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Microscopic tardigrades have thrived on Earth for more than 500 million years, and may well outlive humans, but the tiny creatures don’t leave behind many fossils.
Hiding in plain sight, the third-ever tardigrade fossil on record has been found suspended within a piece of 16-million-year-old Dominican amber.
The find includes a newly named species, Paradoryphoribius chronocaribbeus, as a relative of the modern living family of tardigrades known as Isohypsibioidea. It’s the first tardigrade fossil from the Cenozoic, our current geological era that began 66 million years ago.
The study published Tuesday in the Proceedings of the Royal Society B.
Beneath a microscope, tiny tardigrades look like water bears. Although they are commonly found in water – and at times, serving as the nemesis in “Ant-Man and the Wasp” – tardigrades are known for their ability to survive and even thrive in the most extreme environments.
These tiny, pudgy animals are no longer than one millimeter. They have eight legs with claws at the end, a brain and central nervous system, and something sucker-like called a pharynx behind their mouth that can pierce food. Tardigrades are the smallest-known animal with legs.
All of these details are incredibly well preserved in the new fossil specimen, down to its tiny claws.
“The discovery of a fossil tardigrade is truly a once-in-a-generation event,” said Phil Barden, senior author of the study and assistant professor of biology at New Jersey Institute of Technology, in a statement.
“What is so remarkable is that tardigrades are a ubiquitous ancient lineage that has seen it all on Earth, from the fall of the dinosaurs to the rise of terrestrial colonization of plants,” Barden said. “Yet, they are like a ghost lineage for paleontologists with almost no fossil record. Finding any tardigrade fossil remains is an exciting moment where we can empirically see their progression through Earth history.”
The fossil allowed researchers to see evolutionary aspects that aren’t present in modern tardigrades, which means they can understand how they’ve changed over millions of years.
At first, the researchers didn’t even notice the tardigrade was trapped in the piece of amber.
“It’s a faint speck in amber,” said Barden. “In fact, Pdo. chronocaribbeus was originally an inclusion hidden in the corner of an amber piece with three different ant species that our lab had been studying, and it wasn’t spotted for months.”
Close observational analysis helped the researchers determine where the new species belongs on the tardigrade family tree.
“The fact that we had to rely on imaging techniques usually reserved for cellular and molecular biology shows how challenging it is to study fossil tardigrades,” said Javier Ortega-Hernández, study coauthor and assistant professor of organismic and evolutionary biology at Harvard University, in a statement. “We hope that this work encourages colleagues to look more closely at their amber samples with similar techniques to better understand these cryptic organisms.”
The new species is the first definitive fossil for the modern Isohypsibioidea family of tardigrades found across both marine and land environments today.
“We are just scratching the surface when it comes to understanding living tardigrade communities, especially in places like the Caribbean where they’ve not been surveyed,” said Barden. “This study provides a reminder that, for as little as we may have in the way of tardigrade fossils, we also know very little about the living species on our planet today.”
Tardigrades can tolerate extremes better than most forms of life – like surviving five mass extinction events on Earth – and some recently traveled to the International Space Station. It’s not the first time tardigrades have gone to space – and there may even be some of them on the moon after a mission carrying them crashed into its surface.
The tiny animals are related to arthropods and have a deep origin during the Cambrian Explosion, when multiple species of animals suddenly appear in Earth’s fossil record, 541 million years ago. More tardigrade fossils could be hiding within other pieces of amber that have already been studied – researchers just have to look close enough and have the expertise of what they’re looking for when it comes to microscopic fossils.
And tardigrades could outlive humans. It’s because they would be largely unaffected by things that could potentially spell doom for Earth and human life in the future, like asteroids, supernovae or gamma ray bursts. As long as the world’s oceans don’t boil away, tardigrades will live on.