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 (i.e. they existed around 252 to 66 million years ago), although some Bennettitales appear to have survived into Oligocene times in Tasmania and eastern Australia. The taxon comprises two groups, the Cycadeoidaceae, represented by Cycadeoidea and Monanthesia, and the Williamsoniaceae including Williamsonia, Williamsoniella, Wielandella and Ischnophyton which had slender, branching trunks and either bisporangiate or monosporangiate strobili.
|A Cycadeoid, showing an "inflorescence" in the top-right|
Originally, Bennettitales were thought to be cycads for their strap-like leaves, however their flower-like reproductive parts separate the two groups. The respective groups within Bennettitales (Cycadeoidaceae and Williamsoniaceae) each have their own unique traits. Cycadeoidaceae had stout trunks and bisporangiate strobili(cones serving as their reproductive structures) and Williamsoniaceae can have either bisporangiate or monosporangiate cones, and distinctly slender and branching wood-like trunks. These bisporangiate cones consist of layers of protective bracts, a curved microsporophyll, and an ovulate receptacle. The bisporangiate cones remained closed at maturation, and most likely were obligate self-fertilizers.
In general, Bennettitales have leaves attached adaxially (toward the stem) with a distinct midrib. Veins stem from the midrib at an approximately 90 degree angle. They have tough cuticles as well, as they were able to withstand high sulfur dioxide levels in the Triassic/Jurassic period for a sizeable amount of time. Some were characterized by thick trunks and pinnately compound leaves that bore a superficial resemblance to those of cycads, differing primarily in stomatal arrangement.
Bennetittales were first identified by Engler in 1892 as separate from Cycadales, and then further were differentiated into the two groups Cycadeoidaceae and Williamsoniaceae by Caruthers. The first major hypothesis developed was the Euanthial hypothesis established by Arber and Parking in 1907. This hypothesis posited that angiosperms arose from Bennettitales, as evidenced by the wood-like structures and rudimentary flowers. This theory placed them among the anthophytes, leading it to be known more commonly as the Anthophyte hypothesis. Based on morphological data, however, Bennettitales were classified as a monophyletic group when paired with Gnetales. Genetic data showed that modern extant seed-plants form their own monophyletic group, excluding Bennettitales. Modern theory suggests that Bennettitales, Angiosperms, and Gigantopteridales form a clade based on the presence of oleanane. Recent evidence from examining phase-contrast X-rays of gymnosperm seeds suggested that the Euanthial hypothesis is supported. This is still a hotly debated topic. Mostly, it is understood that by morphological data, Euanthial hypothesis is supported but modern cladistic tests suggest otherwise. Uncovering information about this extinct group is still far from finished, as new species are being discovered such as Nilssoniopteris binggouensis in 2014 and Anomozamites sanjiaocunensis in 2015.
Bennettitales are also linked to the diversification of insects due to their flower-like reproductive parts. Specifically, the origin of insect mouth parts is connected to Bennettitales and Gnetales.
The anthophytes were thought to be a clade comprising plants bearing flower-like structures. The group contained the angiosperms - the extant flowering plants, such as roses and grasses - as well as the Gnetales and the extinct Bennettitales.Detailed morphological and molecular studies have shown that the group is not actually monophyletic, with proposed floral homologies of the gnetophytes and the angiosperms having evolved in parallel. This makes it easier to reconcile molecular clock data that suggests that the angiosperms diverged from the gymnosperms around 300 million years ago.Some more recent studies have used the word anthophyte to describe a group which includes the angiosperms and a variety of fossils (glossopterids, Pentoxylon, Bennettitales, and Caytonia), but not the Gnetales.Archocyrtus
Archocyrtus is an extinct genus of small-headed flies in the family Acroceridae. The genus is known from compression fossils from the Late Jurassic of Kazakhstan.A study on the holotype specimen of Archocyrtus kovalevi was published by Khramov & Lukashevich (2019). They reported evidence of an extremely long proboscis, almost twice the length of the body of the insect. They suggested that it was probably a pollinator of extinct seed plants belonging to the order Bennettitales.Cretaceous
The Cretaceous ( , kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.Cycad
Cycads are seed plants with a long fossil history that were formerly more abundant and more diverse than they are today. They typically have a stout and woody (ligneous) trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female (dioecious). Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly and live very long, with some specimens known to be as much as 1,000 years old. Because of their superficial resemblance, they are sometimes mistaken for palms or ferns, but they are not closely related to either group.
Cycads are gymnosperms (naked seeded), meaning their unfertilized seeds are open to the air to be directly fertilized by pollination, as contrasted with angiosperms, which have enclosed seeds with more complex fertilization arrangements. Cycads have very specialized pollinators, usually a specific species of beetle. They have been reported to fix nitrogen in association with various cyanobacteria living in the roots (the "coralloid" roots). These photosynthetic bacteria produce a neurotoxin called BMAA that is found in the seeds of cycads. This neurotoxin may enter a human food chain as the cycad seeds may be eaten directly as a source of flour by humans or by wild or feral animals such as bats, and humans may eat these animals. It is hypothesized that this is a source of some neurological diseases in humans.Cycadeoidaceae
Cycadeoidaceae is a family of bennettitalean plants which flourished in the Mesozoic era. Two genera, Cycadeoidea and Monanthesia, are currently recognised though most species are poorly known.Cycadeoidea
Cycadeoidea is an extinct genus of bennettitalean plants known from fossil finds in North America and Europe. They lived during the Jurassic and Cretaceous periods.Gigantopterid
Gigantopterids (Gigantopteridales) is the name given to fossils of a group of plants existing in the Permian period, some 299 to 252 million years ago. Gigantopterids were among the most advanced land plants of the Paleozoic Era and disappeared soon after the massive Permian–Triassic extinction event 251.4 million years ago. Though some lineages of these plants managed to persist initially, they either disappeared entirely or adapted radically, evolving into undetermined descendants, as surviving life prospered again in much-altered ecosystems. One hypothesis proposes that at least some "gigantopterids" became the ancestors of angiosperms and/or Bennettitales and/or Caytoniales.Gigantopterid fossils were documented as early as 1883, but only investigated more thoroughly in the early 20th century. Some of their most significant evidence was initially found in Texas, but they might have been present worldwide. Another key region for gigantopterid fossils is in China, and the consolidation of all major continents into Pangea would have allowed for easy global dispersal. They were among the most striking and important plants of the Cathaysian flora of Sino-Malaya, also called Gigantopteris flora to reflect this.Glossophyte
The glossophytes are a clade of seed plants comprising the glossopterids and their descendants. This includes the Gnetales and angiosperms, as well as Bennettitales.Their monophyly is rather well supported by molecular methods, although their internal relationships are somewhat more shaky.The clade had diverged by the Permian, when glossopterids appear in the fossil record.Gnetophyta
Gnetophyta is a division of plants, grouped within the gymnosperms (which also includes conifers, cycads, and ginkgos), that consists of some 70 species across the three relict genera: Gnetum (family Gnetaceae), Welwitschia (family Welwitschiaceae), and Ephedra (family Ephedraceae). Fossilized pollen attributed to a close relative of Ephedra has been dated as far back as the Early Cretaceous. Though diverse and dominant in the Paleogene and the Neogene, only three families, each containing a single genus, are still alive today. The primary difference between gnetophytes and other gymnosperms is the presence of vessel elements, a system of conduits 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.
Though it is clear they are all closely related, the exact evolutionary inter-relationships between gnetophytes are unclear. Some classifications hold that all three genera should be placed in a single order (Gnetales), while other classifications say they should be distributed among three separate orders, each containing a single family and genus. Most morphological and molecular studies confirm that the genera Gnetum and Welwitschia diverged from each other more recently than they did from Ephedra.Gymnosperm
The gymnosperms, also known as Acrogymnospermae, are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes. The term "gymnosperm" comes from the composite word in Greek: γυμνόσπερμος (γυμνός, gymnos, 'naked' and σπέρμα, sperma, 'seed'), literally meaning "naked seeds". The name is based on the unenclosed condition of their seeds (called ovules in their unfertilized state). 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 solitary as in yew, Torreya, Ginkgo.The gymnosperms and angiosperms together compose the spermatophytes or seed plants. The gymnosperms are divided into six phyla. Organisms that belong to the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta) phyla are still in existence while those in the Pteridospermales and Cordaitales phyla are now extinct.By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species).
Roots in some genera have fungal association with roots in the form of mycorrhiza (Pinus), while in some others (Cycas) small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.Jurassic
The Jurassic period (; from Jura Mountains) is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, and the Tithonian event at the end; neither event ranks among the "Big Five" mass extinctions, however.
The Jurassic period is divided into three epochs: Early, Middle, and Late. Similarly, in stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, and Upper Jurassic series of rock formations.
The Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified.
By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north, and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, and many of the arid deserts of the Triassic were replaced by lush rainforests.
On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates.Monanthesia
Monanthesia is an extinct genus of bennettitalean plant that is known from fossil finds in Europe and North America, which existed during the Early Cretaceous period.Nilssonia (plant)
Nilssonia is an extinct genus of plants, called "cycadeoids," belonging to Bennettitales, which were similar to cycads in growth form and leaf morphology, but completely different in reproductive structures. Fossils of the cycadeoid Nilssonia are found in Triassic, Jurassic and Cretaceous-aged terrestrial strata of East Asia, Australia, North and South America, and Europe.Tiaojishan Formation
The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period (Bathonian-Oxfordian stages). It is known for its fossil plants, and is made up mainly of pyroclastic rock interspersed with basic volcanic and sedimentary rocks. Previously, the Tiaojishan Formation was grouped together with the underlying Haifanggou Formation (also known as the Jiulongshan Formation) as a single "Lanqui Formation."
Most researchers now agree that the Daohugou Bed, of formerly controversial dating, is a part of the Tiaojishan formation.Timeline of plant evolution
This article attempts to place key plant innovations in a geological context. It concerns itself only with novel adaptations and events that had a major ecological significance, not those that are of solely anthropological interest. The timeline displays a graphical representation of the adaptations; the text attempts to explain the nature and robustness of the evidence.
Plant evolution is an aspect of the study of biological evolution, predominantly involving evolution of plants suited to live on land, greening of various land masses by the filling of their niches with land plants, and diversification of groups of land plants.Williamsonia (plant)
Williamsonia is an extinct genus of plant belonging to Bennettitales, an order of seed plants which bore a resemblance to cycads. Fossilized specimens of Williamsonia have been discovered worldwide.Williamsoniaceae
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.Yongjiacaris
Yongjiacaris zhejiangensis is an extinct species of shrimp, and the only species in the genus Yongjiacaris. Yongjiacaris represents the second report of freshwater caridean shrimp from the Mesozoic.The name of the genus Yongjiacaris refers to Yongjia County, in the Zhejiang Province of China, while the species name Y. zhejiangensis is derived from the province name. Yonjiacaris was formally described by Alessandro Garassino, Shen Yanbin, Frederick R. Schram, and Rod S. Taylor in 2002. It is described from 138 specimens discovered in the C Member of the Moshishan Formation of Yongjia County, and from specimens found in the Showchang Formation near Jiande, both in southeastern China. These two correlative rock units date to the Barremian age of the Early Cretaceous; volcanic rocks in the C Member of the Moshishan Formation are dated to 120 million years old, and volcanic rocks in the Showchang Formation are dated to 118 million years ago. The C Member of the Moshishan Formation is a heterogeneous rock unit including sandstone, shale, tuff, conglomerate, and rhyolite, while the Showchang Formation is dominantly sandstone and mudstone. The types of plants present in the C Member and the Showchang Formation (relatively abundant ferns and Bennettitales, rare members of the Ginkgoaceae) and characteristics of the plants, such as leaf form and cuticle thickness, indicate a relatively hot and dry climate. The two rock units have fossil assemblages including plants, charophytes, bivalves, ostracods, conchostracans, and insects.While other genera from the family Palaemonidae are known from the Aptian age in the lower Cretaceous period, Yongjiacaris represents the first member described from the Barremian age. It measured from 1.5 to 2 centimetres (0.6 to 0.8 in) in length.Zamites
Zamites is a genus of fossil tree known from the Mesozoic of North America, Europe and India through the Eocene of North America. It is a form taxon for leaves that resemble the extant cycad Zamia. The fronds are linear or lanceolate in shape, and pinnately compound, with pinnae with parallel veins and smooth margins, and symmetrical and constricted at the base where they are attached obliquely to the upper surface of the rachis. It has been interpreted as a cycad in the family Cycadaceae or a Bennettitalean plant.