florida to study the development of tardigrade claws; this line of research could help reveal what forces drove the evolution of tardigrades, leading tardigrades to embrace the plump and familiar body plane we now know and love.
In addition, Mapalo wants to study the first tardigrade fossil ever found, which happens to be housed at Harvard. The fossil, identified as the species Beorn lu, was found in 1964 near Cedar Lake in Manitoba and is approximately 78 million years old, meaning it dates from Upper Cretaceous, note the authors in their report. However, as high-resolution imaging techniques were not available at the time, the exact relationship between the water bear and modern species has not yet been determined.
Originally posted on Live Science.
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