Orthoarthrus fossil map
Where fossils of Orthoarthrus have been found, shown on the Earth as it looked about 15 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 15 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 | 17.5–16.3 million years ago (Burdigalian) |
| Periods | Neogene |
| Named by | Ameghino 1904 |
| Fossil records | 2 occurrences at 1 locations (PBDB) |
| Found in | Argentina |
| Rock formations | Santa Cruz |
About Orthoarthrus
Orthoarthrus ("upright joint") is an extinct species of mammal of unknown affinities that lived in Argentina during the Miocene. It was described by prolific Argentine paleontologist Florentino Ameghino in 1904 on the basis of a single left astragalus (under specimen number MLP 69-IX-5-16,) that had been unearthed from the Santacrucian sediments of Santa Cruz, Argentina. Ameghino described it as a species of pangolin closely related to African species of the group, but this came into question by later 20th-century paleontologists, who concluded that it was an indeterminate genus of mammal. The size of the astragalus and its anatomy was described briefly, with a diameter of 30 millimetres (1.2 in) and a distinct furrowed morphology on its ventral face. The species name mixtus ("mixed") is after the anatomy of the astragalus' rugged bottom surface.
Text in “About” is quoted from the Wikipedia article Orthoarthrus (revision 1358823660), 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: Q119998991.
