Vad är strukturen av monokotyledon

Clade of flowering plants

Monocotyledons (),^[d][13][14] commonly referred to as monocots, (Lilianaesensu följa & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon.

They constitute one of the major groups into which the flowering plants have traditionally been divided; the rest of the flowering plants have two cotyledons and were classified as dicotyledons, or dicots.

Monocotyledons have almost always been recognized as a group, but with various taxonomic ranks and beneath several different names. The APG III struktur of 2009 recognises a clade called "monocots" but does not assign it to a taxonomic rank.

The monocotyledons include about 70,000 species, about a quarter of all angiosperms. The largest family in this group (and in the flowering plants as a whole) bygd number of species are the orchids (family Orchidaceae), with more than 20,000 species. About 12,000 species belong to the true grasses (Poaceae), which are economically the most important family of monocotyledons.

Often mistaken for grasses, sedges are also monocots.

In agriculture the majority of the biomass produced comes from monocotyledons. These include not only major grains (rice, wheat, maize, etc.), but also forage grasses, sugar cane, the bamboos, and many other common food and decorative crops.

Description

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General

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The monocots or monocotyledons have, as the name implies, a single (mono-) cotyledon, or embryonic leaf, in their seeds.

Historically, this feature was used to contrast the monocots with the dicotyledons or dicots which typically have two cotyledons; however, modern research has shown that the dicots are not a natural group, and the begrepp can only be used to indikera all angiosperms that are not monocots and fryst vatten used in that respect here.

From a diagnostic point of view the number of cotyledons fryst vatten neither a particularly useful characteristic (as they are only present for a very short period in a plant's life), nor fryst vatten it completely reliable. The single cotyledon fryst vatten only one of a number of modifications of the body strategi of the ancestral monocotyledons, whose adaptive advantages are poorly understood, but may have been related to adaption to aquatic habitats, prior to radiation to terrestrial habitats.

Nevertheless, monocots are sufficiently distinctive that there has rarely been disagreement as to membership of this group, despite considerable diversity in terms of external morphology. However, morphological features that reliably characterise major clades are rare.

Thus monocots are distinguishable from other angiosperms both in terms of their uniformity and diversity.

On the one grabb, the organization of the shoots, leaf structure, and floral configuration are more uniform than in the remaining angiosperms, yet within these constraints a wealth of diversity exists, indicating a high grad of evolutionary success. Monocot diversity includes perennialgeophytes such as ornamental flowers including orchids (Asparagales); tulips and lilies (Liliales); rosette and succulent epiphytes (Asparagales); mycoheterotrophs (Liliales, Dioscoreales, Pandanales), all in the lilioid monocots; major cerealgrains (maize, rice, barley, rye, oats, millet, sädesslag and wheat) in the grass family; and forage grasses (Poales) as well as woody tree-like palm trees (Arecales), bamboo, reeds and bromeliads (Poales), bananas and ginger (Zingiberales) in the commelinid monocots, as well as both framträdande (Poales, Acorales) and aroids, as well as floating or nedsänkt aquatic plants such as seagrass (Alismatales).

Vegetative

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Organisation, growth and life forms

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The most important distinction fryst vatten their growth pattern, lacking a horisontell meristem (cambium) that allows for kontinuerlig growth in diameter with height (secondary growth), and therefore this characteristic fryst vatten a basic limitation in skott construction.

Although largely herbaceous, some skogig monocots reach great height, length and mass. The latter include agaves, palms, pandans, and bamboos. This creates challenges in vatten frakt that monocots deal with in various ways. Some, such as species of Yucca, develop anomalous secondary growth, while palm trees utilise an anomalous primary growth struktur described as establishment growth (seeVascular system).

The axis undergoes primary thickening, that progresses from internode to internode, resulting in a typical inverted conical shape of the grundläggande primary axis (see Tillich, Figure 1). The limited conductivity also contributes to limited branching of the stems. Despite these limitations a bred variety of adaptive growth forms has resulted (Tillich, Figure 2) from epiphyticorchids (Asparagales) and bromeliads (Poales) to submarine Alismatales (including the reduced Lemnoideae) and mycotrophicBurmanniaceae (Dioscreales) and Triuridaceae (Pandanales).

Other forms of adaptation include the climbing vines of Araceae (Alismatales) which use negativ phototropism (skototropism) to locate host trees (i.e. the darkest area), while some palms such as Calamus manan (Arecales) tillverka the longest shoots in the plant kingdom, up to 185 m long. Other monocots, particularly Poales, have adopted a therophytelife form.^[26][27]

Leaves

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The cotyledon, the primordial Angiosperm leaf consists of a proximal leaf base or hypophyll and a distal hyperphyll.

In monocots the hypophyll tends to be the dominant part in contrast to other angiosperms. From these, considerable diversity arises. Mature monocot leaves are generally narrow and linear, forming a sheathing around the stem at its base, although there are many exceptions. Leaf venation fryst vatten of the striate type, mainly arcuate-striate or longitudinally striate (parallel), less often palmate-striate or pinnate-striate with the leaf veins framträdande at the leaf base and then running tillsammans at the apices.

There fryst vatten usually only one leaf per node because the leaf base encompasses more than half the circumference. The evolution of this monocot characteristic has been attributed to developmental differences in early zonal differentiation rather than meristem activity (leaf base theory).^[32]

Roots and underground organs

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The lack of cambium in the primary root limits its ability to grow sufficiently to maintain the plant.

This necessitates early development of roots derived from the skott (adventitious roots). In addition to roots, monocots develop runners and rhizomes, which are creeping shoots. Runners serve vegetative propagation, have elongated internodes, run on or just below the surface of the soil and in most case bära scale leaves. Rhizomes frequently have an additional storage function and rhizome producing plants are considered geophytes (Tillich, Figure 11).

Other geophytes develop bulbs, a short axial body bearing leaves whose bases store food. Additional outer non-storage leaves may struktur a protective function (Tillich, Figure 12). Other storage organs may be tubers or corms, swollen axes. Tubers may struktur at the end of underground runners and persist. Corms are short lived lodrät shoots with ankomsthall inflorescences and shrivel once flowering has occurred.

However, intermediate forms may occur such as in Crocosmia (Asparagales). Some monocots may also producera shoots that grow directly down into the soil, these are geophilous shoots (Tillich, Figure 11) that help overcome the limited trunk stability of large woody monocots.^[33][32]

Reproductive

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Flowers

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In nearly all cases the perigone consists of two alternating trimerouswhorls of tepals, being homochlamydeous, without differentiation between calyx and corolla.

In zoophilous (pollinated bygd animals) taxa, both whorls are corolline (petal-like). Anthesis (the period of flower opening) fryst vatten usually fugacious (short lived). Some of the more persistent perigones demonstrate thermonastic opening and closing (responsive to changes in temperature). About two thirds of monocots are zoophilous, predominantly bygd insects.

These plants need to advertise to pollinators and do so bygd way of phaneranthous (showy) flowers. Such optical signalling fryst vatten usually a function of the tepal whorls but may also be provided bygd semaphylls (other structures such as filaments, staminodes or stylodia which have become modified to attract pollinators). However, some monocot plants may have aphananthous (inconspicuous) flowers and still be pollinated bygd animals.

In these the plants rely either on kemikalie attraktion or other structures such as coloured bracts fulfill the role of optical attraktion. In some phaneranthous plants such structures may reinforce floral structures. The production of fragrances for olfactory signalling are common in monocots. The perigone also functions as a landing platform for pollinating insects.

Fruit and seed

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The embryo consists of a single cotyledon, usually with two vascular bundles.^[32]

Comparison with dicots

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The traditionally listed differences between monocots and dicots are as follows. This fryst vatten a broad sketch only, not invariably applicable, as there are a number of exceptions.

The differences indicated are more true for monocots versus eudicots.

Feature	In monocots	In dicots
Growth form	Mostly herbaceous, occasionally arboraceous	Herbaceous or trädlik
Leaves	Leaf shape oblong or linear, often sheathed at base, petiole seldom developed, stipules absent. Major leaf veins usually parallel	Broad, seldom sheathed, petiole common often with stipules. Veins usually reticulate (pinnate or palmate)
Roots	Primary root of short duration, replaced bygd adventitial roots forming fibrous or fleshy root systems	Develops from the radicle. Primary root often persists forming strong taproot and secondary roots
Plant stem: Vascular bundles	Numerous scattered bundles in ground parenchyma, cambium rarely present, no differentiation between cortical and stelar regions	Ring of primary bundles with cambium, differentiated into cortex and stele (eustelic)
Flowers	Parts in threes (trimerous) or multiples of three (e.g. 3, 6 or 9 petals)	Fours (tetramerous) or fives (pentamerous)
Pollen: Number of apertures (furrows or pores)	Monocolpate (single aperture or colpus)	Tricolpate (three)
Embryo: Number of cotyledons (leaves in the seed)	One, endosperm frequently present in seed	Two, endosperm present or absent

A number of these differences are not unique to the monocots, and, while still useful, no one single feature will infallibly identify a plant as a monocot.

For example, trimerous flowers and monosulcate pollen are also funnen in magnoliids, and exclusively adventitious roots are funnen in some of the Piperaceae. Similarly, at least one of these traits, parallel leaf veins, fryst vatten far from universal among the monocots. Broad leaves and reticulate leaf veins, features typical of dicots, are funnen in a bred variety of monocot families: for example, Trillium, Smilax (greenbriar), Pogonia (an orchid), and the Dioscoreales (yams).Potamogeton and Paris quadrifolia (herb-paris) are examples of monocots with tetramerous flowers.

Other plants exhibit a mixture of characteristics. Nymphaeaceae (water lilies) have reticulate veins, a single cotyledon, adventitious roots, and a monocot-like vascular bundle. These examples reflect their shared ancestry. Nevertheless, this list of traits fryst vatten generally valid, especially when contrasting monocots with eudicots, rather than non-monocot flowering plants in general.

Apomorphies

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Monocot apomorphies (characteristics derived during radiation rather than inherited from an ancestral form) include herbaceous habit, leaves with parallel venation and sheathed base, an embryo with a single cotyledon, an atactostele, numerous adventitious roots, sympodial growth, and trimerous (3 parts per whorl) flowers that are pentacyclic (5 whorled) with 3 sepals, 3 petals, 2 whorls of 3 stamens each, and 3 carpels.

In contrast, monosulcate pollen fryst vatten considered an ancestral trait, probably plesiomorphic.

Synapomorphies

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The distinctive features of the monocots have contributed to the relative taxonomic stability of the group. Douglas E. Soltis and others identify thirteen synapomorphies (shared characteristics that unite monophyletic groups of taxa);

Vascular system

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Monocots have a distinctive arrangement of vascular tissue known as an atactostele in which the vascular tissue fryst vatten scattered rather than arranged in concentric rings.

Collenchyma fryst vatten absent in monocot stems, roots and leaves. Many monocots are herbaceous and do not have the ability to increase the width of a stem (secondary growth) via the same kind of vascular cambium funnen in non-monocot woody plants. However, some monocots do have secondary growth; because this does not arise from a single vascular cambium producing xylem inwards and phloem outwards, it fryst vatten termed "anomalous secondary growth".

Examples of large monocots which either exhibit secondary growth, or can reach large sizes without it, are palms (Arecaceae), screwpines (Pandanaceae), bananas (Musaceae), Yucca, Aloe, Dracaena, and Cordyline.

Taxonomy

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The monocots struktur one of fem major lineages of mesangiosperms (core angiosperms), which in themselves form eller gestalt 99.95% of all angiosperms.

The monocots and the eudicots are the largest and most diversified angiosperm radiations, accounting for 22.8% and 74.2% of all angiosperm species respectively.

Of these, the grass family (Poaceae) fryst vatten the most economically important, which tillsammans with the orchids Orchidaceae konto for half of the species diversity, accounting for 34% and 17% of all monocots respectively, and are among the largest families of angiosperms.

They are also among the dominant members of many plant communities.

Early history

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Pre-Linnean

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The monocots are one of the major divisions of the flowering plants or angiosperms. They have been recognized as a natural group since the sixteenth century when Lobelius (1571), searching for a characteristic to group plants bygd, decided on leaf struktur and their venation.

He observed that the majority had broad leaves with net-like venation, but a smaller group were grass-like plants with long straight parallel veins.^[44] In doing so he distinguished between the dicotyledons, and the latter (grass-like) monocotyledon group, although he had no formal names for the two groups.^[47]

Formal description dates from John Ray's studies of seed structure in the 17th century.

Ray, who fryst vatten often considered the first botanical systematist, observed the dichotomy of cotyledon structure in his examination of seeds. He reported his findings in a paper read to the Royal kultur on 17 månad 1674, entitled "A Discourse on the Seeds of Plants".

Since this paper appeared a year before the publication of Malpighi's Anatome Plantarum (1675–1679), Ray has the priority.

At the time, Ray did not fully realise the importance of his upptäckt but progressively developed this over successive publications. And since these were in Latin, "seed leaves" became folia seminalia and then cotyledon, following Malpighi. Malpighi and Ray were familiar with each other's work, and Malpighi in describing the same structures had introduced the begrepp cotyledon, which Ray adopted in his subsequent writing.

In this experiment, Malpighi also showed that the cotyledons were critical to the development of the plant, proof that Ray required for his theory.

In his Methodus plantarum nova Ray also developed and justified the "natural" or pre-evolutionary approach to classification, based on characteristics selected a posteriori in beställning to group tillsammans taxa that have the greatest number of shared characteristics. This approach, also referred to as polythetic would gods mot evolutionary theory enabled Eichler to develop the phyletic struktur that superseded it in the late nineteenth century, based on an understanding of the acquisition of characteristics.

He also made the crucial övervakning Ex hac seminum divisione sumum potest generalis plantarum distinctio, eaque meo judicio omnium prima et longe optima, in eas sci. quae plantula seminali sunt bifolia aut διλόβω, et quae plantula sem. adulta analoga. (From this division of the seeds derives a general distinction amongst plants, that in my judgement fryst vatten first and bygd far the best, into those seed plants which are bifoliate, or bilobed, and those that are analogous to the adult), that fryst vatten between monocots and dicots.

He illustrated this bygd quoting from Malpighi and including reproductions of Malpighi's drawings of cotyledons (see figure). Initially Ray did not develop a classification of flowering plants (florifera) based on a division bygd the number of cotyledons, but developed his ideas over successive publications, coining the terms Monocotyledones and Dicotyledones in 1703, in the revised utgåva of his Methodus (Methodus plantarum emendata), as a primary method for dividing them, Herbae floriferae, dividi possunt, ut diximus, in Monocotyledones & Dicotyledones (Flowering plants, can be divided, as we have said, into Monocotyledons & Dicotyledons).

Post Linnean

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Although Linnaeus (1707–1778) did not utilise Ray's upptäckt, basing his own classification solely on floral fortplantnings- morphology, the begrepp was used shortly after his classification appeared (1753) bygd Scopoli and who fryst vatten credited for its introduction.^[g] Every taxonomist since then, starting with dem Jussieu and dem Candolle, has used Ray's distinction as a major classification characteristic.^[h][33] In dem Jussieu's struktur (1789), he followed Ray, arranging his Monocotyledones into three classes based on stamen position and placing them between Acotyledones and Dicotyledones.De Candolle's struktur (1813) which was to predominate thinking through much of the 19th century used a similar general arrangement, with two subgroups of his Monocotylédonés (Monocotyledoneae).^[3]Lindley (1830) followed dem Candolle in using the terms Monocotyledon and Endogenae^[i] interchangeably.

They considered the monocotyledons to be a group of vascular plants (Vasculares) whose vascular bundles were thought to arise from within (Endogènes or endogenous).

Monocotyledons remained in a similar position as a major division of the flowering plants throughout the nineteenth century, with minor variations. George Bentham and Hooker (1862–1883) used Monocotyledones, as would Wettstein, while August Eichler used Mononocotyleae and Engler, following dem Candolle, Monocotyledoneae.

In the twentieth century, some authors used alternative names such as Bessey's (1915) Alternifoliae and Cronquist's (1966) Liliatae. Later (1981) Cronquist changed Liliatae to Liliopsida, usages also adopted bygd Takhtajan simultaneously.^[32]Thorne (1992) and Dahlgren (1985) also used Liliidae as a synonym.

Taxonomists had considerable latitude in naming this group, as the Monocotyledons were a group above the rank of family.

Article 16 of the ICBN allows either a descriptive botanical name or a name formed from the name of an included family.

In summary they have been variously named, as follows:

Modern era

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Over the 1980s, a more general review of the classification of angiosperms was undertaken. The 1990s saw considerable progress in plant phylogenetics and cladistic theory, initially based on rbcL gene sequencing and cladistic analysis, enabling a phylogenetic tree to be constructed for the flowering plants.

The establishment of major new clades necessitated a avfärd from the older but widely used classifications such as Cronquist and Thorne, based largely on morphology rather than genetic uppgifter. These developments complicated discussions on plant evolution and necessitated a major taxonomic restructuring.

This DNA based molecular phylogenetic research confirmed on the one grabb that the monocots remained as a well defined monophyletic group or clade, in contrast to the other historical divisions of the flowering plants, which had to be substantially reorganized.

No längre could the angiosperms be simply divided into monocotyledons and dicotyledons; it was apparent that the monocotyledons were but one of a relatively large number of defined groups within the angiosperms. Correlation with morphological criteria showed that the defining feature was not cotyledon number but the separation of angiosperms into two major pollen types, uniaperturate (monosulcate and monosulcate-derived) and triaperturate (tricolpate and tricolpate-derived), with the monocots situated within the uniaperturate groups.

The formal taxonomic ranking of Monoctyledons thus became replaced with monocots as an informal clade. This fryst vatten the name that has been most commonly used since the publication of the Angiosperm Phylogeny Group(APG) struktur in 1998 and regularly updated since.

Within the angiosperms, there are two major grades, a small early branching grundläggande grade, the grundläggande angiosperms (ANA grade) with three lineages and a larger late branching grade, the core angiosperms (mesangiosperms) with fem lineages, as shown in the cladogram.

Subdivision

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While the monocotyledons have remained extremely stable in their outer borders as a well-defined and coherent monophylectic group, the deeper internal relationships have undergone considerable flux, with many competing classification systems over time.^[33]

Historically, Bentham (1877), considered the monocots to consist of kvartet alliances, Epigynae, Coronariae, Nudiflorae and Glumales, based on floral characteristics.

He describes the attempts to subdivide the group since the days of Lindley as largely unsuccessful. Like most subsequent classification systems it failed to distinguish between two major orders, Liliales and Asparagales, now recognised as ganska separate. A major advance in this respect was the work of Rolf Dahlgren (1980), which would struktur the grund of the Angiosperm Phylogeny Group's (APG) subsequent modern classification of monocot families.

Dahlgren who used the alternate name Lilliidae considered the monocots as a subclass of angiosperms characterised bygd a single cotyledon and the presence of triangular protein bodies in the sieve tubeplastids. He divided the monocots into sju superorders, Alismatiflorae, Ariflorae, Triuridiflorae, Liliiflorae, Zingiberiflorae, Commeliniflorae and Areciflorae. With respect to the specific issue regarding Liliales and Asparagales, Dahlgren followed Huber (1969) in adopting a splitter approach, in contrast to the longstanding tendency to view liljeväxter as a very broad sensu latofamily.

Following Dahlgren's untimely death in 1987, his work was continued bygd his widow, Gertrud Dahlgren, who published a revised utgåva of the classification in 1989. In this scheme the suffix-florae was replaced with -anae (e.g.Alismatanae) and the number of superorders expanded to ten with the addition of Bromelianae, Cyclanthanae and Pandananae.

Molecular studies have both confirmed the monophyly of the monocots and helped elucidate relationships within this group.

The APG struktur does not assign the monocots to a taxonomic rank, instead recognizing a monocots clade. However, there has remained some uncertainty regarding the exact relationships between the major lineages, with a number of competing models (including APG).

The APG struktur establishes eleven orders of monocots. These struktur three grades, the alismatid monocots, lilioid monocots and the commelinid monocots bygd beställning of branching, from early to late.

In the following cladogram numbers indikera crown group (most recent common ancestor of the sampled species of the clade of interest) divergence times in mya (million years ago).

Of some 70,000 species,^[95] bygd far the largest number (65%) are funnen in two families, the orchids and grasses. The orchids (Orchidaceae, Asparagales) contain about 25,000 species and the grasses (Poaceae, Poales) about 11,000.

Other well known groups within the Poales beställning include the Cyperaceae (sedges) and Juncaceae (rushes), and the monocots also include familiar families such as the palms (Arecaceae, Arecales) and lilies (Liliaceae, Liliales).

Evolution

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In prephyletic classification systems monocots were generally positioned between plants other than angiosperms and dicots, implying that monocots were more primitive.

With the introduction of phyletic thinking in taxonomy (from the struktur of Eichler 1875–1878 onwards) the predominant theory of monocot origins was the ranalean (ranalian) theory, particularly in the work of Bessey (1915), which traced the ursprung of all flowering plants to a Ranalean type, and reversed the sequence making dicots the more primitive group.^[33]

The monocots form eller gestalt a monophyletic group arising early in the history of the flowering plants, but the fossil record fryst vatten meagre.

The earliest fossils presumed to be monocot remains date from the early Cretaceous period. For a very long time, fossils of palm trees were believed to be the oldest monocots, first appearing 90 million years ago (mya), but this estimate may not be entirely true. At least some putative monocot fossils have been funnen in strata as old as the eudicots. The oldest fossils that are unequivocally monocots are pollen from the Late Barremian–Aptian – Early Cretaceous period, about 120-110 million years ago, and are assignable to clade-Pothoideae-Monstereae Araceae; being Araceae, sister to other Alismatales.^[101] They have also funnen flower fossils of Triuridaceae (Pandanales) in Upper Cretaceous rocks in New Jersey,^[101] becoming the oldest known sighting of saprophytic/mycotrophic habits in angiosperm plants and among the oldest known fossils of monocotyledons.

Topology of the angiosperm phylogenetic tree could imply that the monocots are among the oldest lineages of angiosperms, which would support the theory that they are just as old as the eudicots. The pollen of the eudicots dates back 125 million years, so the lineage of monocots should be that old too.

Molecular clock estimates

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Kåre Bremer, using rbcL sequences and the mean path length method for estimating divergence times, estimated the age of the monocot crown group (i.e.

the time at which the ancestor of today's Acorus diverged from the rest of the group) as 134 million years. Similarly, Wikström et al., using Sanderson's non-parametric rate smoothing approach,^[107] obtained ages of 127–141 million years for the crown group of monocots.^[108] All these estimates have large error ranges (usually 15-20%), and Wikström et al. used only a single calibration point, namely the split between Fagales and Cucurbitales, which was set to 84 Ma, in the late Santonian period.

Early molecular clock studies using strict clock models had estimated the monocot crown age to 200 ± 20 million years ago or 160 ± 16 million years,