Tardigrade fossils reveal when ‘water bears’ became immortal

Tardigrade fossils reveal when ‘water bears’ became immortal

Mindy Weisberger

Microscopic tardigrades – a family of plump, eight-legged arthropods – are nearly invulnerable, and their superhuman abilities may have helped them survive one of the worst mass extinctions in Earth’s history, according to a new analysis of tardigrade fossils in amber, the first study to estimate when this ability evolved.

Tardigrades, also known as aquatic tardigrades, can withstand extreme heat, cold, pressure, and radiation. They survive harsh environments through a process called cryptobiosis, in which they expel most of the water from their bodies and enter a state of metabolic suspension. There are two lineages of tardigrades that have this ability.

There are only four known tardigrade fossils, all preserved in amber, two of which were found in Canada in the 1940s in amber pebbles dating to between 84 and 71 million years ago. One of the tardigrades found in the pebble was See more It was discovered in 1963. “The other one was too small to identify at the time,” says Mark Mapalo, a graduate student at Harvard University’s Museum of Comparative Zoology.

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New research Nature Communications Biology, Using a high-contrast microscope, Mapalo and his colleagues revealed previously unseen details of the claws in both specimens. “This is a very important taxonomic feature for tardigrades,” Mapalo says. Because tardigrades’ body shapes have changed very little over millions of years, the scientists’ new images of the claw’s shape provided important information about where these amber-locked fossils belonged, says Jasmine Nirodi, an organismal biologist at the University of Chicago who was not involved in the study.

The authors determined that the small tardigrade represents a new genus and species. Aerobius dactylusThey also revised B. RegiDescription and classification of the tardigrades based on the claw articulations. Both species are classified in the same superfamily Hypsibioidea, B. Regi They have now been officially moved to the family Hypsibiidae. This reorganization places the small tardigrades in the same major lineage (class Eutardigrada) as the larger tardigrades, which researchers previously thought belonged to a separate lineage.

This realigned the tardigrade family tree, allowing the researchers to calculate when the two lineages diverged and determine the latest date for the likely acquisition of cryptic life. Their study suggests that cryptic life in tardigrades emerged during the Carboniferous Period (359 to 299 million years ago), predating a devastating event known as the Permian Extinction, or “Great Dying,” which occurred about 252 million years ago. The authors suggest that cryptic life may have helped tardigrades survive this event, which wiped out 96% of marine and 70% of terrestrial life.

Mapalo says studying the evolution of cryptic living is difficult, in part because tardigrade fossils are so scarce. Finding more fossils will help scientists pinpoint details about the emergence of this unique survival strategy. “I hope that by sharing our findings, we can help others discover that tardigrade fossils exist and that others remain to be found,” he says.