Discovery of giant roaming deep sea protist provides new perspective on animal evolution

November 20, 2008

AUSTIN, Texas--Groove-like tracks on the ocean floor made by giant deep-sea single-celled organisms could lead to new insights into the evolutionary origin of animals, says biologist Mikhail "Misha" Matz from The University of Texas at Austin.

Matz and his colleagues recently discovered the grape-sized protists and their complex tracks on the ocean floor near the Bahamas. This is the first time a single-celled organism has been shown to make such animal-like traces.

The finding is significant, because similar fossil grooves and furrows found from the Precambrian era, as early as 1.8 billion years ago, have always been attributed to early evolving multicellular animals.

"If our giant protists were alive 600 million years ago and the track was fossilized, a paleontologist unearthing it today would without a shade of doubt attribute it to a kind of large, multicellular, bilaterally symmetrical animal," says Matz, an assistant professor of integrative biology. "We now have to rethink the fossil record."

The team's discovery was published online today in Current Biology and will appear in a subsequent print issue.

Most animals, from humans to insects, are bilaterally symmetrical, meaning that they can be roughly divided into halves that are mirror images.

The bilateral animals, or "Bilateria," appeared in the fossil record in the early Cambrian about 542 million years ago, quickly diversifying into all of the major animal groups, or phyla, still alive today. This rapid diversification, known as the Cambrian explosion, puzzled Charles Darwin and remains one of the biggest questions in animal evolution to this day.

Very few fossils exist of organisms that could be the Precambrian ancestors of bilateral animals, and even those are highly controversial. Fossil traces are the most accepted evidence of the existence of these proto-animals.

"We used to think that it takes bilateral symmetry to move in one direction across the seafloor and thereby leave a track," explains Matz. "You have to have a belly and a backside and a front and back end. Now, we show that protists can leave traces of comparable complexity and with a very similar profile."

With their find, Matz and his colleagues argue that fossil traces cannot be used alone as evidence that multicellular animals were evolving during the Precambrian, slowly setting the stage for the Cambrian explosion.

"I personally think now that the whole Precambrian may have been exclusively the reign of protists," says Matz. "Our observations open up this possible way of interpreting the Precambrian fossil record."

He says the appearance of all the animal body plans during the Cambrian explosion might not just be an artifact of the fossil record. There are likely other mechanisms that explain the burst-like origin of diverse multicellular life forms.

DNA analysis confirmed that the giant protist found by Matz and his colleagues in the Bahamas is Gromia sphaerica, a species previously known only from the Arabian Sea.

They did not observe the giant protists in action, and Matz says they likely move very slowly. The sediments on the ocean floor at their particular location are very stable and there is no current--perfect conditions for the preservation of tracks.

Matz says the protists probably move by sending leg-like extensions, called pseudopodia, out of their cells in all directions. The pseudopodia then grab onto mud in one direction and the organism rolls that way, leaving a track.

He aims to return to the location in the future to observe their movement and investigate other tracks in the area.

Matz says the giant protists' bubble-like body design is probably one of the planet's oldest macroscopic body designs, which may have existed for 1.8 billion years.

"Our guys may be the ultimate living fossils of the macroscopic world," he says.
-end-


University of Texas at Austin

Related Fossil Record Articles from Brightsurf:

How to fix the movement for fossil fuel divestment
Bankers and environmentalists alike are increasingly calling for capital markets to play a bigger role in the war on carbon.

New fossil ape is discovered in India
A 13-million-year-old fossil unearthed in northern India comes from a newly discovered ape, the earliest known ancestor of the modern-day gibbon.

Fossil pollen record suggests vulnerability to mass extinction ahead
Reduced resilience of plant biomes in North America could be setting the stage for the kind of mass extinctions not seen since the retreat of glaciers and arrival of humans about 13,000 years ago, cautions a new study published August 20 in the journal Global Change Biology.

Australian fossil reveals new plant species
Fresh examination of an Australian fossil -- believed to be among the earliest plants on Earth -- has revealed evidence of a new plant species that existed in Australia more than 359 Million years ago.

Tracking fossil fuel emissions with carbon-14
Researchers from NOAA and the University of Colorado have devised a breakthrough method for estimating national emissions of carbon dioxide from fossil fuels using ambient air samples and a well-known isotope of carbon that scientists have relied on for decades to date archaeological sites.

Fossil record analysis hints at evolutionary origins of insects' structural colors
Researchers from Yale-NUS College in Singapore and University College Cork have analyzed preserved scales from wing cases of two fossil weevils from the Late Pleistocene era to better understand the origin of light-scattering nanostructures present in present-day insects.

Reconstructing the diet of fossil vertebrates
Paleodietary studies of the fossil record are impeded by a lack of reliable and unequivocal tracers.

Fossil is the oldest-known scorpion
Scientists studying fossils collected 35 years ago have identified them as the oldest-known scorpion species, a prehistoric animal from about 437 million years ago.

Canadian tundra formerly covered in rich forest: Ancient plant fossil record shows
Canada's northernmost islands, Ellesmere and Axel Heiberg islands in Nunavut, were home to a vibrant, temperate forest 56 million years ago, according to fossil research just published by University of Saskatchewan (USask) scientists.

New Colorado fossil record documents life's rebound after Cretaceous-Paleogene extinction
Nearly 66 million years ago, the reign of dinosaurs ended and the ascendency of mammals on Earth began.

Read More: Fossil Record News and Fossil Record Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.