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Third tardigrade fossil discovered hidden in a piece of amber

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Again with accidental discoveries! It is the third unexpected find in six weeks. This time, the good news was born out of the rubble in a piece of Dominican amber. The researchers were studying ants from the Miocene period, trapped in a piece of amber. However, a closer look at the “debris” inclusions revealed an even bigger prize than ants. What researchers had thought was just a speck of dust was, in fact, a tardigrade fossil, frozen in time for sixteen million years.

“It’s a wispy bacon in amber,” said Phil Barden, lead author. from The study. “In fact, Pdo. chronocaribbeus it 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 went undetected for months. “

Dime per scale. Image Credit: NJIT / Harvard

Tardigrade fossils are hard to find, because they don’t produce many fossils in the first place. Tardigrades do not form skeletal fossils because, unlike other animals, their tissues do not biomineralize. Generally speaking, tardigrades use chitin as their structural protein, like insects; humans use collagen and collagen calcifies in bone. Tardigrades don’t even do bones. That’s why it’s so exciting that scientists have discovered a fossil tardigrade – this is only the third ever discovered.

The origin of the “phantom lineage” of the tardigrades remains somewhat occluded and it is difficult to make statements about their deep history. We have access to live tardigrades, but we only knew of two fossils in total until the end of last week. “Scientists know where tardigrades fit broadly on the tree of life, that they are related to arthropods and that they have a deep origin during the Cambrian Explosion. The problem is that we have this extremely lonely edge with only three named fossils. Most of the fossils of this phylum are found in amber but, since they are small, even if they are preserved, it can be very difficult to see them, ”said lead author Javier Ortega-Hernández. The new water bear on the block is presented as the type specimen for a new genus and species: Paradoryphoribius chronocaribbeus.

Fig. 2 (b) Sample photographed with autofluorescence under confocal microscope at 488 nm; The different colors indicate the depth z, with a gradient from violet to red representing the shallowest to the deepest planes, respectively. Image credit: study authors.

At half a millimeter long, the new tardigrade was large enough that its macro features were visible under a light microscope. Beyond that level of detail, the inside of the fossil was too confusing for scientists to understand using normal microscopes. However, in a happy coincidence, chitin lights up under a confocal laser microscope. Using their much higher magnification, the researchers captured key features of the “oropharyngeal apparatus and foregut” of the fossil tardigrade.

There are a couple of different types of water bears; one, the “eutardigrade”, is known as “naked” because its outer layer is soft, like skin. The other type, “heterotardigrade”, makes chitinous plates like the armor of a panzerbjorn. This is a eutardigrade, with a smooth outer shell. The scientists also got close-ups of its snout, belly, and claws. Once he was done with his photo shoot, the fossil made its way to its new home at the American Museum of Natural History.

“The discovery of a fossil tardigrade is truly a once in a generation event,” Barden said. “What is so remarkable is that tardigrades are a ubiquitous ancient lineage that has seen everything on Earth, from the fall of the dinosaurs to the rise of terrestrial colonization of plants. However, they are like a ghost lineage to paleontologists with almost no fossil record. Finding tardigrade fossil remains is an exciting time when we can empirically see their progression throughout Earth’s history. “

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