The 60 cm (2 ft) long creature is one of the oldest rodents known. It resembled a
mouse and already had characteristic rodent
incisors.
Ischyromys's hind legs were longer than the forelegs, which could be used for other means than walking. Unlike most other mammals of its time,
Ischyromys was probably
arboreal (along with its relative
Paramys). It was a well-adapted climber that gradually beat out competition from rodent-like arboreal
plesiadapiform primates. The
brain of
I. typus was characterised by an exposed
midbrain. Additionally, it had less developed
olfactory bulbs as compared to
plesiadapiforms, suggesting that early rodents relied less on their sense of smell as compared to
primatomorphs and their relatives. ==References==