By dating fossils of pollen and beetles
Further, certain paleobotanists regard the problem of flowering plant origins, "as intractable a mystery today as it was to Darwin 130 years ago" (page 318, Rothwell et al. Possible Problems with Existing Data Sets: Controversial assertions abound in the scientific literature of the 20th century and three categories of credible hypotheses and theories exist (Rothwell et al. None of these ideas when taken as a whole are neither compelling or plausible to many scientists, including the author. Root Gorelick (2001) challenges the validity of a biotic coevolutionary hypothesis on the origin of flowering plants, which is probably unjustified based on arguments presented in the next several chapters. "Tight coevolution" between animal disperser and plant was probably rare (page 3, Tiffney 2004). Coevolution of insect helix-turn-helix (HTH) homeodomain proteins, seed plant HTH LFY proteins, other phytophagous insect- and seed plant host developmental cis-regulatory modules (CRMs), and their respective developmental tool kits, potentially occurred during the De CARB and/or end-Guadalupian carbon cycle event (Gu CCE), with local hypoxia and temperature extremes as underlying and potentially powerful selective forces.
Coevolution between phytophagous insect antagonists and Carboniferous, Permian, and Triassic seed plant hosts at the level of their respective developmental tool kits with focus on selective forces that drive the logic of transcriptional regulation is proposed in the following essay to explain the origin and evolution of flowering plants and certain Holometabola. (2006, 2011), and Frohlich (2002, 2003, 2006), among others, are also contributions to our knowledge of the origin and evolution of flowering plants. The LFY gene duplication hypothesis by Albert et al.
I discuss potential coevolution of insect and seed plant helix-turn-helix proteins, specifically Engraled and Leafy enzymes that bind to cis-regulatory promoters controlling downstream expression of genes determining paedomorphic insect body patterns and plant cone and floral organ development. both within and outside the paradigm of transcription-encoding factors ..." (page 129, Niklas 2006). Modern syntheses on the abominable mystery of the origin of angiosperms and floral ancestry from unknown gymnosperms, and Mesozoic radiation of the group, are published by Frohlich and Chase (2007), Maheshwari (2007), Sokolov and Timonin (2007), Zavada (2007), J. (2002), and out-of-male and out-of-female hypotheses involving floral quartets in compartments of meristematic cells of developing SAMs of bisexual cone axes (Theißen Saedler 2001, Becker and Theißen 2003, Baum and Hileman 2006, Theißen and Melzer 2007, Melzer et al.
Reproductive organs of some lineages of poorly understood Permo-Triassic or Permo-Carboniferous seed plants were possibly derived from ancestral massive, developmentally plastic, shoot apical meristems (SAMs). Oleananes occur in fossilized leaf material of certain gigantopterids, bennettitaleans, and flowering plants (Moldowan and Jacobson 2002), but are absent from samples of several other fossil seed plants (D. For example, none of the work on Permian gigantopterids published to date convincingly demonstrates physical connections between reproductive structures, stems, roots, and leaves. I advance Takhtajan's ideas on flowering plant origins (1969, 1976) from 21st century research perspectives of evolutionary-developmental (evo-devo) biology, melded with rethinking of the paleontology of detached, fossilized remains of overlooked Paleozoic seed plant organs that might potentially be derived from massive, developmentally plastic, shoot apical meristems (SAMs) of gigantopteroid shrubs, vines, or small trees.
The picture to the right is a flower of Milla biflora (Iridaceae, Asparagales, Lilianae) and several dipteran insect visitors from the upper canyon of the Rio Quebrada de la Ventana, Sierra Madre Occidental of southwestern North America (photographed by the author in 1977). Whole plant morphologies are incompletely known for this group of Paleozoic seed plants (pages 758-763, T. During the hypoxic late Frasnian-Famennian ice-house (De CARB), invertebrate Hox proteins, hemocyanin (Hc) respiratory enzymes, and certain nuclear receptors of plecopteran (stonefly) ancestors diverged, leading to novel multimeric proteins in several hemimetabolous and holometabolous clades of late Paleozoic insects. The pollination of Trimenia moorei (Trimeniaceae): floral volatiles, insect/wind pollen vectors and stigmatic self-incompatibility in a basal angiosperm.
(1985), Farrell (1998), Labandeira (1998), Danforth and Ascher (1999), Grimaldi (1999), Wilf et al. 2007) suggesting that evolution of certain clades of late Mesozoic phytophagous ants, bees, beetles, butterflies, flies, and moths might be independent of the explosive origin and spread of eudicot orders and families. Dilcher from the Lower Cretaceous Dakota Formation of North America. I intend to focus on interactions between coexisting developmentally plastic organisms in deep time from the perspective of paedomorphic heterochrony as Takhtajan (1976) did in his paper on the origin of angiosperms, but with focus on Carboniferous and Permian arthropod and seed plant stem groups. The image was captured in 1981 while the author was visiting Indiana University. Many colleagues suggest a coevolutionary origin and later diversification of flowering plants based on co-radiations between specific groups of animals and seed plant hosts of the Cretaceous Period (Crepet and Niklas 2009). The image to the left is a side view of a 100 million year old eudicot flower unearthed from the North American Lower Cretaceous Dakota Formation. 2010), is equivocal, especially when studies of conifer cone abnormalities are considered (Flores-Rentería et al. First Clues on the Origin of Angiosperms: The first clue that sheds light on the shadowy origin of flowering plants comes surprisingly from study by oil and gas explorers and geochemists of taxon-specific biomarkers (TSBs) and molecular traces which are recoverable from mud logs of well boreholes, or from coal balls, compressions, and permineralizations (Moldowan and Jacobson 2002). Did homeodomain proteins duplicate before the origin of angiosperms, fungi, and metazoa? Certain aspects of coevolution of Mesozoic arthropods and seed plants that have a bearing on the origin and diversity of angiosperms are reviewed by Takhtajan (1969), Raven (1977), Thien et al. The rock was photographed by the writer in 1981 from Indiana University research and teaching specimens with the permission of Professor David L. There are problems associated with co-radiations of angiosperms and insects brought to light by phylogenetics (Ramírez et al. Presumed co-radiations with chrysomelid beetles are asynchronous (Gómez-Zurita et al. The picture of the rock slab to the left is of an indeterminate pentamerous fossil rosid flower (Celastrales, Rosanae) collected by Professor David L. Proceedings of the National Academy of Sciences 94(25): 13749-13753.
The three essays on the succeeding web pages are written from this research perspective. 2010) provide a demonstrably solid evo-devo foundation for continuing debate and evaluation of molecular evolution of angiosperms from unknown gymnosperm ancestors.
Were insect and shrub coevolutionary compartments of the late Paleozoic hypoxic icehouse and later hot house, venues of the first angiosperms? This question among others is explored in this first of three essays on the origin of angiosperms. Support for MMT and the gamoheterotopic hypotheses from the research perspective of gene expression in conifers (Vásquez-Lobo et al. 2001) and the biochemical logic of deeply conserved cone and floral tool kits (Melzer et al. Having compared and discussed some of the previous hypotheses on the origin of flowering plants the next section reevaluates published clues gleaned from geochemical data that might help paleontologists to focus on the interval in geologic time necessary to solve a riddle of angiosperm beginnings.