Nummulites: The biggest single cells that ever lived.

nimmulitesAnyone who has been to the great pyramids of the Giza Plateau next to Cairo in Egypt may have noticed 1-3 Cm lens shaped fossils within the limestone, both underfoot and in the buildings themselves. These are nummulites, the shells of faraminifera. The biggest known are ten cemtimetres wide, and they are used as index fossils to age sedimentary rocks. They were particularly common in the Paleocene and Eocene, a period of high sea levels before glaciation lowered them, when what is now Egypt was under the remnants of the Tethys sea. They are still around today, and were named after the Latin for little coin.

via The Earth Story. Image credit: Fozy Istvan, via chronique du temps

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2 Responses to Nummulites: The biggest single cells that ever lived.

  1. Phil Krause says:

    I really like this blog entry as it started me thinking straight away. Also I guess that its how you define a single cell, wether its an organism or part of one and also how you define biggest (longest, largest volume or heaviest). My first thoughts were that an egg was the largest single cell, especially an ostrich egg. But then what about the extinct elephant bird egg that David Attenborough pieced together while he was in Madagascar. If were talking about extinct, then one of the dinosaurs must have had a bigger egg than a bird. An unfertilized egg is definitely a single cell but its not viable until its fertilized. If its fertilized by a sperm its then viable but is this considered to be two cells? I thought a fertilized egg before it divides (zygote) was classed as a single cell but it is definitely formed from two, the egg and the sperm. Both the egg and the sperm are haploid ( they only have one copy of DNA ) whereas the fertilized egg is diploid (two copies of DNA ), like all the rest of our cells. All the sperm cell offers the egg when it fertilizes it is a male copy of DNA.
    I then started to think about the largest cells within our bodies. Neurons seemed to fit the bill with, sometimes millions of dendrites reaching out to other neurons and its single long axon that conducts electrical signals away from the cell body. The longest axons are the ones that carry signals from our brain to our muscles through our neck and exiting via each vertebrae in our backs. Well, I guess a giraffe has very long axon’s coming down its neck. But some dinosaurs had even longer necks, particularly the surapods. The longest probably being the Supersaurus with its enormous neck.
    If we were only looking at single celled organisms then maybe the Nummulites or the Xenophyophores rarely found only in the depths of the marian trench fit the bill. Or possibly the green algae called Caulerpa that can grow up to a meter long. Can anybody else think of any more?

  2. alfy says:

    There is a spelling mistake in the post. It is not “faramenifera” but “Foramenifera” as the Latin taxonomic name means “hole bearers” (foramen = hole) because of the pores in the calcareous skeleton.
    In trying to define a largest cell you certainly need to include the adjectives “haploid” or “diploid” within the definition. A single fertilsed egg of any kind is one diploid cell even though it is derived from two haploid cells.
    A further complication is provided by the existence of structures which are not divided into separate cells, but where many nuclei are distributed through the cytoplsm, such as the hyphae of most fungi, many green algae, and the cardiac and striped muscle of vertebrate bodies such as our own.
    Keep working on it, Phil.

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