Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

'True grit' erodes assumptions about evolution

05.03.2013
Dining on field grasses would be ruinous to human teeth, but mammals such as horses, rhinos and gazelles evolved long, strong teeth that are up to the task.

New research led by the University of Washington challenges the 140-year-old assumption that finding fossilized remains of prehistoric animals with such teeth meant the animals were living in grasslands and savannas.


R Madden/U of Chicago

University of Washington researchers collect samples from Gran Barranca, Argentina, that offers access to layers of soils, plant remains, volcanic ash and sand going back millions of years. The section pictured represents 800,000 years of layering and is mainly composed of volcanic ash deposited by wind and rivers.

Instead it appears certain South American mammals evolved the teeth in response to the gritty dust and volcanic ash they encountered while feeding in an ancient tropical forest.

The new work was conducted in Argentina where scientists had thought Earth’s first grasslands emerged 38 million years ago, an assumption based on fossils of these specialized teeth. But the grasslands didn’t exist. Instead there were tropical forests rich with palms, bamboos and gingers, according to Caroline Strömberg, UW assistant professor of biology and lead author of an article in Nature Communications.

“The assumption about grasslands and the evolution of these teeth was based on animal fossils,” Strömberg said. “No one had looked in detail at evidence from the plant record before. Our findings show that you shouldn’t assume adaptations always came about in the same way, that the trigger is the same environment every time.”

To handle a lifetime of rough abrasion, the specialized teeth – called high-crowned cheek teeth – are especially long and mostly up in the animals’ gums when they are young. As chewing surfaces of the teeth wear away, more of the tooth emerges from the gums until the crowns are used up. In each tooth, bone-like dentin and tough enamel are complexly folded and layered to create strong ridged surfaces for chewing. Human teeth have short crowns and enamel only on the outside of each tooth.

In Argentina, mammals apparently developed specialized teeth 20 million years or more before grasslands appeared, Strömberg said. This was different from her previous work in North America and western Eurasia where she found the emergence of grasslands coincided with the early ancestors of horses and other animals evolving specialized teeth. The cause and effect, however, took 4 million years, considerably more lag time than previously thought.

The idea that specialized teeth could have evolved in response to eating dust and grit on plants and the ground is not new. In the case of Argentine mammals, Strömberg and her co-authors hypothesize that the teeth adapted to handle volcanic ash because so much is present at the study site. For example, some layers of volcanic ash are as thick as 20 feet (six meters). In other layers, soils and roots were just starting to develop when they were smothered with more ash.

Chewing grasses is abrasive because grasses take up more silica from soils than most other plants. Silica forms minute particles inside many plants called phytoliths that, among other things, help some plants stand upright and form part of the protective coating on seeds.

Phytoliths vary in appearance under a microscope depending on the kind of plant. When plants die and decay, the phytoliths remain as part of the soil layer. In work funded by the National Science Foundation, Strömberg and her colleagues collected samples from Argentina’s Gran Barranca, literally “Great Cliff,” that offers access to layers of soil, ash and sand going back millions of years.

The phytoliths they found in 38-million-year-old layers – when ancient mammals in that part of the world developed specialized teeth – were overwhelmingly from tropical forests, Strömberg said.

“In modern grasslands and savannas you’d expect at least 35 to 40 percent – more likely well over 50 percent – of grass phytoliths. The fact we have so little evidence of grasses is very diagnostic of a forested habitat,” she said.

The emergence of grasslands and the evolution of specialized teeth in mammals are regarded as a classic example of co-evolution, one that has occurred in various places around the world. However, as the new work shows, “caution is required when using this functional trait for habitat reconstruction,” the co-authors write.

Other co-authors are Regan Dunn, a UW doctoral candidate; Richard Madden, University of Chicago; Matthew Kohn, Boise State University; and Alfredo Carlini, National University of La Plata, Argentina.

For more information:
Strömberg is on parental leave, email her at caestrom@uw.edu to arrange interviews

Sandra Hines | EurekAlert!
Further information:
http://www.uw.edu

More articles from Earth Sciences:

nachricht Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center

nachricht NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Global study of world's beaches shows threat to protected areas

19.07.2018 | Earth Sciences

New creepy, crawly search and rescue robot developed at Ben-Gurion U

19.07.2018 | Power and Electrical Engineering

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>