Functional morphology of the hindlimb of fossilized pygmy hippopotamus from Ayia Napa (Cyprus)

Abstract

We studied the functional morphology of the postcranial skeleton of the endemic hippopotamus Phanourios minor, derived from the Upper Pleistocene site of Ayia Napa. The deposit, which consists of a hard limestone substrate on which the species moved, has yielded a great abundance of hippopotamus material, making the Ayia Napa locality one of the most important paleontological sites in Cyprus. The immigration of the large‐sized mainland Hippopotamus to Cyprus led to the emergence of a new insular species with its main characteristic being the extremely reduced body size. In this study, all the hindlimb elements of the Cypriot hippo are described in detail and compared with those of the modern species, with the extant Hippopotamus amphibius being considered similar to the possible ancestor of P. minor. In some cases, the morphological comparison is reinforced using bones of other extinct insular and mainland hippos. Additionally, we provided a functional analysis of the hindlimb joints, suggesting specific locomotor habits for the species. The anatomical examination reveals that the elements in P. minor are robust with marked muscular insertion areas resembling those found in Hippopotamus. However, there are also similarities with Choeropsis liberiensis in certain morphofunctional traits. P. minor adapted to slow but powerful locomotion with remarkable stabilization, particularly in the zeugopodium and the autopodium. The knee was less mobile in the craniocaudal direction compared with that in recent hippos, while the abduction–adduction movements of the thigh were advanced. The pes presented good mobility in the sagittal plane and limitation in transversal movements. Thus, P. minor displayed modifications to its limbs, influenced by the mountainous island environment and the body size reduction, resulting in specialized locomotion, which was different from that of extant hippopotamuses.

Reinforcing the idea of an early dispersal of Hippopotamus amphibius in Europe: Restoration and multidisciplinary study of the skull from the Middle Pleistocene of Cava Montanari (Rome, central Italy)

“…Morphological and biometric comparisons of the Tor di Quinto skull with corresponding specimens of other fossils and extant Hippopotamus [8,14,16,61] were carried out, to evaluate its taxonomic attribution. The dental terminology adopted in this work follows [16,62].…”

“…As aforementioned, the dental remains do not show significant morphological differences, and commonly their identification is based on size (with H. antiquus larger than H. amphibius). For postcranial bones, even if not included in this work, a preliminary analysis for the discrimination between these two species was published by [16], but only a few works attempted to explore and to expand the knowledges for unambiguous cut-criteria [9,22,23,61,63]. Their results are not conclusive, leaving skepticism on the use of these features for specific identification.…”

The Middle Pleistocene Hippopotamus from Malagrotta (Latium, Italy): New Data and Future Perspectives

“…The Malagrotta specimen is characterized by a fairly protruding coracoid process, similar to H. antiquus. Moreover, in MCZR PV 2010.0076, the proximal articular surface for the astragalus projects out of the dorsal margin of the bone, as observed in H. antiquus (NHMMZ PW 1991/2-LS), contrary to H. amphibius [55]. The overall aspect of the bone, and in particular, the protruding proximal-most end also fits the description of KYP4-332 by Athanassiou et al ( [48], p. 187, Figure 7J) ascribed to H. antiquus.…”

“…H. antiquus specimens. Dimensionally, the calcaneum from Malagrotta is closer to H. amphibius, displaying smaller dimensions than H. antiquus [9,21,40,46,48,55]. The available measurements for H. ex gr.…”