Throughout the Cenozoic era the rodents were one of the most successful animal groups in the coniferous forests. Their powerful teeth enabled them to cope with the tough vegetable matter found there and their warm, furry coats helped them to retain body heat during hibernation.
The chiselhead, a rodent and a relation of the temperate woodland chirits, is highly adapted to life in the coniferous forest. Its huge incisor teeth and wormlike body enable it to burrow deep into the living wood, where it can remain protected from the cold in winter. Although in some ways the animal is at an advanced stage of development, its parasitic way of life is really quite primitive. Its staple diet is the bark of trees, which it strips off completely, leaving the tree totally denuded. This, combined with the massive damage it does by burrowing, kills the tree within a few years.As the chiselheads only colonize live trees they must be continually on the move and every spring, after hibernation, the young of the new generation migrate to find new territories. During migration they are very vulnerable and many are taken by predators before they can complete the journey. This balance between chiselhead and predator is highly critical and it needs only a slight reduction in the number of predators to produce an increase in the population of chiselheads that would lead to the total destruction of vast areas of coniferous forest.
No other small rodent found in the coniferous forest is quite so destructive. Most live on shoots, bark and the seeds found in cones. Many are ground dwellers and feed from the cones where they fall. Others are lightly built and agile enough to scramble along the branches to where the cones are actually growing.
One large vole-like rodent, the trevel, is unusual in having a prehensile tail.