Quasi-static Eocene?Oligocene climate in Patagonia promotes slow faunal evolution and mid-Cenozoic global cooling

KHON, M; STRÖMBERG, C.; MADDEN, R.H.; DUNN, R.; EVANS, S.; PALACIOS, A.; CARLINI, A.A.

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 2015 p. 24 - 37

0031-0182

New local/regional climatic data were compared with floral and faunal records from central Patagonia to investigatehow faunas evolve in the context of local and global climates. Oxygen isotope compositions of mammalfossils between c. 43 and 21 Ma suggest a nearly constant mean annual temperature of 16 ± 3 °C, consistentwith leaf physiognomic and sea surface studies that imply temperatures of 16?18 °C. Carbon isotopes in toothenamel track atmospheric δ13C, but with a positive deviation at 27.2 Ma, and a strong negative deviation at21 Ma. Combined with paleosol characteristics and reconstructed Leaf Area Indices (rLAIs), these trends suggestaridification from 45 Ma (c. 1200 mm/yr) to 43 Ma (c. 450 mm/yr), quasi-constant MAP until at least 31 Ma,and an increase to ~800 mm/yr by 21 Ma. Comparable MAP through most of the sequence is consistentwith relatively constant floral compositions, rLAI, and leaf physiognomy. Abundance of palms reflects relativelydry-adapted lineages and greater drought tolerance under higher pCO2. Pedogenic carbonate isotopes implylow pCO2 = 430 ± 300 ppmv at the initiation of the Eocene?Oligocene climatic transition. Arid conditions inPatagonia during the late Eocene through Oligocene provided dust to the Southern Ocean, enhancing productivityof silicifiers, drawdown of atmospheric CO2, and protracted global cooling. As the Antarctic Circumpolar Currentformed and Earth cooled, wind speeds increased across Patagonia, providing more dust in a positive climatefeedback. High tooth crowns (hypsodonty) and ever-growing teeth (hypselodonty) in notoungulates evolvedslowly and progressively over 20 Ma after initiation of relatively dry environments through natural selection inresponse to dust ingestion. A Ratchet evolutionary model may explain protracted evolution of hypsodonty, inwhich small variations in climate or dust delivery in an otherwise static environment drive small morphologicalshifts that accumulate slowly over geologic time.