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.2009 Jul 14;106(28):11646-50.
doi: 10.1073/pnas.0900956106. Epub 2009 Jun 25.

Extinction implications of a chenopod browse diet for a giant Pleistocene kangaroo

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Extinction implications of a chenopod browse diet for a giant Pleistocene kangaroo

Gavin J Prideaux et al. Proc Natl Acad Sci U S A..

Abstract

Kangaroos are the world's most diverse group of herbivorous marsupials. Following late-Miocene intensification of aridity and seasonality, they radiated across Australia, becoming the continent's ecological equivalents of the artiodactyl ungulates elsewhere. Their diversity peaked during the Pleistocene, but by approximately 45,000 years ago, 90% of larger kangaroos were extinct, along with a range of other giant species. Resolving whether climate change or human arrival was the principal extinction cause remains highly contentious. Here we combine craniodental morphology, stable-isotopic, and dental microwear data to reveal that the largest-ever kangaroo, Procoptodon goliah, was a chenopod browse specialist, which may have had a preference for Atriplex (saltbushes), one of a few dicots using the C(4) photosynthetic pathway. Furthermore, oxygen isotope signatures of P. goliah tooth enamel show that it drank more in low-rainfall areas than its grazing contemporaries, similar to modern saltbush feeders. Saltbushes and chenopod shrublands in general are poorly flammable, so landscape burning by humans is unlikely to have caused a reduction in fodder driving the species to extinction. Aridity is discounted as a primary cause because P. goliah evolved in response to increased aridity and disappeared during an interval wetter than many it survived earlier. Hunting by humans, who were also bound to water, may have been a more decisive factor in the extinction of this giant marsupial.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Skull ofP. goliah. (A) lateral view, (B) palatal view, (C) dentary in occlusal view.
Fig. 2.
Fig. 2.
Map of southeastern Australia showing localities yieldingP. goliah and major climatic zones (37). Arid, warm temperate to subtropical, seasonally variable rainfall, 100–300 mm/yr; Subtropical, mainly summer rainfall, 400–1,200 mm/yr; Temperate, mainly winter rainfall, 300–1,200 mm/yr.
Fig. 3.
Fig. 3.
Photosimulation of typical microwear surfaces of 3 kangaroo species. (A) extant C4 grazer (M. giganteus, FU2003.8.27–13). (B) extant C3 browser (W. bicolor, AM M36793). (C) extinct giant kangaroo (P. goliah, AM F105983). (Scale bar = 20 μm.) The grazer is characterized by a more anisotropic surface (more parallel striations), while the browsers have a more complex array of surface features (including those traditionally termed “pits”). (seeSI Text).
Fig. 4.
Fig. 4.
Carbon-isotope data (δ13C) for Pleistocene kangaroos from southeastern Australia. (A–C) Frequency histograms of enamel δ13C values ofP. goliah, grazing kangaroos (Macropus species), browsing/mixed-feeding kangaroos and modern chenopods (e.g.,Atriplex, Maireana) from Arid, Subtropical and Temperate climate zones. Chenopod vegetation samples are expressed as equivalent enamel δ13C values (ε = 13.3%; seeSI Text) and have been corrected by +1.5‰ for the effects of fossil fuel burning over the past century. (D) Enamel δ13C vs. δ18O for Menindee fossil grazing kangaroos. Enamel δ13C and δ18O averages for grazing kangaroo teeth (–6.2 ± 2.1‰,n = 10; δ18O: 4.2 ± 0.9‰,n = 10) differ significantly (P < 0.002) from those ofP. goliah (δ13C: –2.7 ± 2.2‰,n = 10; δ18O: 0.2 ± 1.8‰,n = 10).
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References

    1. Prideaux GJ. Systematics and evolution of the sthenurine kangaroos. Univ Calif Publ Geol Sci. 2004;146:1–623.
    1. Roberts RG, et al. New ages for the last Australian megafauna: Continent-wide extinction about 46,000 years ago. Science. 2001;292:1888–1892. - PubMed
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    1. Prideaux GJ, et al. Mammalian responses to Pleistocene climate change in southeastern Australia. Geology. 2007;35:33–36.

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