Dicroidium Temporal range: | |
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Leaf impression of Dicroidium zuberi | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Order: | † Corystospermales |
Family: | † Corystospermaceae |
Genus: | † Dicroidium Gothan (1912) |
Species | |
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Synonyms | |
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Dicroidium is an extinct genus of fork-leaved seed plants. It is the archetypal genus of the corystosperms, an extinct group of seed plants, often called "seed ferns", assigned to the order Corystospermales or Umkomasiales. Species of Dicroidium were widely distributed and dominant over Gondwana during the Triassic ( 252 to 201 million years ago). Their fossils are known from South Africa, the Arabian Peninsula, Australia, New Zealand, South America, Madagascar, the Indian subcontinent and Antarctica.
Within the form genus classification system used in paleobotany, the genus Dicroidium refers specifically to the leaves. Some authors have suggested dividing Dicroidium up into several genera, including Dicroidiopsis, Diplasiophyllum, Zuberia, Xylopteris, Johnstonia and Tetraptilon, but this is rejected by other authors. [4] The leaves of Dicroidium bifurcate (fork) at their base, which is characteristic of all species. The leaves are highly variable in size and morphology, ranging from simple to tripinnate, with the individual leaflets having varying morphologies, including dissected , lobed, needle-like and entire. [5] Some leaf specimens have more than one type of leaflet morphology, which may have been the result of hybridisation between different species. [4] The venation of the leaves is also highly variable, encompassing taeniopteroid, odontopteroid, alethopteroid and simple morphologies. [5]
Dicroidium plants grew as medium-large sized trees, [5] with some preserved trunk sections 10 metres (33 ft) tall and over 50 centimetres (20 in) wide, [4] with the wood assigned to the genera Kykloxylon and Rhexoxylon. The ovulate reproductive structures are usually assigned to the genus Umkomasia, while the pollen-producing organs are assigned to the genus Pteruchus, with pollen attributable to the genus Falcisporites. These structures are almost never found in organic connection, and their placement as part of the same plant primarily relies on their repeated co-occurrence with each other, and the similarities in the morphology of their cuticles. [6] The leaves grew on short protuberances attached to the stem in a similar way to living Ginkgo biloba . [7] [8] The leaves of Dicroidium are suggested to have been deciduous, and shed along with the reproductive organs during the winter. The seeds and pollen are suggested to have been wind dispersed. [4]
Possible whole plant associations include:
The earliest Dicroidium species are known from the Late Permian aged Umm Irna Formation of Jordan, which inhabited equatorial humid tropical environments, [6] as well as equivalently aged more southerly subtropical deposits on Indian subcontinent. [11] Following the end-Permian mass extinction, Dicroidium expanded its range southwards across Gondwana, including South Africa, Antarctica, Australia, New Zealand, India and South America, [6] with a record also reported from the Middle Triassic of China. [12] Later Triassic Dicroidum-bearing plants were dominant large canopy forming trees in temperate wetland and forested habitats at mid-high latitudes, extending to the South Pole. [4] [5] [6] Dicroidium-dominanted ecosystems in Gondwana collapsed during the end-Triassic mass extinction, with Dicroidium surviving in parts of East Antarctica into the Early Jurassic (Sinemurian). [5]
Glossopteris is the largest and best-known genus of the extinct Permian order of seed plants known as Glossopteridales. The name Glossopteris refers only to leaves, within the framework of form genera used in paleobotany.
Bennettitales is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales were amongst the most common seed plants of the Mesozoic, and had morphologies including shrub and cycad-like forms. The foliage of bennettitaleans is superficially nearly indistinguishable from that of cycads, but they are distinguished from cycads by their more complex flower-like reproductive organs, at least some of which were likely pollinated by insects.
The Caytoniales are an extinct order of seed plants known from fossils collected throughout the Mesozoic Era, around 252 to 66 million years ago. They are regarded as seed ferns because they are seed-bearing plants with fern-like leaves. Although at one time considered angiosperms because of their berry-like cupules, that hypothesis was later disproven. Nevertheless, some authorities consider them likely ancestors or close relatives of angiosperms. The origin of angiosperms remains unclear, and they cannot be linked with any known seed plants groups with certainty.
Sagenopteris is a genus of extinct seed ferns from the Triassic to late Early Cretaceous.
The Callistophytaceae was a family of seed ferns (pteridosperms) from the Carboniferous and Permian periods. They first appeared in late Middle Pennsylvanian (Moscovian) times, 306.5–311.7 million years ago (Ma) in the tropical coal forests of Euramerica, and became an important component of Late Pennsylvanian vegetation of clastic soils and some peat soils. The best known callistophyte was documented from Late Pennsylvanian coal ball petrifactions in North America.
Lepidopteris is a form genus for leaves of Peltaspermaceae, an extinct family of seed plants, which lived from around 260 to 190 million years ago, from the Late Permian to Early Jurassic. Fossils of the genus have been found across both hemispheres. Nine species are currently recognized.Lepidopteris was a common and widespread seed fern, which survived the Permian-Triassic extinction event but was largely wiped out by the Triassic-Jurassic extinction event. Lepidopteris callipteroides is especially common between the first two episodes of the Permian-Triassic extinction event, and L. ottonis forms a comparable acme zone immediately before the Triassic-Jurassic extinction event. Lepidopteris would persist into the Early Jurassic in Patagonia, represented by the species Lepidopteris scassoi.
The Peltaspermales are an extinct order of seed plants, often considered "seed ferns". They span from the Late Carboniferous to the Early Jurassic or the Jurassic-Cretaceous Boundary. It includes at least one valid family, Peltaspermaceae, which spans from the Permian to Early Jurassic, which is typified by a group of plants with Lepidopteris leaves, Antevsia pollen-organs, and Peltaspermum ovulate organs, though the family now also includes other genera like Peltaspermopsis, Meyenopteris and Scytophyllum. Along with these, two informal groups of uncertain taxonomic affinities exist, each centered around a specific genus ; Supaia and Comia, known from the Early Permian of the Northern Hemisphere, especially of North America. Both the "Comioids" and the "Supaioids" are associated with the peltaspermacean ovulate organ Autunia. The Late Triassic-Middle Jurassic genus Pachydermophyllum may also have affinities to the peltasperms.
Umkomasia is a genus of seed bearing organs produced by corystosperm seed ferns, first based on fossils collected by Hamshaw Thomas from the Burnera Waterfall locality near the Umkomaas River of South Africa. He recognized on the basis of cuticular similarities that the same plant produced pollen organs Pteruchus and the leaves Dicroidium. Various other corystosperm seed bearing organs from the Jurassic and Cretaceous have been assigned to this genus, but recently have been given distinct genera, with Umkomasia being restricted to the Triassic.
Dicroidium odontopteroides was a common and widespread species of Dicroidium known from South Africa, Australia, New Zealand, South America and Antarctica. The species was first discovered in Triassic sediments of Tasmania and described by the palaeontologist John Morris in 1845.
Umkomasia macleanii is an ovulate structure of a seed fern (Pteridospermatophyta and the nominate genus of Family Umkomasiaceae. It was first described by Hamshaw Thomas from the Umkomaas locality of South Africa.
Pteruchus africanus is a pollen organ of a seed fern (Pteridospermatophyta). It was first described by Hamshaw Thomas from the Umkomaas locality of South Africa.
Umkomasia feistmantelii is an unusually large species of Umkomasia from the Early Triassic of New South Wales, Australia.
Pteruchus barrealensis is an unusually large species of Pteruchus with very elongate polleniferous heads from Early Triassic of Australia and Argentina.
Pteruchus is a form genus for pollen organs of the seed fern (Pteridospermatophyta family Umkomasiaceae. It was first described by Hamshaw Thomas from the Umkomaas locality of South Africa. It is associated with the seed bearing organs Umkomasia and Dicroidium leaves.
Corystosperms are a group of extinct seed plants belonging to the family Corystospermaceae assigned to the order Corystospermales or Umkomasiales. They were first described based on fossils collected by Hamshaw Thomas from the Burnera Waterfall locality near the Umkomaas River of South Africa. Corystosperms are typified by a group of plants that bore forked Dicroidium leaves, Umkomasia cupulate ovulate structures and Pteruchus pollen organs, which grew as trees that were widespread over Gondwana during the Middle and Late Triassic. Other fossil Mesozoic seed plants with similar leaf and/or reproductive structures have also sometimes been included within the "corystosperm" concept sensu lato, such as the "doyleoids" from the Early Cretaceous of North America and Asia. A potential corystosperm sensu lato, the leaf genus Komlopteris, is known from the Eocene of Tasmania, around 53-50 million years old, over 10 million years after the Cretaceous–Paleogene extinction event.
Lepidopteris callipteroides is a form species for leaves of Late Permian Pteridospermatophyta, or seed ferns, which lived from around 252 million years ago in what is now Australia, and Madagascar. Lepidopteris callipteroides was an immediate survivor of the largest Permian-Triassic extinction event, migrating southward with the post-apocalyptic greenhouse spike.
This article records new taxa of plants that are scheduled to be described during the year 2018, as well as other significant discoveries and events related to paleobotany that occurred in the year 2018.
The Umm Irna Formation is a geological formation in Jordan. It is found in several outcrops in Jordan in the area around the eastern shore of the Dead Sea. It is Late Permian in age, and is the oldest unit in the succession, overlying the Cambrian aged Umm Ishrin Sandstone Formation. The formation predominantly consists of sandstones, claystones and mudstones deposited in fluvial and lacustrine conditions. The formation is of considerable paleobotanical interest, as it preserves the earliest known remains of plant groups that would become widespread during the Mesozoic, including corystosperm "seed ferns", represented by the widespread Triassic genus Dicroidium, cycads, conifers, as well as Bennettitales. Other plant groups present in the formation include Noeggerathiales, gigantopterids, lyginopterids and possible ginkgophytes.
Komlopteris is an extinct genus of "seed fern" with possible corystosperm affinities. Fossils have been found across both hemispheres, dating from the latest Triassic to the early Eocene (Ypresian), making it the youngest "seed fern" in the fossil record.
This paleobotany list records new fossil plant taxa that were to be described during the year 2024, as well as notes other significant paleobotany discoveries and events which occurred during 2024.