Sunday, June 2, 2013

Psittacosaurus, Allosaurus, Baryonyx, Wulatelong, Aurornis and Torvosaurus. Oh my!

You lying fossil! I believed in you!
It seems that within the last month paleontologists have been publishing a lot of new discoveries about some well-known dinosaurs, as well as discoveries from two new guys guy that I'll get to further down. Some of these discoveries have been of great interest to me, and it has encouraged me to write about it here before school ends and I get more free time to talk about other stuff.

*I don't want this blog to become a sort of news blog where people can come and hear about all the latest discoveries, but if there is something in the news that I find interesting, then I'll post about it. I won't be talking about every little news item, though.

To start off I wanted to talk about a heartbreaking discovery concerning Psittacosaurus. Psittacosaurus is a basal ceratopsian, and also currently holds the record of most known species of any non-avian dinosaur genus. It's also one of the best known dinosaurs, with hundreds of specimens that include details about its internal and external anatomy (even including color!), as well as its diet, ontogeny, and behavior. One of the greatest examples of the latter was the discovery of 34 juvenile Psittacosaurus nested underneath the body of the adult animal, for a long time considered to be one of the greatest examples of parental care among any dinosaurs. Until it was found to be a fake.

A re-analysis of the specimen in question by Zhao and associates found it to be a composite. The 34 juveniles and the 'adult' turned out to be glued together, and the 'adult' specimen in question wasn't even of reproductive age. All in all very disappointing, especially for myself, as the magazine article I've been writing for the last month happened to focus on this particular specimen, and with the news having been published four days before my article was due for publication, I was unable to revise it in time to make the deadline. That was really depressing for me, and I felt like I let a lot of people down. Updates are being made for the next issue, however. Or perhaps I'l focus on less-researched topic than dinosaur parental care, which is what I had originally planned. Perhaps I'll discuss discoveries of juvenile dinosaurs together in nests separate from adults. For instance, although the Psittacosaurus composite is no longer considered an example of parental care, the 34 juveniles still died together, and Zhao also talked about a new specimen which preserves multiple juveniles of differing age groups together, so there certainly are a lot of interesting points remaining to discuss.
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In other news, Witmer Lab has been at it again. This time they reconstructed the neck musculature of Allosaurus using computer models and found that, unlike Tyrannosaurus, Allosaurus did not suffer from as much forward inertia. The lighter head allowed the head to swerve and move around faster than big, boxy-headed Tyrannosaurus and thus the animal was probably more agile. This also brings to mind one of my old predator vs. scavenger posts, where I said that T-rex suffered from a large amount of inertia and likely couldn't turn quickly. This was no problem for Allosaurus.

video
Animation by Witmer Lab. I own nothing. Forever alone....
 
Another interesting observation that they made was that they think they revealed the feeding style of this predator. Apparently unlike Tyrannosaurs, which are thought to have used their jaws to violently shake and tear off pieces of meat, Allosaurus seems to have used its jaw to slice off pieces of meat rather like a predatory bird. This really interests me as a study last year also reported that dromaeosaurids had a predation-style similar to eagles, restraining the prey with the limbs while slicing off pieces of meat with the jaw. Perhaps Allosaurus was doing a similar thing as dromaeosaurids, slicing off pieces of meat on large animals like sauropods and stegosaurs, eating them alive. Extremely gruesome and somewhat revolting, but an efficient feeding strategy nonetheless.
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Baryonyx, perhaps not as much of a fish-eater as we thought.


Onto another fan-favorite, remember my post about spinosaurids a few month back? In it I talked about how Emily Rayfield conducted a study of a number of different theropods, including Suchomimus, and found something odd. Despite its length and lack of any notable features that would resist torsion, Suchomimus has a skull that could resist excessive force just as well as other large theropods. At first I thought that this was odd, and even she noted at the end of the paper that her numbers were inconclusive and required more in-depth studies, but now she and Andrew Cuff have come back with a new paper that backs up this idea.

By using the skull of Baryonyx, a close relative of Suchomimus, they ended up with the same results. Not just that but they also cross-reference the skull with that of living crocodilians (an American Alligator, African Slender-snouted Crocodile, and Gharial) and Spinosaurus and found that Baryonyx could withstand just as much torsion as some crocodilians and theropods, contrary to some studies suggesting that Baryonyx could only withstand as much torsion as a gharial. She also found that Baryonyx's skull reacted very different mechanically than a gharial, contrary to many other studies, including her own. One thing that really shocked me though was that she did find that Spinosaurus' skull reacted mechanically similar to that of a gharial, which again is contrary to some reports that it was better at withstanding mechanical forces than members of the Baryonychinae. Despite this, Rayfield and Cuff firmly state that when size is accounted for, both of the skulls "absolutely outperform all crocodilian taxa”.

I've yet to see how the paleontological community has reacted to this discovery, and it hasn't gotten much press, but now Rayfield and Cuff have suggested that perhaps the Spinosauridae as a whole might not have been obligate piscivores, but instead that perhaps diet was more reliant on size of the individual, as it is in living crocodilians. For example, juveniles crocodiles feed on small animals like fish and insects, mid-sized individuals mostly feed on fish and small game, and larger adult crocs mostly feed on land animals. This is an cool theory, and similar theories have been suggested for other theropods, so it certainly seems likely.
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Note the elevated toe claw.
Bear in mind, this is a oviraptorid, not a Deinonychosaurian.
Wulatelong gobiensis is a new species of basal oviraptorid from the Gobi Desert, and is the fifth new species of oviraptorid to be described this year. It's been a cool discovery not just because it is relatively complete, but it also seems to have died articulated in a relatively natural condition. However, the head and neck are preserved badly, and there aren't any unusual traits about it that make it stand out. It looks just like your average, run-of-the-mill oviraptorid at first glance, until you look down at the foot.

Although the original describers said nothing about it, images such as the one above clearly show that the second toe of this oviraptor has a large claw that is elevated off the ground. As I said, this specimen is articulated in a natural position, so it seems the claw was held in that position in life. If you don't know where I'm going with this, let me help you....

IT'S AN OVIRAPTORID WITH A DROMAEOSAUR-LIKE SICKLE TOE CLAW!

Currently there has been a lot of talk about this specimen, and some scientists are even stating that it might have implications for the evolution of such enlarged hyperextendable claws, that perhaps the ancestor of oviraptorids and dromaeosaurids had such a structure, and even that the trait might be common throughout the Ceolurosauria. It's a bit of a mess right now, but the curious thing that myself and the paleontological community are shocked about is the fact that Xu Xing and the original describers of the specimen don't even remotely bring this up in their paper. It's strange. The animal is found articulated in its natural position showing the claw hyperextending like that, and there's no mention of it whatsoever? I hope we get to hear more about this guy and get a confirmation about such an amazing example of a non-Deinonychosaurian sickle claw. As for why an oviraptorid would need such a claw on its foot, I don't know, but here are some ideas:



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New relationships of basal birds. Time to start rewriting the text books.....
Borrowed from Theropoda.


Aurornis xui (and yes, it is named after Xu Xing, although to my knowledge he didn't work on the specimen) is a new species and genus of basal bird from the mid-Jurassic of China, and has dethroned Archaeopteryx as the "earliest bird" by about 15 million years. It's a pretty awesome discovery, as it provides a snapshot of how birds got their start, and in this case, has also provided a new area of analysis for researchers looking into the question of where Archaeopteryx falls on the theropod family tree. In this case, they found that it is more derived than Aurornis, and that it, along with Anchiornis, Xiaotingia, and Rahonavis(!) are all basal birds. Not just that, but they also found that the troodontidae are not closely related to dromaeosaurids or deinonychosaurians at all! Instead, they seem to be apart on an unnamed sister-group to the avialans, which would explain why troodontids share so many similarities with birds, more so than they share with dromaeosaurids.

However, despite this new find nobody should think of the chapter on
Aurornis xui  as being closed, as I'm sure that in a few months we'll be getting another rebuttal paper stating some alternative ideas. The history of birds is filled with a lot of complex data, and we're at the point that defining birds as a group is harder than it looks, as there is literally no major differences between basal birds and other members of Paraves. We still have a lot more work to do, but having Aurornis with us will hopefully make it easier and not fuzzier.

Perhaps the most shocking find of all in this paper was the discovery that they made with Balaur bondoc. Apparently, it's not a dromaeosaurid; it's a basal bird and sister taxon to Pygostylia! That's a shocker, but there's good reason to think this is the case. The conclusion was based on a direct observation of the specimen, and a new monograph that came out that also came to this conclusion.

So, Balaur is some kind of Cretaceous dual-clawed killer dodo. That's going to take A LOT of getting used to...
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We FINALLY get some big theropod eggs and embryos!
And look at them, such cute little baby Torvosaurus.....
Torvosaurus was the largest predator in the Jurassic (ignoring Epanterias and Saurophaganax as they haven't been properly identified yet). This huge, heavily-built predator with serrated teeth, robust arms, and killer demeanor terrified most around it, but now we know that this species had quite a softer side, as Torvosaurus has now provided the first ever non-avetheropod eggs! Talk about a long wait! Nearly 200 years since the first Dinosaurs were described and 100 years since the first Maniraptor eggs were discovered, and it's only now that we're getting some big theropod eggs? Fossilization is horribly bias sometimes, but I'm happy that we finally found them. Now we just need a thyreophora and neoceratopsian nest and I can die peacefully.

Moving on with this amazing find: These eggs are actually not THAT new; apparently they were first unearthed in 2005 but are only being described now. They were found in a clutch along a hillside and consist of a large number (exact number unknown) in the Lourinhã Formation in West Portugal. For those who are also dino-nerds, you'll remember that a clutch of eggs from the the Allosauroid/Coelurosaur Lourinhanosaurus were also found here. This might suggest that perhaps the area was favorable for breeding theropod females, or maybe that the fossilization process there is biased towards dinosaur eggs. Either way, somebody's got to check out that area for more of these clutches.

The microstructure of the eggs is also unique among theropods, as it has only one eggshell layer, while most theropods have two and birds have three. The eggs also seem to have been buried, as the openings in the eggshell are large to let in air, and the eggs themselves are not disturbed, suggesting that they were already buried by the mother. They were either buried in sediment or plant material, similar to what is seen in crocodiles, so perhaps parental care in this species was also crocodilian-like, but I'll save talking about that for my revised article. ;)

So, what's your favorite discovery in paleo-news recently? Feel free to share, and as always, stay tuned and stay sharp!

References:

Cuff AR, Rayfield EJ (2013) Feeding Mechanics in Spinosaurid Theropods and Extant Crocodilians. PLoS ONE 8(5): e65295. doi:10.1371/journal.pone.0065295

Eric Snively, John R. Cotton, Ryan Ridgely, and Lawrence M. Cotton, Ryan Ridgely, and Lawrence M. Witmer (2013) Multibody dynamics model of head and neck function in Allosaurus (Dinosauria, Theropoda). Palaeontologia Electronica Vol 16, Issue 2, 11A 29pp.

Godefroit P., Cau A., Hu D.-Y., Escuillié F., W. Wu, G. Dyke 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature doi:10.1038/nature12168

Qi Zhao, Michael J. Benton, Xing Xu, and Martin J. Benton, Xing Xu, and Martin J. Sander (2013) Juvenile-only clusters and behaviour of the Early Cretaceous dinosaur Psittacosaurus. Acta Palaeontologica Polonica (in press) doi: http://dx.doi.org/10.4202/app.2012.0128

Ricardo Araújo, Rui Castanhinha, Rui M. S. Martins, Octávio Mateus, Christophe Hendrickx, F. Beckmann, N. Schell & L. C. Alves (2013) Filling the gaps of dinosaur eggshell phylogeny: Late Jurassic Theropod clutch with embryos from Portugal. Scientific Reports 3 : Article number: 1924
doi:10.1038/srep01924

Xu X., Tan Q.-w., Wang S., Sullivan, C., Hone, D. W. E., Han F.-l., Ma Q.-y., Tan L. & Xiao D. 2013. A new oviraptorid from the Upper Cretaceous of Nei Mongol, China, and its stratigraphic implications. Vertebrata PalAsiatica 51 (2): 85–101.