Early birds may have been too hefty to sit on their eggs

Mar 23, 2018

By John Pickrell

Birds that lived at the time of the dinosaurs might have been too heavy to sit on clutches of eggs without breaking them, according to an analysis of primitive avian fossils. The findings suggest that incubation might be a defining feature of modern birds, evolving only in the past 100 million years.

Some palaeontologists have criticized the study, in part because the idea flies in the face of evidence that some non-avian dinosaurs closely related to birds sat atop nests on the ground. The accepted view by many researchers was that some dinosaurs were already brooding nests to incubate their eggs, which would suggest that the behaviour evolved long before the proliferation of modern groups of birds, following a mass-extinction event 66 million years ago.

Many fossils of early birds have been discovered in the past three decades — particularly in China — but direct evidence of their reproductive behaviour has been elusive, says palaeontologist Charles Deeming at the University of Lincoln, UK, who led the analysis.

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6 comments on “Early birds may have been too hefty to sit on their eggs

  • There is a lot more to this story. Not least the use of microbial heating from vegetable matter and guano in the earliest egg layers. Collecting vegetable matter probably started on the ground to improve what was originally merely found. It could be that improvements consisted of rottable material on top of thermally insulating twigs. This may have been carried increasingly aloft at some point evolving into tree nests. Further we can imagine a warming blanket of vegetable matter contained in a sculpted pocket offering substantial load bearing capacity to begin with especially with smaller eggs, allowing incubation to happen of both the eggs and the exothermal microbes. (Small compost heaps don’t work on their own, they increasingly need to be “lit”and insulated as they shrink.) The evolutionary process of more extensively covering and increasingly remaining represents a process of energy optimisation, swapping cleverer design for a miniaturised nest.

    Hypotheses that propose transition are more important in validating what happened than hypotheses about what is self consistent.

    This transitional hypothesis will make predictions tying shell porosity with moisture in the environment. Wetter surroundings allow water permeable shells.

    Hollower bones miniaturised organs (brains!) will have done Weightwatchers job eventually for the flying reptiles, and the development of pair bonding to share body heat incubation and the covering vegetable matter could be dispensed with….I hypothesize.



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  • phil rimmer #1
    Mar 25, 2018 at 8:31 am

    There is a lot more to this story. Not least the use of microbial heating from vegetable matter and guano in the earliest egg layers.
    Collecting vegetable matter probably started on the ground to improve what was originally merely found.
    It could be that improvements consisted of rottable material on top of thermally insulating twigs.

    Evolution will exploit behavioural opportunities which aid survival at the time!

    https://en.wikipedia.org/wiki/Maleo

    The maleo (Macrocephalon maleo) is a large megapode and the only member of the monotypic genus Macrocephalon. The maleo is endemic to the Indonesian island of Sulawesi.
    It is found in the tropical lowland and hill forests, but nests in the open sandy areas, volcanic soils or beaches that are heated by the sun or geothermal energy for incubation.

    Maleo birds breed all year round, but peak breeding season varies depending upon the location on the island.[2]
    When prepared to lay her eggs, the female maleo bird, accompanied by her mate, will leave the cover of Sulawesian forest in search of historic coastal breeding grounds. Females can lay anywhere between 8-12 eggs over the course of a year.
    Once an optimal spot is chosen, the maleo dig a deep hole and lay the egg inside. After the egg is laid, the parents bury the egg securely in sand, sometimes covering the sand with other debris to better camouflage the hole.[4]
    After the egg has been securely buried, the parents leave and never return, leaving the maleo chick to fend for itself.

    The hot sand of Sulawesi acts as an incubator for maleo eggs, which are warmed with geothermal heat or solar heat.[5]
    A maleo chick is completely self-sufficient only hours after hatching.
    For this reason, maleo eggs are approximately five times the size of a domestic chicken’s, as they contain nearly full-formed maleo birds inside.
    It must dig its way up through the sand immediately after birth, and subsequently has the ability to fly and feed itself.

    Even birds which do not sit on the nest at all, build some structure!



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  • The weight on the egg can be imagined like this….

    If the bird is a large elastic bag of liquid the egg experiences the weight of the column of liquid above it, the column being as wide as the point at which the bag (body) touches the ground. This accommodates skin elasticity and the elasticity of an additional internal meaty sponge, with hydrostatic pressure being internally uniform.

    Adding material around the egg can both reduce the effective width of the supported column if the added material is essentially rigid, or, if elastic, soggy seaweed, say, can redirect some part of the weight to around the egg in a uniform manor, playing to the shape’s natural strength. This is how the egg survives laying.



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  • phil rimmer #4
    Mar 28, 2018 at 3:19 am

    Adding material around the egg can both reduce the effective width of the supported column if the added material is essentially rigid, or, if elastic, soggy seaweed, say,

    When considering the elasticity or flexibility of birds’ eggs, or supporting materials, we should remember their reptilian ancestry, and the leathery nature of the “shells” of crocodilian and turtle eggs!



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  • I found this which, if I have understood it, says the full weight of the bird does not go on the eggs as in an open nest structure??? Has this been factored in?



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