Tardigrade trapped in amber is a never-before-seen species

Scientists have discovered a rare fossil that was suspended in amber 16 million years old. It is a species of tardigrade that has never been seen before. This pudgy aquatic creature rarely appears in fossil records.
The modern-day tardigrade, also called water bears or water piglets, can be found anywhere there is liquid water. This includes the ocean depths and the thin water films that cover terrestrial mosses. These tiny creatures are known for their survival skills. They eliminate most of the water from their bodies and dramatically slow down their metabolism to become a suspended animation state that allows them to withstand extreme temperatures, pressure, and radiation.

Although tardigrades can be destroyed almost instantly when they are alive, due to their small size and absence of hard tissue, very few tardigrade fossils were ever discovered. Only three have been found. Two of the fossils have been officially named, one in Canada and one in New Jersey. The other is still unknown.

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Scientists have now discovered a new species of tardigrade in amber from the Dominican Republic in a study published in Proceedings of the Royal Society B: Biological Sciences. The fossil is Miocene (23 million to 53 million years ago) and was so well preserved that scientists were able to include the new water bear, Paradoryphoribius chronocaribbeus in the tardigrade "tree to life."

Frank Smith, an evolutionary developmental biologist, assistant professor at the University of North Florida, said that there are only two distinct tardigrades in the fossil record. He was not involved with the new study. Smith explained that the researchers were able use the same techniques to identify living tardigrades to help them determine the relationship between the new species and modern-day water bears because of the fossil's quality.

It measures in at 0.02 inches (0.6 m) in length. So how did researchers spot it? Marc Mapalo, a Harvard University doctoral student in the Department of Organismic and Evolutionary Biology, said that it was luck.

Mapalo's collaborators from the New Jersey Institute of Technology acquired the amber initially to search for ants in it; the team, headed by evolutionary biologist Phillip Barden studies the evolution of social insects like termites and ants.

Mapalo stated that although they had been using the amber for several months, they were only looking at ants. One day, a lab member saw a caterpillar-like, stumpy shape. It had tiny, clawed legs that protruded from its underside. They found a tardigrade in the amber along with three ants and a beetle.

The new tardigrade was found in Dominican amber. It also contained three ants and a beetle. (Image credit: Harvard/NJIT. Photo by Phillip Barden.

Mapalo stated that it was more luck that they found it, as it isn't something they are looking for. Mapalo was surprised to learn about the fossil as the chances of finding one are slim. Mapalo is a water bear lover who once wrote a song about them. He was excited to see one of the few tardigrade fossils.

The team was able to find the fossil in addition to the fact that it was located very close to the amber's surface, which allowed light from their microscopes to easily reach the specimen. The researchers used techniques such as transmitted light and confocal fluorescent microscopy to examine both the exterior anatomy of the tardigrade, such its claws, and the internal morphology. They also examined the foregut, which contained hard structures similar to the "throat" of the animal.

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Mapalo stated that this is the first time we have been able to see the internal morphology of a tardigrade fossil.

The researchers determined that the water bear was part of the Isohypsibioidea superfamily. This superfamily is a diverse group modern-day tardigrades. P. chronocaribbeus is the oldest member of this superfamily.

However, the internal anatomy of the water bear sets it apart from other tardigrades. A hard structure between the mouth and the esophagus was called a macroplacoid. Other Isohypsibioidea members had two to three thick macroplacoids. The new tardigrade fossil only had one thin one marked with a line.

Mapalo stated that it doesn't correspond to any extant species or genus in this superfamily because of this. To accommodate P. chronocaribbeus, the team devised a new genus and species.

Smith stated that P. chronocaribbeus lived in similar circumstances to modern-day water bears during its peak, snorting liquid from plant cells and resting on moss cushions. This species would be found all over the world if we could go back 16 million years. He said that there might be more tardigrade fossils in Dominican amber, which is also found in other amber deposits throughout the world.

Mapalo stated that as of right now, not many people are looking for tardigrade fossils amber. However, if more scientists joined in the hunt, there might be more tardigrade fossils.

Smith stated that to the naked eye, Smith doesn't know if it would look like a speck or dust. You probably wouldn't be able to see it at all. Scientists would need to examine all amber samples carefully under a microscope in order to identify the pudgy sea creatures. He said that it is more likely that there was a tardigrade living near the tree producing amber. It's worth checking any amber samples for signs of this.

Mapalo will continue to research the genetic and molecular mechanisms behind growth and development of living tardigrades until more fossils of tardigrades are discovered. He is currently visiting Smith's Florida lab to study the development of tardigrade claws. This research could reveal what factors drove tardigrade evolution and lead to the plump, familiar body we all love.

Mapalo also wants to study the first known fossil tardigrade, which is housed at Harvard. According to their report, the fossil, which was identified as Beorn leggi (a species of water bear), was discovered near Cedar Lake, Manitoba in 1964. It is approximately 78 million years old and dates back to the Upper Cretaceous. High-resolution imaging techniques weren't available at that time so the exact relationship of the water bear to the modern-day species is still unknown.

Original publication on Live Science