Pterosaur with 2 eggs?

Understanding reproduction in extinct animals can be extremely difficult as we lack the necessary information of soft tissues. However, there are certain things we can learn from fossils, and particularly well preserved fossils are even better.

3D preserved Hamipterus eggs with soft impressions
showing a soft pliable egg (Wang et al. [4]).

For example, we know that pterosaurs were egg-layers like other reptiles. In a phylogenetic context, pterosaurs are located in between crocodiles and birds in terms of modern animals, which both lay eggs, meaning it was most likely pterosaurs would have too. Thanks to fossils, we know that they did. While pterosaur egg fossils are rare, they do exist. The first pterosaur eggs were found in China[1-2], and Argentina[3] and come from Early Cretaceous pterodactyloids. The eggs have embryos preserved, and the material from Argentina can even be identified as Pterodaustro. Further pterosaur eggs have been found, and we know that pterosaur eggs were softer (much like those found in snakes) rather than hard calcareous shells like those seen in birds, thanks to one of the first finds that suggested pterosaur shells were leathery[2], and some 3D preserved eggs with impressions in them, from the Hamipterus bonebed in China[4].

Kunpengopterus counterslab and drawing showing 2 eggs
in black from Wang et al. [5]

This is a recent study that I saw presented at Flugsaurier 2 weeks ago, where Alex Kellner mentioned it in his talk on pterosaur reproduction. A pterosaur described a few years ago has been recently restudied, and is potentially teaching us a bit more about pterosaur reproduction in a paper published in July. Wang et al. [5] discovered some interesting features in the counterslab of the pterosaur Kunpengopterus. The counterslab is not fantastically preserved, in fact the images make it hard to see things, but what they have pointed out are not one but two eggs present with the individual. One egg is visible just below the pelvis, as if it had been expelled shortly before or after death, while the other is still visible within the body cavity. In close up images, you can see two rounded egg-shaped structures in these areas. The first egg, the one below the pelvis, was identified initially when this specimen was first described. The second one, however, is new. For the first time, it seems that pterosaurs could have 2 eggs in their body at once.

Outline of eggs from A) the pelvic region, and B) inside the body cavity from Wang et al. [5].

So what does that mean? Who cares if they have 2 eggs? Wang et al. [5] further go into the significance of this find. They suggest that this pterosaur was actually a pregnant female, pregnant with 2 eggs when it died. Having 2 eggs at once is a sign of having 2 functioning oviducts, which is interesting because while most extant reptiles have 2, birds have only 1 functioning oviduct. In birds, this has been thought of as relating to decreasing mass for the evolution of flight, especially as non-avian dinosaurs appear to have 2 functioning oviducts as well. The thought was that having only 1 functioning oviduct was essential to decrease mass in order to achieve flight. However, that seems not to be the case if pterosaurs were able to have 2 oviducts, while being the largest animals ever to achieve powered flight.

This new study provides a lot of interesting information about pterosaur reproduction that we previously didn’t know, and of course for me, it’s interesting when it comes to the evolution of flight. I’m always interested when people suggest that flight couldn’t have evolved without things like the reduction of an oviduct. I think this study shows that mass reduction to achieve flight is not as straight forward or “black and white” as we may have previously thought. Different taxa do different things, and what may be valid in birds, is not valid in pterosaurs, and vice versa.

References:
1. Wang and Zhou. 2004. Pterosaur embryo from the Early Cretaceous. Nature 429: 621. 
2. Ji et al. 2004. Pterosaur egg with a leathery shell. Nature 432: 572. 
3. Chiappe et al. 2004. Argentinean unhatched pterosaur fossil. Nature 432: 571-572.
4. Want et al. 2014. Sexually dimorphic tridimensional preserved pterosaurs and their eggs from China. Current Biology 24: 1323-1330.
5. Wang et al. 2015. Eggshell and histology provide insight on the life history of a pterosaur with two functional ovaries. Annals of the Brazilian Academy of Sciences.

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9 thoughts on “Pterosaur with 2 eggs?

  1. As interesting as the flight implications are, I'm more interested in the potential import with regards to the concept of absent parentage in pterosaurs. Lu et al. suggested the ratio of egg to body mass, combined with the soft shells support the idea of little to no parentage. I've always had some issues with the idea that all pterosaurs were absentees, given that every tetrapod group has members which show at least some level of parental care and visa versa combined with the phylogentic bracket within archosauria which supports some level of care (including soft shelled examples in crocodylomorphs). I find the size and number of the eggs intriguing. While relatively small, they are larger in relation to body size than what we find in Oviraptor or other nesting dinosaurs, and only 2 eggs in an animal which needs to abandon those eggs. The example has been made towards some birds which make large ground nests which house few eggs which they monitor and defend, without caring for the chick but I would consider that a form of parental care.

    Hmmm. It just seems that Darwinopterus at least is more K-selected than one might expect.

    I suppose there's a lesson on generalisation and random speculation in internet blog comments…but I refuse to learn it!

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  2. Hadn't thought about that, but it's definitely an interesting though. Unfortunately I think we need a heck of a lot more information to determine what kind of a parent pterosaurs were. Ultimately I think that information on the embryos is more important than the size of the eggs. Small size could mean anything. If they are small but completely ossified, then maybe they just are small?

    Can someone please find a nesting pterosaur? Like one protecting it's eggs? That would be great…

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  3. Maybe producing soft-shelled eggs aren't costly to mass and flight as hard-shelled eggs, presumably because the calcium makes the egg heavier, which could be why pterosaurs could have two functioning oviducts.

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  4. That's possible, but I would expect that the tissues surround a second oviduct, as well as the large size of the egg itself would be substantially heavier than just hard calcium eggs. The egg shell isn't going to add nearly as much mass as the second egg in general, and I'd be surprised if it was that small difference in mass would affect it's ability to fly that much.

    It's possible that this is somehow linked though. Thanks for the comment! I will now contemplate that for a bit 🙂

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  5. If there is to be a discussion of pterosaur eggs and their implications for pterosaur reproductive biology it should include information to be found in several additional works (listed below) most of which, for some inexplicable reason, are not cited by Wang et al. 2015, or the original post here. Admittedly, there is not a lot of data to go on and there are reasonable doubts regarding the identity of the second Pterodaustro egg reported on by Grellet-Tinner et al. 2014. These caveats aside there is much still be done and written on this topic. That said, consideration of the reproductive biology of extant oviparous tetrapods emphasizes the need to approach fossil evidence with extreme caution. The one idea upon which there does seem to be widespread agreement is that, taken collectively, the evidence we have for reproduction in pterosaurs (key features of which include: relatively small egg size; pliable eggshell; and incubation at ambient temperatures) are all consistent with the reproductive biology of extant reptiles and do not share any derived features in common with birds. The recent discovery that pterosaurs seem to have paired oviducts is consistent with this idea which, incidentally, was first implied by Wang et al. 2004 and explicitly stated by Unwin 2005, Unwin et al. 2006, 2008, Grellet-Tinner et al. 2008 and Lü et al. 2011. Wang et al. 2015 have also recently adopted this idea, seemingly unaware that it is already well established in the literature.

    Grellet-Tinner, G, Wroe, S., Thompson, M. B. & Ji Qiang 2007. A note on pterosaur nesting behaviour. – Historical Biology, 19: 273–277.

    Grellet-Tinner, G., Thompson, M., Fiorelli, L. E., Argañaraz, E., Codorniú, L., Hechenleitner, E. M., 2014. The first pterosaur 3-D egg: Implications for Pterodaustro guinazui nesting strategies, an Albian filter feeder pterosaur from central Argentina, Geoscience Frontiers (2014), doi: 10.1016/j.gsf.2014.05.002.

    Lü Junchang, Unwin, D. M., Deeming, D. C., Jin Xingsheng, Liu Yongqing and Ji Qiang. 2011. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331, 321-324.

    Unwin, D. M. 2005. The Pterosaurs from Deep Time. Pi Press, New York, 347pp.

    Unwin, D. M. & Deeming, D. C. 2008. Pterosaur eggshell structure and its implications for pterosaur reproductive biology. In: Hone, D. & Buffetaut, E. (eds) Flugsaurier – The Wellnhofer pterosaur meeting, Munich, 2007, Zitteliana, 28, 199-207.

    Unwin, D. M., Lü Junchang and Deeming, D. C. 2006. Were all pterosaurs oviparous? Pp. 143-169. In: Lü, J. C., Kobayashi, Y., Huang, D. & Lee, Y.-N. Papers from the 2005 Heyuan International Dinosaur Symposium. Geological Publishing House, Beijing.

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  6. Hi Dave, thanks for posting. Of course there is substantially more that can be discussed when it comes to pterosaur eggs and reproduction that I didn't mention here. I'll admit that I hadn't seen it elsewhere in the literature, but recently heard about pterosaurs having 2 oviducts in the Wang et al. 2015 paper, and didn't know it was not the first time this had been suggested. It is still, to my knowledge, the first pterosaur preserved with 2 eggs, right? Or are there other ones I'm unaware of? I'll take a look at the papers you've listed. I did, however, want to discuss this as it is a cool new fossil and interesting ideas, even if not the first time it's mentioned. I'll update the post to include references to some of the earlier works as well

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  7. Hello,
    I am not a scientist, paleontologist, archaeologist or anyone of like mind perhaps, yet just very fascinated by something I picked up as it appeared at my two left feet one day sometime ago. However, with having what may very well be the best pterosaur egg discovered, could anyone of you direct me on what to do with it?

    Sincerely,
    Kiyana Satre

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  8. Hi Kiyana Satre,
    If you have something that you think may be a fossil, I would recommend bringing it to your local natural history museum or university, or contacting someone from the Earth Sciences department of a university to see who you could bring it to. They should be able to tell you at the very least if it is a fossil or rock, and then you can go further from there to determine exactly what it is. Where did you find it?

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  9. Thankyou for your response. I stumbled upon it after sinking my bare feet into the sand of an old dried up riverbed in Utah. I am not from that area, but could prossibly find the location on a map. Yet the rock itself is the same shape of a couple others shown online. What is quite remarkable about this one is it appears to have an exposed, well developed, embryonic, skeletal structure on one side beside what could be the yoke sac. The other side still shows amall fragments of the outer shell and the inprint of the wings. One upper side edge shows the thickness of the neck and large wide head with the eye sockets faintly visible. From pictures I have seen, this most closely resembles a Dimorphadon as it has a very large head in comparison to the size of its skeletal form. At the bottom the vertebra of a short tail is also visible with a spade shape at its end. The approximate size is about 2 and 1/2 inches wide by 3 and1/2 inches tall. It has not been flattened. I would send photos if interested.

    Thanks again for the information on those I should contact as I believe this is quite a remarkable piece for those who have an interest.

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