100 Million Years: Oldest Evidence Of Reproduction In Flowering Plants Discovered
    By News Staff | January 3rd 2014 09:49 AM | 5 comments | Print | E-mail | Track Comments

    The oldest evidence of sexual reproduction in a flowering plant – a cluster of 18 tiny flowers from the Cretaceous Period, with one of them in the process of making some new seeds for the next generation - has been found in a 100-million-year old piece of amber. 

    The perfectly-preserved scene, in a now-extinct plant, appears identical to the reproduction process that "angiosperms," or flowering plants still use today.  The fossils were discovered from amber mines in the Hukawng Valley of Myanmar, known to most as Burma. The newly-described genus and species of flower was named Micropetasos burmensis.

    The flowers themselves are in remarkable condition, as are many such plants and insects preserved for all time in amber. The flowing tree sap covered the specimens and then began the long process of turning into a fossilized, semi-precious gem. The flower cluster is one of the most complete ever found in amber and appeared at a time when many of the flowering plants were still quite small.

    This flower preserved in 100-million-year old amber is one of the most complete ever found. Photo courtesy of Oregon State University

    Even more remarkable is the microscopic image of pollen tubes growing out of two grains of pollen and penetrating the flower's stigma, the receptive part of the female reproductive system. This sets the stage for fertilization of the egg and would begin the process of seed formation – had the reproductive act been completed.

    "In Cretaceous flowers we've never before seen a fossil that shows the pollen tube actually entering the stigma," said George Poinar, Jr., a professor emeritus in the Department of Integrative Biology at Oregon State University. "This is the beauty of amber fossils. They are preserved so rapidly after entering the resin that structures such as pollen grains and tubes can be detected with a microscope."

    The pollen tubes penetrating the stigma on this ancient flower are the only known fossil of this type, showing the process of sexual reproduction in a flowering plant. Photo courtesy of Oregon State University

    The pollen of these flowers appeared to be sticky, Poinar said, suggesting it was carried by a pollinating insect, and adding further insights into the biodiversity and biology of life in this distant era. At that time much of the plant life was composed of conifers, ferns, mosses, and cycads. During the Cretaceous, new lineages of mammals and birds were beginning to appear, along with the flowering plants. But dinosaurs still dominated the Earth.

    "The evolution of flowering plants caused an enormous change in the biodiversity of life on Earth, especially in the tropics and subtropics," Poinar said. "New associations between these small flowering plants and various types of insects and other animal life resulted in the successful distribution and evolution of these plants through most of the world today. It's interesting that the mechanisms for reproduction that are still with us today had already been established some 100 million years ago."

     Published in the Journal of the Botanical Institute of Texas.
    Source: Oregon State University


    This is not to suggest that these are the oldest flowering plants observed.  According to Wikipedia:

    The ancestors of flowering plants diverged from gymnosperms (conifers, Ginkgo, and others) around 245–202 million years ago, and the first flowering plants known to exist are from 160 million years ago.

    Indeed Amborella, a flowering plant that diverged about that time from all the others we know today, has been recently subjected to genetic analysis, indicating that chromosome doubling was what led to their great capacity for diversification [1].  These plants are today found only in New Caledonia, far out in the South Pacific.

    However, what is interesting is that, in terms of reproduction, this is the earliest fossil of an angiosperm captured in flagrante delicto.  Although this legal term simply means “caught red-handed”, because of its widespread use in divorce cases, it has come to mean in colloquial usage as being caught in that act.

    One of the authors of the Micropetasos paper kindly sent me a copy, as I was interested to find out how closely related it was to any living plants.  It is however, difficult to tell.  As the paper puts it:

    In terms of phylogenetic systematics, Micropetasos appears to represent an early member of the Pentapetalae clade (Cantino et al. 2007), also known as core eudicots. We prefer to leave the question of its exact familial relationships open at this time.

    “Core eudicots” is a pretty wide-ranging group.  In this figure taken from the Amborella paper, it is the group covered (by myself) under the transparent yellow rectangle.  Non-core eudicots, here represented by the Sacred Lotus (Nelumbo nucifera), are also pretty diverse, including the buttercup, the “standard” dicot one was taught at school.  But interestingly, the Sacred Lotus is still a eudicot, quite distinct from the superficially similar waterlilies.

    Now if one could do a “Jurassic Park” extraction of DNA from the amber, could one pin it down more closely?

    [1] Amborella Genome Project; Science 342, 1241089 (2013); DOI: 10.1126/science.1241089

    [2] Poinar GO,. Chambers KL, Wunderlich J.  Journal of the Botanical Research Institute of Texas 7(2): 745 – 750. 2013

    Robert H. Olley / Quondam Physics Department / University of Reading / England
    Right, they are talking about sexual reproduction...well, that fancy foreign term you used, anyway.
    E pluribus unum — how foreign is that?

    Robert H. Olley / Quondam Physics Department / University of Reading / England
    Oliver Knevitt
    It's nice, but it's kind of meh compared to the Rhynie Chert fossils, where preservation is so good that it even the nuclei of cells are preserved exquisitely; all in rock that is 400 million years old. At the Paleontological Association general meeting a couple of weeks ago, Hans Kerp presented a full sequence of fossil plants preserved at the cellular level, showing every reproductive stage of the plants, right from the gametophytes and the spores to the adult plants, all in situ.
    Worthy piece of news and meta-news, yet the peculiarity of its immersion in time as compared to what "news" as a meta-data tag apparently should mean, perhaps explains how the first sentence of this blog post could pass quality control despite the ridicule of its grammatical tautology or self-contradiction: "The oldest evidence of sexual reproduction in a flowering plant".

    Excuse me, but does not _knowledge that a plant fossil is that of a flowering plant,_ by definition imply that was tracked to success evidence of its sexual reproduction?

    Of course, I am there only harking on half a prefixing sentence, that's about as sensical as tearing away the first lens of an optical system to criticize it in abstraction of its justification by the rest of the optical system.

    But I have a more serious question. Assume exist open and sincere evolution skeptics. The case is obviously an opportunity for them to "challenge Darwinists" with: Now, can you show us with accuracy how the fossil shows characters of an intermediate form as evolution predicts to exist?

    I surmise the case is perfect - or at least ripe for the purpose of elucidating the scientific meaning of "to predict" over the case of its application to origins in the past.

    Also, it affords a good pretext to reshuffle the deck of evolution theory while promoting sexual selection to better acknowledgement (in the role of representing the more creatively planning or "intelligent" side of evolution), this, through a reappraisal of flowering plants as showing how superior powers of sexual selection dependent on animal mobility were harnessed by plants, or more exactly by their symbiosis with pollinating insects.