Skull Bone Anatomy of the Young Common Hippopotamus (Hippopotamus Amphibius)

Abstract

Hippopotamidae family is nowadays represented by two species within two different genera: pygmy hippopotamus (Choeropsis liberiensis) and common hippopotamus (Hippopotamus amphibius). The common hippopotamus has a very unique anatomy, and the shape of the body, especially the head is adapted for a semi-aquatic life style. The morphological examination and description of the gross anatomical features of the hippopotamus skull is described in this paper. The shape of the skull is adapted for the amphibian way of life. Their eyes, ears and nostrils are placed high on the roof of the skull which allows these organs to remain above the surface of the water while the animal is being submerged underwater. The skull is massive, but the brain case (neurocranium) is extremely small compared with the splanchnocranium and complete head. The dental formula of the common hippopotamus is: incisors (I) 2/2, canines (C) 1/1, premolars (P) 3-4/3-4 and molars (M) 3/3. Incisors and canine teeth are formed in the shape of tusks and are used for threat or “demonstration of power” among animals when vigorously fi ghting. Incisor teeth grow continuously and are twice bigger in males than in females.

Chewing, dentition and tooth wear in Hippopotamidae (Hippopotamus amphibius and Choeropsis liberiensis)

“…Skull and mandible . The dimensions of the cranium ( S1 Fig in S1 File ) were gathered by measuring the distance between the Processus palatinus ossis incisivi (rostral margin the premaxilla) and the caudal margin of the Os palatinum (caudal margin of palatine), and the distance between the Processus palatinus ossis incisivi and the caudal margin of the Os occipitale ( Basis occipitale ) [terminology from 41 ]. The length of the mandible was measured from the caudal indentation of the Ramus mandibulae to the cranial margin of the Corpus mandibulae ( S2A Fig in S1 File ).…”

Evolution and development of the cetacean skull roof: a case study in novelty and homology

“…In a neonate Choeropsis liberiensis ( pygmy hippopotamus), the occiput, which may or may not include the interparietal, is separated from the frontal by a fontanelle [51]. In a subadult of Hippopotamus amphibius, the parietals meet and separate the frontals from the occiput [52]. The interparietal in non-cetacean mammals always contacts the supraoccipital posteriorly, but a possible synapomorphy of Xenorophidae † or subclade within, is loss of contact between these bones.…”