Mylodon darwini

Overview

Mylodon darwini is an extinct ground sloth studied through skin and hair preserved in caves as well as its skeleton. Even small bones within the skin provide clues to its body. It invites us to examine forms of preservation different from fossils retaining only bones.^[1][2]

Key facts

Even fossils in museum storage can regain their identities. A partial skeleton collected near Oriente in the mid-1920s was once cataloged as Glossotherium. Later research examined the head and forelimb material and identified it again as Mylodon.^[1]

Time and place

It is a ground sloth known from Pleistocene South America. A skeleton from near Oriente in present-day Buenos Aires Province, Argentina, and separate cave skin material have been studied. The Pleistocene spanned approximately 2.6 million to 12,000 years ago.^[1][2][3]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The Oriente material includes a skull, an astragalus (an ankle bone), vertebrae including the first neck vertebra, and elements of the left forearm and hand. Separate cave material preserves hair and small bones within the skin. Different forms of preservation reveal the skeleton and body covering separately.^[1][2]

A 2003 study estimated a body mass of approximately 1–2 tonnes from a well-preserved skull. This gives a sense of the scale of a ground sloth that supported a heavy body.^[5]

Habitat and reproduction

Researchers studying the forelimb interpreted it as possibly supporting the body on the outer side of the hand. They compared wrist and hand bones together to investigate how the large body was supported. Adding traces of the body covering allows the outside and inside of the ground sloth to be examined side by side.^[1][2]

Fossil discovery

The partial skeleton collected near Oriente in the mid-1920s entered the Field Museum collection. A 2016 study examined new postcranial material and forelimb function from this specimen. Research on cave skin adds stories of hair and skin obtained from separate discoveries.^[1][2]

References

1. McAfee (2016) — New postcranial bones and forelimb function of Mylodon
2. 2018 study — Mylodon skin preserved in a cave
3. International Commission on Stratigraphy (2024) — Geological time chart
4. Lopes et al. (2021) — Ice Age fossil mammals of the Chuí River
5. Christiansen·Fariña (2003) — Estimating body mass in two ground sloths

Research questions

How can we connect different kinds of fossils to understand the body of the same animal? We can examine diagnostic features of the head and forelimbs separately from the preservation of skin and hair. Reassessing the names of museum specimens is also part of understanding bodies and ways of life.^[1][2]

Observation

Move your gaze from the head and shoulders to the forelimbs, wrists, and hands. Then picture the body’s hair covering and small bones within the skin to connect the different kinds of information conveyed by fossils.^[1][2]