'Once-in-a generation' tardigrade fossil discovery reveals new species
in 16-million-year-old amber

Date:
October 5, 2021
Source:
New Jersey Institute of Technology
Summary:
They've famously survived the vacuum of space, and even returned to
life after being frozen for decades in Antarctic moss. But as hard
as it is to kill the bizarre microscopic animal, the tardigrade,
it's harder to find one fossilized. In fact, only two have ever
been discovered and formally named -- until now.



FULL STORY ========================================================================== They've famously survived the vacuum of space, and even returned to life
after being frozen for decades in Antarctic moss. But as hard as it is
to kill the bizarre microscopic animal, the tardigrade, it's harder to
find one fossilized.

In fact, only two have ever been discovered and formally named --
until now.


==========================================================================
In in the Proceedings of the Royal Society B, lead researchers at New
Jersey Institute of Technology and Harvard University have described
just the third fossil tardigrade on record -- a new genus and species Paradoryphoribius chronocaribbeusgen. et sp. nov. (Pdo. chronocaribbeus),
which is fully preserved in 16-million-year-old Dominican amber from
the Miocene.

Measured at just over half a millimeter, the specimen has been
identified as a relative of the modern living tardigrade superfamily, Isohypsibioidea, and represents the first tardigrade fossil recovered from
the Cenozoic, the current geological era beginning 66 million years ago.

Researchers say the pristine specimen is the best-imaged fossil
tardigrade to date -- capturing micron-level details of the eight-legged invertebrate's mouthparts and needle-like claws 20-30 times finer than a
human hair. The new fossilis deposited at the American Museum of Natural History Division of Invertebrate of Zoology.

"The discovery of a fossil tardigrade is truly a once-in-a-generation
event," said Phil Barden, senior author of the study and assistant
professor of biology at New Jersey Institute of Technology. "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." "At first glance, this
fossil appears similar to modern tardigrades due to its relatively
simple external morphology," said Marc A. Mapalo, lead author of the
study and graduate student at Harvard's Department of Organismic and Evolutionary Biology. "However, for the first time, we've visualized
the internal anatomy of the foregut in a tardigrade fossil and found combinations of characters in this specimen that we don't see in living organisms now. Not only does this allow us to place this tardigrade in
a new genus, but we can now explore evolutionary changes this group of organisms experienced over millions of years." Tardigrades, or water
bears, are renowned for their unusual appearance and self-preservation abilities -- certain species are known to survive extreme conditions by
curling into a dehydrated ball and entering a state of suspended animation where their metabolism is virtually paused, known as cryptobiosis.



==========================================================================
Rare tardigrade fossil finds such as Pdo. chronocaribbeus, the team
suggests, could provide new molecular estimates that offer fresh insight
into major evolutionary events that have shaped the more than 1,300
species found across the planet today, such as the miniaturization of
their body plan into one ofEarth's smallest-known animals with legs.

Perhaps the greatest challenge in unearthing tardigrade fossils, however,
is their size.

"It's a faint speck in amber," said Barden. "In fact, Pdo. chronocaribbeus
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 wasn't spotted for months." Barden says tardigrades' microscopic non-biomineralized bodies are also uniquely suited to preservation in
amber derived from plant resin, which is capable of safely enveloping
and preserving organisms as minute as water bears and even individual bacterium.

"This particular mode of fossilization helps explain the patchy fossil
record," explained Barden. "Fossil amber with arthropods trapped inside
is only known from 230 million years ago to the present ... that's less
than half of the history of tardigrades." Placing Pdo. chronocaribbeus
on the Tardigrade Tree


========================================================================== While it is estimated that tardigrades diverged from other panarthropod lineages before the Cambrian 540 million years ago, only two definitive tardigrade fossils have formally been described, both from Cretaceous
fossil deposits in North America.

To explore Pdo. chronocaribbeusandits place on the tardigrade ancestral
tree, Mapalo used high-powered laser confocal fluorescence microscopy
to finely image the specimen. The team then compared it across a range
of morphological features associated with major tardigrade groups
alive today -- including key identifiers such as body surface, claws, buccopharyngeal apparatus and egg morphology.

"The fact that we had to rely on imaging techniques usually reserved
for cellular and molecular biology shows how challenging it is to study
fossil tardigrades," said Javier Ortega-Hernandez, assistant professor
of organismic and evolutionary biology at Harvard. "We hope that this
work encourages colleagues to look more closely at their amber samples
with similar techniques to better understand these cryptic organisms."
The team's analysis places Pdo. chronocaribbeus in one of three core
classes of tardigrade, Eutardigadra, and makes it the first definitive
fossil member of the superfamily called Isohypsibioidea -- a diverse
species that today inhabits aquatic and land environments and is typically characterized by their distinct claws that vary in size leg-to-leg.

The finding also puts a minimum age on the Isohypsibioidea family.

"We are just scratching the surface when it comes to understanding living tardigrade communities, especially in places like the Caribbean where
they've not been surveyed," said Barden. "This study provides a reminder
that, for as little as we may have in the way of tardigrade fossils,
we also know very little about the living species on our planet today." ========================================================================== Story Source: Materials provided by
New_Jersey_Institute_of_Technology. Original written by Jesse
Jenkins. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mapalo MA, Robin N, Boudinot BE, Ortega-Herna'ndez J, Barden P. A
tardigrade in Dominican amber. Proc. R. Soc. B, 2021 DOI: 10.1098/
rspb.2021.1760 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211005191012.htm

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