Sciency Thoughts: Fossil Wood

Showing posts with label Fossil Wood. Show all posts

Sunday, 26 May 2019

Ancient forest on Welsh coast exposed by storm.

A forest of petrified trees on the coast of Ceredigion County, Wales, has been exposed by a storm this week. The forest, which comprises the stumps of hundreds of Pine, Pinus, Alder, Alnus, Oak, Quercus, and Birch, Betula, stumps stretches from Ynyslas to Borth, and is thought to be between 4500 and 6000 years old. While the forest is usually covered by sediment, it is periodically exposed following storms, having last been seen in 2014, and is even found in local folklore, as Cantre'r Gwaelod, a mythical kingdom on the west coast of Wales that sunk into the sea, sometimes known as the 'Welsh Atlantis'.

Exposed tree stumps on the Ceredigion Coast in May 2019. Matthew Horwood/Getty Images.

Most of the trees show a distinctive growth pattern of growth, with most of the roots spreading along the surface, with only a few roots extending downwards as anchors. The exception to this rule is the Alder stumps, which have consistently deeper root systems. This style of growth is typical of trees growing in wetland environments with a high water table, where most trees struggle to get oxygen to deep roots submerged in water, something which Alder trees are adapted for such environments. Alder trees typically lower the water table where they live, and often form the first stage of the colonisation of wetland environments by terrestrial woodlands, but in this case the reverse seems to have happened, with the waters rising and eventually drowning the trees.

Exposed tree stumps on the Ceredigion Coast in May 2019. Matthew Horwood/Getty Images.

A study of the Ceredigion Submerged Forest published in the journal New Phytologist in 1938 by Harry Godwin and Lily Newton, based largely on pollen and Foraminifera extracted from boreholes by Florence Campbell James, suggested that an ancient Reed-bed trapped a raised bogland behind it, which was then colonised by first the peat-forming Moss Sphagnum sp., then an Alder woodland, which was in turn overwhelmed by marine waters.

The Ceredigion Submerged Forest exposed in May 1923. Challinor in Godwin & Newton (1938).

Monday, 1 October 2018

Paraphyllanthoxylon cf. alabamense: A large Angiosperm Tree from the early Late Cretaceous of Utah.

Angiosperms (Flowering Plants) underwent a major diversification in the Middle Cretaceous and became ubiquitous members of terrestrial floras from then onwards. However, exactly when large Angiosperm trees first appeared is unclear. The last common ancestor of all living Angiosperms is thought to have been woody, but it is unclear how large it was, and the earliest fossil Angiosperms are all herbaceous. Fossil Angiosperm wood is known in the fossil record from about 113 million years ago onwards, but these fragments are rare and small before about 83.8 million years ago, which has led to speculation that Angiosperm trees were overshadowed by larger Gymnosperms (Conifers etc.) throughout much of the Cretaceous.

In a paper published in the journal Science Advances on 26 September 2018, Nathan Jud of the Department of Biology at William Jewell College, Michael D’Emic of the Department of Biology at Adelphi University, the Burpee Museum of Natural History, and the Department of Anatomical Sciences at Stony Brook University, Scott Williams, also of the Burpee Museum of Natural History, and of the Museum of the Rockies and Department of Earth Sciences at Montana State University, Josh Mathews, again of the Burpee Museum of Natural History, and of the Department of Biological Sciences at Northern Illinois University, Katie Tremaine, once again of the Burpee Museum of Natural History, and of the Museum of the Rockies and Department of Earth Sciences at Montana State University, and Janok Bhattacharya of the School of Geography and Earth Sciences at McMaster University, describe a large Angiosperm Tree trunk from the early Late Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah.

The new angiosperm log in the field. Michael D’Emic in Jud et al. (2018).

The fossil described takes the form of a silicified log with a preserved length of 11 m and a maximum preserves width of 1.6 m. As this is clearly only the inner part of the log, and the specimen shows no sign of significant taphonomic distortion (swelling of the wood), it is estimated to have had a minimum living diameter of 1.8 m. A tree with a diameter of 1.8 m at breast height would be expected to have a height of somewhat over 50 m, suggesting that this was a canopy tree of significant size. Examination of the wood leads Jud et al. to assign the specimen to the genus Paraphyllanthoxylon, and probably to the species alabamense (they cannot find all of the features diagnostic of this species, but neither can they find any features that rule it out). The Mancos Shale Formation is calculated to be about 92 million years old, suggesting that large Angiosperm Trees had evolved at least 15 million years earlier than previously suggested by the fossil record.

Paraphyllanthoxylon cf. alabamense. (A) Photograph of the log in the field. (B) Transverse section (XS) showing diffuse porous wood with vessels in short radial multiples of 2 to 11, growth rings absent, axial parenchyma rare, radial bands of fibers, and rays roughly the same width. (C) Tangential longitudinal section (TLS) showing crowded, hexagonal pits on the vessel wall. (D) TLS showing closely spaced lens-shaped 2- to 4-seriate rays among elongate fibres. (E) Radial longitudinal section showing rows of procumbent and upright ray parenchyma cells. (F) XS showing thin-walled ray cells (at left) and medium thick-walled fibres (at right). Scale bars: 500 μm (B); 100 μm (C); 250 μm (D); 200 μm (E); and 50 μm (F). Michael D’Emic and Nathan Jud in Jud et al. (2018).

Jud et al. also describe several other Plant fossils from the Mancos Shale Formation, though not from the same location, including a number of leaf shoots assigned to the Angiosperm species Elatides curvifolia, and some fragments of Ferns.

Plant compression fossils from the Ferron Sandstone of Utah. (A) Leafy shoot of Elatides curvifolia. (B) Indeterminate angiosperm leaf. (C) Close-up of (A). (D) Isolated Fern pinnule. Scale bars, 5 mm (A) to (C) and 3 mm (D). Nathan Jud in Jud et al. (2018).

Also reported are a number of Vertebrate fossils, also from the Ferron Sandstone of Utah. These include a single Shark tooth, assigned to the Lamniform species Cretodus crassidens, a common species in the Western Interior Seaway during this time, several Crocodyliform teeth, a large Turtle scute, roughly 9 cm in length and 1 cm thick, and part of the sacrum of an Ornithopod Dinosaur.

Vertebrate fossils from the Ferron Sandstone of Utah. (A) Tooth of Cretodus crassidens. (B) Crocodyliform teeth. (C) Dorsal Turtle scute. (D) Ornithopod sacrum. Scott Williams in Jud et al. (2018).

Wednesday, 31 August 2016

Podocarpoxylon donghuaiense: Podocarp Wood with growth rings from the Eocene of Guangxi Province in South China.

Podocarps are the second largest family of Conifers today, with 194 species in 19 genera known. Unlike most Conifers, Podocarps are entirely tropical distribution, with most species being found in montain rainforests, though they are also found in lowland forests. The group is quite ancient, becoming widespread in both hemispheres early in the Jurassic, which suggests an origin late in the Triassic or very early in the Jurassic, though molecular evidence suggests most living species are descended from a common ancestor that lived in the late Cretaceous ot early Palaeocene.

In a paper published in the journal Scientific Reports on 30 August 2016, Long Li and Jian-Hua Jin of the State Key Laboratory of Biocontrol at Sun Yat-sen University, Cheng Quan of the Research Center of Paleontology & Stratigraphy at Jilin University and Alexei Oskolski of the Department of Botany and Plant Biotechnology at the University of Johannesburg and the Komarov Botanical Institute of the Russian Academy of Sciences, describe the discovery of fossil Podocarp wood from the Donghuai coal-mine in Baise City in Guangxi Province.

The wood is described as Podocarpoxylon donghuaiense, where Podocarpoxylon is an existing genus name applied to fossil Podocarp wood, and donghuaiense means 'from Donghaui'. The wood comes from the Eocene Nadu Formation, and is the first described fossil Podocarp wood from China, though fossil Podocarp leaves have been described from the Eocene of Hainan Island and Guangdong Province in South China.

Wood structure of Podocarpoxylon donghuaiense. Transverse section showing distinct growth rings (arrow). Scale bar = 400 μm. Li et al. (2016).

Podocarpoxylon donghuaiense is unusual in a Podocarp wood, in that it has growth rings, something not seen in modern or previosly described wood of the group, and which implies the wood comes from a tree that was growing in a seasonal climate. However the wood shows enough features distinctive to Podocarp woods, such as smooth horizontal and tangential walls of ray cells without indentures, cupressoid and taxodioid pits on cross fields, that Li et al. are confident in its assignment to the Podocarpaceae.