From Newsgroup: sci.anthropology.paleo


https://www.frontiersin.org/news/2025/07/29/how-much-time-did-our-ancestors-spend-up-trees-studying-these-chimpanzees

A new study on savannah-living chimpanzees
could help answer some of paleoanthropologyrCOs
oldest questions about the origins of walking
on two legs. Some theories suggest that the
spread of savannahs pushed hominins to walk
upright on the ground, a more efficient way to
move in this environment. But many early
hominins are still well-adapted for climbing.
The study found that chimpanzees living in a
savannah-mosaic environment continued foraging
in trees, and spent most time in trees foraging
for the most abundant or nutritious foods. These
results suggest that those arboreal adaptations
remained critical for early homininsrCO survival
after bipedalism appeared. They might even have
contributed to the development of walking on two
feet.
...
rCLOur previous research found that, compared to
chimpanzees living in forests, Issa Valley
chimpanzees spent just as much time moving in the
trees,rCY said Drummond-Clarke. rCLWe wanted to test
if something about how they foraged could explain
their unexpectedly high arboreality.
Savannah-mosaics are characterized by more
sparsely distributed trees, so we hypothesized
that adapting behavior to forage efficiently in
a tree would be especially beneficial when the
next tree is further away.rCY

Researchers monitored the adults of the Issa
community during the dry season, watching how
they foraged in trees and what they ate there.
The size, height, and shape of the trees were
recorded, as well as the number and size of
branches.

Issa chimpanzees mostly ate fruit, followed by
leaves and flowers rCo foods found at the ends of
branches, so the chimpanzees needed to be capable
climbers to reach them safely.
...
Because they are relatively large, chimpanzees
move within trees not by climbing on thin branches
but by hanging under them, or standing upright and
holding on to nearby branches with their hands.
Although these rCysaferCO behaviors are traditionally
associated with foraging in dense forest, these
findings show theyrCOre also important for chimpanzees
foraging in a savannah-mosaic.

rCLWe suggest our bipedal gait continued to evolve in
the trees even after the shift to an open habitat,rCY
said Drummond-Clarke. rCLObservational studies of
great apes demonstrate they can walk on the ground
for a few steps, but most often use bipedalism in
the trees. ItrCOs logical that our early hominin
relatives also engaged in this kind of bipedalism,
where they can hold onto branches for extra balance.
If Issa Valley chimpanzees can be considered suitable
models, suspensory and bipedal behaviors were likely
vital for a large-bodied, fruit-eating,
semi-terrestrial hominin to survive in an open
habitat.rCY
...


https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2025.1561078/full

Foraging strategy and tree structure as drivers
of arboreality and suspensory behaviour in
savannah-dwelling chimpanzees

Introduction: The association between an open
habitat (e.g., savannah-mosaics) and increased
terrestriality is central to hypotheses of
hominin evolution, especially the emergence and
evolution of bipedalism, as well as ape
evolution as far back as the early Miocene.
However, the selective pressures that act on
apes in an open habitat remain poorly understood.
Observations of chimpanzees that live in
savannah-mosaics, analogous to some reconstructed
hominoid palaeohabitats, can provide valuable
insight into the behavioural adaptations of a
large-bodied, semi-arboreal ape to an open
habitat, characterised by sparsely distributed
food sources and a broken canopy. We previously
showed that savannah-dwelling chimpanzees in the
Issa Valley, western Tanzania, maintain a high
level of arboreality, and particularly suspensory
behaviour, largely associated with foraging. Here,
we investigate how chimpanzee foraging strategy in
a savannah-mosaic may drive a high frequency of
arboreal behaviours despite reduced arboreal
pathways. Specifically, we hypothesized that Issa
chimpanzees would spend more time foraging (and
moving) per tree to maximize utilization of food
in a sparse landscape. This foraging strategy
would be facilitated by foraging in trees with
large crowns and abundant terminal-branch foods,
which are characteristic of miombo woodlands.
However, the link between foraging positional
behaviour and tree structure remains
understudied.


--- Synchronet 3.21a-Linux NewsLink 1.2