TY  - JOUR
A1  - Kehlmaier, Christian
A1  - Barlow, Axel
A1  - Hastings, Alexander K.
A1  - Vamberger, Melita
A1  - Paijmans, Johanna L. A.
A1  - Steadman, David W.
A1  - Albury, Nancy A.
A1  - Franz, Richard
A1  - Hofreiter, Michael
A1  - Fritz, Uwe
T1  - Tropical ancient DNA reveals relationships of the extinct bahamian giant tortoise Chelonoidis alburyorum
JF  - Proceedings of the Royal Society of London : Series B, Biological sciences
N2  - Ancient DNA of extinct species from the Pleistocene and Holocene has provided valuable evolutionary insights. However, these are largely restricted to mammals and high latitudes because DNA preservation in warm climates is typically poor. In the tropics and subtropics, non-avian reptiles constitute a significant part of the fauna and little is known about the genetics of the many extinct reptiles from tropical islands. We have reconstructed the near-complete mitochondrial genome of an extinct giant tortoise from the Bahamas (Chelonoidis alburyorum) using an approximately 1000-year-old humerus from a water-filled sinkhole (blue hole) on Great Abaco Island. Phylogenetic and molecular clock analyses place this extinct species as closely related to Galapagos (C. niger complex) and Chaco tortoises (C. chilensis), and provide evidence for repeated overseas dispersal in this tortoise group. The ancestors of extant Chelonoidis species arrived in South America from Africa only after the opening of the Atlantic Ocean and dispersed from there to the Caribbean and the Galapagos Islands. Our results also suggest that the anoxic, thermally buffered environment of blue holes may enhance DNA preservation, and thus are opening a window for better understanding evolution and population history of extinct tropical species, which would likely still exist without human impact.
KW  - Bahamas
KW  - biogeography
KW  - extinction
KW  - palaeontology
KW  - phylogeny
Y1  - 2017
U6  - https://doi.org/10.1098/rspb.2016.2235
SN  - 0962-8452
SN  - 1471-2954
VL  - 284
PB  - The Royal Society
CY  - London
ER  - 
TY  - JOUR
A1  - Schultze, Dina
A1  - Wirth, Richard
A1  - Wunder, Bernd
A1  - Loges, Anselm
A1  - Wilke, Max
A1  - Franz, Gerhard
T1  - Corundum-quartz metastability
BT  - the influence of a nanometer-sized phase on mineral equilibria in the system Al2O3-SiO2-H2O
JF  - Contributions to mineralogy and petrology
N2  - The metastable paragenesis of corundum and quartz is rare in nature but common in laboratory experiments where according to thermodynamic predictions aluminum-silicate polymorphs should form. We demonstrate here that the existence of a hydrous, silicon-bearing, nanometer-thick layer (called "HSNL") on the corundum surface can explain this metastability in experimental studies without invoking unspecific kinetic inhibition. We investigated experimentally formed corundum reaction products synthesized during hydrothermal and piston-cylinder experiments at 500-800 degrees C and 0.25-1.8 GPa and found that this HSNL formed inside and on the corundum crystals, thereby controlling the growth behavior of its host. The HSNL represents a substitution of Al with Si and H along the basal plane of corundum. Along the interface of corundum and quartz, the HSNL effectively isolates the bulk phases corundum and quartz from each other, thus apparently preventing their reaction to the stable aluminum silicate. High temperatures and prolonged experimental duration lead to recrystallization of corundum including the HSNL and to the formation of quartz + fluid inclusions inside the host crystal. This process reduces the phase boundary area between the bulk phases, thereby providing further opportunity to expand their coexistence. In addition to its small size, its transient nature makes it difficult to detect the HSNL in experiments and even more so in natural samples. Our findings emphasize the potential impact of nanometer-sized phases on geochemical reaction pathways and kinetics under metamorphic conditions in one of the most important chemical systems of the Earth's crust.
KW  - Experimental
KW  - Metastability
KW  - Corundum
KW  - Quartz
KW  - Nanolayers
KW  - Aluminium– silicates
Y1  - 2021
U6  - https://doi.org/10.1007/s00410-021-01786-5
SN  - 0010-7999
SN  - 1432-0967
VL  - 176
IS  - 4
PB  - Springer
CY  - Berlin ; Heidelberg
ER  -