Paleontologists have described a new genus and species of tardigrade found in a 16-million-year-old piece of amber from the Dominican Republic. Named Paradoryphoribius chronocaribbeus, it is the third fossil tardigrade from Miocene-period Dominican amber, the first tardigrade fossil described from the Cenozoic Era, and the first unambiguous fossil representative of the diverse tardigrade superfamily Isohypsibioidea.
Tardigrades are a diverse group of charismatic microscopic invertebrates that are best known for their ability to survive extreme conditions.
Despite their long evolutionary history and global distribution in both aquatic and terrestrial environments, the tardigrade fossil record is exceedingly sparse.
Due to their microscopic size and non-biomineralizing body, the chance of tardigrades to become fossilized is small.
“Tardigrade fossils are rare. With our new study, the full tally includes only four specimens, from which only three are formally described and named, including Paradoryphoribius chronocaribbeus,” said Professor Javier Ortega-Hernández, a researcher in the Department of Organismic and Evolutionary Biology at Harvard University.
“The discovery of a fossil tardigrade is truly a once-in-a-generation event,” added Dr. Phil Barden, a researcher in the Department of Biological Sciences at New Jersey Institute of Technology and the Division of Invertebrate Zoology at the American Museum of Natural History.
“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.”
Paradoryphoribius chronocaribbeus is only the third tardigrade amber fossil to be fully described and formally named to date.
The other two fully described modern-looking tardigrade fossils are Milnesium swolenskyi and Beorn leggi, both known from Cretaceous-period amber in North America.
The new species is also the first fossil to be found embedded in Miocene Dominican amber and the first fossil representative of the tardigrade superfamily Isohypsibioidea.
“Scientists know where tardigrades broadly fit in the tree of life, that they are related to arthropods, and that they have a deep origin during the Cambrian Explosion,” Professor Ortega-Hernández said.
“The problem is that we have this extremely lonely phylum with only three named fossils.”
“Most of the fossils from this phylum are found in amber but, because they’re small, even if they are preserved it may be really difficult to see them.”
Using confocal laser microscopy, Professor Ortega-Hernández and colleagues were able to fully visualize two very important characters of Paradoryphoribius chronocaribbeus: the claws and the buccal apparatus, or the foregut of the animal.
“Even though externally it looked like a modern tardigrade, with confocal laser microscopy we could see it had this unique foregut organization that warranted for us to erect a new genus within this extant group of tardigrade superfamilies,” said Marc Mapalo, a Ph.D. candidate in the Department of Organismic and Evolutionary Biology at Harvard University.
“Paradoryphoribius chronocaribbeus is the only genus that has this specific unique character arrangement in the superfamily Isohypsibioidea.”