A scientific study led by specialists from CONICET and the Argentine Museum of Natural Sciences “Bernardino Rivadavia” (MACNBR) reshapes what was known about the evolution of dung beetles (subfamily Scarabaeinae).
The research, published in the journal Palaeontology, shows that some species began to feed on carrion tens of millions of years earlier than previously thought, explaining their evolutionary success and their crucial role in current ecosystems.
From coprophagy to necrophagy: an early change
Until now, the most accepted hypothesis held that the transition to necrophagy occurred after the extinction of the Late Pleistocene megafauna (about 129 thousand years ago), when the availability of dung from large herbivores decreased.
The new study refutes that idea. According to researcher Liliana F. Cantil, the first author of the work, fossil evidence found in Argentina, Chile, Uruguay, and Ecuador shows that some species were already consuming carcasses more than 37 million years ago (Middle-Late Eocene).
“This new hypothesis greatly changes what was known about the evolutionary history of beetles, positioning the origin of necrophagy in an environment where large herbivores were abundant,” explained Cantil.
Grasslands and competition for resources
The emergence of grasslands in Patagonia about 45 million years ago favored the expansion of large herbivores and, with them, coprophagous beetles. The abundance of species that used dung generated intense competition for resources, leading to a shift in ecological niche.
In this context, some species began to use carrion instead of dung, marking the beginning of necrophagy as an adaptive strategy.
Fossil evidence: the brood balls
The team analyzed more than 5,000 Coprinisphaera, that is, fossil brood balls of Scarabaeinae beetles found in paleosols from different formations in Argentina (Tucumán, La Pampa, Buenos Aires, Chubut, Santa Cruz), as well as Uruguay, Chile, and Ecuador.
Brood balls are spherical structures of food (dung or carrion) containing an egg protected by a soil wall. Upon hatching, the larva consumes the food deposited by the adults.
The study allowed differentiation between the balls constructed by coprophagous producers and those made by necrophagous producers, thanks to the comparison with the behavior of current beetles.
New attributions and evolutionary lineages
The fossil balls Coprinisphaera tonnii and Coprinisphaera akatanka were attributed to necrophagous beetles.
- The producers of C. tonnii would be related to the current genus Coprophanaeus.
- The producers of C. akatanka with necrophagous species of the genus Canthon.
In the Sarmiento Formation (Chubut), specimens of C. tonnii were found that represent the oldest evidence of necrophagy, with 37.7 million years.
Evolutionary and ecological implications
The research constitutes a key contribution to the study of the evolution of Scarabaeinae, by reformulating the origin of necrophagy as an early adaptive innovation.
“Scarabaeinae beetles include more than six thousand species and today occupy fundamental roles in ecosystems, acting as environmental engineers by recycling nutrients and aerating the soil. Their evolutionary flexibility explains why they remain successful,” highlighted Cantil.
A collaborative work
The study also involved M. Victoria Sánchez, Jorge F. Genise, Eduardo S. Bellosi, José H. Laza, Mirta G. González, and Laura C. Sarzetti, all members of the Ichnology Division of MACNBR-CONICET.
The finding rewrites the evolutionary history of dung beetles, demonstrating that necrophagy emerged much earlier than previously believed. This paradigm shift not only provides new perspectives on the evolution of insects but also reinforces the importance of fossils as tools for understanding the dynamics of ecosystems over millions of years.
