Nature | Vol 586 | 15 October 2020 | 403the deep-time record of geobiology into a modern context have been
almost entirely missing.
To address this deficit, we report δ^13 C and δ^18 O data for 269 modern
and historical specimens, representing 63 species of mammal found in
Southeast Asia. We compare these to 644 previously published δ^13 C and
δ^18 O values from fossil taxa that span from the Early Pleistocene to the
present. For consistency and comparability, in all cases the δ^13 C values
obtained from the specimens have been corrected to an estimate of the
δ^13 C value of the diet of the mammal (δ^13 Cdiet). To our knowledge, our
combined dataset represents the largest compilation of δ^13 C and δ^18 O
data from mammals in Asia, and allows us to examine broad trends in
the distribution of C 3 and C 4 plants associated with faunal communities
and hominins over time.
Our results show that during the Early Pleistocene, consumers of
both C 3 and C 4 resources were present in Southeast Asia (Fig. 2 ). How-
ever, these mammals were unevenly distributed across the region
(Extended Data Table 2); consumers of C 3 resources were predominately
found in Indochina (δ^13 Cdiet quartile 1 to quartile 3 range (Q1–Q3) of
–29.3‰ to –26.4‰), and consumers of C 4 resources were located largely
in Sundaland (δ^13 Cdiet Q1–Q3 of −20.0‰ to −13.3‰). The distribution
of herbivores and omnivores was not significantly different across
ecosystems dominated by C 3 or C 4 plants (Extended Data Fig. 1) during
this period (χ^2 (2, n = 120) = 1.95, P = 0.377). By the Middle Pleistocene,
Sundaland records very few consumers of C 3 resources (Extended Data
Figs. 1, 2); most species fall into the range associated with feeding on
C 4 resources or—to a lesser extent—mixed feeding on C 3 and C 4 resources
(Q1–Q3 of −15.8‰ to −13.3‰). The beginning of the Middle Pleistocene
sees a peak in δ^13 Cdiet (Extended Data Fig. 2), which—in Indochina—
corresponds to a shift of herbivores consuming C 3 plants towards
higher δ^13 C values (χ^2 (2, n = 308) = 40.754, P < 0.001). This appears not
to have affected omnivores, the distributions of which across both
regions remain similar to their Early Pleistocene distributions
(χ^2 (2, n = 39) = 0.23, P = 0.893). Carnivores favour grazers of C 4 plants
during this time (x = −14.6‰, n = 7). By the Late Pleistocene, most Sun-
danese and Indochinese herbivores and omnivores were consuming
predominately C 3 resources (xherbivore = −25.3‰, n = 149 and
xomnivore = −22.3‰, n = 38). This stands in marked contrast to the carni-
vores, most of which were found at the C 4 end of the dietary spectrum
(xcarnivore = −16.2‰, n = 14). By the Holocene, Southeast Asian mammals
were consuming diets dominated by C 3 resources across the entire
trophic spectrum (xherbivore = −25.5‰, n = 270; xomnivore = −23.5‰, n = 38;
and xcarnivore = −24.0‰, n = 15).
Beyond prominent distinctions between C 3 and C 4 resources, we also
find considerable variation in δ^13 C and δ^18 O values within ecosystems
dominated by C 3 plants. The lowest δ^13 Cdiet values (below −29.0‰) cor-
respond to closed-canopy and subcanopy habitats^21 ,^22. Conversely,WallacelineBoh DambangNam LotSanhe CaveTham Wiman NakinPha BongBaxianQinlingMountainsIsthmus
of KraKangar–Pattani
lineIndochinese subregionSundaic subregionJavaSumatraBorneoSulawesiJuyuandongLonggudongQuzaiMohuiPadang Caves
SibrambangCirebon
BumiayuCipendeuy SemedoSu BangKarang BolongYai RuakKhok SungUpper PubuLast Glacial Maximum
land extent (above –116 m)SavannahSite (approximate location)Site100º E 120º E0º20º NPunungSangiranKedung
BrubusHoekgrotWajakSambungmacan
TrinilNgandong Sunggu, BloraJava500 kmFig. 1 | Map of the Indochinese and Sundaic subregions. Locality map showing the biogeographical subregions examined, land extent during the Last Glacial
Maximum and the proposed extent of the ‘savannah’ corridor (after ref. ^7 ). Map from CartoGIS CAP Australian National University 20-217_KP.