Palaeoecology and palaeophytogeography of the Rhynie chert plants: evidence from integrated analysis of in situ and dispersed spores

Abstract

The Rhynie cherts yield exceptionally preserved early land plants, and provide a unique insight into the nature of Lower Devonian vegetation. Hitherto they have been poorly age constrained, and the palaeoecology and palaeophytogeography of the flora are poorly understood. Well-preserved dispersed-spore assemblages have been recovered from a number of borehole cores through the stratigraphical sequence of the Rhynie outlier. They are all similar and belong with the polygonalis-emsiensis (PE) spore zone, indicating an Early Devonian age (Early (but not earliest) Pragian to earliest Emsian). Comparisons with PE sporezone assemblages from elsewhere suggest that the flora of the Rhynie drainage basin was slightly impoverished, with certain plant taxa that occurred at other locations not represented. This probably reflects differences between the flora of an inland intermontaine basin (Rhynie) and that of the lowland floodplains. In situ spores have been characterized for all seven Rhynie chert plants. Analysis of the distribution of these spore types in the Rhynie sequence, in addition to those of coeval deposits from elsewhere, enables interpretation of the palaeoecology and palaeophytogeography of the Rhynie chert plants. It is concluded that at least some of the plants were not highly specialized or adapted to the peculiar hot-springs environment in which they are preserved. Rather, they were components of a diverse and widespread flora, but were the only elements able to tolerate the inhospitable hot-springs environment (i.e. they were preadapted).

A high-precision U–Pb age constraint on the Rhynie Chert Konservat-Lagerstätte: time scale and other implications

“…)earliest Emsian (Wellman 2004(Wellman , 2006. Accordingly, the Pragian-Emsian boundary must post-date or closely approximate to 411.5  1.3 Ma, while the Lochkovian-Pragian boundary must pre-date 411.5  1.3 Ma.…”

“…Horizons occurring within the Tillybrachty Sandstone Formation (including a fine-grained sandstone from within the Longcroft Tuffs), the Windyfield Shales Member, and the Milton Flags and Shales Member have yielded spore assemblages which are similar, and indicate an early (but not earliest) Pragian to (? )earliest Emsian age (polygonalis-emsiensis Spore Assemblage Biozone of Richardson & McGregor 1986;Wellman 2004Wellman , 2006. This biostratigraphical age range is potentially further constrained by the presence of Dictyotriletes subgranifer (Wellman 2006).…”

Trigonotarbid arachnids from the Lower Devonian (Siegenian) of Bürdenbach (Lahrbach Valley, Westerwald area, Rhenish Slate Mountains, Germany)

“…The Givetian Gilboa deposits are believed to have accumulated in continental interior equatorial lowlands in the northern part of Laurussia (Shear et al 1987), whereas the Bürdenbach sediments were deposited in a land/sea transitional facies at the southern margin of the Old Red Sandstone Continent. In contrast, the Rhynie cherts were deposited in an intermontane basin located in the Caledonian highlands within the Old Red Sandstone Continent (Wellman 2004). Thus, palaeocharinids not only seem to have inhabited pretty much all of Laurussia, but also a considerable range of palaeoenvironments from warm coastal areas to presumably chillier habitats at higher altitudes.…”

A silicified bird from Quaternary hot spring deposits

“…Although fossils of microbes (Cady & Farmer 1996), plants (Powell et al 2000;Wellman 2004) and arthropods (Anderson & Trewin 2003) are common in ancient hot spring deposits, thus indicating that these environments are conducive to exceptional morphological preservation, there are few records of vertebrate remains from similar deposits. The dearth of vertebrate material preserved in hot spring deposits is related to a combination of factors.…”