Fossil cycad from Patagonia solves the puzzle of the “Byfield Fern”

This post was published on the 17th of May 2017 on my old blog page, and was updated on the 4th of September 2020. 

 

The first tranche of my work for my doctoral thesis has seen the light of publication in the journal BMC Evolutionary Biology (and it’s open to everyone). In this article, myself and my collaborator Christian Pott (from the Stockholm Museum of Natural History, now at the Westphalian Museum of Natural History) rederscribe a fossil leaf fragment from the Early Cretaceous of Patagonia, from material stored at the Natural History Museum in London. Using a combination of molecular and morphological data, we identify it as the oldest fossil relative of the quirky cycad genus Bowenia.

fig1
Specimen v52264 of Eobowenia incrassata and interpretative drawing. Scale bar:1 cm

The fossil leaf in question was first described by the Argentinian palaeobotanist Sergio Archangelsky, back in the 1960s. Archangelsky had recently visited some new outcrops from the Lower Cretaceous in Patagonia. These localities yielded plant material with exquisite preservation of organic material (pollen and cuticles). To learn more about cuticular analysis, Archangelsky decided to visit the prominent Palaeobotanist Thomas Harris in Reading, during a British tour financed by the British Council. This trip resulted in two publications about the Early Cretaceous flora from Patagonia in the Bulletin of the British Museum (Natural History). Moreover, Archangelsky decided to leave some of the specimens as a donation to the British Museum itself, so that European scholars could still access this beautiful Argentinian material.

In the Early Cretaceous flora of Patagonia, Archangelsky found many leaflets with potential cycadalean affinities. One of these, represented by two fragmentary specimens, was unique in having a dentate margin of the leaflets, as well as some peculiar dark-stained cells in its cuticle. Archangelsky noticed that these characteristics were present in a leaf that the Swedish palaeobotanist Rudolf Florin had described in its pivotal “Studien über die Cycadales der Mesozoikums”, back in 1933. These Early Cretaceous leaves from the Almargem locality, in Portugal, had been assigned by Florin to an entire new genus and species, Almargemia dentata. Archangelsky decided that the similarities between Almargemia dentata and his new Patagonian leafles were strong enough to assign these to a new species of the same genus, which he named Almargemia incrassata.

II0A2678
Specimen of Almargemia dentata

After almost fifty years from the original publication, I had the opportunity to visit the collections at the Swedish Natural History museum and the Natural History Museum in London to study the cycads described by Rudolf Florin and Thomas Harris. These visits were part of my project of revision of the fossil record of the cycads, and were possible thanks to the funding from the marvelous EU SYNTHESYS scheme. These visits allowed me to closely examine the cuticles of Almargemia dentata, which are stored in Stockholm, and to get familiar to its combination of unique and widespread characters. Afterwards, I visited the NHM in London and had the opportunity to look at Archangelsky’s material. I was particularly interested in Almargemia incrassata because of one very peculiar character described by Archangelsky: the guard cells of this fossil leaf are in fact placed at the same level as the other epidermal cells, and not sunken in a stomatal pit like in most cycads. This character is only present among extant Zamiaceae in Stangeria, a monotypic genus endemic to South Africa,  and Bowenia, an endemic Australian genus with two species.

MAX_v_almargemia_incrassata_03-1.jpg
Stoma of Eobowenia incrassata, with raised guard cells.

A closer observation of the cuticle of Almargemia incrassata allowed me to identify a set of characters which clearly separated this Argentinian fossil with its Portuguese counterpart. Moreover, I also identified new characters which seemed to show a closer link with extant Bowenia. Talking with my collaborator Christian Pott, we decided that Almargemia incrassata had to be transferred to a new genus, and we decided to erect the new genus Eobowenia. A phylogenetic analysis of fossil and extant Cycadales, integrating for the first time morphological and molecular data, confirmed the affinities of Eobowenia to extant Bowenia.

Fig 6.png
Phylogeny of fossil and extant cycads from our analysis.

This finding allows us to have a much clearer picture of the evolution of Bowenia. Until now, this genus had been a bit of an oddball, with a unique morphology and a quite isolated phylogenetic position. The only fossils assignable to this genus have been found in Australia, spanning from the Late Cretaceous to the Eocene. The placement of Eobowenia incrassata as sister to Bowenia fills the gap between the genus and the rest of the Zamiaceae, and implies a Gondwanan origin for the lineage. This pattern of ancient Gondwanan lineages that only survive in Australia is quite common among many southern plant groups, and shows the importance of the Australian tropical forests as a refugium for ancient lineages.

Since its publication, our study has been quite useful to make inferences on the morphology and the physiological evolution of Bowenia (see Hill et al. 2019a,b), as well as helping to reinterpret some of the cuticular characters of the Zamiaceae (see Erdei et al. 2019).

The story of this article also shows the importance of international collaboration and of museum collections. There are still many more discoveries to be made even in well-studied collections, if collaborative efforts like SYNTHESYS allow the free movement of researchers and material.

References:

Coiro, M. and Pott, C., 2017. Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia?. BMC Evolutionary Biology, 17(1), p.97.

Archangelsky, S. New gymnosperms from the Tico flora, Santa Cruz province, Argentina. British Museum (Natural History), 1966.

Archangelsky, S. 2014. Paleobotánica y arte: experiencia de una vida. Ciencia e Investigación, Reseñas 2(3): 6-19.

Erdei, B., Coiro, M., Miller, I., Johnson, K. R., Griffith, M. P., & Murphy, V. 2019. First cycad seedling foliage from the fossil record and inferences for the Cenozoic evolution of cycads. Biology letters 15(7):20190114.

Florin, R. 1933. Studien uber die Cycadales des Mesozoikums nebst Erorterungen uber die Spaltoffnungs Apparate der Bennettitales. Kungl. Svensk. Vet. Handl 12, no. 5 1-134.

Hill, K. E., Hill, R. S., & Watling, J. R., 2019a. Pinnule and stomatal size and stomatal density of living and fossil bowenia and eobowenia specimens give insight into physiology during cretaceous and eocene paleoclimates. International Journal of Plant Sciences 180(4): 323-336.

Hill, R. S., Hill, K. E., Carpenter, R. J., & Jordan, G. J., 2019b. New macrofossils of the Australian cycad Bowenia and their significance in reconstructing the past morphological range of the genus. International Journal of Plant Sciences 180(2):128-140.

 

 

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