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Troodon

First Cretaceous Bird Found with Unlaid Egg

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Auspex

This is pretty amazing! I never even considered the possibility...
Time for all the museums to dust off their reference collections and look for this.;)

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Fossildude19

Topics merged, and moved to Fossil News  ;) 

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CBchiefski

Wow @Troodon and @Kasia you both are fast on this incredible news.

To add my two cents, it is near impossible to understate the significance of this specimen. We can now link the eggshell to this new bird and it greatly increases the understanding of egg development with medullary bone likely being present. On top of those two major points, the odd multi-layering of the eggshell is very likely a pathology which can in turn help reveal the potential nesting behavior of the bird given everything else with the eggshell.

Beyond the egg, even in China, birds from the early Cretaceous are still very rare so having one this complete is amazing.

 

1 hour ago, Auspex said:

This is pretty amazing! I never even considered the possibility...
Time for all the museums to dust off their reference collections and look for this.;)

Please let me know if you do find any eggs! haha

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Auspex
10 minutes ago, CBchiefski said:

odd multi-layering of the eggshell

I am very interested in this feature. It is so unlike any in my experience that I wonder whether it might be an artifact of the unusual preservation.
If it was indeed laid down in discrete layers, it could be a huge clue to the metabolism of enantiornithine birds, and even their origins.

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CBchiefski
27 minutes ago, Auspex said:

I am very interested in this feature. It is so unlike any in my experience that I wonder whether it might be an artifact of the unusual preservation.
If it was indeed laid down in discrete layers, it could be a huge clue to the metabolism of enantiornithine birds, and even their origins.

Agreed, with the eggshell so clearly altered it could perhaps be too much of a leap. I personally am inclined to agree with the authors and the 3 points used for their reasoning.
As a comparison here is, in my opinion, one of the best pictures of abnormal eggshell morphology, left, with the new eggshell, right. What are your thoughts between the example abnormalities and this new shell?

 

5c9298895b896_comparisonabnormaleggs2004and2019.JPG.d16928cc1d83774fdcae21dd49a8e9d4.JPG

Left pic is from: "Jackson, F. D. et al. 2004. Abnormal, multilayered titanosaur (Dinosauria: Sauropoda) eggs from in situ clutches at the Auca Mahuevo locality, Neuquén Provi"

Yes if in fact actual layers, which I suspect, then wow this could be even more significant for avian metabolism and evolution. I am also very curious about medullary bone still being present after the eggshell had been deposited completely, maybe this is further evidence for an abnormality as the authors point out. Assuming the layer turns out to be just diagenetic, then perhaps the mother was preparing to start depositing shell for a 2nd egg. Either way, many major ramifications and am very fascinated by the possibilities.

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Auspex

Layering certainly appears to be a structural feature with this fossil, and it is not so with neornithines. This could be important, as you note.
My pet theory, for several supportable reasons, is that 'birds' evolved twice, with a nearest shared ancestor that was in no way birdlike. Structural clues include the direction in which bone groups fused together (proximal-to-distal vs. the reverse): this is a process that could not have reversed itself. For a time, in the Cretaceous, both enantiornithine and neornithines coexisted, but only one got past the K-Pg extinction.

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CBchiefski
17 hours ago, Auspex said:

My pet theory, for several supportable reasons, is that 'birds' evolved twice, with a nearest shared ancestor that was in no way birdlike. Structural clues include the direction in which bone groups fused together (proximal-to-distal vs. the reverse): this is a process that could not have reversed itself. For a time, in the Cretaceous, both enantiornithine and neornithines coexisted, but only one got past the K-Pg extinction.

 

Wow, initially was unsure but after giving your idea some thought, it does make a great deal of sense. The time gap between the appearance of neornithines and enantiornithines then might be real and not just due to preservational bias. Interestingly, since we do see many different animals take to the sky independently over time, two similar groups doing so is not actually far fetched. Any idea where hesperornithiformes fit or do you think the current clade position is accurate?

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