The subfamily of rodents known as Murinae (mice, rats, etc.), which first appeared in Asia 12 million years ago, spread across the entire Old World (Eurasia, Africa, Australia) in less than 2 million years, a remarkably fast rate. Researchers have long suspected that one of the reasons for their evolutionary success is related to their unique masticatory apparatus. Now, researchers have used the brilliant X-ray beams produced at the European Synchrotron (ESRF) to study several hundred specimens, both extant and extinct, to describe the evolutionary processes that caused rats and mice to acquire this characteristic feature. The study was published in the journal Evolution on 28 November 2013.
The research team, from the Institut de Paloprimatologie, Palontologie Humaine: volution et Paloenvironnements (CNRS / Universit de Poitiers), was able to determine the diet of extinct species and to trace the evolutionary history of these rodents. Today, the Murinae comprise 584 species, which represents over 10% of the diversity of present day mammals.
In their study the researchers were able to identify two key evolutionary moments in the acquisition of this masticatory apparatus.
The first one occurred around 16 million years ago when the ancestors of the Murinae changed from a herbivorous diet to an insectivorous diet. This new diet was encouraged by the acquisition of chewing movements that are unusual in mammals, forwardly directed but continuing to interlock opposing teeth. This aquisition helped them reduce tooth erosion and better preserve pointed cusps, which are used to puncture the exoskeletons of insects.
Then, twelve million years ago, the very earliest Murinae returned to a herbivorous diet, while at the same time retaining their chewing motion. This also enabled them to use both their mandibles simultaneously during mastication. The change in diet gave way to the formation of three longitudinal rows of cu
|Contact: Claus Habfast|
European Synchrotron Radiation Facility