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In the remote soils of Magallanes, at the southern tip of Chile, a group of paleontologists made a discovery that adds a new piece to the puzzle of mammal evolution. It is the Yeutherium pressor, a tiny species that coexisted with dinosaurs in the late Cretaceous period.
This fossil, discovered in the Valle del Río de Las Chinas, corresponds to the third species of Mesozoic mammal identified in Chilean territory. It was found by researchers from the University of Chile and the Núcleo Milenio EVOTEM during an expedition focused on fossil vertebrates.
The Yeutherium pressor weighed only 40 grams, comparable in size to a domestic mouse. Unlike the giants around it, this small Cretaceous inhabitant discreetly lived among vegetation, likely feeding on seeds or hard plant materials.
Through the analysis of its skull and a fossil tooth, scientists determined it was a new species. Its dental characteristics revealed a surprising adaptation that sets it apart from other mammals found in the region.
This would be the small mammal that lived with the dinosaurs. Photo: University of Chile.
The “juicer” of the dinosaur era
The name Yeutherium pressor is not random. It combines words from the Aonikenk language, Greek, and Latin, describing a “mountain beast that squeezes”. The final reference alludes to its dentition, specially designed to crush hard foods.
The teeth of this species had curved ridges and edges with reliefs reminiscent of a fruit juicer. This type of dentition indicates a specialized diet and represents a key transitional point in mammalian evolution.
The discovery is particularly interesting because Yeutherium exhibits features that are not fully developed, helping to understand how more advanced dental structures emerged. These fossils provide a window into the adaptive processes that defined many of the modern mammals.
Additionally, this finding links it to a very scarce lineage in the fossil record, shared only by a previous discovery in Argentina. This new specimen represents the second documented case of this group on the continent.
A group of paleontologists found the remains of a small mammal. Photo: University of Chile.
An evolutionary footprint in Patagonian land
Until a few years ago, there were no fossil records of Mesozoic mammals in Chile. The scenario began to change with the discovery of Magallanodon in 2020 and Orretherium in 2021. Yeutherium joins as the third member of this unexpected group.
Although rodent-like in appearance, it was not placental. It probably laid eggs or had offspring at very early stages, like marsupials. Its position in the evolutionary tree places it between monotremes and later mammalian lineages.
This species is part of a crucial moment in evolutionary history, when the diversification we know today had not yet occurred. The Patagonian region, in this sense, emerges as a unique repository of information about the past of Gondwana and biological evolution at the end of the world.
With each discovery, a story that remained buried is rewritten. What started as a fossil hunt ended up expanding the horizons of what we knew about life in the dinosaur era.
A group of paleontologists found the remains of a small mammal. Photo: University of Chile.
The ecological contribution of rescuing history
From an ecological perspective, rediscovering extinct species like Yeutherium pressor allows us to understand how ecosystems evolved and how species responded to past climate and geographical changes.
Understanding these dynamics is crucial to interpret the present. Many of the current ecological challenges, such as biodiversity loss, can be better addressed by understanding the mechanisms that allowed the adaptation—or extinction—of previous species.
Thus, paleontology not only reveals fossils but also offers lessons for the future, helping to build a stronger framework to preserve life as we know it today.
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