Palaeoecology of the Pliocene large carnivore guild at Hadar, Lower Awash Valley, Ethiopia

Abstract

The Hadar Formation at Hadar (Lower Awash Valley, Ethiopia, ∼3.45–2.95 Ma) is one of the most well-known and studied Pliocene hominin-bearing sequences in eastern Africa, yielding numerous fossils of the species Australopithecus afarensis. While much research has been conducted on the palaeoecology of the Hadar Formation broadly, little attention has been placed on the carnivore guild. Here, we present new stable carbon and oxygen isotope data for Hadar carnivores that contribute to the palaeoenvironmental reconstructions of the Hadar Formation and facilitate inference of predator-prey relationship between the large carnivore and herbivore guilds at Hadar. Overall, the members of the Hadar carnivore guild had relatively high carbon values (−4.6 ± 1.4‰), with the highest values in the middle part of the sequence (Denen Dora Member, ∼3.2 Ma). These values are higher than the carbon values of carnivores from penecontemporaneous sediments in the Turkana Basin (southern Ethiopia and northern Kenya). Stable oxygen isotope values are variable throughout the Hadar Formation, but reconstruction of estimated meteoric water oxygen values indicates a wetter and more pluvial climate than that at the present. Carbon isotope mixing models weighted by a prey selectivity index based on established predator-prey body size relationships reveals that two large-bodied taxa (Homotherium and Crocuta venustula) had partitioned their dietary niches only to a limited extent. Understanding the nature of the large carnivore guild at Hadar allows us to predict which taxa may have been competitors or predators of Au. afarensis, offering insights into the palaeoecological context beyond what can be inferred from palaeoenvironmental reconstructions alone. Moreover, our analyses provide a valuable insight into the little-known isotopic ecology of fossil African carnivores.