In recent times, I have been interested in the way that fossil plants are represented (or more often, not represented) in palaeoartistic works. Though I have started a project trying to combat this issue, I wanted to weight in on the issue in a more direct way by using my expertise in a particularly charismatic and often portrayed group of plants: the cycads. This was inspired by the beautiful and informative series “Botany for Paleoartists” by Maija Karala.
Here I will be talking about the order Cycadales, i.e. the group including the extant Cycadaceae and Zamiaceae and their close fossil relatives. The Bennettitales, although presenting very similar leaf morphology and being an important element in the Mesozoic floras, are a whole other kettle of fish, and good palaeoartistic representations of their diversity are already available in the literature.
The most common approach I have seen to represent fossil cycads in paleoartistic works is by using extant examples as a reference. Although this is usually a good practice for many groups, in practice it does not make use of our knowledge of the unique morphologies of fossil cycads which are not found among extant species, and usually only uses a limited amount of the extant diversity of the group.
The most commonly used references are some species from the extant genera Cycas, Dioon and Encephalartos. Usually this leads to representation of cycads as stout, unbranched palm-like plants, with somewhat coriaceous pinnate leaves, living in somewhat open habitats. However, this is only a partial view of extant and fossil cycad diversity.
Cycads include ~350 extant species. Although they have the reputation of being ‘living fossils’, with limited morphological variability and little amount of change through time, they are in fact quite disparate in both their leaf shape (see an example here), their growth form, and their habitat. For example, the australian genus Bowenia has subterranean stems with large bipinnate leaves (i.e., with two sets of rachises like in some ferns), while the genus Dioon includes quite tall trees (~12 meters in Dioon mejiae), with both types of plants found growing in wet forest understorey. Relatives of Bowenia are found in the fossil record of the Mesozoic.
Even within the genus Zamia (a recent genus, probably originated during the Middle Miocene) we can find species with subterranean stems and small coriaceous leaves growing in sand, species with broader leaflets growing in the walls of sinkholes, and species with slender, long trunks and enormous leaflets growing in the understorey of everwet forest.
Although we have little direct evidence of whole-plants cycads from the fossil record, the evidence we have points towards a similar variability. For example, Leptocycas gracilis from the Triassic of Arizona shows a slender, long trunk, while Leptocycas yangcaogouensis from the Triassic of China shows a more stout trunk. The anatomy of the Triassic Antarcticycas from Antarctica suggests a mostly subterraneous stem analogous to extant Bowenia. Bipinnate leaves are found in the genus Mesosingeria and Pseudoctenis babinensis from the Early Cretaceous of Argentina and Late Cretaceous of Czechia respectively.
Among the more common Mesozoic cycads, the leaf genus Ctenis is probably the most divergent from the commonly represented idea of cycads. This cycad leaf is found in sediments from the Triassic up to the Eocene, though its distribution shrank towards higher latitudes from the Early Cretaceous onwards. Though our understanding of this genus is far from complete, there are some interesting features that could add more accuracy and variety to paleoartistic reconstruction of these plants. First, the venation of these leaves presents veins that ‘fuse’ to form a disorganized net. Second, some of the species present very broad leaflets, with terminal leaflets being particularly wide (see below).
Even the habitat of some of these Ctenis seem to be rather different from other cycads. In the Big Cedar Ridge locality from the Late Cretaceous of north America, where plants are preserved in situ, Ctenis grows in the ‘fern wetland’, and it’s represented as a small plant with a subterranean stem (see here).
I hope this has given you some new ideas on how to represent cycads in paleoartistic reconstructions. In case there is more that you wish to know, please let me know in the comments here!
I wish to thank Michael Calonje for help with the extant cycad photos.
Apart from the Extinct Plant Paleoart database, and the reference linked in the text, here are a few more references:
The Montgomery Botanical Center, a garden specialized in palms and cycads, has a lot of beautiful pictures of extant cycads https://www.montgomerybotanical.org
The World List of Cycads is a great resource for extant morphology of the cycads http://cycadlist.org/index.php
Calonje, C., Knowles, L., Calonje, M. and Husby, C., 2014. Variability of vegetative flush colors in Zamia (Cycadales). Journal of the Botanical Research Institute of Texas, 8(2), pp.531-540.
Kvaček, J., 2008. New cycad foliage of Pseudoctenis babinensis from the Bohemian Cenomanian. Acta Musei Nationalis Pragae, Series B, Historia Naturalis (Sborník Národního Muzea Řada B, Přírodní Vědy), 64, pp.125-131.
Hermsen, E.J., Taylor, E.L. and Taylor, T.N., 2009. Morphology and ecology of the Antarcticycas plant. Review of Palaeobotany and Palynology, 153(1-2), pp.108-123.
Zhang, J.W., Yao, J.X., Chen, J.R. and Li, C.S., 2010. A new species of Leptocycas (Zamiaceae) from the Upper Triassic sediments of Liaoning Province, China. Journal of Systematics and Evolution, 48(4), pp.286-301.