Cycads are a thought to have been among the earliest Gymnosperm Plants to have appeared, with molecular clock estimates suggesting that they diverged from other Gymnosperms in the Late Carboniferous or Early Permian. The group underwent a major evolutionary radiation in the Early Triassic, and fossils are abundant in Mesozoic and Cainozoic deposits. These fossils tend to closely resemble modern Cycads, despite these sharing a fairly recent common ancestor, suggesting a high degree of morphological conservatism within the group. Palaeozoic fossils are much less common, and can be more difficult to interpret. These comprise possible Cycad megasporophylls (leaves) from the Late Carboniferous and Early Permian, although it is difficult to be confident about the affinities of these.
In a paper published in the International Journal of Plant Sciences on 11 October 2023, Ludwig Luthardt of the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Research, Ronny Rößler of the Museum für Naturkunde Chemnitz and the Department of Palaeontology at the Technische Universität Bergakademie Freiberg, and Dennis Stevenson of the New York Botanical Garden and the School of Integrative Plant Science at Cornell University, describe a new species of Cycad based upon a piece of stem wood from the Holocene gravel deposits of the Zwickauer Mulde river, which are known to produce silicified woods derived from the Permian Chemnitz Fossil Lagerstätte.
The new species is named Cycadodendron galtieri, where 'Cycadodendron' means 'Cycad-tree' (the suffix '-dendron' is commonly used for fossil woods, on the basis that chunks of wood of any size must have come from a tree), and 'galtieri' honours Jean Galtier, a renowned palaeobotanist from Montpellier, France, for his significant contributions to the knowledge of the evolution and anatomy of Palaeozoic fossil Plants. It is described from a single piece of polished wood, K9883, roughly 69 mm by 56 mm, thought to have derived from a larger stem, as the outer parts, including the cortex and vestiges of leaf bases, are not preserved.
While foliage can be difficult to ascribe to a particular plant group, due to convergent evolution among plants living in similar environments, the wood of Cycads is highly distinctive, with vascular stands arranged in medullary bundles within a wide inner pith, surrounded by consecutive vascular segments each producing centripetal secondary xylem and centrifugal phloem. The presence of these features within Cycadodendron galtieri marks the specimen as an unequivocable Cycad, and therefore the oldest known fossil which can be confidently assigned to the group.
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Online courses in Palaeontology.
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