Archive for December, 2022

Microraptor ate mammals!

Ok, if we are being totally reductionist, one Microraptor ate part of one mammal once. But that’s certainly indicative of a pattern and that’s quite exciting. As you might guess, I have a new paper out today describing a Chinese specimen that shows this, though those with excellent memories and niche dinosaur knowledge might already know about this because it’s been announced before and way back in 2010!

Yes, this paper has been on the cards for a very long while. Back in 2010 Hans Larsson was over in the IVPP with his then PhD student Alex Dececchi and looking at various theropods. I was based there at the time working alongside my fellow Postdoc Corwin Sullivan under Professor Xu Xing. While looking over some flattened Yixian specimens, Hans spotted something that really people should have seen before (including me!). Clear as day in the holotype of Microraptor zhaoianus was the foot of a small mammal. Under the ribs.  Yeah, one of the most important and studied early feathered theropod finds had an obvious and very interesting set of stomach contents that had been completely missed.

Hans rather generously asked us all to collaborate on this find and we put in an abstract to SVP that year and so if you have the right knowledge you may have spotted this (or even seen his talk in Pittsburgh). In that regard this isn’t exactly news, and so it might come as a surprise that we ever got this out and so much later. Well, I’ll blame the others for that, (OK, mostly Hans!) but the fact remains it is now out and properly described, documented and put into some context and it’s the first, to my knowledge, example of a dinosaur eating a mammal, so that alone is nice and novel.

We don’t, annoyingly, know what the mammal actually is, despite having a much of things to compare it to, but we do know it’s small (mouse sizes) and doesn’t appear to have much in the way of climbing adaptations so would have been pretty terrestrial. That contrasts with interpretations of Microraptor as some kind of arboreal adapted flier that’s spending a lot of time in the trees. Still, we can’t say if this was predation or scavenging – though either way, it was likely this was picked up on the ground so it’s an interesting nugget of info on Microraptor diet.

On that note, this is now the fourth reported set of stomach contents for this genus with fish, lizards and birds also on the menu. Rather oddly, both fish and birds have been suggested to be something that Microraptor was specialised for, despite showing a) a diverse diet and b) no particularly obvious anatomical specialisations for either of these. Indeed, there’s a greater diversity of things eaten known for this animal now than any other dinosaur and that rather points to a generalist diet of any small thing going down the hatch. This of course comes with a few caveats here, there’s multiple specimens of Microraptor at play from more than one putative species and it’s at least possible that 1 species preferred things like lizards and mammals say, while another took birds etc. or these varied over time and space. Still, if there was any kind of specialistion we would expect to see multiple examples of single clades being taken, and I think that a generalist diet is likely.

That also fits with what we see in other small theropods as there are several with stomach contents or pellets featuring multiple taxa (e.g., Scipionyx) and suggesting they tended to eat a variety of things and specifically those that were rather smaller than them. This is in fact a bit of a pattern in general and while mammals aren’t always the best analogies, there is lots of data for them, and this is a trend seen there so it might well be that small theropod (be they small taxa or juveniles of big ones) tended to be more generalist. We do need to be careful here of course as we also then have preservation biases – Microraptor might, for example, have predated primarily on things like invertebrates and we know there were loads of beetles, spiders and the like around in the Jehol. But those don’t tend to fossilise well (especially not if crunched up and partially digested) compared to small bones, so perhaps these are just missing.

So one other thing we worked in here was to look at the jaw shape of dromaeosaurs in general and how this might fit with biting mechanics and so diet. While generally having incomplete skulls, Microraptor has a rather short head and lies in contrast to animals like Velociraptor with a longer and more slender skull, pointing to a proportionally harder but lest quick bite in the former (for its size) b. That also points to them not being especially adapted for things like insects where a hard bite wouldn’t be too necessary to kill or process them, but a quick bite would be an advantage. So while Micrioraptor might well have taken invertebrates as part of its diet, it doesn’t appear to be especially well suited to the task and biting small vertebrates looks like it was something more normal.

So there we have it, dinosaurs – perhaps unsurprisingly – ate mammals (and at least got their own back for Rapenomammus) at least on occasion. And more than that, Microraptor was (probably) a generalist predator of small vertebrate prey, though we can’t rule out scavenging or indeed other things like insects or even fruit as occasional parts of the diet. This might well be something common to many small theropods, though the general lack of data inhibits us from saying too much, the overall pattern of what information we have would tend to confirm this. It has taken us far too long to get this information out into the world but it’s finally made it and adds a nice note on theropod ecology and behaviour.

Finally, a quick thanks to my coauthors for sticking through all of this but also especially Ralph Attanasia III who kindly provided the illustration that went out with the press release and is shown above.

Hone, D.W.E., Dececchi, T.A., Sullivan, C., Xu, X., and Larsson, H.C.E. 2023. Generalist diet of Microraptor zhaoianus included mammals. Journal of Vertebrate Paleontology.

Larsson, H.C.E., Hone, D.W.E., Dececchi, T.A., Sullivan, C. & Xu, X. 2010. The winged non-avian dinosaur Microraptor fed on mammals: implications for the Jehol Biota ecosystems. Society of Vertebrate Paleontology (SVP), Pittsburgh, U.S.A.

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