New species of ancient tardigrade found preserved in amber

A brand-new species of ancient tardigrade has been discovered in 16-million-year-old Dominican amber.

The newly found fossil, described in Proceedings of the Royal Society, dates back to the Miocene epoch, looks like a modern-day tardigrade, and represents a whole new genus and species: Paradoryphoribius chronocaribbeus (aka beusty boi).

This is only the third tardigrade amber fossil to be described and named to date. The other two fossils are Milnesium swolenskyi (aka swole boi) and Beorn leggi (aka leggi boi), which are older than the new fossil – both date back to the Cretaceous age. This means that Paradoryphoribius fills a gap in the evolutionary history of modern-day tardigrades.

“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,” says senior author Ortega-Hernández, of Harvard University, US.

“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.”

Even though the fossil was well preserved, the tiny specimen was just 559 micrometres long – only slightly over half a millimetre.

“The difficulty of working with this amber specimen is that it’s far too small for dissecting microscopes, we needed a special microscope to fully see the fossil,” says lead author Marc A. Mapalo, also of Harvard.

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Fortunately, tardigrade cuticle is made of chiton, which is tough and fluorescent under the right light. Using a special confocal microscope that visualises small samples with lasers, the researchers identified two important characteristics of the little critter: claws, and a type of foregut found in the mouth called a buccal apparatus.

“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,” says Mapalo.

“Paradoryphoribius is the only genus that has this specific unique character arrangement in the superfamily Isohypsibioidea.

“If you look at the external morphology of tardigrades, you might assume that there are no changes that occurred within the body of tardigrades.

“However, using confocal laser microscopy to visualise the internal morphology, we saw characters that are not observed in extant species but are observed in the fossils.

“This helps us understand what changes in the body occurred across millions of years. Furthermore, this suggests that even if tardigrades may be the same externally, some changes are occurring internally.”

The new fossils are a rare treat for evolutionary biologists because well-preserved tardigrade fossils are exceptionally uncommon.

“Tardigrade fossils are rare,” says Ortega-Hernández. “With our new study, the full tally includes only four specimens, from which only three are formally described and named, including Paradoryphoribius.

“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.”