Diverse assemblages of Mid Devonian megaspores from Libya

Steemans, Philippe; Breuer, Pierre; Petus, Elodie; Prestianni, Cyrille; Goyet, Frédéric de Ville de; Gerrienne, Philippe

doi:10.1016/j.revpalbo.2011.02.007

Cited by 14 publications

(15 citation statements)

References 23 publications

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“…Some new levels have been investigated for a PhD research work on miospores (PB) and for a master degree on megaspores (FDVDG). All samples contain miospores and, in addition, nine samples contain megaspores (Steemans et al, 2011) . The level containing enigmatic palynomorphs, "acritarch-like" V. cucurbitulum and tintinnid-like palynomorphs is situated at 1293 ft of depth.…”

Section: Methodsmentioning

confidence: 99%

A Givetian tintinnid-like palynomorph from Libya

Steemans

Breuer

Goyet³

et al. 2014

Review of Palaeobotany and Palynology

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Section: Methodsmentioning

confidence: 99%

A Givetian tintinnid-like palynomorph from Libya

Steemans

Breuer

Goyet³

et al. 2014

Review of Palaeobotany and Palynology

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“…Spores of extant free‐sporing homosporous plants rarely exceed 100 µm diameter (fewer than 3% of species in Table 5.2 of Traverse, ), while spore diameters reached 50 µm only in the Silurian, did not pass the 100 µm threshold until the Pragian stage of the Early Devonian, and reached the 200 µm mark only in the Emsian, just over 400 million years ago (Chaloner, ; Traverse, ). By the Givetian stage of the Middle Devonian, megaspores were abundant and phylogenetically diverse and extreme heterospory had evolved, including the occurrence of so‐called seed‐megaspores with diameters in excess of 1000 µm (Traverse, ; Steemans et al ., ). A diameter of 200 µm is the conventional threshold for assigning megaspore status to dispersed fossil spores (Bateman & DiMichele, ), although the size at which weak heterospory initially emerged may have been somewhat less.…”

Section: The Model Of Haig and Westobymentioning

confidence: 97%

Why did heterospory evolve?

Petersen

Burd

2016

Biological Reviews

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The primitive land plant life cycle featured the production of spores of unimodal size, a condition called homospory. The evolution of bimodal size distributions with small male spores and large female spores, known as heterospory, was an innovation that occurred repeatedly in the history of land plants. The importance of desiccation-resistant spores for colonization of the land is well known, but the adaptive value of heterospory has never been well established. It was an addition to a sexual life cycle that already involved male and female gametes. Its role as a precursor to the evolution of seeds has received much attention, but this is an evolutionary consequence of heterospory that cannot explain the transition from homospory to heterospory (and the lack of evolutionary reversal from heterospory to homospory). Enforced outcrossing of gametophytes has often been mentioned in connection to heterospory, but we review the shortcomings of this argument as an explanation of the selective advantage of heterospory. Few alternative arguments concerning the selective forces favouring heterospory have been proposed, a paucity of attention that is surprising given the importance of this innovation in land plant evolution. In this review we highlight two ideas that may lead us to a better understanding of why heterospory evolved. First, models of optimal resource allocation - an approach that has been used for decades in evolutionary ecology to help understand parental investment and other life-history patterns - suggest that an evolutionary increase in spore size could reach a threshold at which small spores yielding small, sperm-producing gametophytes would return greater fitness per unit of resource investment than would large spores and bisexual gametophytes. With the advent of such microspores, megaspores would evolve under frequency-dependent selection. This argument can account for the appearance of heterospory in the Devonian, when increasingly tall and complex vegetative communities presented competitive conditions that made large spore size advantageous. Second, heterospory is analogous in many ways to anisogamy. Indeed, heterospory is a kind of re-invention of anisogamy within the context of a sporophyte-dominant land plant life cycle. The evolution of anisogamy has been the subject of important theoretical and empirical investigation. Recent work in this area suggests that mate-encounter dynamics set up selective forces that can drive the evolution of anisogamy. We suggest that similar dispersal and mating dynamics could have underlain spore size differentiation. The two approaches offer predictions that are consistent with currently available data but could be tested far more thoroughly. We hope to re-establish attention on this neglected aspect of plant evolutionary biology and suggest some paths for empirical investigation.

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“…Megaspores presenting gula have been studied by certain authors (e.g., Dybová-Jachowicz et al 1979, 1987, Candilier et al 1982, Archangelsky et al 1989, Cúneo et al 1991, ricardi-Branco et al 2002, Arioli et al 2007, Wellman et al 2009, Steemans et al 2011 and even principles for their classification have been proposed (Dybová-Jachowicz et al 1979). there are several genus within the gulate megaspores, Infraturma Gulati (Bhardwaj 1957), such as Lagenicula and Lagenoisporites, which have been well documented and studied at an ultrastructural level.…”

Section: Introductionmentioning

confidence: 99%

Morphology of the megaspore Lagenoisporites magnus (Chi and Hills 1976) Candilier et al. (1982), from the Carboniferous (lower Mississippian: mid-upper Tournaisian) of Bolivia

Quetglas

Macluf

Pasquo

2019

An. Acad. Bras. Ciênc.

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the morphology and structure of megaspores assigned to Lagenoisporites magnus from the toregua Formation, retama Group, mid-upper tournaisian of Bolivia were studied. the analysis was performed with light, fluorescence and scanning electron microscopy. Megaspores were laterally compressed and presented a spherical body with a proximal gula, of the hologula type. Gula had verrucae ornamentation and the spore body presented complex processes consisting of a bulbous base and an internally partitioned projection with sharp apex. In addition to this main ornamentation, perforations were present throughout the spore surface. Megaspores showed well marked curvaturae perfectae due to the abrupt transition existing between the gula ornamentation and the spore body processes. these megaspores were assigned to heterosporous arborescent lycopsids of the Lepidocarpaceae family, as in section view, exospore structure presented a three-dimensional network of fused elements. Likewise, due to a similarity found between sporoderm and Isoetes L. structure, it is evident that megaspores structure has remained intact inside the heterosporous lycopsids. therefore; the L. magnus structure not only would confirm its affinity with the Lycophyta fossils but also with the living ones.

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Diverse assemblages of Mid Devonian megaspores from Libya

Cited by 14 publications

References 23 publications

A Givetian tintinnid-like palynomorph from Libya

A Givetian tintinnid-like palynomorph from Libya

Why did heterospory evolve?

Morphology of the megaspore Lagenoisporites magnus (Chi and Hills 1976) Candilier et al. (1982), from the Carboniferous (lower Mississippian: mid-upper Tournaisian) of Bolivia

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