Unusual fossilised tracks might show ancient birds of prey on the hunt

A fossilised trackway in Portugal’s Malhão formation may be evidence of an ancient predator-prey interaction.

The tracks were found in a layer which dates to between 27,000 and 187,000 years ago during the Pleistocene period. They are described in a paper published in the Quaternary Science Reviews journal.

Among the footprints are two new bird trackways. These have been identified as Corvidichnus odemirensis, attributed a western jackdaw (Corvus monedula), and Buboichnus vicentinus, interpreted as the footprints of a Eurasian eagle-owl (Bubo bubo).

Pink slab and colour diagram next to greyscale diagram
Trackway belonging to a Western jackdaw (Corvus monedula) preserved in sandstone alongside that of a rabbit (Leporidichnites malhaoi). A) False colour image shows impression depths in the rock, B) enhanced view of trackways with greyscale shading, C) 3D model of the fossil-bearing slab, and D) interpretive trackways of the jackdaw (red and yellow) and rabbit (pink) with isolated footprints in white and green. Credit: Neto de Carvalho et al. 2023.

The Buboichnus vicentinus track is believed to represent the first evidence preserved in a trace fossil, of a raptor (bird of prey) hunting another animal.

Alongside the avian tracks are the fossilised footprints of straight-tusked elephants, rabbits, red deer, foxes and Iberian lynx – giving a tantalising glimpse into the broader ecosystem of the time.

Fossilised traces (not bones or other direct bodily remains) are known as ichnotaxa. These, like animals and plants, are given ichnogenus and ichnospecies names. Other fossil footprints, such as sauropod tracks in China or ancient bipedal hominin footsteps, can provide a great deal of information about how animals lived and interacted.

Researchers created three-dimensional models of the Portuguese tracks by taking hundreds of photographs in order to study the traces. The photogrammetry allowed the scientists to generate false-colour images to highlight features of the trackway and interpret what kinds of interactions have been preserved.

Measurements such as the size of tracks, digits, angle of digits, divergence of each footprint from the track mid-line, as well as pace and stride length all give clues as to the movements and interactions of the ancient animals. For example, increased stride length indicates speeding up.

The western jackdaw footprints show the bird walking at a slow place near a rabbit which hops to change direction. Pleistocene-age western jackdaw fossils are common in Portuguese caves and the birds can still be seen foraging on beaches and dunes along the coast today.

Dusty pink slab and drawing underneath
Eurasian eagle-owl (Bubo bubo) trackway (Buboichnus vicentinus, red and green footprints) intersecting the tracks of two smaller birds, suggesting a prey-predator scenario. A) 3D model of trackways, and B) interpretive drawing of the multiple trackways with central area highly disturbed. Credit: Neto de Carvalho et al. 2023.

Impressions left by the Eurasian eagle-owl intersect two trackways belonging to other birds. At the centre of the slab containing the tracks, the sediment is highly disturbed due to overprinting of footsteps.

While it is possible that the tracks overlap due to mere coincidence and the tracks show the birds converging on the same spot at different times, the scientists believe the confluence of footprints in one spot suggests a potential predator-prey interaction.

Such finds can breathe life into ancient ecosystems, opening a window to how animals interacted tens of thousands of years ago.

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