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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.


Related in: MedlinePlus

Comparison between the stomatal complexes of Eobowenia incrassata (a, specimen v52265), Bowenia spectabilis (b), Almargemia dentata (c, specimen S085614) and Macrozamia plurinervia (d). a Stomatal complex in Eobowenia incrassata with flush guard cells, thickening of the apertural cuticle of the guard cells and cuticular ridge. b Stomatal complex in Bowenia spectabilis, showing similarities to Eobowenia.c Stomatal complex in Almargemia dentata, showing the sunken guard cells. d Stomatal complex in Macrozamia heteromera, showing similarly sunken guard cells. a and b are maximum intensity projections of confocal stacks, c a light micrograph and d a fluorescence micrograph. Scale bars: 50 μm
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Fig4: Comparison between the stomatal complexes of Eobowenia incrassata (a, specimen v52265), Bowenia spectabilis (b), Almargemia dentata (c, specimen S085614) and Macrozamia plurinervia (d). a Stomatal complex in Eobowenia incrassata with flush guard cells, thickening of the apertural cuticle of the guard cells and cuticular ridge. b Stomatal complex in Bowenia spectabilis, showing similarities to Eobowenia.c Stomatal complex in Almargemia dentata, showing the sunken guard cells. d Stomatal complex in Macrozamia heteromera, showing similarly sunken guard cells. a and b are maximum intensity projections of confocal stacks, c a light micrograph and d a fluorescence micrograph. Scale bars: 50 μm

Mentions: The cuticle fragments examined show that the leaflets are hypostomatic with epidermal pavement cells longitudinally elongated parallel to the leaflet axis (Fig. 2 c, d). Ordinary epidermal cells are elongate and moderately cutinised. On the adaxial side, rows of cells with thicker cuticle than the ordinary pavement cells can be observed (darker staining; equivalent to the thin-walled cells of most Zamiaceae (see [54])), which seem to be arranged preferably in rows of short cells. The anticlinal walls of these dark-staining cells tend to be slightly concave. On the abaxial side, rows of darker staining cells as well as single darker staining cells are present. The stomata are confined to the abaxial side and are distributed uniformly in broad intercostal bands on the leaflet surface, with the guard cells oriented longitudinally (Fig. 3a, c). Guard cells are in average 38.63 (35.53–42.30) μm long and 17.90 (16.86–19.71) μm wide, with an aperture that is 20.89 (14.78–23.98) μm long. The stomatal complexes are monocyclic, with four to six subsidiary cells that have a thicker, darker staining cuticle than the ordinary pavement cells. The cuticle of the guard cells presents a ventral thickening in the correspondence of the aperture as well as ridges that run parallel to the dorsal wall (Fig. 2 d; Fig. 3 c, e; Fig. 4 a). In some stomatal complexes, is possible to observe differentially thickened or perforated cell walls, which are similar to the cell wall of the substomatal complex in extant Bowenia (Fig. 2 d; Fig. 3 e).Fig. 3


Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia ?
Comparison between the stomatal complexes of Eobowenia incrassata (a, specimen v52265), Bowenia spectabilis (b), Almargemia dentata (c, specimen S085614) and Macrozamia plurinervia (d). a Stomatal complex in Eobowenia incrassata with flush guard cells, thickening of the apertural cuticle of the guard cells and cuticular ridge. b Stomatal complex in Bowenia spectabilis, showing similarities to Eobowenia.c Stomatal complex in Almargemia dentata, showing the sunken guard cells. d Stomatal complex in Macrozamia heteromera, showing similarly sunken guard cells. a and b are maximum intensity projections of confocal stacks, c a light micrograph and d a fluorescence micrograph. Scale bars: 50 μm
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig4: Comparison between the stomatal complexes of Eobowenia incrassata (a, specimen v52265), Bowenia spectabilis (b), Almargemia dentata (c, specimen S085614) and Macrozamia plurinervia (d). a Stomatal complex in Eobowenia incrassata with flush guard cells, thickening of the apertural cuticle of the guard cells and cuticular ridge. b Stomatal complex in Bowenia spectabilis, showing similarities to Eobowenia.c Stomatal complex in Almargemia dentata, showing the sunken guard cells. d Stomatal complex in Macrozamia heteromera, showing similarly sunken guard cells. a and b are maximum intensity projections of confocal stacks, c a light micrograph and d a fluorescence micrograph. Scale bars: 50 μm
Mentions: The cuticle fragments examined show that the leaflets are hypostomatic with epidermal pavement cells longitudinally elongated parallel to the leaflet axis (Fig. 2 c, d). Ordinary epidermal cells are elongate and moderately cutinised. On the adaxial side, rows of cells with thicker cuticle than the ordinary pavement cells can be observed (darker staining; equivalent to the thin-walled cells of most Zamiaceae (see [54])), which seem to be arranged preferably in rows of short cells. The anticlinal walls of these dark-staining cells tend to be slightly concave. On the abaxial side, rows of darker staining cells as well as single darker staining cells are present. The stomata are confined to the abaxial side and are distributed uniformly in broad intercostal bands on the leaflet surface, with the guard cells oriented longitudinally (Fig. 3a, c). Guard cells are in average 38.63 (35.53–42.30) μm long and 17.90 (16.86–19.71) μm wide, with an aperture that is 20.89 (14.78–23.98) μm long. The stomatal complexes are monocyclic, with four to six subsidiary cells that have a thicker, darker staining cuticle than the ordinary pavement cells. The cuticle of the guard cells presents a ventral thickening in the correspondence of the aperture as well as ridges that run parallel to the dorsal wall (Fig. 2 d; Fig. 3 c, e; Fig. 4 a). In some stomatal complexes, is possible to observe differentially thickened or perforated cell walls, which are similar to the cell wall of the substomatal complex in extant Bowenia (Fig. 2 d; Fig. 3 e).Fig. 3

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.


Related in: MedlinePlus