A new fossil cercopithecid tibia from Laetoli and its implications for positional behavior and paleoecology

Area of Science:

• Paleontology and paleoanthropology
• Primate evolutionary biology
• Fossil hominin site paleoecology

Background:

• Plio-Pleistocene cercopithecid fossils offer insights into Old World monkey evolution and locomotor diversity.
• Understanding fossil primate behavior aids in reconstructing Plio-Pleistocene hominin site paleoenvironments.

Purpose of the Study:

• To describe a new fossil cercopithecid tibia (EP 1100/12) from the Upper Laetolil Beds (Laetoli, Tanzania).
• To determine the taxonomic affinity and positional behavior of the fossil tibia.
• To infer paleoenvironmental conditions and their implications for Australopithecus afarensis.

Main Methods:

• Qualitative and quantitative analysis of the fossil tibia (EP 1100/12).
• Three-dimensional landmark comparisons with 190 extant cercopithecid species.
• Discriminant function analyses to assess taxonomic affinity and positional behavior.

Main Results:

• The fossil tibia (EP 1100/12) is attributed to cf. Rhinocolobus sp., a common colobine at Laetoli.
• Shape analyses clustered EP 1100/12 with extant colobines, particularly large-bodied genera like Nasalis and Rhinopithecus.
• The tibia indicates arboreal pronograde quadrupedalism in a large-bodied monkey.

Conclusions:

• The presence of cf. Rhinocolobus sp. supports inferences of woodland and forest environments at Laetoli.
• These diverse habitats provided Australopithecus afarensis access to resources and refuge.
• The findings highlight the ecological context of early hominin evolution.