Xyronomys fossil map
Where fossils of Xyronomys have been found, shown on the Earth as it looked about 66 million years ago and on today’s map.
Dots are fossil collections recorded in the Paleobiology Database. The “then” view moves today’s fossil sites back to their positions 66 million years ago (the time slice nearest the median age of the fossils) using the Merdith et al. (2021) plate model; positions are approximate. Open on the timeline map →
| Group | Early mammals |
|---|---|
| Lived | 66–60.9 million years ago (Danian to Selandian) |
| Periods | Paleogene |
| Family | Neoplagiaulacidae |
| Named by | Rigby 1980 |
| Fossil records | 12 occurrences at 5 locations (PBDB) |
| Found in | United States, Canada |
| Rock formations | Ravenscrag, Fort Union, Denver, Paskapoo |
About Xyronomys
Xyronomys is an extinct genus of small mammals from the Paleocene of North America, with two described species. The genus lies within the extinct order Multituberculata within the suborder Cimolodonta and family Neoplagiaulacidae.
The species Xyronomys swainae (J. K. Rigby, 1980) was found in Torrejonian (Paleocene)-age strata of Swain Quarry in Wyoming, United States. Represented by a couple of teeth, this genus was originally assigned to Eucosmodontidae. Kielan-Jaworowska and Hurum (2001, p. 406) refer it to Neoplagiaulacidae on the basis of its possession of microprismatic enamel, i.e. the tooth enamel is built up from small prisms.
A second species Xyronomys robinsoni was found in Puercan (Lower Paleocene)-age strata of Colorado, US and was named by Middleton and Dewar in 2004.
Material assigned to this genus has also been reported from Rav W-1 in Saskatchewan, Canada.
Text in “About” is quoted from the Wikipedia article Xyronomys (revision 1368552506), licensed under CC BY-SA 4.0; introduction excerpted verbatim, formatting removed. Ages, family, authority and fossil records: Paleobiology Database, accessed 23 October 2026. Ages are those of the rock layers the fossils were found in. Wikidata: Q8045587.
