A shrew-rat that lacks molars and has oddly shaped incisors is an evolutionary anomaly among more than 2,200 known species of rodent.
Rats, mice and their kin owe their success in part to their ability to gnaw, which enables them to access foods that other mammals cannot. Jacob Esselstyn of McMaster University in Hamilton, Ontario, and his colleagues report that the shrew-rat Paucidentomys vermidax (pictured) has a long, pointed face, incisors that differ in shape from those of other rodents, and no molars. These features could be adaptations that help the animal to find its favoured food — soft-bodied earthworms that do not need chewing. The loss of a previously successful evolutionary modification has allowed P. vermidax to take advantage of the available food in its forest home.
Biol. Lett. http://dx.doi.org/10.1098/rsbl.2012.0574 (2012)