Pucadelphys andinus

Overview

Pucadelphys andinus was a small metatherian from Paleocene South America. It belongs to an ancient group close to living marsupials. Fossils left by several individuals together tell an especially remarkable story beyond that of a single small body.^[3]

Key facts

Fossils of 35 individuals were collected from a small area in Bolivia. Juveniles and adults lay close together, leading researchers to propose that they lived together or tolerated one another. This is an intriguing example of reading relationships between small animals from fossils.^[3]

Time and place

This animal lived in South America during the early Paleocene, around 64 million years ago. Its fossils came from Tiupampa in present-day Bolivia. This locality preserves small mammals from not long after the dinosaur mass extinction.^[3]

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

Size, form and skeleton

It brings to mind a small, mouse-sized body and a long tail. Many parts of the skull, jaws, trunk, and limbs survive across several specimens. The 22 individuals covered by a 2011 study included nearly complete skulls with postcranial bones.^[3]

The adult specimen MHNC 8266 of Pucadelphys andinus was estimated to weigh approximately 49 g. This value was obtained by comparison with juvenile gray short-tailed opossums of similar skull length, offering one clue to its small body size.^[6]

Habitat and reproduction

Differences in age and the clustered arrangement of the fossils provide clues to their way of life. Researchers proposed social interaction because juveniles and adults were buried very close together. This suggests that early metatherians may not have lived exclusively solitary lives.^[3]

Fossil discovery

An initial skeletal study in 1988 was followed by research using CT to look inside the head. In 2011, the discovery of many individuals was published, raising questions about behavior as well as body form. The number and arrangement of fossils can be as important as the shape of a single bone.^[1][2][3]

References

1. Marshall & de Muizon (1988), The Dawn of the Age of Mammals in South America, National Geographic Research 4:23–55.
2. Macrini, de Muizon, Cifelli & Rowe (2007), DigiMorph Pucadelphys andinus specimen page.
3. Ladevèze et al.2011 — Earliest evidence of mammalian social behaviour in the basal Tertiary of Bolivia
4. Ladevèze et al.2011 — Earliest evidence of mammalian social behaviour in the basal Tertiary of Bolivia
5. Gelfo, López & Bond (2024) · New insights on the anatomy, paleobiology, and biostratigraphy of Xenungulata (Mammalia) from the Paleogene of South America · Palaeontologia Electronica 27(2):a30 · DOI 10.26879/1360
6. Macrini et al. (2007) — Inside the skull of Pucadelphys

Research questions

Did animals buried together also live together? Researchers must consider whether there was a single burial event, the age composition of the group, and how close the individuals lay to one another. Pucadelphys illustrates ways of studying behavior through fossils.^[3]

Observation

Examine how the small head, limbs, and tail connect.^[3]