Wednesday, 21 January 2015

Microfossil of the Month: Plant Stomata

For 2015 I have decided to replace my Micrograph of the Month feature with Microfossil of the Month. I will likely return to the thin section micrographs at some point, but as I am going to be working on phytolith and ash samples for most of this year, I figured it would make sense to feature some of these on the blog! Who knows how long I will be able to keep it up - from past experience of the sites I am working on, I may be limited in the range of examples that I will find! As a refresher (and for those of you new to the blog), microfossils are any fossil remains that are too small to see easily with the naked eye, but can be identified under the microscope. I work on plant microfossils, specifically silica phytoliths, which are 3D 'impressions' of plant cells and tissue. When the plant is alive, it takes up silica from the ground, which is then deposited inside and between the cells, forming 3D replicas of the cells that preserve when the organic part of the plant decays. The formation of phytoliths is complex and not well understood, but is controlled by a wide range of factors, with water availability being an important one. The more water that is taken up, the more silica that is taken up, and so plants which have a high water availability tend to produce lots of phytoliths.

The example here shows a sections of plant tissue (i.e. lots of single cells joined together). The rounded shapes that you can see are a distinctive type of plant structure, the plant stoma (plural stomata), a pore/opening in the skin which is formed from two guard cells. These openings are where the plant takes up carbon dioxide and releases oxygen in respiration, and also where water vapour leaves the plant during transpiration. This fragment of reed leaf/stem comes from an ashy midden deposit at the early Neolithic site of Boncuklu in Turkey, and are a blackish colour from burning.

Tuesday, 13 January 2015

Goats and reeds in the Neolithic

Bulliform cells in modern Zea mays tissue (source: Visuals Unlimited, Inc)
Fellow animal dung enthusiast Sarah Elliot at the University of Bournemouth shared this fab little article describing the use of 'Eco goats' to manage invasive plants in the US. It is especially interesting that they note the use of goats as a pesticide-free way to manage Phragmites reeds. These reeds have distinctive phytoliths which archaeologists call 'keystone' bulliforms, which are relatively large single cell phytoliths that are named as they are said to resemble a Roman keystone arch in cross section.  In transverse section they look a bit sausage shaped, and within a plant these cells are 'stacked' next to each other as part of the upper epidermis (the plant 'skin'), and are related to water storage. If you're a botanist you might also call these motor cells, because during times of water stress, they shrink and cause leaves to fold or curl up. Phragmites phytoliths are seen frequently in ash deposits at Neolithic sites in the Near East, including Boncuklu and Catalhoyuk, and are also found contained within ovicaprid dung pellets, giving a direct indicator that these plants were consumed by the animals. Identification of plant types within preserved animal dung can be used to understand where animals may have been grazing within a landscape, or help understand past climates, environments and water availability. The modern Eco Goats can munch their way through half an acre of dense vegetation in a period of four days. Sheep/goats make up the majority of animal bones at Catalhoyuk, although estimating herd sizes is difficult. Nevertheless it is likely that they played an important role in managing the local reed beds!

Phragmites bulliform cells embedded within ovicaprid dung pellet from Catalhoyuk