Bennettitales

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Bennettitales
Temporal range: Permian - Late Cretaceous,
Kungurian –Maastrichtian
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Possible Oligocene record
Williamsoniaceae Therese Ekblom.webp
Restoration of a member of Williamsoniaceae by Thérèse Ekblom
Williamsonia life restoration - MUSE.jpg
Life restoration of "Williamsonia" sewardiana from the Early Cretaceous of India, which may represent an early member of Cycadeoidaceae
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Spermatophytes
Order:† Bennettitales
Engler, 1892
Families

Bennettitales (also known as cycadeoids) 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. [1]

Contents

Although certainly gymnosperms sensu lato (cone-bearing seed plants), the relationships of bennettitaleans to other seed plants is debated. Their general resemblance to cycads is contradicted by numerous more subtle features of their reproductive systems and leaf structure. Some authors have linked bennettitaleans to angiosperms (flowering plants) and gnetophytes (a rare and unusual group of modern gymnosperms), forming a broader group known as Anthophyta. Molecular data contradicts this, with gnetophytes found to be much more genetically similar to conifers. The exact position of Bennettitales remains uncertain.

Description

Bennettitales foliage assigned to the genus Pterophyllum Pterophyllum longifolium - Swedish Museum of Natural History - Stockholm, Sweden - DSC00682.JPG
Bennettitales foliage assigned to the genus Pterophyllum
Restoration of the willamsoniacean shrub Wielandiella angustifolia showing divaricate branching habit Williamsonia life restoration.png
Restoration of the willamsoniacean shrub Wielandiellaangustifolia showing divaricate branching habit

Bennettitales are divided into two families, Cycadeoidaceae and Williamsoniaceae, which have distinct growth habits. Cycadeoidaceae had stout, cycad-like trunks with bisporangiate (containing both megaspores and microspores) strobili (cones) serving as their reproductive structures. Williamsoniaceae either had bisporangiate or monosporangiate cones, and distinctly slender and branching woody trunks. [1] The Williamsoniaceae grew as woody shrubs with a divaricate branching habit, similar to that of Banksia. [2] It has been suggested that Williamsoniaceae are a paraphyletic (not containing all descendants of a common ancestor) assemblage of all Bennettitales that do not belong to the Cycadeoidaceae. [2]

Foliage

In general, bennettitalean leaves are attached to the stem with a helical (corkscrew) arrangement. Some leaves (most species of Nilssoniopteris , etc.) are narrow, solitary blades with a smooth-edged ("entire") margin. [3] Most leaf morphotypes ( Pterophyllum , Ptilophyllum , Zamites , Otozamites , etc.) are pinnate (feather-shaped), with many small leaf segments attached to a central shaft. Others ( Anomozamites , a few species of Nilssoniopteris) are incompletely pinnate (sawtooth-shaped) and transitional between these two end members. One unusual leaf form, Eoginkgoites , even approaches a palmate appearance similar to early species of Ginkgo . [4]

The foliage of bennettitaleans resembles that of cycads to such an extent that the foliage of the two groups cannot be reliably distinguished based on gross morphology alone. However, fossil foliage which preserves the cuticle can be assigned to either group with confidence. The stomata of bennettitaleans are described as syndetocheilic. This means that the main paired guard cells develop from the same mother cells as the subsidiary cells which surround them. This contrasts with the haplocheilic stomata of cycads and conifers. In haplocheilic stomata, the ring of subsidiary cells are not derived from the same original structures as the guard cells. This fundamental difference is the main way to differentiate bennettitalean and cycad foliage. [5]

Cones and seeds

Diagram of male Williamsoniaceae reproductive structure Weltrichia. Labels: CFR Centrifugal ray; CPR Centripetal ray; MR Median ridge; FS Fibrous strand; PS Pollen sac position (in this case, pollen sac attachment); CC Central cup; RBA Resin (resinous) body or attractant; ST Stalk Weltrichia diagram.png
Diagram of male Williamsoniaceae reproductive structure Weltrichia. Labels: CFR Centrifugal ray; CPR Centripetal ray; MR Median ridge; FS Fibrous strand; PS Pollen sac position (in this case, pollen sac attachment); CC Central cup; RBA Resin (resinous) body or attractant; ST Stalk
Cross section of the female williamsoniaceous seed cone Williamsonia harrisiana Williamsonia harrisiana seed cone cross section.svg
Cross section of the female williamsoniaceous seed cone Williamsonia harrisiana

Like other gymnosperms, bennettitalean reproductive inflorescences come in the form of cones, which produce pollen and ovules (unfertilized seeds). The cones have a thick central receptacle surrounded by simple, helically-arranged fertile and infertile structures. Tissue at the base of the cone forms layers of scale-like or petal-like bracts to protect the radiating inner structures. Some authors refer to bennettitalean cones as “flowers”, though they are not equivalent to true angiosperm flowers. Pollen is often enclosed in paired synangia (pollen sacs). The synangia lie on the adaxial (inner) edge of pollen-bearing leaf-like structures known as microsporophylls. This contrasts with cycads, all of which lack discrete synangia and bear pollen on the abaxial (outer) surface of their microsporophylls. [6]

Many bennettitaleans are bisporangiate, where the pollen and ovules are hosted on the same (bisexual or hermaphrodite) cone. Cavities filled with curved synangia-bearing microsporophylls are encased by thin radiating structures, including thick, infertile interseminal scales and fertile sporophylls with ovules at their tips. The presence of ovules at the tips of sporophylls, rather than the tips of stems, is a major difference between the cones of bennettitaleans and gnetophytes. As the cone is fertilized and matures, the microsporophylls wither away and the ovules transform into seeds. [6]

Most bennettitaleans in the family Williamsoniaceae are instead monosporangiate, with separate pollen and ovule-producing (unisexual) cones on the same plant. The ovule-producing (female) cones ( Williamsonia, etc.) are similar to mature bisporangiate cones, with interseminal scales and ovule-tipped sporophylls enclosed by bracts. Pollen-producing (male) cones ( Weltrichia, etc.), on the other hand, feature an exposed crown of tapering microsporophylls with adaxial rows of synangia. The microsporophylls may host a single linear row of paired synangia, or instead synangia arranged in a pinnate (feather-shaped) pattern. [6]

Seeds are dicotyledonous (possess two embryonic leaves), with a central embryo surrounded by three layers: the thin megagametophyte, the slightly thicker nucellus, and the protective integument. The upper tip of the seed is tapered and opens through a thin and often extended micropyle. A long, narrow micropyle extending out of the seed is superficially similar to the condition in living gnetophytes. Once the seed is fertilized, the micropyle is sealed by a plug-shaped extension of the nucellus. Unlike living gymnosperms, the tip of the nucellus lacks a pollen chamber (receptacle for stored pollen). The integument is dense and thick, with many layers of differentiated cells. This contrasts with the thin, biseriate (two cell-layer) integument of gnetophytes. Bennettitaleans also lack another gnetophyte-like trait: a sheath of fused bracteoles enveloping the seed. Most integument cells are not unusual in size or shape. However, near the micropyle the innermost layer of integument cells become radially-oriented and elongated, partially closing in on the micropyle. The nucellus and integument are unfused above the chalaza (base of the seed), unlike cycads or gnetophytes, where the layers are fused for much of their height. [6]

Cycadeoidaceans have been suggested to have been self-pollinating, with their stems and cones buried underground, [1] [7] although it has alternatively been proposed that they were pollinated by beetles. [8] The flower-like williamsoniacean male reproductive structure Weltrichia is associated with the female reproductive structure Williamsonia, though it is uncertain whether the parent plants were monoecious (male and female reproductive structures being present on the same plant) or dioecious (where each plant has only one gender of reproductive organ). Weltrichia was likely primarily wind-pollinated, with some species possibly pollinated by beetles. [9]

Several groups of Jurassic and Early Cretaceous insects possessed a long proboscis, and it has been suggested that they fed on nectar produced by bennettitalean reproductive structures, such as the bisexual williamsoniacean reproductive structure Williamsoniella, which had a long, narrow central receptacle which was likely otherwise inaccessible. [10] Early Cretaceous bennettitalean pollen has been found directly associated with a proboscis bearing fly belonging to the extinct family Zhangsolvidae, providing evidence that this family acted as pollinators for the group. [11] The interseminal scales of Bennettitales ovulate cones may have become fleshy at maturity, which could have potentially made then attractive to wild animals that served as seed dispersers. [12]

Taxonomy

History of discovery

The Cycadeoideaceae (originally “Cycadeoideae”) were named by English geologist William Buckland in 1828, from fossil trunks found in Jurassic strata on the Isle of Portland, England, which Buckland gave the genus name Cycadeoidea . Buckland provided a description of the family and two species, but failed to give a description of the genus, which has led to Buckland's description of the family being considered invalid by modern taxonomic standards. [13] In publications in 1870, Scottish botanist William Carruthers and English paleobotanist William Crawford Williamson described the first known reproductive organs of the Bennettitales from Jurassic strata of Yorkshire and Jurassic-Cretaceous strata of the Isle of Wight and the Isle of Portland. [14] [15] [16] Caruthers was the first to recognise that Bennettitales had distinct differences from cycads, and established the tribes "Williamsonieae" and "Bennettiteae", [16] with the latter being named after the genus Bennettites named by Caruthers in the same publication, the name being in honour of British botanist John Joseph Bennett. [14] [17] The order Bennettitales was erected by German botanist Adolf Engler in 1892, who recognised the group as separate from the Cycadales. [18]

Relationships to other seed plants

The Anthophyte hypothesis erected by Arber and Parking in 1907 [19] posited that angiosperms arose from Bennettitales, as suggested by the wood-like structures and rudimentary flowers. [1] Based on morphological data, however, Bennettitales were classified as a monophyletic group when paired with Gnetales. [20] a study in 2006 suggested that Bennettitales, Angiosperms, and Gigantopteridales form a clade based on the presence of oleanane. [21] Molecular evidence has consistently contradicted the Anthophyte hypothesis, finding that Angiosperms are the sister group to all living gymnosperms, including Gnetales. [22] Some authors have suggested due to similarities between their seed coats, Bennettitales form a clade with the gymnosperm orders of Gnetales and Erdtmanithecales, dubbed the "BEG group". [23] However, this proposal has been contested by other authors, who contend that these similarities are only superficial and do not indicate a close relationship. [24] A 2017 phylogeny based on molecular signatures of fossilised cuticles found that Bennettitales were more closely related to the Ginkgo+Cycads clade than conifers, and were closely related to Nilssonia and Ptilozamites. [25]

Evolutionary history

The oldest confirmed fossils of bennettitaleans are leaves of Nilssoniopteris shanxiensis, a species from the upper part of the Upper Shihhotse Formation in Shanxi Province, China. [5] This strata is dated to the early Kungurian stage of the early Permian (Cisuralian), around 281 million years ago. [26] Supposed Carboniferous-Permian records of Pterophyllum do not have conclusive bennettitalean affinities or have been reinterpreted as cycad foliage in the form genus Pseudoctenis . [27] True Permian records of benettitalean leaves are rare; outside of the Shihhotse Formation they are only found in the Late Permian (likely Changhsingian)-age Umm Irna Formation in Jordan. [5] This formation is notable for the early occurrence of other Mesozoic-style flora, including the earliest records of corystospermalean foliage ( Dicroidium ). [28] The order Fredlindiales (containing the genus Fredlindia ) from the Late Triassic of Gondwana appears to be closely related to Bennettitales, but differs from it in some aspects of its reproductive organs. [16]

The bennettitalean fossil record reappeared in the Middle Triassic, and williamsoniaceans became globally distributed by the end of the period. [29] [5] The oldest bennettitalean reproductive structures are small Williamsonia "flowers" from the Middle Triassic Esk Formation of Australia. [16] While Williamsoniaceae had a global distribution, Cycadeoidaceae appear to have been primarily confined to the western parts of Laurasia, and are primarily known from the Cretaceous. [16] Bennettitales were widespread and abundant during the Jurassic and Early Cretaceous, however Bennettitales severely declined during the Late Cretaceous, coincident with the rise of flowering plants, being mostly extinct by the end of the period, with the final known remains from the Northern Hemisphere being found in the polar latitude Kakanaut Formation in Chukotka, Russia, dating to the Maastrichtian, assignable to Pterophyllum. [30] A possible late record has been reported from the early Oligocene of eastern Australia and Tasmania, assignable to the genus Ptilophyllum, but no cuticle was preserved, making the referral inconclusive. [31]

Subgroups

Bennettitales is typically considered the sole order in the class BennettitopsidaEngler (1897) or CycadeoideopsidaScott (1923). Most paleobotanists prefer the two families as used here, though some authors, such as Anderson & Anderson (2007), classify the order via a larger number of families. [33] Anderson & Anderson also classified the orders Fredlindiales Anderson & Anderson (2003) [34] and Pentoxylales Pilger & Melchior (1954) within Bennettitopsida. [33]

Related Research Articles

The anthophytes are a paraphyletic grouping of plant taxa bearing flower-like reproductive structures. The group, once thought to be a clade, contained the angiosperms – the extant flowering plants, such as roses and grasses – as well as the Gnetales and the extinct Bennettitales.

<span class="mw-page-title-main">Ginkgoales</span> Order of plants

Ginkgoales are a gymnosperm order containing only one extant species: Ginkgo biloba, the ginkgo tree. It is monotypic, within the class Ginkgoopsida, which itself is monotypic within the division Ginkgophytaghing-KOF-it-ə. The order includes five families, of which only Ginkgoaceae remains extant.

<span class="mw-page-title-main">Cycad</span> Division of naked seeded dioecious plants

Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly and live very long. Because of their superficial resemblance, they are sometimes mistaken for palms or ferns, but they are not closely related to either group.

<span class="mw-page-title-main">Gnetophyta</span> Division of plants containing three genera of gymnosperms

Gnetophyta is a division of plants, grouped within the gymnosperms, that consists of some 70 species across the three relict genera: Gnetum, Welwitschia, and Ephedra. The earliest unambiguous records of the group date to the Jurassic, and they achieved their highest diversity during the Early Cretaceous. The primary difference between gnetophytes and other gymnosperms is the presence of vessel elements, a system of small tubes (xylem) that transport water within the plant, similar to those found in flowering plants. Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have brought this hypothesis into question, with many recent phylogenies finding them to be nested within the conifers.

<span class="mw-page-title-main">Gymnosperm</span> Clade of non-flowering, naked-seeded vascular plants

The gymnosperms are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae. The term gymnosperm comes from the composite word in Greek: γυμνόσπερμος, literally meaning 'naked seeds'. The name is based on the unenclosed condition of their seeds. The non-encased condition of their seeds contrasts with the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or on their own as in yew, Torreya, Ginkgo. Gymnosperm lifecycles involve alternation of generations. They have a dominant diploid sporophyte phase and a reduced haploid gametophyte phase which is dependent on the sporophytic phase. The term "gymnosperm" is often used in paleobotany to refer to all non-angiosperm seed plants. In that case, to specify the modern monophyletic group of gymnosperms, the term Acrogymnospermae is sometimes used.

<span class="mw-page-title-main">Sporophyll</span>

A sporophyll is a leaf that bears sporangia. Both microphylls and megaphylls can be sporophylls. In heterosporous plants, sporophylls bear either megasporangia and thus are called megasporophylls, or microsporangia and are called microsporophylls. The overlap of the prefixes and roots makes these terms a particularly confusing subset of botanical nomenclature.

<span class="mw-page-title-main">Entomophily</span> Form of pollination by insects

Entomophily or insect pollination is a form of pollination whereby pollen of plants, especially but not only of flowering plants, is distributed by insects. Flowers pollinated by insects typically advertise themselves with bright colours, sometimes with conspicuous patterns leading to rewards of pollen and nectar; they may also have an attractive scent which in some cases mimics insect pheromones. Insect pollinators such as bees have adaptations for their role, such as lapping or sucking mouthparts to take in nectar, and in some species also pollen baskets on their hind legs. This required the coevolution of insects and flowering plants in the development of pollination behaviour by the insects and pollination mechanisms by the flowers, benefiting both groups. Both the size and the density of a population are known to affect pollination and subsequent reproductive performance.

<i>Williamsonia</i> (plant) Extinct genus of plant

Williamsonia is a genus of plant belonging to Bennettitales, an extinct order of seed plants. Within the form classification system used in paleobotany, Williamsonia is used to refer to female seed cones, which are associated with plants that also bore the male flower-like reproductive structure Weltrichia.

<i>Dioon</i> Genus of cycads in the family Zamiaceae

Dioon is a genus of cycads in the family Zamiaceae. It is native to Mexico and Central America. Their habitats include tropical forests, pine-oak forest, and dry hillsides, canyons and coastal dunes.

A strobilus is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but some botanists restrict the use of the term cone to the woody seed strobili of conifers. Strobili are characterized by a central axis surrounded by spirally arranged or decussate structures that may be modified leaves or modified stems.

<span class="mw-page-title-main">Cheirolepidiaceae</span> Extinct family of conifers

Cheirolepidiaceae is an extinct family of conifers. They first appeared in the Triassic, and were widespread during most of the Mesozoic era. They are united by the possession of a distinctive pollen type assigned to the form genus Classopollis. The name Frenelopsidaceae or "frenelopsids" has been used for a group of Cheirolepidiaceae with jointed stems, thick internode cuticles, sheathing leaf bases and reduced free leaf tips. The leaf morphology has been noted as being similar to that of halophyte Salicornia. Several members of the family appear to have been adapted for semi-arid and coastal settings, with a high tolerance of saline conditions. Cheirolepidiaceae disappeared from most regions of the world during the Cenomanian-Turonian stages of the Late Cretaceous, but reappeared in South America during the Maastrichtian, the final stage of the Cretaceous, increasing in abundance after the K-Pg extinction and being a prominent part of the regional flora during the Paleocene, before going extinct.

<span class="mw-page-title-main">Caytoniales</span> Extinct order of Gymnosperms

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.

<span class="mw-page-title-main">Medullosales</span> Extinct order of Late Carboniferous seed ferns

The Medullosales is an extinct order of pteridospermous seed plants characterised by large ovules with circular cross-section and a vascularised nucellus, complex pollen-organs, stems and rachides with a dissected stele, and frond-like leaves. Their nearest still-living relatives are the cycads.

<span class="mw-page-title-main">Seed plant</span> Clade of seed plants

A seed plant or spermatophyte, also known as a phanerogam or a phaenogam, is any plant that produces seeds. It is a category of embryophyte that includes most of the familiar land plants, including the flowering plants and the gymnosperms, but not ferns, mosses, or algae.

<span class="mw-page-title-main">Williamsoniaceae</span>

Williamsoniaceae is a family within the Bennettitales, an extinct group of seed plants within the Cycadophyta subdivision. Members of this family are believed to have been around two meters tall and with widely serrate leaves along a central stem. Reproductive organs of the Williamsoniaceae have varied widely in the fossil record but almost all have been found to be borne on stalks emerging from a ring of leaves.

<i>Cycadeoidea</i> Extinct genus of plants

Cycadeoidea is an extinct genus of bennettitalean plants known from the Cretaceous of North America, Europe and Asia. They grew as cycad-like plants with a short trunk topped with a crown of leaves.

Eucommiidites is an angiosperm look-alike pollen type from the Mesozoic Era. When it was first described in Sweden, it was thought to represent pollen from the earliest angiosperms. However, it was subsequently shown, due to morphology, that it could not be angiospermous. Later, Eucommidites pollen was discovered in the pollen chambers of fossil gymnosperm seeds. It was later shown to be the pollen of the extinct gymnosperm order Erdtmanithecales, suggested to have close affinities with Bennettitales and Gnetales.

Pentoxylales is an extinct order of seed plants known from the Jurassic and Early Cretaceous of East Gondwana.

Nilssoniopteris is an extinct form genus of leaves belonging to the Bennettitales. Leaves are slender and often entire-margined (smooth-edged), though some species have dissected leaves with numerous small segments extending down to the rachis of the leaf. Nilssoniopteris-like leaves are distinguished by their syndetocheilic stomata, indicating bennettitalean affinities. Similar "taeniopterid" leaves are placed in the genus Nilssonia if their stomata are instead haplocheilic, or Taeniopteris if the cuticle is not preserved. Leaves of Nilssoniopteris vittata from the Middle Jurassic of England are associated with bisexual Williamsoniella reproductive structures.

<i>Weltrichia</i> Extinct genus of bennettitalean plant

Weltrichia is a genus belonging to the extinct seed plant group Bennettitales. It is a form genus representing flower-like male pollen-producing organs. It is associated with the female ovulate cone Williamsonia.

References

  1. 1 2 3 4 Peñalver, Enrique; Arillo, Antonio; Pérez-de la Fuente, Ricardo; Riccio, Mark L.; Delclòs, Xavier; Barrón, Eduardo; Grimaldi, David A. (2015). "Long-Proboscid Flies as Pollinators of Cretaceous Gymnosperms". Current Biology. 25 (14): 1917–1923. doi: 10.1016/j.cub.2015.05.062 . PMID   26166781. S2CID   13022302.
  2. 1 2 Pott, Christian; McLoughlin, Stephen (2014-06-01). "Divaricate growth habit in Williamsoniaceae (Bennettitales): unravelling the ecology of a key Mesozoic plant group". Palaeobiodiversity and Palaeoenvironments. 94 (2): 307–325. doi:10.1007/s12549-014-0157-9. S2CID   84440045.
  3. ↑ Ray, M.M.; Rothwell, G.W.; Stockey, R.A. (September 2014). "Anatomically Preserved Early Cretaceous Bennettitalean Leaves: Nilssoniopteris corrugata n. sp. from Vancouver Island, Canada". Journal of Paleontology. 88 (5): 1085–93. doi:10.1017/S002233600005767X. S2CID   232349931.
  4. ↑ Pott, Christian; Axsmith, Brian J. (February 2015). "Williamsonia carolinensis sp. nov. and Associated Eoginkgoites Foliage from the Upper Triassic Pekin Formation, North Carolina: Implications for Early Evolution in the Williamsoniaceae (Bennettitales)". International Journal of Plant Sciences. 176 (2): 174–185. doi:10.1086/679471. S2CID   44559347.
  5. 1 2 3 4 Blomenkemper, Patrick; Bäumer, Robert; Backer, Malte; Abu Hamad, Abdalla; Wang, Jun; Kerp, Hans; Bomfleur, Benjamin (2021). "Bennettitalean Leaves From the Permian of Equatorial Pangea—The Early Radiation of an Iconic Mesozoic Gymnosperm Group". Frontiers in Earth Science. 9: 162. Bibcode:2021FrEaS...9..162B. doi: 10.3389/feart.2021.652699 .
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  7. ↑ Osborn, J.M.; Taylor, M.L. (2010). "Pollen and coprolite structure in Cycadeoidea (Bennettitales): implications for understanding pollination and mating systems in Mesozoic cycadeoids". Plants in deep Mesozoic time: morphological innovations, phylogeny, and ecosystems. Bloomington, IN: Indiana University Press. pp. 34–49. ISBN   978-0-253-00199-3.
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  9. ↑ Popa, Mihai Emilian (2019-02-27). "Review of the bennettitalean genus Weltrichia". Journal of Palaeogeography. 8 (1): 12. Bibcode:2019JPalg...8...12P. doi: 10.1186/s42501-019-0023-9 . S2CID   85458053.
  10. ↑ Khramov, Alexander V.; Lukashevich, Elena D. (July 2019). "A Jurassic dipteran pollinator with an extremely long proboscis". Gondwana Research. 71: 210–215. Bibcode:2019GondR..71..210K. doi:10.1016/j.gr.2019.02.004. S2CID   134847380.
  11. ↑ Peñalver E, Arillo A, Pérez-de la Fuente R, Riccio ML, Delclòs X, Barrón E, Grimaldi DA (July 2015). "Long-Proboscid Flies as Pollinators of Cretaceous Gymnosperms". Current Biology. 25 (14): 1917–23. doi: 10.1016/j.cub.2015.05.062 . PMID   26166781.
  12. ↑ Friis, Else Marie; Pedersen, Kaj Raunsgaard; Crane, Peter R., eds. (2011), "Angiosperms in context: extant and fossil seed plants", Early Flowers and Angiosperm Evolution, Cambridge: Cambridge University Press, pp. 101–140, ISBN   978-0-521-59283-3 , retrieved 2023-03-20
  13. ↑ Doweld, Alexander B. (2016-05-03). "The nomenclature of Cycadeoidea (fossil Spermatophyta: Cycadeoideopsida)". Taxon. 65 (2): 372–379. doi:10.12705/652.16.
  14. 1 2 Carruthers, William (May 1870). "XVIII. On Fossil Cycadean Stems from the Secondary Rocks of Britain". Transactions of the Linnean Society of London. 26 (4): 675–708. doi:10.1111/j.1096-3642.1870.tb00201.x.
  15. ↑ Williamson, W. C. (May 1870). "XVII. Contributions towards the History of Zamia Gigas, Lindl. & Hutt.*". Transactions of the Linnean Society of London. 26 (4): 663–674. doi:10.1111/j.1096-3642.1870.tb00200.x.
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