Arsinoitherium zitteli was a large herbivorous mammal living in what is now northern Africa during the late Eocene and early Oligocene, about 36-30 million years ago.
Despite looking like a double-horned rhino this resemblance was only superficial, and for most of the 20th century it was actually the only known representative of an entire order of mammals – the embrithopods – with its wider evolutionary relationships being unknown. Since the 1970s, however, more members of this group have been discovered and embrithopods are now understood to be afrotheres, a very early offshoot of the tethythere lineage, with their closest living relatives being modern elephants and sirenians.
Arsinoitherium was by far the most abundant embrithopod, with numerous fossil remains making it one of the most completely known African fossil mammals. It stood around 1.8m tall at the shoulder (6'), similar in size to modern white rhinos, and would have been a massively-built slow-moving animal with elephant-like columnar limbs.
Its pair of enormous nose horns (and smaller brow horns) were structurally more similar to those of bovids than rhinos, with large hollow bony cores that probably bore thick keratinous sheaths that would have increased their apparent size even more. Both males and females appear to have had these horns, and muscle attachments at the back of the skull suggest Arsinoitherium could powerfully swing its head upwards – possibly wrestling with each other in combat over territories, competing for mates, or in establishing dominance hierarchies.
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