# Ischyromys

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***Ischyromys*** is an [extinct](/source/Extinction) [genus](/source/Genus) of [rodent](/source/Rodent) from [North America](/source/North_America).

## Description

The 60 cm (2 ft) long creature is one of the oldest rodents known. It resembled a [mouse](/source/Mouse) and already had characteristic rodent [incisors](/source/Incisor). *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](/source/Arboreal) (along with its relative *[Paramys](/source/Paramys)*). It was a well-adapted climber that gradually beat out competition from rodent-like arboreal [plesiadapiform](/source/Plesiadapiformes) [primates](/source/Primate).[1]

The [brain](/source/Brain) of *I. typus* was characterised by an exposed [midbrain](/source/Midbrain). Additionally, it had less developed [olfactory bulbs](/source/Olfactory_bulb) as compared to [plesiadapiforms](/source/Plesiadapiformes), suggesting that early rodents relied less on their sense of smell as compared to [primatomorphs](/source/Primatomorpha) and their relatives.[2]

## References

1. Palmer, D. (ed.) (1999). *The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals*. London: Marshall Editions. p. 283. ISBN 978-1-84028-152-1.

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"](https://www.tandfonline.com/doi/full/10.1080/02724634.2016.1095762#abstract). *[Journal of Vertebrate Paleontology](/source/Journal_of_Vertebrate_Paleontology)*. **36** (3). [Bibcode:2016JVPal..36E5762B](https://ui.adsabs.harvard.edu/abs/2016JVPal..36E5762B). [doi:10.1080/02724634.2016.1095762](https://doi.org/10.1080/02724634.2016.1095762). [ISSN 0272-4634](https://www.worldcat.org/issn/0272-4634). Retrieved 7 April 2025. – via Taylor and Francis Online.

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Adapted from the Wikipedia article [Ischyromys](https://en.wikipedia.org/wiki/Ischyromys) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Ischyromys?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.