Sadly I have to report that after many years working on various diapsids and having published plenty of papers on dinosaurs generally and theropods specifically, and yes even sauropods, I’ve gone and published two papers on ornithischians. I hang my head in shame, obviously, and I hope too many readers won’t think too little of me (though I doubt Tom Holtz will ever return my calls now). The first is on the wonderful Protoceratops and delves deep into dinosaur behaviour (and should be out on Wednesday), but this time it’s the monstrous hadrosaur Shantungosaurus, which has not really had anything like enough attention given just how much material is floating around.
The paper is a chapter in the new ‘Hadrosaurs’ volume that has been long in the making (and indeed publishing, since it as basically done a year ago) and if at this point effectively out. Actually I’m not sure quite how available things are, but the volume has appeared on Google Books (with the incorrect date of 2015 on it) and copies are apparently in mail, plus at least some coverage of various chapters is already out. As a result, I don’t think I’m jumping any particular embargo. though I appreciate not everyone may be able to read it in the next few days. Anyway, onto colossal hadrosaurs.
After the initial excavations of the 1960s, not much happened in the quarries where the remains of Shantungosaurus were first found. It was identified as a giant hadrosaur, plenty of isolated remains were collected and distributed to various collections and then, well, not much. The new digs over the last decade or so have seen a raft of new finds, but all the attention has really been on the other things coming out of the quarries, namely the new tyrannosaurs, ceratopsians and other beasties. That’s a shame as there are literally thousands of elements available to study and these are coming out in multiple quarries.
Over several visits, my good friend and longtime collaborator Corwin Sullivan and I went over the largest of the three main sites at Zhucheng, the Kugou Quarry, and took note of every bone that we could find and identify. The quarry maxes out at some 300 by 30 m, so it’s truly giant, and both ends are missing thanks to the erosion of the hill and it’s not clear how deep it might be. We also could not access every part of it safely and thus although we noted some 3000 elements, we estimate there are closer to 5000 exposed, and there could be huge numbers still to find. Out of these, barely a handful belonged to anything other than Shantungosaurus – a tyrannosaur tooth, a couple of tyrannosaur bones, a croc osteoderm and a bit of turtle. (And, oddly the near complete and articulated Zhuchengceratops, though I suspect it is from a different horizon). In short, this entire area and material essentially represents just one genus and probably a single aggregation.
All the material is essentially disarticulated and while basically every part of the skeleton is there, it is horribly jumbled. There’s no evidence of scavenging or trampling, and little sorting either, so this looks like a pretty major event that led to a rapid burial of the remains. We don’t dwell on what might have done this, but bearing in mind the size of these animals and how many there were and this is clearly something big, and also probably quick (this is not a long term accumulation of material).
Already 5000 elements is quite a bit, but the bones are also big. Shantungosaurus is well known as being a really large hadrosaur, but more than that, it’s absolutely colossal. While femur length is not the best size proxy out there, neither is it that bad, and was the only thing we could reliably measure for large numbers of the elements preserved that would give a decent size estimate. The largest femur we could accurately measure was 172 cm long – bigger than the largest specimens of Diplodocus and comparable to many big sauropods like Apatosaurus and Antarctosaurus. While they do have very different builds as animals, don’t forget that hadrosaurs were not pneumatic, so it’s quite reasonable that these animals had similar masses to those huge sauropods. Similarly that also means that perhaps many sauropods were not as heavy as the largest hadrosaurs which does have implications for how we look at things like the reasons sauropods did get so large. Mass estimates that are available or can be calculated for Shantungosaurs are extremely varied and this is perhaps due to it being so much larger than anything else known when it comes to hadrosaurs or even other ornithischians. Is is basically off the charts (few ornithischians have femora that exceed 1 m in length, and the smallest specimens we measured were bigger than this) and it probably needs to be tackled with a specific rigorous analysis to get a good estimate. Still, I’d be very surprised if the larger individuals were under 10 tons, and it is probably the heaviest ornithischian known and by extension, probably the heaviest terrestrial biped, since I didn’t see anything in the available material to suggest it could not walk bipedally.
Femora were also measured as they are large elements that are relatively easy to identify correctly and were in relatively decent condition, and so go some way to determining a minimum number of animals in the quarry. We counted 110 and so there is a minimum of 55 animals here, and I would be stunned if there were not very considerably more than that in reality (or indeed many more femora in there that are simply not exposed). But any measure then, this is a lot of animal – over 50 individuals, the smallest of which had a femur over 1 m long, and many of which were large sauropod sized. Indeed, the distribution of the femora actually tells us something too.
The range of sizes seen is actually really narrow: almost 85% of them fall between 135 and 175 cm and aside from three small ones that were little more than a meter, the rest form an almost perfect normal distribution. In short, this looks like a natural population of adult animals and we can infer they are adult both on the general size and the fact that all the elements of things like sacra in the quarry were fully fused. It has been suggested before that hadrosaurs form separate groups and that adults may have aggregated without juveniles, and with juvies and /or subadults forming separate groups, and that fits well with what we see here (and this also fits with the ideas covered in the forthcoming Protoceratops paper).
Collectively then the remains from this quarry do look something close to a natural aggregation, representing a pretty massive accumulation of biomass (over 50 animals and likely closer to 100, and probably over 10 tons each). It’s hard not to think about just what this means for a Mesozoic landscape, even a big Zhuchengtyrannus would be pretty much outclassed by one of these, let alone dozens together, and they would presumably have been able to strip huge swathes of vegetation clear as they foraged. For me at least it’s a nice evocative image, though perhaps not a long lasting one given that something massive rather dismembered and buried them shortly afterwards. Happily for palaeontologists we have now found this graveyard and there’s a massive amount of material available on these massive dinosaurs, and I hope that there is much more to come now that it is becoming available for study.