Stable isotopes in early Eocene mammals as indicators of forest canopy structure and resource partitioning

Secord, Ross; Wing, Scott L.; Chew, Amy E.

doi:10.1666/0094-8373(2008)034[0282:siieem]2.0.co;2

Cited by 52 publications

(53 citation statements)

References 80 publications

(119 reference statements)

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“…In the latter case, only a few taxa were analyzed, probably compromising estimates of average compositions. Several other paleoenvironments were viewed as particularly wet, either from paleobotanical and paleofaunal observations or because of geographic location (20,21,25,26). For three of these studies, estimates of average MAP for these localities exceed 2;000 mm∕yr.…”

Section: Discussionmentioning

confidence: 99%

Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate

Kohn

2010

Proc. Natl. Acad. Sci. U.S.A.

1,161

799

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A broad compilation of modern carbon isotope compositions in all C3 plant types shows a monotonic increase in δ 13 C with decreasing mean annual precipitation (MAP) that differs from previous models. Corrections for temperature, altitude, or latitude are smaller than previously estimated. As corrected for altitude, latitude, and the δ 13 C of atmospheric CO 2 , these data permit refined interpretation of MAP, paleodiet, and paleoecology of ecosystems dominated by C3 plants, either prior to 7-8 million years ago (Ma), or more recently at mid-to high latitudes. Twenty-nine published paleontological studies suggest preservational or scientific bias toward dry ecosystems, although wet ecosystems are also represented. Unambiguous isotopic evidence for C4 plants is lacking prior to 7-8 Ma, and hominid ecosystems at 4.4 Ma show no isotopic evidence for dense forests. Consideration of global plant biomass indicates that average δ 13 C of C3 plants is commonly overestimated by approximately 2‰.aridity | carbon cycle | closed canopy | paleoprecipitation P lants exhibiting C3 photosynthesis have dominated the history of terrestrial vegetation, as CAM plants occupy only a small percentage of typical ecosystems (e.g., 1), and C4 plants became abundant in grasslands only within the last 7-8 million years (2). C3 plants exhibit a large range of carbon isotope compositions (−20 to −37‰, V-PDB; Fig. 1), generally reflecting a physiological response to aridity (anomalously high δ 13 C) and a combination of low light levels plus leaf litter recycling (anomalously low δ 13 C; 3). Past studies have conflicted on the dependence of δ 13 C on mean annual precipitation (MAP). Most studies support a negative correlation (e.g., 4), but some have reported no correlation (5) or even a positive correlation (6).This study explores carbon isotope systematics of C3 plants through a comprehensive compilation of literature data, minimizing local differences that have given rise to disparate interpretations. This work directly benefits paleodietary and paleoecological studies by providing estimates of MAP in ancient environments as well as clearer boundaries for identifying the understory of closed-canopy forests and the contribution of non-C3 plants to diet, which is used to gain insights into C4 origins (2). The new compilation also helps refine models of the modern carbon cycle by providing a better estimate of global C3 δ 13 C values (7). The present analysis differs from a recent investigation of correlations between tree þ shrub δ 13 C and MAP or plant functional type (8) in that it is several times larger on a site-by-site basis, spans the full range of plant growth forms (including trees, bushes, grasses, and herbs), averages data from each site to minimize sampling bias (4), and regresses an arguably more appropriate function to the data. Selection criteria of climate and isotopic data also differ slightly. This broader approach of considering all C3 plants and averaging compositions is important when evaluating herbivore paleodiets, whic...

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Section: Discussionmentioning

confidence: 99%

Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate

Kohn

2010

Proc. Natl. Acad. Sci. U.S.A.

1,161

799

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“…By contrast, clades that correspond to all other extant genera diverged in the Early to Mid-Eocene (ca 49-40 Myr ago), and these contain primarily arboreal species (figure 2). The latter could point to an adaptive radiation, owing to increased ecological opportunity [61], associated with expansion of forest environments in Africa and Madagascar connected to Greenhouse Earth conditions during the Early Eocene Climatic Optimum ca 51-53 Myr ago [62][63][64][65][66][67]. Post-Palaeocene Madagascar left a subtropical arid belt as it drifted northward towards the equator, which led to a significant increase in moisture levels on the island.…”

Section: Discussionmentioning

confidence: 99%

Large-scale phylogeny of chameleons suggests African origins and Eocene diversification

2013

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Oceanic dispersal has emerged as an important factor contributing to biogeographic patterns in numerous taxa. Chameleons are a clear example of this, as they are primarily found in Africa and Madagascar, but the age of the family is post-Gondwanan break-up. A Malagasy origin for the family has been suggested, yet this hypothesis has not been tested using modern biogeographic methods with a dated phylogeny. To examine competing hypotheses of African and Malagasy origins, we generated a dated phylogeny using between six and 13 genetic markers, for up to 174 taxa representing greater than 90 per cent of all named species. Using three different ancestralstate reconstruction methods (Bayesian and likelihood approaches), we show that the family most probably originated in Africa, with two separate oceanic dispersals to Madagascar during the Palaeocene and the Oligocene, when prevailing oceanic currents would have favoured eastward dispersal. Diversification of genus-level clades took place in the Eocene, and species-level diversification occurred primarily in the Oligocene. Plio-Pleistocene speciation is rare, resulting in a phylogeny dominated by palaeo-endemic species. We suggest that contraction and fragmentation of the Pan-African forest coupled to an increase in open habitats (savannah, grassland, heathland), since the Oligocene played a key role in diversification of this group through vicariance.

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“…δ 13 C E in mammalian herbivores reflects the δ 13 C value of the vegetation they consume, with predictable enrichment (19). Plants in turn track the δ 13 C value of atmospheric CO 2 , with influences from environmental factors such as humidity and vegetation density (20,21). At Cabin Fork, phenacodontids (Ectocion and Copecion) record a negative shift of ~4.6 per mil (‰) in δ 13 C E at the onset of the CIE (Figure 2A).…”

mentioning

confidence: 99%

“…Coryphodon was a large water-dependent or semi-aquatic mammal (21,23). Studies of ecologically similar living mammals have shown that their δ 18 O E faithfully records the δ 18 O of surface water (24,25), which in turn is strongly correlated with air temperature at mid-to high latitudes (26).…”

mentioning

confidence: 99%

Evolution of the Earliest Horses Driven by Climate Change in the Paleocene-Eocene Thermal Maximum

Secord

Bloch

Chester

et al. 2012

Science

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205

141

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Warming and Shrinking In most mammals, individual body sizes tend to be smaller in warmer regions and larger in cooler regions. Secord et al. (p. 959 ; see the Perspective by Smith ) examined a high-resolution 175,000-year record of equid fossils deposited over a past climate shift—the Paleocene-Eocene Thermal Maximum—for changes in body size. Using oxygen isotopes collected from the teeth of co-occurring mammal species to track prevailing environmental temperature, a clear decrease in equid body size was seen during 130,000 years of warming, followed by a distinct increase as the climate cooled at the end of the period. These results indicate that temperature directly influenced body size in the past and may continue to have an influence as our current climate changes.

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Stable isotopes in early Eocene mammals as indicators of forest canopy structure and resource partitioning

Cited by 52 publications

References 80 publications

Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate

Carbon isotope compositions of terrestrial C3 plants as indicators of (paleo)ecology and (paleo)climate

Large-scale phylogeny of chameleons suggests African origins and Eocene diversification

Evolution of the Earliest Horses Driven by Climate Change in the Paleocene-Eocene Thermal Maximum

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