At the base of the giant indricotheres
we find Pappaceras (Fig. 1). To that everyone agrees. Where the disagreements start is what came before Pappaceras? In the large reptile tree (LRT, 1012 taxa) it’s Miohippus (Fig.1 1) and Equus the extant horse.
Wang et al. 2017
bring new insight into the chewing mechanism in Pappaceras. They write: “The paraceratheriid Pappaceras is the earliest unequivocal rhinocerotoid genus to date, for which the osteological morphology is relatively unique compared to other perissodactyls. The reconstruction of the masticatory muscles suggests that Pappaceras meiomenus is strictly herbivorous, probably folivorous, with a primary component of vertical biting.”
Distinct from the LRT
The Wang et al. cladogram nests horses at the base of the Perissodactyla. Chalicotheres and brontotheres nest together without resolution. Indricotheres nest with rhinos as sisters to tapirs. The LRT does not support that tree topology at all. The Wang et al. cladogram also nests a perissodactyl outgroup taxon I had never heard of before: Cambaytherium. which I just added to the LRT and we’ll talk about tomorrow. It is not related to perissodactyls in the LRT.
The freehand drawing of Pappaceras
by Wang et al. (Fig. 1`) is distinct in certain subtle aspects from their CT scan (Fig. 1). It’s better to trace directly from photos. Or just use the CT scans. Freehand drawing, by its nature, emphasizes things that catch the eye and deemphasizes things that don’t catch the eye, but perhaps should.
Wang H-B, Bai B, Gong Y-X, Meng J and Wang Y-Q 2017. Reconstruction of the cranial musculature of the paraceratheriid rhinocerotoid Pappaceras meiomenus and inferences of its feeding and chewing habits. Acta Palaeontologica Polonica 62 (2): 259–271.