A set of weathered bones found in Costa Rica is opening a window onto a much larger animal and a very different landscape. The fossils belong to Eremotherium, a giant ground sloth that lived near the end of the Ice Age.
The animal has been nicknamed Tobi. It was not a slow, leafy bundle hanging from a branch like the sloths we know today. The National Museum of Costa Rica says this extinct herbivore may have reached about six metres in height and weighed close to five tonnes. Even allowing for the uncertainty that comes with incomplete fossils, that is an extraordinary relative to place beside a modern tree sloth.
What makes Tobi especially interesting is not just size. The bones, the sediment around them and a piece of ancient charcoal are helping researchers ask when the animal lived, what happened to its body after death and what Costa Rica may have looked like thousands of years ago.
A chance discovery with a memorable name
According to the National Museum's preliminary taxonomic report, geologist María Sequeira reported the find. The excavation took place on 30 December 2024 with museum specialists and two children, Tobías Sequeira and Ara Paula Chinchilla, taking part. The nickname Tobi recognises that human story behind the scientific work.
The material recovered so far includes four vertebrae, a shoulder blade and part of the pelvis. Palaeontologist S. G. Lucas made the preliminary identification as Eremotherium, a genus of giant ground sloth known from fossils across a wide stretch of the Americas.
Preliminary matters here. Scientists are not looking at a complete skeleton posed neatly in the ground. They are working from separate pieces that must be cleaned, preserved, measured and compared with other specimens. The museum describes the current assignment as a starting point for detailed study and future scientific publication.
The sediment provides the clock
Fossils do not arrive with labels showing their age. Researchers have to build that timeline from the geological context. At the Tobi site, known as Orosi 1, they collected a fragment of carbonised wood from the clay layer associated with the giant sloth remains.
The museum's radiocarbon dating update reports an age of about 14,400 years before present for that sample. This dates the associated deposit rather than directly dating the sloth bone, an important distinction. It places the find near the end of the Late Pleistocene, when large mammals still shared Central American landscapes with the earliest human communities in the region.
A nearby site called Orosi 2 contains remains of Cuvieronius, an extinct elephant relative often called a mastodon. Carbonised wood from that deposit produced a younger date of about 13,400 years before present. The two sites therefore preserve different moments in the same broad Ice Age story, separated by roughly a millennium according to the reported samples.
One spine carried signs of a long life
Tobi's vertebrae contain osteophytes, bony growths that the museum says suggest severe arthritis in the spine. That does not tell us every detail of the animal's health or behaviour, but it turns an abstract extinct giant into an individual whose skeleton recorded wear and ageing.
Researchers will need to study the bones carefully before drawing wider conclusions. A few vertebrae cannot tell us how common this condition was in Eremotherium, how old Tobi was or exactly how the arthritis affected movement. They can, however, preserve evidence of what happened during one animal's lifetime, not merely what happened to the species over evolutionary time.
A traveller from an older America
The museum describes Eremotherium as a plant-eater that browsed leaves and grasses in tropical and subtropical environments. Its wider fossil record stretches from Brazil to the United States. That distribution reflects one of the great movements in mammal history.
Sloths evolved in South America. After land connections formed between the continents, different groups of mammals moved north and south during the Great American Biotic Interchange. Giant ground sloths were among the travellers that spread northwards. Tobi is part of that much bigger story, preserved at the narrow Central American meeting point between two continents.
It is tempting to call an animal like Tobi the direct ancestor of today's sloths, but that would be too simple. Eremotherium was an extinct relative within the wonderfully varied sloth family tree. Modern tree sloths are surviving branches of that tree, not miniature copies of this particular giant.
Tiny clues can rebuild a giant's habitat
The most dramatic finds are the large bones, yet some of the most useful evidence can be almost invisible. The museum's palaeobotany overview explains how wood, leaves, seeds and pollen in fossil-bearing sediment help researchers reconstruct ancient plant communities and climate.
Those clues can show which trees grew nearby, whether the environment was wooded and how vegetation shifted as the Ice Age ended. Wood and charcoal can also help date a deposit. Signs of burning may eventually contribute evidence about fire, drought or volcanic disturbance, although each possibility needs testing rather than guesswork.
This is why palaeontologists document the position and surrounding layer of every find. A bone removed without its context can still identify an animal. A bone studied together with sediment, plant remains and geological layers can help recreate an ecosystem.
Why Tobi's story is still being written
The National Museum published its detailed project updates in March 2026, but the work is not finished. Fossils need conservation and curation before researchers can make reliable comparisons. Sediment samples still hold information about plants, climate and the processes that buried and preserved the remains.
That unfinished quality is part of the appeal. Science rarely delivers a complete prehistoric scene in one dramatic reveal. It builds the picture piece by piece: a shoulder blade, four vertebrae, part of a pelvis, a charcoal sample and countless grains of sediment.
Tobi reminds us that sloth history is far bigger than the treetops. Today's small, specialised canopy dwellers belong to a lineage that once included immense animals walking across the ground from South America into Central and North America. Costa Rica's living sloths are remarkable, but the fossils beneath their forests show just how surprising their wider family has always been.
Sources and image credit
- Museo Nacional de Costa Rica: preliminary taxonomy of the Eremotherium and Cuvieronius finds
- Museo Nacional de Costa Rica: radiocarbon dates and future research
- Museo Nacional de Costa Rica: palaeobotany and ancient environmental clues
Featured image: a fossilised shoulder blade attributed to Eremotherium. Image credit: Museo Nacional de Costa Rica.