Figure 2
Stylized reconstruction of branch bearing Dicroidium odontopteroides -type fronds and short shoots with attached Umkomasia uniramia cupules, based on plants from the “Alfie's” locality, Antarctica / reconstrucción de una rama con hojas del tipo Dicroidium odontopteroides y con braquiblastos portando cúpulas de Umkomasia uniramia , basada en las plantas de la localidad fosilífera Alfie en Antártida.
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Much is now known about the Mesozoic pteridosperm order Corystospermales based on over seventy years of research. However, several concepts of corystosperm evolution have been proposed that avoid well-established phylogenetic methodology and arbitrarily discount evidence of the group from Antarctica. Here, we focus on the "New approach to Corystosp...
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The aim of this paper is to revise populations of Macrothrix cf. hirsuticornis (Cladocera: Anomopoda: Macrothricidae) from different regions of the southern hemisphere. It is demonstrated that M. hirsuticornis Norman and Brady, 1867 s. str. is absent there, and five related species occupy different Subantarctic islands and the southernmost portions...
Citations
... Corystosperms, especially as Dicroidium leaves, are abundantly preserved in the Middle and Late Triassic of Gondwana, and extensive collections of Gondwanan Triassic corystosperms have greatly expanded our understanding of these plants (e.g. Townrow 1962Townrow , 1965Archangelsky 1968;Holmes & Ash 1979;Playford et al. 1982;Retallack 1983Retallack , 1995Cantrill et al. 1995;Yao et al. 1995;Axsmith et al. 2000Axsmith et al. , 2007Klavins et al. 2002;Anderson & Anderson 2003;Holmes & Anderson 2005;Bomfleur & Kerp 2010;Pattemore 2016a, b;Anderson et al. 2019aAnderson et al. , b, 2020. However, a complete understanding of the structure and homology of their reproductive structures has been hindered by their preservation as compression or impression fossils. ...
... The recognition and description of Jarudia from the Early Cretaceous of Inner Mongolia, China, adds to the significant expansion of knowledge about corystosperms that has occurred over the past two decades, as a result of research on material from the Permian and Triassic (Thomas 1933;Holmes 1987;Kirchner & M€ uller 1992;Axsmith et al. 2000Axsmith et al. , 2007Klavins et al. 2002;Anderson & Anderson 2003;Chandra et al. 2008;Zan et al. 2008;Blomenkemper et al. 2018Blomenkemper et al. , 2020Anderson et al. 2019aAnderson et al. , b, 2020 as well as from the Early Cretaceous (Stockey & Rothwell 2009;Rothwell & Stockey 2016;Shi et al. 2016Shi et al. , 2019Shi et al. , 2021a. Based in part on these discoveries, including the new information provided by the well-preserved material of Jarudia, we have proposed that the reflexed cupules of the doyleoids, umkomasioids, Caytonia and Petriellaea, perhaps also including the ovule-bearing structures of glossopterids, are all fundamentally similar (Shi et al. 2021a). ...
The group referred to informally as the corystosperms, described initially based on compression fossils from the Triassic of Gondwana, have long been considered critical extinct plants for understanding seed plant phylogeny, the evolution of seed plant reproductive structures and the relationships of angiosperms. Here we describe a new genus and species of corystosperm seed-bearing structure, Jarudia zhoui gen. et sp. nov., based on abundant silicified material collected from the newly discovered chert in the Early Cretaceous Huolinhe Formation of eastern Inner Mongolia, north-eastern China. Jarudia zhoui is a lax seed cone consisting of a flexible central axis bearing deciduous, helically arranged, lateral seed-bearing units. Individual seed-bearing units consist of an elongate bract partially fused to an unbranched cupule stalk that bears a single, reflexed cupule apically. Each cupule is formed by the strongly reflexed cupule stalk and one median and two lateral flaps. The cupule stalk supplied by two vascular bundles and three unvascularized flaps partially enclose two three-angled seeds. Jarudia zhoui bears a striking resemblance to Doylea tetrahedrasperma from the Early Cretaceous of Canada and similar plants from the Early Cretaceous of Mongolia. There are also strong similarities with ovulate structures of Umkomasia from the Triassic of Gondwana in the structure and anatomy of individual cupules, their axial nature, and the architecture of the entire seed-bearing structure that has two orders of branching. New information from Jarudia zhoui, together with information on other corystosperm ovulate organs from the Northern Hemisphere, significantly expands our understanding of this key group of extinct plants, suggests that the cupules of the Early Cretaceous and Triassic corystosperms are homologous, and raises critical questions about the definition and phylogenetic circumscription of the corystosperms, including how Early Cretaceous and Triassic corystosperms are related to each other and to other groups of seed plants, including angiosperms.
... From 'Alfie's Elbow' ridge southeast of Schroeder Hill in the Shackleton Glacier region (Fremouw or Falla Formation), Antarctica, Axsmith et al. (2000Axsmith et al. ( , 2007 reported D. odontopteroides as attached to a stem (see discussion herein). ...
... By comparison with extant Ginkgo biloba, all the leaves grow from new season long shoots or in fascicles from short shoots. Axsmith et al. (2007) defended the attachment and provided further photographs (different orientation) to which Artabe & Brea (2007) responded and were still not convinced of the attachment. A strange reconstruction of a branch, bearing leaves and cupulate organs, was provided by Axsmith et al. (2007, fig . ...
... The most convincing example of leaves attached to short shoots and stems in the Gondwanan Triassic are the numerous Dicroidium leaves described from the Ipswich Flora, Australia . This Australian find raises further questions regarding the reported attached single Dicroidium leaf to a mature long shoot stem from Antarctica (Axsmith et al. 2000(Axsmith et al. , 2007, which was previously questioned by Artabe & Brea (2003. ...
Anderson, H.M., Barbacka, M., Bamford, M.K., Holmes, W.B.K. & Anderson, J.M., XX. 2019. Dicroidium (foliage) and affiliated wood; Part 3 of a reassessment of Gondwana Triassic plant genera and a reclassification of some previously attributed. Alcheringa XXX, X–X. ISSN 0311-5518
Dicroidium belonging to Umkomasiaceae (Corystospermaceae) in the polyphyletic pteridosperms (seed-ferns) is reassessed comprehensively worldwide and emended. All records are analysed and some attributed to the genus previously are reclassified. Dicroidium leaves are clearly affiliated with Umkomasia ‘megasporophylls’ and Pteruchus ‘microsporophylls’. The attachments of Dicroidium leaves to stems and associated wood genera are reviewed. Dicroidium is shown to be restricted to the Triassic of Gondwana, where it is by far the most prominent and diverse genus with 23 accepted species. It is well represented in collections from South America, Antarctica, India, Australia, New Zealand and southern Africa from where the Molteno Formation is the most comprehensively sampled stratigraphic unit, yielding numerous species from 75 assemblages. The problems of defining the limits of Dicroidium and its species are addressed. The records of leaf fragments from the Indian Nidpur Flora, Early Triassic, are questionably referable to Dicroidium, whereas the multiple forking leaves from the Cisuralian of India await description as a new peltasperm genus. The forked leaves from the (?)Lopingian of Jordan, previously classified as Dicroidium, are reassessed and placed in the new genus Jordaniopteris.
Heidi M. Anderson [hmsholmes@googlemail.com], Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg 20150, South Africa; Maria Barbacka [maria.barbacka@gmail.com], W. Szafer Institute of Botany, Polish Academy of Sciences, Lubicz 46, Kraków 31-512, Poland, Botanical Department, Hungarian Natural History Museumartmem H-1431, Budapest, Pf. 137, Hungary; Marion K. Bamford [marion.bamford@wits.ac.za], Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg 20150, South Africa; W. B. Keith Holmes [wbkholmes@hotmail.com], 46 Kurrajong Street, Dorrigo, NSW 2453, Australia, University of New England, Armidale, NSW 2351, Australia; John M. Anderson [jmanderson.gondwana@googlemail.com], Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg 20150, South Africa.
... In our opinion, Umkomasia is a validly erected genus with well-defined characters and should be retained as such. This approach is shared by Artabe & Brea (2007), who wrote that U. uniramia should be assigned to another taxon. In conclusion, this Antarctic material does not belong in Umkomasia, nor in any other described genus and is thus placed in the new genus Axsmithia as A. uniramia. ...
The genus Umkomasia, a megasporophyll, belonging to the pteridosperms (seed ferns) in the family Umkomasiaceae (Corystospermaceae), is reassessed comprehensively worldwide. All previous records are analysed. Certain fertile structures previously attributed are reclassified. Umkomasia is shown to be restricted to the Triassic of Gondwana where it is associated with the genus Pteruchus, a microsporophyll, and the genus Dicroidium, a vegetative leaf. It is well represented from Argentina, Australia and southern Africa where the Molteno Formation is by far the most comprehensively sampled with eight species described. Two specimens from the upper Permian of India attributed to Umkomasia are reclassified as cf. Arberiopsis sp. A whorled fertile structure from Antarctica, previously assigned to Umkomasia, is reclassified in a new genus as Axsmithia uniramia. Another compression fossil and the permineralized Umkomasia resinosa remain as valid records from Antarctica. The material described as Umkomasia from the Triassic of China is reclassified as Stenorachis asiatica. The Lower Jurassic record from Germany is placed in a new genus as Kirchmuellia franconica. The records of Umkomasia sp. from the Rhaetic of Germany are reclassified as cf. Kirchmuellia sp. and the single specimen from the Jurassic of Libya as genus et sp. indet. The Lower Cretaceous record from Mongolia has been reclassified by other researchers as Doylea mongolica. A pictorial key to Umkomasia species is provided, geographic and stratigraphic distributions are tabulated.
... Doyle & Donoghue, 1986). Peltasperms represent an enigmatic and isolated fossil lineage (Fig. 1) that has been variously placed in different morphological phylogenetic analyses, most recently as closely related to the Mesozoic pteridosperm order Corystospermales (Doyle, 2006;Axsmith, Taylor & Taylor, 2015). Remarkably clear leaf-surface images of the Mesozoic corystosperm leaf-genus Dicroidium illustrated by Hamad et al. (2008) show at least some stomata possessing two distinct LSCs, although this feature appears highly variable. ...
Stomata play a critical ecological role as an interface between the plant and its environment. Although the guard‐cell pair is highly conserved in land plants, the development and patterning of surrounding epidermal cells follow predictable pathways in different taxa that are increasingly well understood following recent advances in the developmental genetics of the plant epidermis in model taxa. Similarly, other aspects of leaf development and evolution are benefiting from a molecular–genetic approach. Applying this understanding to extinct taxa known only from fossils requires use of extensive comparative morphological data to infer ‘fossil fingerprints’ of developmental evolution (a ‘palaeo‐evo‐devo’ perspective).
The seed‐plant order Bennettitales, which flourished through the Mesozoic but became extinct in the Late Cretaceous, displayed a consistent and highly unusual combination of epidermal traits, despite their diverse leaf morphology. Based on morphological evidence (including possession of flower‐like structures), bennettites are widely inferred to be closely related to angiosperms and hence inform our understanding of early angiosperm evolution. Fossil bennettites – even purely vegetative material – can be readily identified by a combination of epidermal features, including distinctive cuticular guard‐cell thickenings, lobed abaxial epidermal cells (‘puzzle cells’), transverse orientation of stomata perpendicular to the leaf axis, and a pair of lateral subsidiary cells adjacent to each guard‐cell pair (termed paracytic stomata). Here, we review these traits and compare them with analogous features in living taxa, aiming to identify homologous – and hence phylogenetically informative – character states and to increase understanding of developmental mechanisms in land plants.
We propose a range of models addressing different aspects of the bennettite epidermis. The lobed abaxial epidermal cells indicate adaxial–abaxial leaf polarity and associated differentiated mesophyll that could have optimised photosynthesis. The typical transverse orientation of the stomata probably resulted from leaf expansion similar to that of a broad‐leaved monocot such as Lapageria, but radically different from that of broad‐leafed eudicots such as Arabidopsis. Finally, the developmental origin of the paired lateral subsidiary cells – whether they are mesogene cells derived from the same cell lineage as the guard‐mother cell, as in some eudicots, or perigene cells derived from an adjacent cell lineage, as in grasses – represents an unusually lineage‐specific and well‐characterised developmental trait. We identify a close similarity between the paracytic stomata of Bennettitales and the ‘living fossil’ Gnetum, strongly indicating that (as in Gnetum) the pair of lateral subsidiary cells of bennettites are both mesogene cells. Together, these features allow us to infer development in this diverse and relatively derived lineage that co‐existed with the earliest recognisable angiosperms, and suggest that the use of these characters in phylogeny reconstruction requires revision.
... In these aberrant forms, the lateral ovule-bearing structures have two collateral vascular bundles similar to those of corystosperms. (u) Umkomasia uniramia, modified from Axsmith et al. (2000Axsmith et al. ( , 2007) showing five reflexed cupules. Successive transverse sections from the base to the chalaza showing position and orientation of vascular bundles (black, xylem; white, phloem). ...
... Their attribution to Umkomasia and the reported organic connection has been questioned by Anderson and Anderson (2003), Holmes and Anderson (2005), and Anderson et al. (2008) on the basis of long and short shoot development. However, their reasoning was shown to be doubtful using an example from a living Gingko biloba L. (Axsmith et al. 2007); that species has complex and highly variable shoot development that is strongly influenced by environmental conditions (Leigh et al. 2011, Little et al. 2013. The suggestion by Artabe and Brea (2003) Anderson and Anderson (2003, p. 240) noted the diversity of branching mode that has been included in the genus. ...
The plant fossil genera Umkomasia Thomas 1933 and Pteruchus Thomas 1933 emend. Townrow 1962 are known chiefly from the Middle and Upper Triassic of Gondwana. The structure of these fructifications has been conjectural, some being identified as pinnate, others as helically arranged. Specimens from the Ladinian-lower Norian of Queensland (northeastern Australia) show that the female and male fructifications - U. geminata (Shirley 1898) Rigby in Playford et al. 1982 emend. nov. and P. dubius Thomas 1933 emend. Townrow 1962, respectively - have a bipinnate structure. Those fructifications and the bipinnate leaf, Dicroidium feistmantelii (Johnston 1894) Gothan 1912, probably all belonged to the same parent plant. It was first suggested by John Townrow in 1962 that the sporangial heads of P. dubius have a pinnate structure; this character is confirmed herein. Pteruchus is recorded for the first time from the Carnian Tarong Basin, Queensland.
The holotype of Stachyopitys simmondsii Shirley 1898 is shown to be ovuliferous. The species is recombined as Umkomasia simmondsii (Shirley 1898) comb. et emend. nov. Genuine male fructifications, previously identified as S. simmondsii, and later as Pteruchus simmondsii (Shirley 1898) Jones and de Jersey 1947, are assigned to P. minor Thomas 1933. That species comprises the smallest fructifications of the genus. Townrovia polaris Bomfleur et al. 2011 and Stachyopitys lacrisporangia Anderson & Anderson 2003 are identified as junior synonyms to P. minor. The diagnosis of Townrovia Retallack 1981 is inaccurate and the genus is insufficiently distinguished from Pteruchus.
... This association was disputed by Anderson and Anderson (2003), Holmes and Anderson (2005a) and Anderson et al. (2008) on the basis of shoot development (Holmes and Anderson, 2005a, p. 2). However, their arguments were refuted by Axsmith et al. (2007) based on shoot development in a living Ginkgo Linnaeus, 1771. The diagnosis of Umkomasia uniramia Axsmith, Taylor, Taylor and Cúneo, 2000 included foliage considered conformable with Dicroidium odontopteroides (Morris, 1845) Gothan, 1912. ...
Pteridosperms are preserved abundantly in the Gondwanan Triassic, with many species exhibiting considerable morphological variation that has been attributed to a hybridization model of speciation. This is an improbable explanation given that hybridization is very rare in gymnosperms. Allopatric speciation resulting from geographic and climatic provincialism is a more likely explanation for the morphological diversity which is well represented in Anisian–Norian (Middle and Upper Triassic) floras of Australasia and elsewhere in Gondwana. Most specimens are distributed among three families: Umkomasiaceae, Peltaspermaceae and Matatiellaceae. These families, together with other possibly pteridospermous genera, are reviewed herein. Diversity in these families apparently declined by the Rhaetian and they did not persist into the Gondwanan post-Triassic. Australasian post-Triassic strata contain remarkably different floral assemblages to those of the Triassic. No fructifications are clearly pteridospermous and no remains show any obvious relationship with pteridosperms of the Gondwanan Triassic. Caytonialean fructifications are not known in Australasian strata; however, associated foliage has been reported from the Eastern Gondwanan Upper Triassic through Middle Jurassic including Australia. Much fern-like foliage, claimed to be pteridospermous from the Lower Jurassic through Eocene of Eastern Gondwana, lacks supporting evidence of such affiliation. © 2015, Instituto Geologico y Minero de Espana. All rights reserved.
... N. Phipps et al. 1998), subterranean organs of sphenophytes (Bomfleur et al. 2013b), and abundant debris of leafy and thallose bryophytes (Bomfleur et al. 2014a). At the Alfie's Elbow site, petriellalean remains occur only in the level 2 bed, which also yielded (1) the only known occurrence of corystosperm reproductive organs attached to short shoots Axsmith et al. 2000Axsmith et al. , 2007, (2) one of only three known occurrences worldwide of attached Dicroidium leaves (Axsmith et al. 2000), and (3) the only known record of dipterid ferns in the Antarctic Triassic (Escapa et al. 2011). We interpret this rich assortment of otherwise rare plant taxa and organs and the extraordinary proportion of attached organs to reflect high-energy depositional events (e.g., catastrophic river flooding or riverbank collapse after heavy rainstorms) that caused traumatic removal of living plants and plant parts, especially cryptogamic ground cover (Bomfleur et al. 2014a). ...
Premise of research. Well-preserved Triassic plant fossils from Antarctica yield insights into the physiology of plant growth under the seasonal light regimes of warm polar forests, a type of ecosystem without any modern analogue. Among the many well-known Triassic plants from Antarctica is the enigmatic Petriellaea triangulata, a dispersed seedpod structure that is considered a possible homologue of the angiosperm carpel. However, the morphology and physiology of the plants that produced these seedpods have so far remained largely elusive.
Methodology. Here, we describe petriellalean stems and leaves in compression and anatomical preservation that enable a detailed interpretation of the physiology and ecology of these plants.
Pivotal results. Our results indicate that the Petriellales were diminutive, evergreen, shade-adapted perennial shrubs that colonized the understory of the deciduous forest biome of polar Gondwana. This life form is very unlike that of any other known seed-plant group of that time. By contrast, it fits remarkably well into the “dark and disturbed” niche that some authors considered to have sheltered the rise of the flowering plants some 100 Myr later.
Conclusions. The hitherto enigmatic Petriellales are now among the most comprehensively reconstructed groups of extinct seed plants and emerge as promising candidates for elucidating the mysterious origin of the angiosperms.
... It is, however, possible that the long-lived traces vascularized short shoots, a common feature in both extant and fossil gymnosperms (Little et al., 2013). For the corystosperms in particular, the presence of short shoots is well documented based on stem compressions from Antarctica (Axsmith et al., 2000(Axsmith et al., , 2007 and Australia (Anderson et al., 2008) that bear short shoots with attached Dicroidium leaves. Occurrences of short shoots have also been suggested for the South African plant reconstructed from Rhexoxylon tetrapteridoides and Dicroidium odontopteroides by Retallack and Dilcher (1988). ...
... Some authors interpreted this latter feature as included phloem produced by supernumerary cambia (e.g., Artabe and Brea, 2003;Bodnar, 2012). While the taxonomic value of such characters is disputable (Artabe and Zamuner, 2007;Axsmith et al., 2007), they have been used to reconstruct hypothetical phylogenies of the corystosperms (Artabe and Brea, 2003;Bodnar, 2008). However, the present work and a reinvestigation of previous literature demonstrate that in some taxa two of these characters (unequal cambial activity and dilatation parenchyma) only occur in mature stems. ...
Anatomically preserved trunks and young stems of corystosperm seed ferns are described from the Triassic of Fremouw Peak, Beardmore Glacier area, Antarctica. Based on characters of the primary and secondary vascular system, these new specimens are assigned to Kykloxylon, a genus that was established based on young stems with attached Dicroidium leaf bases. The largest specimens illustrate how some secondary growth characters, such as unequal cambial activity, appeared during later development, which enables a better comparison of Kykloxylon with trunks assigned to other corystosperm genera. Jeffersonioxylon from the Gordon Valley, Antarctica, and Cuneumxylon from South America show strong similarities with the newly described larger Kykloxylon trunks from Fremouw Peak, and might be considered congeneric. Our results provide further support for the presence of two anatomically and morphologically distinct kinds of Dicroidium-bearing trees in the Triassic vegetation of Gondwana, one with a palm-like habit and Rhexoxylon stems and the other with a more Ginkgo-like habit and Kykloxylon/Cuneumxylon-type stems.
... Archangelsky and Brett (1961), have long been of interest to botanists and paleobotanists. Some, like Kykloxylon Meyer-Berthaud et al. (1993), a Triassic axis from Antarctica, lacks anomalous secondary growth, and has pycnoxylic wood with attached Dicroidium leaves and reproductive structures, thus indicating an affinity with the Corystospermales (Axsmith et al., 2007;Taylor et al., 2009). Jeffersonioxylon Del Fueyo et al. (1995, also with pycnoxylic wood, from the Triassic of Antarctica, Cuneumxylon Artabe and Brea (2003), Elchaxylon Artabe and Zamuner (2007), Tranquiloxylon Herbst and Lutz (1995) all from the Triassic of Argentina, and Rhexoxylon from the Triassic of Africa and South America have also been assigned to this order. ...
... Jeffersonioxylon Del Fueyo et al. (1995, also with pycnoxylic wood, from the Triassic of Antarctica, Cuneumxylon Artabe and Brea (2003), Elchaxylon Artabe and Zamuner (2007), Tranquiloxylon Herbst and Lutz (1995) all from the Triassic of Argentina, and Rhexoxylon from the Triassic of Africa and South America have also been assigned to this order. Based on the assignment of the above taxa to the Corystospermales, Axsmith et al. (2007) concluded that anomalous secondary growth is not necessarily basic to the corystosperms. ...
A new genus and two new species of an incertae sedis spermatophyte are erected based on large, petrified and permineralized axes from Middle to Upper Jurassic strata of central Queensland and northeastern New South Wales in Australia and the South Island of New Zealand. Specimens of this genus were previously considered by some to be a form of the Indian taxon, Pentoxylon. The new genus, Donponoxylon, however, differs from Pentoxylon and other spermatophytes in having very small, round (in cross section) sympodial strands characterized primarily by centrifugal secondary xylem development in individual segments. Furthermore, these segments form a complex anastomosing system that branches and coalesces throughout the stem. Donponoxylon consists of two species: Donponoxylon bennettii and Donponoxylon jacksonii. D. bennettii is diagnosed by atypical secondary growth with continuous or discontinuous concentric outer vascular rings, and by a generally irregular arrangement of vascular segments around the pith. D. jacksonii differs from D. bennettii in having the vascular segments regularly arranged around the pith and the absence of the outer vascular rings. In the absence of attached foliage or reproductive structures, the phylogenetic relationships of Donponoxylon remain uncertain beyond its assignment to Spermatopsida. Donponoxylon was an arborescent component of Middle to Late Jurassic high-latitude forests along the southeast coast of East Gondwana where it thrived in moist, volcaniclastic-derived soils.
