Researchers from the University of Western Attica successfully reconstructed the skull of the extinct dwarf hippopotamus, Hippopotamus creutzburgi, using 3D digital imaging techniques. The study, published in Digital Applications in Archaeology and Cultural Heritage, represented the first complete skull reconstruction of this species and shed new light on its anatomy, evolution, and survival adaptations.
Led by researcher Nikolaos Gerakakis and Professor Dimitrios Makris, the team utilized four fossil remains excavated between 1998 and 2002 to embark on a digital reconstruction of the skull. The fossils, which were poorly preserved, fragmentary, and worn, posed challenges for traditional reconstruction methods. According to Phys.org, the team overcame these obstacles by employing 3D imaging and photogrammetry techniques.
"The skull and the flattened lower jaw posed challenges due to their severe distortion, which required innovative digital techniques for reconstruction," said Gerakakis. The team adapted the retrodeformation methodology of De Vries et al. (2022), utilizing Blender's armature system. "However, the complexity and extensive deformation of the mandible required us to innovate further. We designed a 'spider-like' exoskeleton with 23 armatures, enabling precise retrodeformation. Standard, undistorted specimens served as references throughout the process," he added.
Hippopotamus creutzburgi lived on the island of Crete during the Early to early Middle Pleistocene, more than 200,000 years ago. Despite going extinct, many remains of this species have been fossilized on the Katharó plateau, which is known for being rich in fossil remains. The exact causes of their extinction remain unclear, but ongoing studies aim to determine whether factors such as physical catastrophes, natural disasters, cooling periods, food shortages, or competition with deer that arrived on Crete in the late Pleistocene played a role.
During the Pleistocene, the genus Hippopotamus spread to many islands, including Cyprus, Madagascar, Malta, Sicily, and Crete. Hippopotamus creutzburgi was one such species that inhabited Crete. Gerakakis hypothesizes that a herd of Hippopotamus antiquus, the ancestor of Hippopotamus creutzburgi, traveled from the Peloponnese to Crete. Fossil remains of Hippopotamus antiquus have been found in the Peloponnese, and during cold phases of the Pleistocene, sea levels were lower, altering the geography of the Aegean Sea.
"Hippopotamuses do not float in freshwater; while moving, they maintain contact with the ground, typically with only one foot at a time. However, in salt water, they can float," Gerakakis explained, according to a report by Vecernje Novosti. "The young, which make up the largest part of the herd, probably survived better and managed to establish a population in Crete." This higher survival rate for juveniles potentially allowed them to establish a viable population of Hippopotamus creutzburgi on Crete.
Once on the island, the ancestors of Hippopotamus creutzburgi grew smaller, following the "island rule" hypothesized by biologist Leigh Van Valen, which states that large animals become smaller and small animals may become bigger under certain circumstances upon arriving on an island. This phenomenon is consistent with adaptations observed in other island species.
The research team found that Hippopotamus creutzburgi's morphology was similar to that of African hippopotamuses, Hippopotamus antiquus, and dwarf Malagasy hippopotamuses. The size of Hippopotamus creutzburgi likely came close to that of dwarf Malagasy hippopotamuses or a juvenile male African hippopotamus.
Using 3D imaging and photogrammetry, the team was able to digitally reconstruct the entire skull of Hippopotamus creutzburgi, filling in the blanks using a modern model of a hippopotamus skull. This digital reconstruction can be printed and used for museum exhibitions, such as a planned future exhibition at the Katharó plateau.
"A digital reconstruction of the entire skeleton has already been completed," Gerakakis noted. "A physical reconstruction of the entire skeleton, based on the digital model, was created by the Laboratory of Vertebrate Paleontology at the National and Kapodistrian University of Athens with the assistance of two conservators. The corresponding scientific paper is currently in preparation," he said, as reported by Phys.org.
"As for their extinction, several hypotheses exist, including physical catastrophes, another cold event, illness, food scarcity, or competition with deer that arrived on Crete in the late Middle to Late Pleistocene. Ongoing research aims to determine the exact causes," Gerakakis stated, according to Phys.org.
This article was written in collaboration with generative AI company Alchemiq