Rhinos, horses and paraceratheres: untangling a tradition

While searching
for a cladogram that includes rhinos, horses AND paraceratheres, I ran across the following papers and taxa:

Orientolophus
Bai et al. 2020 discussed the origin of Rhinoceratoidea and the phylogeny of Ceratomorpha (rhinos). The authors included rhinos and paraceratheres, but not horses (= Equus and Miohippus). An included taxon was Orientolophus (known from a mandible and teeth). The Bai et al. cladogram (their Fig. 7) included several dozen taxa, including tapirs, Heptadon, Hyrachus and many other rhinos, Fostercooperia, Pappaceras, Juxia, Paraceratherium, , but, alas… no horses.

Personal reminder: Ancylopods are chalicotheres and kin.

Bai et al. 2018 continued:
“Based on ancestral reconstructions of the geographic distribution using the parsimonious criterion, we suggest that equids originated in Europe. One clade dispersed to the Indian-subcontinent giving rise to Ghazijhippus, probably along the northern margin of the Neotethys, while the other clade gave rise to European Cymbalophus and Pliolophus quesnoyensis.
The European equids dispersed to North America via the Greenland land bridge giving rise to Arenahippus and Sifrhippus, which immigrated to Asia via the Bering Strait giving rise
to Erihippus during the PETM.”

Much of the data in Bai, Wang and Meng 2018 are dental.
Sadly, their cladogram includes several other horse-like ‘hippus’ taxa, but not Miohippus and Equus and no paraceratheres (Fig. 1). Their outgroup, Radinskya, nests in the large reptile tree (LRT, 1879+ taxa) with Procavia, the hyrax, basal to elephants, not perissodactyls. Their other outgroup taxon, Cambaytherium, nests in the LRT with Cornwallius between hippos and anthracobunids, not close to perissodactyls. Matching the LRT, brontotheres are close to rhinos, but the authors nest Danjiangia with brontotheres. In the LRT Danjiangia is a pig. No pigs are included in the Bai, Wang and Meng 2018 taxon list, so taxon exclusion bites the hand again.

Bottom line:
Try not to cherry-pick taxa. Let your wide-gamut cladogram pick taxa for you. To make sure you have a wide-gamut cladogram, keep adding taxa. Dental traits can converge. Don’t trust genes in deep time studies.

References
Bai B, Wang Y-Q and Meng J 2018. The divergence and dispersal of early perissodactyls as evidenced by early Eocene equids from Asia. Nature Communications Biology 1:115 | DOI: 10.1038/s42003-018-0116-5 | http://www.nature.com/commsbio
Bai B et al. (4 co-authors) 2020. The origin of Rhinocerotoidea and phylogeny of Ceratomorpha (Mammalia, Perissodactyla). Nature Communications Biology 3:509 | https://doi.org/10.1038/s42003-020-01205-8 | http://www.nature.com/commsbio