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Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia ?

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ABSTRACT

Background: Even if they are considered the quintessential “living fossils”, the fossil record of the extant genera of the Cycadales is quite poor, and only extends as far back as the Cenozoic. This lack of data represents a huge hindrance for the reconstruction of the recent history of this important group. Among extant genera, Bowenia (or cuticles resembling those of extant Bowenia) has been recorded in sediments from the Late Cretaceous and the Eocene of Australia, but its phylogenetic placement and the inference from molecular dating still imply a long ghost lineage for this genus.

Results: We re-examine the fossil foliage Almargemia incrassata from the Lower Cretaceous Anfiteatro de Ticó Formation in Patagonia, Argentina, in the light of a comparative cuticular analysis of extant Zamiaceae. We identify important differences with the other member of the genus, viz. A. dentata, and bring to light some interesting characters shared exclusively between A. incrassata and extant Bowenia. We interpret our results to necessitate the erection of the new genus Eobowenia to accommodate the fossil leaf earlier assigned as Almargemia incrassata. We then perfom phylogenetic analyses, including the first combined morphological and molecular analysis of the Cycadales, that indicate that the newly erected genus could be related to extant Bowenia.

Conclusion: Eobowenia incrassata could represent an important clue for the understanding of evolution and biogeography of the extant genus Bowenia, as the presence of Eobowenia in Patagonia is yet another piece of the biogeographic puzzle that links southern South America with Australasia.

Electronic supplementary material: The online version of this article (doi:10.1186/s12862-017-0943-x) contains supplementary material, which is available to authorized users.

No MeSH data available.


Almargemia dentata from the Lower Cretaceous of Portugal. a-e Several leaflets of the middle portion of a leaf, note the lobe-like teeth on the basiscopic margin of the leaflets, specimen 23,217; f-g More apical portion of a leaf where leaflets are inserted in much lower angles, specimen 23,213, both specimens stored in the Museu Geológico, Lisbon, Portugal; h Overview of lower epidermis, note the intercostal fields separated by a costal field (horizontal, middle of image), specimen S085620; j Close-up of a stoma, specimen S085620, stored in the Swedish Museum of Natural History, Stockholm, Sweden. Scale bars: a, c, g 1 cm; d, e 5 mm; h 100 μm; j 25 μm
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Fig1: Almargemia dentata from the Lower Cretaceous of Portugal. a-e Several leaflets of the middle portion of a leaf, note the lobe-like teeth on the basiscopic margin of the leaflets, specimen 23,217; f-g More apical portion of a leaf where leaflets are inserted in much lower angles, specimen 23,213, both specimens stored in the Museu Geológico, Lisbon, Portugal; h Overview of lower epidermis, note the intercostal fields separated by a costal field (horizontal, middle of image), specimen S085620; j Close-up of a stoma, specimen S085620, stored in the Swedish Museum of Natural History, Stockholm, Sweden. Scale bars: a, c, g 1 cm; d, e 5 mm; h 100 μm; j 25 μm

Mentions: Remarks: Based on the new characters identified and a re-evaluation of the epidermal anatomy of extant Bowenia and fossil Almargemia dentata (Fig. 1) and A. incrassata, we erect the new genus Eobowenia. In our opinion, the leaflets of A. incrassata share interesting characters with Bowenia, but are distinct enough to deserve the institution of a new genus. Eobowenia is distinguished from Almargemia by the leaflets with serrate margin, the veins converging at the base of the leaflets, the guard cells at the same level of the epidermis arranged longitudinally with respect to the leaflet axis, and the monocyclic stomatal complexes. From Bowenia, it is distinguished by the presence of darker-staining cells arranged in rows, the broad attachment of the leaflets, and the smaller size of the leaflets.Fig. 1


Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia ?
Almargemia dentata from the Lower Cretaceous of Portugal. a-e Several leaflets of the middle portion of a leaf, note the lobe-like teeth on the basiscopic margin of the leaflets, specimen 23,217; f-g More apical portion of a leaf where leaflets are inserted in much lower angles, specimen 23,213, both specimens stored in the Museu Geológico, Lisbon, Portugal; h Overview of lower epidermis, note the intercostal fields separated by a costal field (horizontal, middle of image), specimen S085620; j Close-up of a stoma, specimen S085620, stored in the Swedish Museum of Natural History, Stockholm, Sweden. Scale bars: a, c, g 1 cm; d, e 5 mm; h 100 μm; j 25 μm
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5383990&req=5

Fig1: Almargemia dentata from the Lower Cretaceous of Portugal. a-e Several leaflets of the middle portion of a leaf, note the lobe-like teeth on the basiscopic margin of the leaflets, specimen 23,217; f-g More apical portion of a leaf where leaflets are inserted in much lower angles, specimen 23,213, both specimens stored in the Museu Geológico, Lisbon, Portugal; h Overview of lower epidermis, note the intercostal fields separated by a costal field (horizontal, middle of image), specimen S085620; j Close-up of a stoma, specimen S085620, stored in the Swedish Museum of Natural History, Stockholm, Sweden. Scale bars: a, c, g 1 cm; d, e 5 mm; h 100 μm; j 25 μm
Mentions: Remarks: Based on the new characters identified and a re-evaluation of the epidermal anatomy of extant Bowenia and fossil Almargemia dentata (Fig. 1) and A. incrassata, we erect the new genus Eobowenia. In our opinion, the leaflets of A. incrassata share interesting characters with Bowenia, but are distinct enough to deserve the institution of a new genus. Eobowenia is distinguished from Almargemia by the leaflets with serrate margin, the veins converging at the base of the leaflets, the guard cells at the same level of the epidermis arranged longitudinally with respect to the leaflet axis, and the monocyclic stomatal complexes. From Bowenia, it is distinguished by the presence of darker-staining cells arranged in rows, the broad attachment of the leaflets, and the smaller size of the leaflets.Fig. 1

View Article: PubMed Central - PubMed

ABSTRACT

Background: Even if they are considered the quintessential “living fossils”, the fossil record of the extant genera of the Cycadales is quite poor, and only extends as far back as the Cenozoic. This lack of data represents a huge hindrance for the reconstruction of the recent history of this important group. Among extant genera, Bowenia (or cuticles resembling those of extant Bowenia) has been recorded in sediments from the Late Cretaceous and the Eocene of Australia, but its phylogenetic placement and the inference from molecular dating still imply a long ghost lineage for this genus.

Results: We re-examine the fossil foliage Almargemia incrassata from the Lower Cretaceous Anfiteatro de Ticó Formation in Patagonia, Argentina, in the light of a comparative cuticular analysis of extant Zamiaceae. We identify important differences with the other member of the genus, viz. A. dentata, and bring to light some interesting characters shared exclusively between A. incrassata and extant Bowenia. We interpret our results to necessitate the erection of the new genus Eobowenia to accommodate the fossil leaf earlier assigned as Almargemia incrassata. We then perfom phylogenetic analyses, including the first combined morphological and molecular analysis of the Cycadales, that indicate that the newly erected genus could be related to extant Bowenia.

Conclusion: Eobowenia incrassata could represent an important clue for the understanding of evolution and biogeography of the extant genus Bowenia, as the presence of Eobowenia in Patagonia is yet another piece of the biogeographic puzzle that links southern South America with Australasia.

Electronic supplementary material: The online version of this article (doi:10.1186/s12862-017-0943-x) contains supplementary material, which is available to authorized users.

No MeSH data available.