A new species of tardigrade has been discovered fossilized in 16-million-year-old Dominican amber. As well as being only the fourth tardigrade fossil ever discovered and formally named, it is the first recovered from the Cenozoic – the current geological era.
The famously hardy beastie measures just over half a millimeter (0.02 inches) according to the study published in Proceedings of the Royal Society B and is a member of the Isohypsibioidea superfamily.
Paradoryphoribius chronocaribbeus, as it has been named, is also the best-imaged tardigrade fossil to date, the researchers say – details of the creature’s mouthparts and teeny tiny claws are unrivaled in the fossil record.
“The discovery of a fossil tardigrade is truly a once-in-a-generation event,” Phil Barden, co-author of the study and assistant professor of biology at New Jersey Institute of Technology, said 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. 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.”
“With our new study, the full tally includes only four specimens, from which only three are formally described and named, including Paradoryphoribius," senior author Professor Javier Ortega-Hernández added. "This paper basically encompasses a third of the tardigrade fossil record known to date. Furthermore, Paradoryphoribius offers the only data on a tardigrade buccal apparatus in their entire fossil record.”
Despite being notoriously resilient (they can survive being fired out of a gun and have lived through all five known mass extinction events), tardigrades are extremely difficult to come by in fossilized form. As a result, little is known about their evolutionary history.
This is, perhaps, because of their size. Barden admits that Pdo. chronocaribbeus “wasn’t spotted for months” owing to its microscopic proportions, describing it as “a faint speck in amber”. Thankfully, the tiny critter was eventually discovered and imaged using confocal microscopy – a technique that uses lasers, instead of light, to visualize subjects. The extra detail and view of internal morphology that this allowed meant that what initially, and externally, looked like a modern tardigrade, could in fact be confirmed as a new species.
“[F]or the first time, we’ve visualized the internal anatomy of the foregut in a tardigrade fossil and found combinations of characters in this specimen that we don’t see in living organisms now. Not only does this allow us to place this tardigrade in a new genus, but we can now explore evolutionary changes this group of organisms experienced over millions of years,” said Marc A. Mapalo, lead author of the study and graduate student at Harvard’s Department of Organismic and Evolutionary Biology.
Just by dating the amber, for example, the team was able to put a minimum age on the Isohypsibioidea family.
The study also suggests that the sparsity of the tardigrade fossil records could be explained by their preferential preservation in amber, which could serve as an untapped resource for tardigrade fossils. The team hopes their work might encourage others to look more closely at amber samples in the quest to learn more about these mysterious invertebrates.
“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.”