The research team surveyed the enormous osteological collections excavated from the site’s two main quarries, VM3 and VM4, and identified just 18 bird bones — a striking contrast with the roughly 24,000 skeletal remains of 24 large mammal taxa unearthed from the same stratum. Birds preserve poorly at open-air sites because most species are small, their skeletons are lightweight and pneumatized, and they lack durable mineralised tissues such as teeth. Yet from these meagre fragments, seven wing bones allowed the identification of at least three distinct taxa: the Common Shelduck Tadorna tadorna, a giant crane assigned to Grus cf. primigenia, and the Pleistocene raven subspecies Corvus corax antecorax. The remaining specimens, though too broken for firm identification, add to the picture of a diverse avian community.

The shelduck material, all from quarry VM4, includes a distal humerus, a proximal ulna and a femur fragment found in close spatial association and consistent in size and shape with a single individual. Careful comparison with 22 modern duck species and detailed analysis of subtle anatomical characters — the shape of the brachialis muscle fossa, the configuration of the olecranon fossa, and the absence of a diagnostic ridge running from the ectepicondylar prominence — confirmed the assignment to the Common Shelduck rather than its close relative, the Ruddy Shelduck. This identification carries real palaeoenvironmental weight, because modern shelducks favour coastal mudflats, estuaries and brackish lagoons, where they feed on aquatic invertebrates such as the saltwater snail Peringia ulvae.

The crane bones are even more spectacular. An ulna exceeding 286 millimetres in length, found alongside a radius diaphysis that may have belonged to the same left wing, is larger than that of any living European crane and comparable only to the Sarus Crane of Asia, a species whose breeding biology makes its presence in Pleistocene Europe exceedingly unlikely. The team tentatively assigned the fossils to Grus cf. primigenia, an extinct crane larger than the living Eurasian Crane. If correct, Venta Micena preserves the oldest known record of this Giant Crane in Europe, pushing its first appearance back into the late Early Pleistocene. Together, the shelduck and the crane point to a mild, wet landscape of oligohaline open water fringed by brackish marshes.

That reconstruction fits beautifully with the geology of the Baza Basin, an inland depression that was cut off from the Mediterranean in the Late Miocene and became an endorheic basin, accumulating some 600 metres of continental sediments. During the Early Pleistocene the basin hosted an extensive permanent palaeolake covering more than 1,100 square kilometres, with slightly saline waters fed by rainfall and thermal springs, surrounded by an emerged plain dotted with freshwater ponds. Rainfall at the time is estimated at 830 to 940 millimetres per year — roughly three times today’s figure — and the giant aquatic hippopotamus Hippopotamus antiquus, which fed on submerged vegetation, independently confirms the abundance of open water. The wetland vanished during the Middle or Late Pleistocene, when the Guadiana Menor River captured the basin’s drainage and erosion replaced sedimentation, creating the arid badlands seen today.

The raven specimen, a distal humerus from quarry VM3, is smaller than those of modern Common Ravens and falls within the size range of the fossil subspecies Corvus corax antecorax, previously recorded in Europe from the Late Pliocene to the Middle Pleistocene. Because Venta Micena is older than the earliest Iberian record of this subspecies at Sima del Elefante, dated to 1.3 to 1.2 million years ago, the new find represents the earliest occurrence of C. c. antecorax in the Iberian Peninsula. Its presence is hardly surprising given the site’s origin: a giant hyaena den packed with ungulate carcasses would have been an irresistible buffet for an opportunistic scavenger.

Indeed, the taphonomic evidence shows that birds were not merely bystanders in this ecosystem — they were on the menu. Half of the 18 bird bones show digestive corrosion, and several bear pits and scores produced by carnivore teeth. The shelduck bones from VM4 display both types of damage, as does the raven humerus itself, indicating that even this scavenger ended up inside a predator. The tooth marks, measuring between 0.4 and 0.7 millimetres in width, were most likely produced by juvenile hyaenas, whose sharper, more blade-like milk teeth leave precisely this kind of nibbling damage, although the jackal-sized wolf Canis orcensis cannot be ruled out. Modern spotted hyaenas have occasionally been observed preying on birds, lending plausibility to the interpretation.

The most provocative result comes from modelling the ecosystem’s energy flows. Using a palaeosynecological framework called PSEco, which estimates the annual biomass of herbivores available to carnivores and distributes it among the members of the predator guild, the researchers added the raven as a secondary consumer for the first time. Assuming a body mass of 1.16 kilograms, a density of 1.5 individuals per square kilometre, and an intermediate meat intake between winter and summer values for modern ravens, the model calculated that the Venta Micena raven population would have consumed about 62 kilograms of meat per square kilometre each year — some 13.2 percent of the total ungulate biomass available to the carnivore community. That figure is only one to five percent lower than the consumption estimated for each of the site’s major predators, including the giant hyaena, the sabretooths Homotherium latidens and Megantereon whitei, the jaguar Panthera gombaszoegensis and the pack-hunting wild dog Xenocyon lycaonoides.

The implications ripple through the entire food web. Adding ravens to the model reduces the share of meat available to every other consumer; for the giant hyaena, the decline from 21.0 to 18.1 percent of available biomass would translate into a population drop of roughly 17 percent, from six to five individuals per 100 square kilometres. The result echoes observations of modern ecosystems, where ravens following wolf packs can strip 2 to 20 kilograms of food per day from a carcass, and small wolf packs may lose up to three-quarters of an ungulate to these birds — a pressure that may even have driven the evolution of larger, more social wolf packs. In the Early Pleistocene of Iberia, a bird weighing little more than a kilogram was quietly competing with hyaenas and sabretooths for carrion.

The study also resolves a taphonomic puzzle: why nearly 90 percent of the bird bones come from VM4, even though that quarry has yielded only a fraction of the large mammal fossils found in VM3. The two quarries, just 350 metres apart, appear to represent denning sites used by different hyaena clans in different years, with the bones at VM4 buried more quickly by rising lake waters and therefore less thoroughly destroyed by weathering and gnawing. For the fragile, hollow bones of birds, only such rapid burial could preserve anything at all. The few species identified at Venta Micena almost certainly represent a tiny sample of a far richer avifauna, as suggested by the more than fifty bird species that still visit the small remnant wetland of El Baíco in the same basin today, where shelducks and cranes continue to winter. The fossil birds of Venta Micena thus reveal an Early Pleistocene ecosystem more intricate than anyone had imagined — one in which waterbirds signalled a vanished wetland paradise, and ravens carved out a substantial place at the carcass table alongside the giants.

Subject of Research: Early Pleistocene avian fossils from Venta Micena, Spain, and their palaeoenvironmental and trophic implications

Article Title: Avian remains from Venta Micena (Baza Basin, Granada Geopark) shed light on the Early Pleistocene wetland environments and trophic dynamics of the Southern Iberian Peninsula

Article References: Serrano, F. J., Espigares, M. P., Rodríguez-Gómez, G., Martínez-Navarro, B., Ros-Montoya, S., Terol, J. C., Sanisidro, Ó., Guerra-Merchán, A., García-Aguilar, J. M., Campaña, I., Granados, A., & Palmqvist, P. (2026). Avian remains from Venta Micena (Baza Basin, Granada Geopark) shed light on the Early Pleistocene wetland environments and trophic dynamics of the Southern Iberian Peninsula. Swiss Journal of Palaeontology, 145, 597-623. https://doi.org/10.3897/sjp.145.182523

Image Credits: AI Generated

DOI: 10.3897/sjp.145.182523

Keywords: Venta Micena, Baza Basin, Early Pleistocene, palaeornithology, Tadorna tadorna, Grus primigenia, Corvus corax antecorax, Pachycrocuta brevirostris, wetland palaeoenvironments, taphonomy, scavenging, trophic dynamics