Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tiny teeth are new mouse species, a rare "living fossil"

25.05.2011
Birch mouse is now 9 million years older than previously known and migrated from Asia to North America

Tiny fossil teeth discovered in Inner Mongolia are a new species of birch mouse, indicating that ancestors of the small rodent are much older than previously reported, according to paleontologist Yuri Kimura, Southern Methodist University in Dallas.

Fossils of the new species were discovered in sediments that are 17 million years old, said Kimura, who identified the new species and named it Sicista primus to include the Latin word for "first."

Previously the oldest prehistoric ancestor of the modern-day birch mouse was one that inhabited Inner Mongolia 8 million years ago.

Adding 9 million years to the ancestry of the rodent family that includes birch mice and jumping mice distinguishes this genus, Sicista, as a "living fossil," Kimura said. That places the genus among some of the most unique rodents on earth — those whose ancestry spans 2 to 3 times the average, she said.

Kimura identified Sicista primus from 17 tiny teeth, whose size makes them difficult to find. A single molar is about the size of half a grain of rice. The teeth, however, are distinctive among the various genera of rodents known as Dipodidae. Cusps, valleys, ridges and other distinguishing characteristics on the surface of the teeth are identifiable through a microscope.

"We are very lucky to have these," Kimura said. "Paleontologists usually look for bones, but a mouse is very tiny and its bones are very thin and fragile. The teeth, however, are preserved by enamel. Interestingly, small mammal teeth are very diverse in terms of their structure, so from that we can identify a species."

Kimura reported the new species in the article "The earliest record of birch mice from the Early Miocene Nei Mongol, China" in the scientific journal Naturwissenschaften. Images of the research and expedition are posted on the SMU Research flickr site. Go to SMUVideo's "Inner Mongolia yields 'living fossil'" to watch Kimura discuss the research.

An SMU doctoral student in the Huffington Department of Earth Sciences, Kimura was part of the international team that discovered the fossils during expeditions to Inner Mongolia in 2004, 2005 and 2007.

Microscopic evidence of a living fossil
The new fossils of Sicista primus from the Early Miocene age are also now the earliest known record of Sicista, the birch mouse genus that comprises 13 modern and 7 fossil species, said Kimura. As a result, Sicista now boasts the most ancient ancestry of the 326 genera in the largest rodent suborder to which it belongs, Myomorpha. The suborder includes laboratory mice and rats.

"The birch mouse is a rare case of a small mammal genus persisting from the Early Miocene without significant morphological changes," Kimura said in reporting the findings.

Rodents, both modern and prehistoric, rank as the most prolific mammals on earth. After the reign of dinosaurs, 65 million years ago, rodents evolved and dispersed worldwide during the Cenozoic, the "Age of Mammals." They comprise about 42 percent of all living mammals. Scientists know now that only 1.5 percent of modern rodent genera, however, go as far back as the Early Miocene or older.

"Diversity within a rodent genus is not unusual, but the long record of the genus Sicista, first recognized at 17 million years ago, is unusual," said Kimura. "The discovery of Early Miocene S. primus reveals that Sicista is fundamental to understanding how a long-lived genus persisted among substantially fast-evolving rodent groups."

Birch mice migrated from Asia to North America
Previously the record for the oldest species of Sicista belonged to an 8 million-year-old species identified in Eurasia, Kimura said.

In identifying the new species, Kimura also reverses the long-held hypothesis that ancestors of birch mice migrated from North America to Asia. That hypothesis has been based on a 14.8 million-year-old specimen from South Dakota, which was identified in 1977 as the separate rodent genus Macrognathomys. Kimura's analysis, however, concludes that Macrognathomys is actually Sicista. For that reason, she concluded, Sicista first inhabited the forests and grasslands of prehistoric Asia and then dispersed to North America via the Bering Land Bridge, Kimura said.

In a comparison of the molars and premolars from Macrognathomys and Sicista primus, Kimura reported finding 12 shared dental characteristics. In addition, phylogenetic analysis to identify evolutionary relationships indicated that both belong to the same genus, Sicista, she said.

Reconnaissance of earlier Central Asiatic Expedition localities yields small mammals

The teeth of Sicista primus were discovered in fine sediments gathered from Gashunyinadege, a fossil locality in the central region of Inner Mongolia.

Gashunyinadege is one of several fossil localities near Tunggur, a fossil site discovered in the 1920s by the Central Asiatic Expedition, which was led by Roy Chapman Andrews from the American Museum of Natural History.

Kimura is a member of an international scientific team sponsored by the Chinese Academy of Sciences Institute of Vertebrate Paleontology and Paleoanthropology and the Natural History Museum of Los Angeles County. The team's expeditions have been led by paleontologists Qiu Zhuding, IVPP; Wang Xiaoming, Natural History Museum of Los Angeles County; and Li Qiang, IVPP. Their expeditions retrace important classic localities, as well as prospect new fossil localities.

Kimura and other members of the team discovered the birch mouse fossils by first prospecting Gashunyinadege for small mammal fossils visible to the naked eye. Those fossils indicated the possibility of even smaller mammal fossils, so the team gathered 6,000 kilograms, more than 13,000 pounds, of Early Miocene sediment. Using standing water from recent rains, they washed the sediments repeatedly through continually smaller screens to separate out small fossils. Bags of concentrate containing particles the size of mouse teeth were returned to IVPP laboratories to hunt for fossils with a microscope.

The research was funded by the Institute for the Study of Earth and Man at SMU, Dallas Paleontological Society, Geological Society of America, Chinese Academy of Sciences Institute of Vertebrate Paleontology and Paleoanthropology. — Margaret Allen

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with SMU's Yuri Kimura or to book her in the SMU studio, call SMU News & Communications at 214-768-7650.

Margaret Allen | EurekAlert!
Further information:
http://www.smu.edu

More articles from Earth Sciences:

nachricht Filling the gap: High-latitude volcanic eruptions also have global impact
20.11.2017 | Institute of Atmospheric Physics, Chinese Academy of Sciences

nachricht Antarctic landscape insights keep ice loss forecasts on the radar
20.11.2017 | University of Edinburgh

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Researchers at IST Austria define function of an enigmatic synaptic protein

22.11.2017 | Life Sciences

Fine felted nanotubes: CAU research team develops new composite material made of carbon nanotubes

22.11.2017 | Materials Sciences

Women and lung cancer – the role of sex hormones

22.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>