Dietary Shifts in the Hipparion Fauna of the Northern Black Sea Region

The Miocene epoch (approximately 23 to 5.3 million years ago) represents the most recent warm interval in Earth's geological history. From the late Miocene through the Pliocene (about 5.3 to 2.6 million years ago) and continuing into the Pleistocene Ice Age (about 2.6 million years ago to the present), the planet's average temperature has generally followed a long-term cooling trend. For this reason, studying Miocene ecosystems provides an important bridge for understanding how biological communities evolved during the transition from a warm world to the cooler climates that characterize the modern Earth.

In this study, researchers examined the dietary habits of mammals belonging to the Hipparion fauna that inhabited the northern Black Sea region during the late Miocene and early Pliocene. By reconstructing the feeding ecology of these animals, the study aimed to clarify how their diets differed from those of modern mammalian communities and how those differences reflected environmental change.

Before the middle Miocene, the global climate was warm and precipitation was abundant. These conditions supported extensive forests across Eastern Europe. During this time, the region was dominated by the Anchitherium fauna. As the Miocene progressed into its middle and later stages, however, global temperatures began to decline and rainfall gradually decreased. The vast forests of Eastern Europe became fragmented, and open grasslands increasingly replaced wooded habitats. Correspondingly, the Anchitherium fauna declined. By the late Miocene, forests had largely retreated to areas surrounding river valleys, while much of the remaining landscape had become a savanna-like environment resembling the modern East African grasslands. At the same time, the Hipparion fauna replaced the Anchitherium fauna as the dominant large mammal community in the northern Black Sea region.

Based on the environmental context and the dental morphology of herbivores within the Hipparion fauna, researchers had traditionally assumed that these animals were primarily grazers, or at least mixed feeders consuming both grasses and leaves. The research team conducting this study argued that such assumptions required more direct evidence. To obtain a more reliable understanding of dietary habits, they analyzed tooth wear patterns from representative species within the fauna.

Analytical Process

Fossil specimens were collected from three localities: Tudorovo and Cioburciu 1 in Moldova, and Grebeniki in the Odessa region of Ukraine.

Hipparion fossil（Image source：PePeEfe， CC BY-SA 4.0 ）

Among the horses, two species of the genus Hipparion were examined: Hipparion verae and Hipparion tudorovense.

Chilotherium fossil（Image source：laikayiu， CC BY-SA 3.0 ）

The rhinoceroses included Chilotherium schlosseri and Aceratherium incisivum.

Because the classification of small antelopes from these deposits remains uncertain, all antelope fossils were grouped under Antilopinae gen. indet.

The suid Microstonyx major was also included in the analysis.

From the giraffe family, the species Palaeotragus rouenii was studied.

Ictitherium viverrinum skull fossil（Image source：Ghedoghedo，CC0 1.0 ）

Carnivores included the hyena Adcrocuta eximia and the civet-like hyena Ictitherium viverrinum.

Machairodus copei life reconstruction（Image source：Jesus Gamarra Gonzalez， CC BY-SA 4.0 ）

Machairodus copei skull fossil（Image source：Ghedoghedo， CC BY-SA 3.0 ）

Finally, the saber-toothed cat Machairodus copei represented the felids in the assemblage.

To analyze dietary signals, the researchers first cleaned the occlusal surfaces of fossil teeth using acetone followed by ethanol. Silicone molds were then taken from the tooth surfaces, and transparent casts were produced using epoxy resin. These casts were examined under a microscope at 35× magnification. Patterns of microscopic wear were recorded and categorized according to the types of pits and scratches present on the enamel surface. The resulting data were organized into matrices for statistical analysis and compared with known wear patterns from modern mammals whose diets are well understood.

Results

The results revealed a complex pattern of dietary diversity within the Hipparion fauna.

Among the horses, the earlier species Hipparion verae primarily consumed leaves, while Hipparion tudorovense displayed a mixed feeding strategy that included both leaves and grasses. This contrasts with modern zebras, which are specialized grazers feeding mainly on grasses.

Both rhinoceros species were identified as true grazers, feeding predominantly on grasses. Their diet closely resembles that of the modern white rhinoceros.

The small antelopes were primarily leaf browsers, and those from the Cioburciu 1 locality appear to have included fruits in their diet. Modern antelopes display a wide range of feeding strategies, including browsing, suggesting a degree of continuity in dietary flexibility between these ancient and modern forms.

The giraffid Palaeotragus rouenii appears to have been a mixed feeder, consuming both leaves and grasses. When compared with modern giraffids, its feeding ecology resembles that of the okapi more closely than that of the more selective modern giraffe.

The pig-like Microstonyx major exhibited a clearly omnivorous diet, which would have allowed it to exploit a wide variety of food sources.

The hyena Adcrocuta eximia appears to have occupied an ecological role similar to that of the modern spotted hyena, feeding primarily on large herbivores. Researchers suggest that it likely lived in social groups capable of cooperative hunting.

The civet-like hyena Ictitherium viverrinum seems to have been an opportunistic feeder. It hunted small prey but also consumed carrion and possibly plant material such as fruit when available.

The saber-toothed cat Machairodus copei displayed clear signs of hypercarnivory, meaning that it specialized in consuming large animals and relied almost entirely on meat. Its ecological role likely resembled that of modern lions.

When the proportions of herbivore feeding types were analyzed, the researchers found that leaf-eating species still outnumbered grass-eating species within the Hipparion fauna. This indicates that although grasslands were expanding, substantial wooded areas still existed in the northern Black Sea region at that time. Over time, however, these forests continued to retreat, and by the later stages of the Hipparion fauna the landscape had largely transitioned into open grassland ecosystems.

Conclusion

This study provides strong evidence for the environmental transition from forests to grasslands during the late Miocene in the northern Black Sea region. The fossil record captured here documents a critical phase in which herbivorous mammals gradually shifted from browsing on leaves to grazing on grasses. Among the species examined, rhinoceroses appear to have been the earliest herbivores to adopt a predominantly grazing diet. Meanwhile, members of the genus Hipparion show clear signs of dietary adaptation as they transitioned toward mixed feeding strategies.

The results highlight the intricate relationship between climate change, vegetation shifts, and the dietary evolution of large mammals. By reconstructing these interactions, the study offers valuable insight into how ecosystems reorganized during one of the most important climatic transitions in Earth's recent geological past.

Author: Bai Leng

Reference:

Rivals, F., Belyaev, R. I., Basova, V. B., Prilepskaya, N. E. (2024). A tale from the Neogene savanna: Paleoecology of the hipparion fauna in the northern Black Sea region during the late Miocene. Palaeogeography, Palaeoclimatology, Palaeoecology.

（Paid content. Unauthorized reproduction or use is prohibited.）