How many eggs were laid?

Here is a nice pile of eggs on display at the IVPP. As is quite common in dinosaur nests, there are several layers here and while it is subtle, there is a curve to the arrangement of the eggs to give an indication that these eggs were originally laid in a broad circle.

Clearly this nest is rather incomplete and would have originally contained many more eggs. Taking an estimate of that total from this little is probably a bad idea but there are more complete nests out there and some are apparently absolutely complete and every egg can be identified and counted. Great news in general of course, but does this mean we know how many eggs were laid by the mother?

You might think ‘well, obviously’ but sadly the situation is far less clear than this. Looking to the birds a great many small passerines lay two or sometimes even more clutches a year. Just finding a nest of half a dozen eggs doesn’t mean that this was the some total of the eggs laid by a mother that summer. Other birds are communal nesters with lots of females all dumping their eggs together into a single nest. Or males can solicit females to lay in their nest and so accumulate eggs from multiple females, though perhaps only one or two from each.

In short, even finding a nest of a couple of dozen eggs being brooded by an animal is no great guarantee that those eggs were laid by one female, or that was all she laid. It’s not, I hasten to add, a poor assumption but equally it’s far from certain. Which is rather a shame as obviously and understanding of the reproductive output of an individual (and thus a conceptual one for a species) can really help our understanding on dinosaur biology and ecology. I wouldn’t argue against using this kind of data, but I’d be quite cautious about how it could be used.

8 Responses to “How many eggs were laid?”

  1. 1 Zhen 26/02/2012 at 3:37 pm

    Ok, there’s this strange thing I’ve heard about dinosaur eggs during excavation and I was wondering if anyone can confirm if this is true. I heard that you can still smell the rotting stench of the eggs when it’s unearth from the ground, because the smell was trapped among the rocks.

    I saw this watching a Chinese TV show where the reporter suddenly noticed the stench as the paleontologist lifted the nest out from the ground.

    • 2 David Hone 26/02/2012 at 4:52 pm

      I’ve never heard it before and I can’t imagine it could be true. Any methane etc. from decay would leech out through the pore in the egg shell (hence you can smell rotten eggs even if they’re not broken). That’s not going to remain localised for a could of weeks let alone millions of years.

      • 3 Zhen 26/02/2012 at 5:31 pm

        Eh, figures it’s some sensational garbage.

        Thought it would be funny if it was true. Now you too can enjoy the smell of the Cretaceous 65 million years later.

    • 4 Howard 27/02/2012 at 12:19 am

      This might be one of those stories that has a “grain of truth”. The smell of rotten eggs comes from hydrogen sulphide (H2S). Many sedimentary rocks, especially organic mudstones/shales contain a lot of sulphur, in the form of pyrite (iron sulphide) or gypsum (calcium sulphate), which can break down, releasing small concentrations of H2S. It’s not unusual at all to smell “rotten eggs” when breaking these sorts of rocks. Therefore, depending on the rock matrix that the fossil eggs were found in, it could be quite possible to smell “rotten eggs” but the smell would not have come from the fossil eggs themselves, but rather the rock matrix.

      • 5 David Hone 27/02/2012 at 8:12 am

        Ah interesting, that’s certainly a plausible explanation and the sort of thing that could be very easily be misinterpreted and conflated. Thanks.

      • 6 Zhen 28/02/2012 at 2:26 am

        Interesting. Thanks for further elaborating on this issue Howard. I guess it’s not as far-fetched as I originally thought. This is also the reason why I love this place. So many experts sharing knowledge at their leisure.

  2. 7 Tim Donovan 02/03/2012 at 6:35 pm

    Theropod eggs, I presume.

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