Two more odd ‘hornless rhinos’ nest slightly elsewhere in the LRT

First a little backstory
Earlier, Paracerathierium and Juxiatwo traditional hornless rhinos, nested with three-toed horses in the large reptile tree (LRT, 1009 taxa, Fig. 3).

Figure 1. Metamynodon nests with Eotitanops. It had large fangs and a bulky body like a hippo.

Figure 1. Metamynodon nests with Eotitanops. It had large fangs and a bulky body like a hippo.

Today
the giant hippo-like traditional rhino, Metamynodon planifroms (Scott and Osborn 1867; Early Eocene; 4m long), nests with Eotitanops, the basal brontothere, though not far from Ceratotherium, the white rhino.

Figure 2. Amynodon was formerly linked to Metamynodon as a basal rhino, but here nests with Mesohippus.

Figure 2. Amynodon was formerly linked to Metamynodon as a basal rhino, but here nests with Mesohippus.

And
the smaller long-necked traditional rhino, Amynodon, nests with Mesohippus, the basal horse. Both were derived from a sister to Hyracotherium, basal to both rhinos and horses.

Amynodon advenus (Marsh 1877; 1m in length; Oligocene-Eocene, 40-23 mya) was originally considered an aquatic rhino. Here it nests with Mesohippus. The long neck and other traits are more horse-like than rhino-like. Manual digit 5 was retained. The skull was deeper as in basal forms like Hyracotherium.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Traditional cladograms
nest horses separate from tapirs + rhinos. The LRT nests horses with rhinos both derived from a sister to Hyracotherium and a sister to tapirs + chalicotheres. Traditional cladograms also avoid mixing brontotheres, horses and rhinos, like we do here.

References
Marsh OC 1877. Notice of some new vertebrate fossils. American Journal of Arts and Sciences 14:249-256
Scott WB and Osborn HF 1887. Preliminary account of the fossil mammals from the White River formation contained in the Museum of Comparative Zoology. Bulletin of the Museum of Comparative Zoölogy at Harvard College 13(5):151-171.

wiki/Mesohippus
wiki/Amynodontidae
wiki/Metamynodon

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