Ctenis is a genus of fossil foliage attributable to the
Cycadales, being one of the most common genera of cycad fossil leaves in the
Mesozoic.
Taxonomy
The genus was first erected by
Lindley and
Hutton in "The fossil flora of Great Britain",[2] based on material of Ctenis falcata from the
Jurassic of
Yorkshire. This species was later
synonymized with Cycadites sulcicaulis, leading to the new combination Ctenis sulcicaulis[3]. Later,
Seward,[4]Florin, and
Harris[5] added details of the cuticle to the diagnosis of the genus.
Due to the leaves of Ctenis possessing characters unknown in any living cycad, Ctenis is thought to belong to an extinct lineage distinct from modern cycads, with a 2023 analysis finding that the genus was
paraphyletic with respect to Dioonopsis and Pterostoma, with this group suggested to be the sister group to Cycadaceae, from which they split in the
Permian period.[6]
Description
The leaves of Ctenis are once pinnate, and the pinnae have multiple parallel veins that often anastomosize (i.e. fuse together).[7][8] The cuticle of Ctenis has stomata with guard cells arranged in a random fashion, and the stomatal apparatus has often a cuticular ring surrounding the stomatal pit. The cuticular surface is usually striate.
Distribution
Though Ctenis-like leaves are known from the
Late PermianUmm Irna Formation of
Jordan,[9]Ctenis becomes more common from the
Late Triassic onwards. In the
Jurassic, many Ctenis species are retrieved from Europe, North America, and Asia.[10][7] In the
Early Cretaceous, Ctenis is still found in Europe (i.e. in the
Wealden[11]) and Asia,[12] but from the Late Cretaceous it seems to retreat to more Northern Latitudes in the Siberian region[13] and North America[14] and Southern latitudes in Australia. The last members of this genus are found in the
Eocene of North America.[8]
Paleoecology
Little is known about the ecology of the Ctenis-producing plants. However, in the
Big Cedar Ridge locality in
Wyoming (
Campanian), Ctenis is found in the fern wetland together with ferns from the
Dipteridaceae,
Gleicheniaceae, and
Matoniaceae.[15] This suggests that at least some members of the genus inhabited wet environments with peaty soils.
References
^Lindley, J. and Hutton, W., 1834. The Fossil Flora of Great Britain, Vol. 2. Ridgway & Sons, London.