hostmaster.vclean.life/big-thinkin-jodey.php The shaded area represents the percent of species in the flora that were given fossil generic names based on a modern genus to which they were perceived to be similar. His rates of evolution were based on the various modern genera described in the fossil record of North America and currently living in southeastern Asia or South America.
His arguments about the rates of evolution from the fossil record may have some validity when based on fossils from the Miocene about 25 million years and younger. However, many of the fossils from the Paleocene, Eocene, and Oligocene reported as living genera have been subject to revisions Manchester, as shown in Fig. This trend that had dominated angiosperm paleobotany for more than years continued into the early s.
The supposed failure of the fossil record to contribute to understanding the evolution of the early angiosperms was still evident in when Stebbins published Flowering Plants: Evolution Above the Species Level Stebbins, The theories and hypothesis. Representation of the Middle Eocene Clarno Flora from eastern Oregon Manchester, based on several thousands of fruits and seeds collected over 60 years.
The bars represent the percent of the genera identified to angiosperm genera of various degrees of similarity to living genera. However, at the same time, the early s, special attention was being focused on the fine features of the morphology of angiosperm leaf venation and the cuticular anatomy of living and fossil angiosperms Hickey, ; Dilcher, ; Hickey and Wolfe, ; Doyle and Hickey, Most of the early angiosperms from the Cretaceous and early Tertiary were being found to be extinct or only distantly related to living genera Fig.
Grades and clades of relationships were being established upon the basis of careful character analysis Dilcher et al. During this time, it became scientifically acceptable to be unable to identify a fossil to a modern genus. Fossil angiosperms were analyzed on the basis of multiple detailed objective characters, and degrees of relationships could be established based on the extent to which these same combinations of characters were found in living families, sub-families, or genera Jones and Dilcher, Analyses of the fossil angiosperm record were being constructed that included vast amounts of data based on careful anatomical and morphological analysis of the diversity of characters found in living genera and modern families.
Large collections of cleared leaves and cuticular preparations were developed, and whole families were surveyed to establish their range of venation and. Representation of modern vs. This flora is based on leaves. This new paradigm shift opened the door for a new synthesis of the fossil record of angiosperms. New questions about the evolutionary biology of the fossil record of angiosperms could now be addressed based on detailed character-based data of living and fossil angiosperms often organized with the help of cladistic analysis Crane ; Doyle and Donoghue , ; Doyle et al.
At this same time there was renewed interest in exploring the fossil plant record to determine the origin and early evolutionary history of the angiosperms Doyle, ; Doyle and Hickey, ; Dilcher, The techniques of careful analysis and the concerted effort to open up a new fossil record of early angiosperms by the use of small, often charcoalified plant remains Kovach and Dilcher, , or fragments of cuticle sieved from sediment Huang, from newly collected material of the Jurassic to the Upper Cretaceous were very successful.
A whole new area of the study of intermediate-sized fossil plants, often termed mesofossils as opposed to microfossils or megafossils, expanded to occupy the majority of angiosperm research in some laboratories with good success Nixon and Crepet, ; Crepet and Nixon a, b; Gandolfo et al.
It is the success of these new techniques applied to the fossil record of angiosperms that now provides a new database from which to analyze some of the major trends in angiosperm evolution and allows us to ask new questions. The study of angiosperm fossils has undergone rapid and profound changes during the past 30 years as discussed in the introduction to this paper. Although the study of angiosperm fossils is only as reliable as the individual investigator, resources are now available, such as cleared leaf collections and cuticular reference slide collections from vast herbarium holdings.
This allows angiosperm paleobotanists to survey the nature of. It is now understood that some organs may contain more useful characters for determining relationships than others. It is not only acceptable, but desirable, to list the available characters and how these are distributed among several living genera in a family rather than to select only a single living genus that has such characters and on this basis refer the fossil to that living genus. We are moving toward a well-defined and repeatable objective character-based analysis of the angiosperm fossil record.
Much of this analysis is based on the study of the anatomy and morphology of fossil plant organs. However, using the new tools, it became apparent that there were many fossils that could not be related to living taxa even when such careful analyses were applied Fig. There came a time when it was necessary to give names to the various organs of fossil angiosperms that reflected their extinct nature, recognizing them as separate from any living genus Dilcher and Crane, With few exceptions Sun et al. The great strides in developing techniques of investigation for understanding Devonian fossil plants, on the basis of seemingly nondescript structurally-preserved compressed remains Leclercq and Andrews, ; Leclercq and Banks, , and the excellent application of anatomy and morphology to the study of Pennsylvanian age plants i.
The amount of information that can be determined about a fossil leaf, fruit, flower, pollen grain, or wood by using these techniques allows character-based comparisons to be made. These data have become available at the same time that cladistic-based i. Now, with the study of megafossils, mesofossils, and microfossils all yielding new information about the characters of the early angiosperms, there are huge amounts of new data available each year.
In particular, because they had not been studied before, mesofossils are adding a new set of valuable information that is changing our concept of early angiosperm diversity. The Lower Cretaceous sediments from Portugal have yielded different kinds of flowers with 13 associated pollen types Friis et al. Angiosperm diversity as recognized through Cretaceous time.
The solid bars extend from the earliest identified fossils of the clades listed on the right side.
Character variation in angiosperm families . Goldberg, Aaron. National Museum of Natural History (U.S.) [Corporate Author] Dept. of Systematic Biology. Populations of species of four families of Angiosperms were sampled in Colombia in . all variability based on large numbers of characters, a sample size of.
The closed carpel is the one major feature that separates the angiosperms from other vascular seed plants. The closure most often is complete and entirely seals off the unfertilized ovules from the outside environment. Suggestions that this provided protection for the vulnerable ovules from beetles or other herbivores have been proposed as a reason for the closure of the carpel. However, I think that the closure of the carpel may be more directly related to the evolution of the bisexual flower Dilcher, During the evolution of the flower, as the male and female organs of the flower were brought into proximity, the need for protection against self-fertilization was so important that biochemical and mechanical barriers were developed very early in flowering plant ancestors.
The mechanical barrier is the closed carpel and the biochemical barrier is the incompatibility systems that developed to prevent the successful growth of pollen tubes.
Some living angiosperms have loosely closed carpels or lack any firm closure at all. It has been suggested that these have sufficient exudates to fill the carpel opening so that the carpel has a biochemical barrier against self-fertilization Endress, Although the closed carpel is the fundamental strategy for preventing self-pollination, the addition or loss of sepals, petals, and stamens must have been important events ensuring outcrossing. It is reasonable to assume that the development of attractive colored organs and nectaries, the clustering together of female ovule-bearing organs and male pollen-bearing organs, and, finally, the association of the female and male organs together on the same axis were all changes designed to increase the effectiveness of insect pollination.
The closed carpel and biochemical incompatibility are natural early steps that followed or took place at the same time as the evolution of the floral features just mentioned. The closed carpel in a showy flower ensured outcrossing by animal pollinators while increasing pollen exchange with bisexual flowers. The closed carpel serves as a plant's control mechanism to guarantee that outcrossing happens. Any mechanical protection it offered probably always has been of secondary importance and can be easily overcome by insects. Radial symmetry.
The floral organs of all early angiosperms are radially symmetrical, a symmetry exhibited by all of the floral organs and flowers whether they are small or large, unisexual or bisexual. The earliest known angiosperm flowers suggest that individual carpels were borne. Similarly, the early small flowers Friis et al. In small flowers the elongation of many early flowering axes is compressed so that the organs appear radially arranged. This organization is clearly seen in larger flowers such as Archaeanthus Dilcher and Crane, and the Rose Creek flower Basinger and Dilcher, This radial arrangement of organs dominated floral form until late into the Late Cretaceous or the Paleocene and still persists in many flowers today.
Bilateral symmetry. By Paleocene and Eocene time, there are several evidences in the fossil record of bilateral flowers. This evolution probably began during the Upper Cretaceous. The evolution of bilateral flowers is associated with the presence of social insects in the Upper Cretaceous Michener and Grimaldi, a, b and the coevolution of bilateral flowers occurred at different stages in the evolution of several living families. In some angiosperm families, bilateral symmetry may be present in only a part of the family, while in other families the entire family, is characterized by bilateral symmetry.
As discussed below, this must relate to the time at which different groups evolved in relation to these coevolutionary events. Flower size in living angiosperms is quite variable. Only during the past 25 years have numerous new fossil flowers been discovered from the Cretaceous. The record that has been developed demonstrates that both medium- and small-sized flowers are present very early. Certainly, flower size must relate to pollinator size. The variability in size of the early flowers suggests that a variety of pollinators were involved in their pollination biology Grimaldi, In addition to insect pollinators, both wind and water were important in the pollination of early angiosperms.
Because the wind and the water have changed very little since the Cretaceous, there has been little change in the floral anatomy and morphology of these plants. Therefore, they are examples of some of the most ancient lines of living flowering plants. Those angiosperms that have modified their pollination biology to accommodate new or different animal pollinators are plants that probably have undergone the most extensive changes and whose fossil ancestors should be the most different from their modern descendants.
These would include bird and bat pollinated flowers. In flowers that are insect pollinated, the display of the flower is critical. There seem to be clear distinctions between the presentation of the large Archaeanthus flower and the small fossil dichasial Dilcher and Muller, flowers.
The large Archaeanthus flower appears to have been terminal on a moderately large axis similar to the flowers of Liriodendron or Magnolia today. This allows for sturdy support and a colorful display to attract a pollinator. The dichasial flower, in contrast, is small and clustered into an umbel-like arrangement. This allows for a showy display of flowers in different stages of maturity and a broad area of clustered flowers upon which a pollinator can land and move about.
However, small unisexual florets such as those of wind pollinated platanoid-like inflorescences and water pollinated ceratophylloid-like plants have been little affected by animal pollinators. For this reason, they persist today only slightly changed from their forms in the Early Cretaceous.
The earliest flowers now known appear to be gynodioecious.
One axis has only carpels with a clear indication that no other organs subtended them, while an attached axis has both carpels and stamens Sun et al. So, was the first flower unisexual or bisexual? It appears to have had the potential to be both. Some early flowers, such as the platanoids and ceratophylloids, appear to be unisexual and never to have had a bisexual ancestry. Others such as Archaefructus, many of the small flowers from Portugal and the larger flowers from the Dakota Formation, are certainly bisexual.
I suggest that the ancestral lineage of the angiosperms was most likely unisexual, and that with the availability of insect pollinators the efficiency of bisexual flowers won the day. There are three major nodes or events through time that resulted in major radiations of the angiosperms. These nodes include the evolution of showy flowers with a closed carpel, the evolution of bilateral flowers, and the evolution of nuts and fleshy fruits. At each of these events, there is a burst of adaptive radiation within the angiosperms that can be interpreted as an attempt to maximize the event for all of the diversity possible and to use the event for increased reproductive potential.
The evolution of the closed carpel and the evolution of the showy radial flower must have occurred at nearly the same time. This was the first. The success of this involvement of insects in the reproductive biology of plants was not new. Dating back into the Paleozoic, insects most probably were involved in pollination of some of the seed ferns such as Medullosa Dilcher, ; Retallack and Dilcher, During the Mesozoic, several non-angiospermous plants were certainly using animals for pollination as part of their reproductive biology.
These include plants such as the Cycadoidea, Delevoryas, ; Crepet, Williamsonia, Williamsoniella, and, perhaps, some seed ferns such as Caytonia. Insect diversity increased parallel to the increasing diversity of the angiosperms during the Mesozoic Labandeira et al. This node of evolution corresponds to the initial coevolution of animals and flowering plants in gamete transport. These early showy flowers came in many sizes, were displayed on the plant in many different ways, and were uniform in the types of organs they contained and the radial symmetry of these organs.
They must have accommodated many different types of pollinators as evidenced by the variety of their anthers, stigmatic surfaces, nectaries, and the sizes and positions of the floral organs Dilcher et al. It was through the success of this coevolution that the angiosperms became the dominant vegetation during the early Late Cretaceous. Ordinal and family clades began to become identifiable during the later Early Cretaceous and the early Late Cretaceous Crepet and Nixon, a, b; Gandolfo et al. However, at the same time, some of the angiosperms never developed showy flowers and used other means of gamete transport for cross-pollination such as wind early platinoids and water early ceratophylloids.
At the period of fertilization the embryo sac lies in close proximity to the opening of the micropyle, into which the pollen-tube has penetrated, the separating cell-wall becomes absorbed, and the male or sperm -cells are ejected into the embryo sac. Zeng and colleagues Fig. Evolution of syncarpy in angiosperms: theoretical and phylogenetic analyses of the effects of carpel fusion on offspring quantity and quality. The characteristic feature of angiosperms is the flower. Asarum canadense Wild Ginger- The furryness and color of A. Gamopetalae !
The evolution of bilateral flowers happened about 60 million years after the origin of the angiosperms. This node in coevolution never affected the water- or wind-pollinated groups that were already established. The evolution of the bees late in the Late Cretaceous Michener and Grimaldi, a, b was a coevolutionary event with the evolution of bilateral flowers.
This occurred independently in many different clades of flowering plants that were already established by the mid-Late Cretaceous. The potential for flowers to further direct the behavior of insects to benefit their pollination had a profound influence on those clades that evolved during the late Upper Cretaceous and early Tertiary.
Flowers not only presented their sex organs surrounded by sterile floral organs with attractive patterns and colors, exuding attractive fragrances and filled with nectar and pollen for food, but the bilateral flowers could show the animals which way to approach them and how to enter and exit them. This allowed flowers to maximize the potential for precise gamete ex-. Such clades as the Papilionoideae legume subfamily , Polygalaceae, and Orchidaceae, among others, demonstrate this coevolution.
The success of these clades and especially the Orchidaceae, with its vast number of species, demonstrates the potential of this coevolutionary event. The evolution of large stony and fleshy fruits and seeds is the last major coevolutionary node of the angiosperms. This is not to say that there were not the occasional attractive fruits produced earlier, but a large radiation of fruit and seed types of the angiosperms occurred during the Paleocene and Eocene.
The change in angiosperm fruit size was noted by Tiffney who associated this change with the radiation of rodents and birds. This coevolutionary node allowed for both the further radiation of the angiosperms and the radiation of the mammals and birds.
Stone noted that there was a tendency to develop animal-dispersed fruit types in the Juglandaceae several times in different clades of this family. Many angiosperm families took advantage of the potential to disperse their fruits and seeds by bird and mammal vectors during the early Tertiary as evidenced by the bursts of the evolution of fruits and seeds during this time Reid and Chandler, ; Manchester, It is interesting to note that at this same time the angiosperms also were experiencing a radiation of wind-dispersed fruits and seeds Call and Dilcher, This radiation of fruit and seed dispersal strategies in the angiosperms, late in their evolution early Tertiary , is yet one more example of a means to promote outcrossing for the group.
Coevolutionary events are largely responsible for the origin and subsequent nodes of evolution and radiation of the angiosperms. As we begin to find reproductive material of very early angiosperms Taylor and Hickey, ; Sun et al. The coevolution with insects sparked a tremendous potential for plants to outcross by co-opting animals to carry their male gametes pollen to other individuals and other populations of the same species.
Each node of angiosperm evolution established genetic systems that favor outcrossing. The showy bisexual flower, the more specialized bilateral flower, and the nutritious nuts and fleshy fruits all are means by which the flowering plants increase their potential for outcrossing. The majority of angiosperm evolution is centered on this increased potential for outcrossing through coevolution with a wide variety of animals.
Wind and water pollination syndromes also allowed for outcrossing and have continued to exist since the Early Cretaceous. However, they have never developed the diversity of those angiosperms pollinated by animals. Also several abiotically pollinated angiosperms, for example the Fagaceae Quercus or oaks and the Juglandaceae Carya or pecans , later accommodated themselves for animal dispersal of their fruits or seeds. The importance of outcrossing cannot be underestimated as a driving force in the evolution of the angiosperms Dilcher, , The ability of the angiosperms to accommodate and maximize benefits from animal behavior has been responsible for the evolutionary success of the group.
As individual clades made use of particular coevolutionary strategies the diversity of both the angiosperms and animal groups increased. The benefits to the angiosperms were the benefits of the genetics of outcrossing. Water-lilies are important ornamental components of water gardens around the world. Cabombaceae is listed as a separate family in your flora. Examples: Nuphar advena Spatterdock; Nymphaea odorata var. Cabombaceae sometimes included with Nymphaeaceae : Brasenia schreberi , 2 , 3 Water-shield; Cabomba caroliniana Carolina Fanwort. Illiciaceae: Illicium floridanum , gynoecium American Star Anise.
Schisandraceae: Schisandra glabra male , female Bay Starvine. Identification characteristics: Magnoliaceae have tepals in multiples of three which range in number from 6 to many. The outer 3 are often distinctly more sepaloid. The stamens are numerous and laminar. Carpels are numerous and arranged on an elongate receptacle in cone-like fashion. These separate carpels may sometimes form follicles that partially fuse before releasing arillate seeds, or may stay separate as an aggregation of wind-borne samaras. Leaves of Magnoliaceae are alternate and show a characteristic ring around the stem a scar left by the deciduous stipules at every petiole base and old node.
Magnoliaceae also produce volatile oils that often make their vegetation aromatic when crushed. Interesting stuff: Magnoliaceae have sometimes been hypothesized to be the basalmost angiosperm family due to the resemblance of their gynoecium to the cones of gymnosperms. However, this resemblance is superficial, and the structures are non-homologous. Magnolias and Tulip Tree are well-known ornamentals and valued timber trees.
Examples: Liriodendron tulipifera , 2 , fruit Tulip Tree; Magnolia acuminata , stipule scar Cucumber Magnolia; Magnolia ashei , closer Ashe Magnolia; Magnolia grandiflora , androecium and gynoecium , stamens Southern Magnolia. Annonaceae: Asimina angustifolia Slimleaf Pawpaw; A.
Identification characteristics: Lauraceae are alternately-leaved shrubs or trees in our range. They can be identified by their 6 tepals, usually 9 stamens, anthers which release pollen through flapped valves, and a unilocular, superior ovary which forms a drupe as the fruit. Many species are dioecious all in North Georgia , and many possess staminodes or glands in place of one or more whorls of stamens. All vegetative parts of Lauraceae are extremely fragrant when broken due to copius quantities of volatile turpenoids.
Interesting stuff: Lauraceae are one of the largest basal angiosperm families and are common in tropical forests. One genus, Cassytha , is parasitic and viney, strongly resembling members of the genus Cuscuta Convolvulaceae: in Asterids in a striking case of convergent evolution. Bay leaves, cinnamon, and avocado are important economically. Sassafras root was once the 2nd largest export from North America behind tobacco in colonial times, but tea and root beer produced from it has fallen into disfavor because of the presence of small quantities of carcinogenic compounds therein.
Examples: Lindera benzoin male inflorescence , 2 female inflorescence , 2 Spicebush; Sassafras albidum male flower , male inflorescence , female flowers , female inflorescence. Calycanthaceae: Calycanthus floridus , 2 Carolina Allspice; C. Identification characteristics: Flowers in Aristolochiaceae may be zygomorphic or actinomorphic. Most members lack petals, but have three pigmented sepals that are fused together. There are 6 to 12 stamens that are often semi-fused to the style, and the inferior ovary is comprised of 4 to 6 fused carpels. Most species produce capsules as the fruit. Aristolochiaceae have alternate leaves that are very often reniform or cordate in outline.
Interesting stuff: Many members of Aristolochiaceae produce maroon or brownish, foetid flowers that are carrion fly or beetle pollinated. Members of the genus are often called "Pipevine" or "Dutchman's Pipe" for their shape. They produce Aristolochic Acids, which are concentrated in the wings of Pipevine Swallowtails to make them distasteful to predators. It is a strong-enough deterrant that it has shaped the evolution of many other eastern North American Butterfly species to be Batesian mimics of the black-and-blue color pattern of Pipevine Swallowtails.
Examples: Aristolochia arborea , 2 , 3 ; A.