Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

University of California, Riverside study dates our ancestors

27.09.2002


Photo Caption: A type of branching burrow system that first appear at the base of the Cambrian (circa 545 million years before the present). The trace consists of a series of curved open tunnels that extended into the muddy sea floor. The tunnels were later filled with sand and the mud weathered away resulting in a cast of burrow system. The producer of this trace fossil is not known but these trace fossil nevertheless are important in that they mark the beginning of the sea floor being churned by sediment processing animals. Compared to the much simpler trace fossils in older rocks they also bear witness to the appearance of more complex animal behavior. The figured specimen is from the Lower Cambrian of Sweden. The length of each curved element is about 7 mm.


Photo Caption: A trace fossil made on the top of the sediment surface. The trace is about 1-2 mm in width. This is a common form found in Late Proterozoic sedimentary rocks. The figured specimen is from Flinders Range, South Australia.


Study suggests macroscopic bilaterian animals did not appear until 555 million years ago

The traces left behind by ancient animals may hold the key to determining when macroscopic bilaterians -- animals that are symmetric about a central axis, with a body divided into equivalent right and left halves, and with an anterior-posterior polarity (e.g., this includes worms, ants, and ranging up to humans) -- first appeared. A team led by Dr. Mary Droser, professor of geology at the University of California, Riverside, studied "trace" fossils, e.g., burrows, trails and tracks left behind by the earliest bilaterian animals. Results from their study suggest that bilaterian animals did not appear until approximately 555 million years ago.

The authors publish their findings in a paper entitled "Trace fossils and substrates of the terminal Proterozoic-Cambrian transition: Implications for the record of early bilaterians and sediment mixing" in the Proceedings of the National Academy of Sciences (PNAS). They report that these trace fossils, found in many different locations around the world, were preserved very well in sediment beds from the Early Cambrian (544 to 510 million years ago), both in terms of quality of detail and in preserving traces made close to this sediment-water interface. Trace fossils can shed light on an organism’s behavioral activity.



"The timing of the appearance of bilaterian animals, while clearly by 555 million years ago, is the subject of some debate," said Droser. "One of the most important pieces of evidence for early animals is the record of trace fossils. That is, animal burrows, tracks and trails preserved in the rock record. Based on evidence from functional morphology, many of the features that define bilaterians could only have originated in a relatively large animal that inhabited the seafloor and thus produced trace fossils. Early bilaterians, in particular, were soft-bodied and thus difficult to preserve."

The trace fossils examined in the study are from the transition between the Proterozoic Era (2.5 billion to 544 million years ago), where few animal body fossils are found, and the Cambrian (544 to 490 million years ago), where diverse animal body fossils such as trilobites are found. Proterozoic trace fossils, typically only a few millimeters wide, are found at the interface between water and sediment. The Cambrian trace fossils are more diverse in size, shape and depth of penetration into the sediment.

The researchers examined and did field work on thousands of meters of rock. "We collected samples from Australia, Newfoundland, the western United States, Scandinavia and Namibia," said Soren Jensen, co-author of the PNAS paper and a postdoctoral researcher in the department of earth sciences at UC Riverside. "These samples of ancient marine rocks were then carefully inspected, x-rayed, and thin-sectioned for microscopic examination to provide us with an even closer look."

The authors attribute the exceptional preservation of Early Cambrian trace fossils to the low levels of sediment mixing, which resulted in relatively firm substrates less prone to resuspension. Close inspection of these fossils could help determine exactly when bilaterian animals emerged, a topic of much controversy.

"There have been reports of trace fossils as old as 1 billion years old," said Droser. "But these records are scarce and, on critical examination, are not convincing. On examining the trace fossil record from 565 million years ago through until 535 million years ago, we found that the substrate conditions -- for example, the bottom of the ocean -- were such that if animals were burrowing or walking or crawling along the seafloor, their traces would have likely been preserved. We see a gradual increase in diversity and complexity of trace fossils from about 555 million years ago, known as the Cambrian Explosion and which likely reflects the appearance of bilaterians. We found no evidence for a long history of large animals before this time."

News Media Contact:
Name: Iqbal Pittalwala
Phone: 909.787.2645
Email: iqbal@citrus.ucr.edu

Iqbal Pittalwala | EurekAlert!
Further information:
http://www.earthscience.ucr.edu/
http://www.pnas.org/
http://www.ucr.edu/

More articles from Earth Sciences:

nachricht From volcano's slope, NASA instrument looks sky high and to the future
27.04.2017 | NASA/Goddard Space Flight Center

nachricht Penn researchers quantify the changes that lightning inspires in rock
27.04.2017 | University of Pennsylvania

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>