Ischyromys is an extinct genus of rodent from North America.
Description
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.1
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.2
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References
Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 283. ISBN 978-1-84028-152-1. 978-1-84028-152-1 ↩
Bertrand, Ornella C.; Silcox, Mary T. (3 May 2016). "First virtual endocasts of a fossil rodent: Ischyromys typus (Ischyromyidae, Oligocene) and brain evolution in rodents". Journal of Vertebrate Paleontology. 36 (3): e1095762. doi:10.1080/02724634.2016.1095762. ISSN 0272-4634. Retrieved 7 April 2025 – via Taylor and Francis Online. https://www.tandfonline.com/doi/full/10.1080/02724634.2016.1095762#abstract ↩