We reconstruct ancient temperature and elevation gradients across the early Eocene (52-49 Ma) northern Sierra Nevada (California, United States) using organic molecular proxies that record atmospheric and ground-level effects of topography. Paleoelevation was determined by reconstructing the change in the hydrogen isotopic composition of precipitation (Δδ ΔδD precip) and mean annual temperature (ΔT GDGT) (glycerol dialkyl glycerol tetraethers) from the isotopic composition of fossil angiosperm leaf n-alkanes and the distribution of microbially produced soil tetraethers preserved in leaf-bearing sediments. Organic molecular data produce equivalent range-scale (δD n-alkane) and channel (T GDGT) paleoelevation estimates that show the northern Sierra Nevada was a warm (>6-8 °C warmer than modern), high-elevation (>2 km), and moderate-to low-relief landscape at the Eocene Climatic Optimum. Modern northern Sierra Nevada topography likely refl ects post-Paleocene reduction of mean surface elevation and late Cenozoic increases in relief.
High diversity and endemism in the California Floristic Province (CFP) are an alleged response to the late Cenozoic advent of Mediterranean-type climate in this region. Ceanothus comprises two divergent subgenera with centers of diversity in the CFP. We reconstruct the evolution of Ceanothus by using DNA sequence data from the nuclear gene nitrate reductase. We find that the timing of diversification events is related to geological and climatic history. In both subgenera, diversification is characterized by recent divergence of extant taxa and geographically structured phylogenetic relationships. A strong north-south divergence of subgenus Cerastes across the Transverse Ranges indicates that phylogenetic relationships may be structured by climatically divergent regions of the CFP. Divergence-time estimation suggests that the age of extant diversification in both subgenera is ;6 Ma. This agrees with the fossil record but predates the hypothesized Quaternary (2-Ma) origin of Mediterranean-type climate in the region.
A rhizomorph of Paurodendron with an intact apex recently has been discovered in Upper Pennsylvanian sediments of Ohio, and this provides the anatomical evidence necessary to interpret structure, ontogeny and homologies among lycophyte rooting organs. The basal meristem of Paurodendron is radial and lenticular, and produces an apical plug of parenchymatous tissue similar to a root cap. The plug is surrounded by a furrow associated with radially aligned cells that demonstrate a developmental correspondence to the furrow(s) of Isoetes. Based on external structural similarities at the rhizomorph apices of Paurodendron, Stigmaria, and young Nathorstiana, and on the anatomical similarities of Paurodendron to Isoetes, Stigmaria, Chaloneria, and Lepidocarpon embryos, all are interpreted as having a rooting organ that represents a modified shoot system that is fundamentally unlike the primary root system of seed plants. Likewise, the rootlets of rhizomorphic lycophytes are interpreted as leaves modified for rooting, and that have the equivalent of exogenous origin. As such, they are fundamentally unlike the adventitious roots of rhizomatous lycophytes like Lycopodium and Selaginella.
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