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Third tardigrade fossil discovered hidden in piece of amber

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Again with the accidental discoveries! This is the third unexpected discovery in six weeks. This time the good news arose out of debris in a large chunk of Dominican amber. The researchers were studying ants from the Miocene period, trapped in a piece of amber. A closer examination of the “debris” inclusions, however, revealed an even greater price than the ants. What the researchers thought was a speck of dust was actually a tardigrade fossil, frozen in time for sixteen million years.

It’s a slight dot in the amber, said Phil Barden, lead author of the study. In reality, PDO. chronocaribeus was originally an inclusion hidden in the corner of a piece of amber with three different ant species our lab had studied, and it hasn’t been spotted for months.

Ten cents for the scale. Image Credit: NJIT / Harvard

Tardigrade fossils are hard to find because they don’t make a lot of fossils in the first place. Tardigrades do not form skeletal fossils, because unlike other animals, their tissues do not biomineralize. Generally, tardigrades use chitin as a structural protein, like insects; humans use collagen, and the collagen calcifies in the bones. The tardigrades don’t even do it Make BONE. This is why it is so exciting that scientists have discovered a tardigrade fossil: it is only the third that has ever been discovered.

The origin of the tardigrade “ghost line” remains somewhat obscured and it is difficult to make statements about its deep history. We have access to living tardigrades, but we only knew of two fossils in total until the end of last week. Scientists know where the tardigrades are in the tree of life, that they are related to arthropods, and that they have a deep origin during the Cambrian explosion. The problem is, we have this extremely solitary phylum with only three named fossils. Most of the fossils of this phylum are found in amber but, because they are small, even if they are preserved, it can be very difficult to see them, said lead author Javier Ortega-Hernndez. The new water bear on the block is presented as the type specimen of a new genus and a new species: Paradoryphoribius chronocaribbeus.

Fig. 2 (b) Specimen photographed by autofluorescence under a confocal microscope at 488 nm; different colors indicate depth z, with a purple to red gradient representing the shallower and deepest planes, respectively. Image credit: study authors.

Measuring half a millimeter in length, the new tardigrade was large enough that its macro-features could be seen under a light microscope. Beyond this level of detail, the interior of the fossil was too confusing for scientists to understand using ordinary microscopes. However, by a happy coincidence, the chitin illuminates under a confocal laser microscope. Using its much higher magnification, the researchers captured key features of the tardigrade fossil’s “oral and forepharyngeal apparatus and foregut”.

There are two distinct types of water bears; one, the “eutardigrade”, is called “naked” because its outer layer is smooth, like skin. The other type, the “heterotardigrades”, make chitinous plates like the armor of a panzerbjorn. This one is a eutardigrade, with a smooth outer layer. Scientists have also obtained close-ups of its muzzle, stomach and claws. After completing its vanity shoot, the fossil headed 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 an ancient ubiquitous lineage that has seen everything on Earth from the fall of dinosaurs to the rise of terrestrial colonization of plants. Yet they are like a ghost line to paleontologists with almost no fossil record. Finding tardigrade fossil remains is an exciting time where we can empirically see their progression through Earth’s history.

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