Hapalops elongatus

Overview

Hapalops elongatus was a ground sloth from Miocene South America. Its skull and lower jaw provide evidence for studying how it chewed food. The elongated heads of Hapalops also preserve attachment sites for chewing muscles.^[1]

Key facts

Even muscles that have vanished leave clues on bones. Researchers examined muscle attachment marks on Hapalops skulls to reconstruct its chewing apparatus. Comparing them with the muscles of living sloths helped trace how its jaws moved.^[1]

Time and place

This was a Miocene sloth from South America. Research on the head and feeding of Hapalops draws on the Santa Cruz Formation in present-day Argentina. The Miocene spanned approximately 23–5.3 million years ago.^[1][2]

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

Size, form and skeleton

Material assigned to this species includes Field Museum skulls P13138 and P13145, and the skull and lower jaw P13133. The Hapalops specimens compared in the study have elongated heads and cheekbone processes extending upward and downward. The jaw and cheekbones are important for understanding the arrangement of chewing muscles.^[1]

Hapalops elongatus was much heavier than living tree sloths that hang from branches. A 2014 study calculated the masses of three skeletal specimens individually, obtaining estimates of approximately 28–45 kg. For two specimens, results from several equations were combined while accounting for prediction error; a single equation was applied to the third.^[3]

Habitat and reproduction

A researcher in 2014 linked the head structure of Hapalops to selective feeding. Chewing was interpreted as involving sideways movements of the lower jaw to grind food. This research connects bone shape with the act of eating.^[1]

Fossil discovery

Several skulls and lower jaws at the Field Museum were used in comparative research. Researchers examined structures across the specimens to reconstruct the organization of the head. Several fossils housed in one museum thus helped reveal the chewing apparatus of an ancient sloth.^[1]

References

1. 2014 study — The skull and chewing muscles of Hapalops
2. International Commission on Stratigraphy (2024) — Geological time chart
3. Toledo et al. (2014) — Body-mass estimates for Santa Cruz sloths
4. 2023 study — Lestodon fossils in the Roth collection
5. Reassessment of names and species counts in Lestodon

Research questions

Might different head shapes mean different ways of chewing in sloths? A researcher compared the elongated head of Hapalops with shorter-headed living sloths, including three-toed sloths. Considering head length, cheekbones, and muscle arrangement together helps explore the variety of feeding methods among sloths.^[1]

Observation

Move your gaze from the elongated head to the cheekbone processes and lower jaw. Imagining the muscles that would have attached between them and the sideways movements of the jaw connects small marks on the skull with chewing movements.^[1]