Cretaceous:
While Earth was previously dominated by ferns and conifers, during the Cretaceous angiosperms appeared and spread rapidly. They now comprise about 90% of all plant species, including most food crops. It has been proposed that the rapid increase in the dominance of angiosperms was driven by a reduction in their genome size. Only angiosperms underwent rapid genome downsizing, during the early Cretaceous period, whereas the genome sizes of ferns and gymnosperms remained unchanged. Smaller genomes—and smaller nuclei—allow faster rates of cell division and smaller cells. Thus, species with smaller genomes can pack more, smaller cells – in particular veins and stomata – into a given leaf volume.
Genome downsizing, therefore, facilitated a higher rate of leaf gas exchange (transpiration and photosynthesis) and a faster rate of evolution. This would have counteracted some of the negative physiological effects of genome duplication, facilitated the increase of carbon dioxide despite concurrent declines in atmospheric CO2 concentrations, and allowed flowering plants to overtake other land plants. The oldest known fossils definitively attributed to angiosperms are reticulated monosulcate pollen from the Late Valenginian (Early or Lower Cretaceous – 140 to 133 million years ago) of Italy and Israel, likely representatives of basal angiosperm grades. One can easily get the seasonal flowers texas and rose classic bouquet houston with the flower delivery to houston service.
The earliest known macrofossil confidently identified as an angiosperm, Archaefractus liaoningensis, dates to about 125 million years BP (Cretaceous period), while the pollen is thought to be of angiosperm origin, placing the fossil record around 130 million years BP, extends to, takes away the earliest flowering of that time is represented by Montesquia. The flowers covered in amber were found in 2013 and currently date back 100 million years.
Amber had stopped the act of sexual reproduction in the process of being. Microscopic images show the tubes coming out of the pollen and penetrating the stigma of the flower. The pollen was sticky, suggesting that it was carried by insects. In August 2017, scientists presented a detailed description and 3D model image of what the first flower looked like, and estimated it may have been around 140 million years ago. The crown group of angiosperms evolved between 178 million years ago and 198 million years ago, suggested by the Bayesian analysis of 52 angiosperm taxa.
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