Scientists discovered 16-million-year-old tardigrade fossil

The discovery represents the first tardigrade fossil recovered from the Cenozoic.

Tardigrades, also called water bears, can survive in extreme environments. They are short (0.05mm – 1.2mm in body length), plump, bilaterally symmetrical, segmented organisms.

It is almost impossible to kill this bizarre microscopic animal. Therefore, it’s quite rare, or let’s say harder, to find one fossilized. Only two have ever been discovered and formally named — until now.

In a new study, scientists at the New Jersey Institute of Technology and Harvard University have reported discovering tardigrade fossil. This newly discovered tardigrade fossil is of a new genus and species Paradoryphoribius chronocaribbeus gen. et sp. nov. (Pdo. chronocaribbeus).

This is the third fossil tardigrade on record. It measures over half a millimeter and is identified as a relative of the modern living tardigrade superfamily, Isohypsibioidea.

Scientists noted, “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 fossil is deposited at the American Museum of Natural History Division of Invertebrates of Zoology.

Phil Barden, a senior author of the study and assistant professor of biology at New Jersey Institute of Technology, said, “The discovery of a fossil tardigrade is truly a once-in-a-generation event. 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.”

Tardigrade Fossil Discovery
Credit: NJIT/Harvard

Marc A. Mapalo, a lead author of the study and graduate student at Harvard’s Department of Organismic and Evolutionary Biology, said, “At first glance, this fossil appears similar to modern tardigrades due to its relatively simple external morphology. 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.”

The discovery of the tardigrade fossil gives molecular estimates that offer fresh insight into major evolutionary events that have shaped the more than 1,300 species found across the planet today.

Barden said, “It’s a faint speck in amber. 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.”

“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 model of fossilization helps explain the patchy fossil record. 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.”

Scientists determined the place of Pdo. chronocaribbeuson the tardigrade ancestral tree by using high-powered laser confocal fluorescence microscopy. By imaging the specimen and compared it based on morphological features, including critical identifiers such as body surface, claws, buccopharyngeal apparatus, and egg morphology.

Javier Ortega-Hernandez, assistant professor of organismic and evolutionary biology at Harvard, said, “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. We hope that this work encourages colleagues to look more closely at their amber samples with similar techniques to understand these cryptic organisms better.”

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.

Barden said“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.”

Journal Reference:
  1. Mapalo MA, Robin N, Boudinot BE, Ortega-Hernández J, Barden P. 2021, A tardigrade in Dominican amber. Proc. R. Soc. B 20211760. DOI: 10.1098/rspb.2021.1760

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