Habib et al. 2021 report:
“The Fayum province, northeast Egypt, is considered one of the best windows for vertebrate evolution during the Eocene–Oligocene of Africa. It is the best site for the occurrence of Arsinoitherium, which contains extensive skeletal remains for both A. zitteli and A. andrewsi.
Arsinoitherium (Fig. 1) nests in the large reptile tree (LRT, 1991 taxa) with Phenacodus, uintatheres and basal hornless taxa with enlarged lacrimals, like Periptychus. This little-known and misunderstood taxon was featured recently here.
Habib et al. continue:
“Arsinoitherium is a mysterious genus of paenungulate mammal.”
Mystery is a result of taxon exclusion. Traditionally Paenungulata includes elephants, manatees and hyraxes. In the LRT (Fig. 2) Arsinoitherium nests with Gobiatherium and Periptychus in the Phenacodus clade, far from paenungulates. Simply adding taxa recovers these results.
Habib et al. continue:
“It resembled extant rhinos in ornamentation with its massive cranium and protuberant horns, and by the great magnitude of its skeletal frame. However, Arsinoitherium is more closely related to elephants, which invaded the upper Eocene and lower Oligocene of northern Africa.”
According the LRT this is false, a myth resulting from taxon exclusion.
“The upper Paleogene succession in the Fayum province consists of the nearshore marine and
fluvial upper Eocene Qasr El Sagha Formation overlain by the fluvial Oligocene Jebel Qatrani Formation, and Widan El Faras Basalt. Preliminary results of the reevaluation of the previously collected fauna of Arsinoitherium from the Fayum province, illustrate a challenge in the lateral distribution of Paleogene Arsinoitherium in Africa and the Afro-Arabian region.”
“We conclude that there is a migration of Arsinoitherium from Africa to the Afro-Arabian region through Egypt by the late Eocene and the early Oligocene. However, the mysterious appearance and disappearance of Arsinoitherium in Egypt and elsewhere in Africa is still a big puzzle.”
Arsinoitherium zitteli
(Beadnell 1902, Figs. 1, 2; late Eocene, early Oligocene, 36-30 mya) was a sister to Gobiatherium. Wikipedia describes as, “an extinct genus of paenungulate mammal belonging to the extinct order Embrithopoda. It is related to elephants, sirenians, hyraxes and the extinct desmostylians.” None of these candidates have any hint of the huge nasal and tiny frontal horns that make Arsinoitherium distinct. Another trait that makes Arsinoitherium distinct is its nearly complete arcade of teeth, none of them tusks, in which the canine is absent (or at least indistinct) and the medial incisor is missing. The premaxilla also redevelops an ascending process of the premaxilla, a trait not seen in mammals since their origin in the Triassic.
References
Beadnell HGC 1902. A preliminary note on Arsinoitherium zitteli, Beadnell, from the Upper Eocene strata of Egypt. Public Works Ministry, National Printing Department. Cairo: 1–4.
Habib F, et al. 2021. Lateral distribution of the Paleocene Arsinoitherium in Africa and the Afroarabian region. Journal of Vertebrate Paleontology abstracts.
The Pterosaur Heresies 