Dataset to: Kampouridis et al. (2025) "Unique pathological phalangeal fusion in the chalicothere subfamily Chalicotheriinae and the interphalangeal immobilization in chalicotheres"

MicroCT scan of a phalange of Chalicotheriidae.

Chalicotheres are bizarre extinct herbivore mammals closely related to today’s rhinoceroses, tapirs and horses. Chalicotheriidae includes two subfamilies, the Chalicotheriinae and the Schizotheriinae. Some members of the schizotheriines form a duplex bone by fusing the proximal and the medial phalanges of the second digit of the hand. Here, we report the only known fused set of proximal and medial phalanges in a specimen of the subfamily Chalicotheriinae from the Late Miocene of Höwenegg in Germany. This specimen has been the center of some confusion regarding its identity and the nature of the fusion. In our study, we conduct a detailed comparison to chalicotheriines and schizotheriines, identifying the specimen as a chalicotheriine. We additionally acquired CT-scans of this specimen and two schizotheriines, Metaschizotherium fraasi from the Middle Miocene of Steinheim (Germany) and Ancylotherium pentelicum from the Late Miocene of Pikermi (Greece), to compare the internal structure of the fused phalanges, which revealed great differences between the fusion in the Höwenegg specimen and in schizotheriines. Furthermore, we found that both subfamilies show a trend towards immobilizing their digits, expressed in different ways, with chalicotheriines forming a notched-joint between the phalanges in some digits that hinders their movement and schizotheriines regularly fusing the phalanges.

System: YXLON FF 35 CT

Beam: FXE Direct Beam, Helix trajectory

Detector: Perkin Elmer Y.Panel 4343 CT

Scan Parameters: 190 kV, 350 µA, 500 ms exposure time, 5670 projection images

Isotropic voxel size: 30 µm