Sunday, 29 March 2015

Ptiny pterosaurs of the Late Cretaceous

Forgive me for the title, it was just too tempting when talking about little pterosaurs!

Azhdarchid pterosaurs are known from the Late Cretaceous mostly of North America, Europe, and Africa, with fossils found in Alberta, Montana, Texas, Romania, the Baltics and more. Several genera are known ranging from 2.5 m wingspan Montanazhdarcho all the way up to 10-11 m Quetzalcoatlus and Hatzegopteryx. 

Pterosaurs have been shown to increase in size over the Cretaceous, with the largest pterosaurs ending up at the end of the Cretaceous in the azhdarchids. In the mid-Jurassic, birds started to appear, giving the pterosaurs competition in the skies. Some studies have suggested that both groups were able to survive by occupying different niches [1], others have shown that pterosaur diversity did not decrease until the Late Cretaceous so this was unlikely to be caused by birds [2], while recently it has been suggested that birds outcompeted small pterosaurs, driving them to the gigantic sizes seen in Late Cretaceous azhdarchids [3]. Of course, this is not agreed upon, and other studies suggest it's a preservational bias that is keeping the small Late Cretaceous pterosaurs from being preserved, not that they didn't exist at all [4].

There is some evidence of smaller pterosaurs from the Late Cretaceous including those of Montanazhdarcho and Eurazhdarcho, but also some smaller fragments around that point to some very small pterosaurs. Another small pterosaur is one called Piksi, known from small fragments from the Two Medicine Formation. First described as a bird, only a few small wing fragments have been found including the distal humerus, and the proximal radius and ulna [5]. It had an estimated wingspan of just 1 m, and is thought not to be an azhdarchid, but an ornithocheiroid, a group not really present in the Late Cretaceous. This is the first example of a possible small pterosaur in the Late Cretaceous, but there are also potential examples of small pterosaurs from other parts of the world, but no clear examples yet.

While small pterosaurs are obviously not common in the Late Cretaceous, there do seem to be some examples which suggest there is something else going on than just them being outcompeted by birds. Another interesting fact is that there are no confirmed records of azhdarchid juveniles from this time either. Obviously for there to be giant pterosaurs, they have to be juvenile at some point. While there are reports of other pterosaur juveniles at different time periods around the world (e.g. "Nemicolopterus", Pterodactylus, Hamipterus) and even embryos (like Pterodaustro), we would expect to find juvenile azhdarchids, yet these haven't been found. Often in the fossil record we find that that are biases in what is preserved and what isn't, and these biases change between environments, throughout time, and in different localities. One such bias is known from Dinosaur Provincial Park in Alberta, where azhdarchid pterosaurs are known from. Very few small dinosaurs or animals in general are found in this area, and this is especially seen in juveniles. Juveniles are extremely rare. If this is known from other areas and taxa, why not for pterosaurs?
"Nemicolopterus" which may be a juvenile Sinopterus, a tapejarid from the Lower Cretaceous of China. Image copyright John Conway. 

The fact that no juvenile Late Cretaceous pterosaurs have been found makes me extremely reluctant to agree that no small pterosaurs existed during this time. There must be some kind of preservational bias keeping small pterosaurs and juveniles from being preserved. As we find more localities and more fossils, more evidence is suggesting that there were more than just giant pterosaurs around in the Late Cretaceous, we just need to find them!

Next week I'm off to Romania on the hunt for these tiny pterosaurs (and the big ones too)... Wish me luck!

1. McGowan, A. J., and Dyke, G. J. 2007. A morphospace-based test for competitive exclusion among flying vertebrates: did bats, birds and pterosaurs get in each other's space? Journal of Evolutionary Biology 20: 1230-1236.
2. Butler, R. J. et al. 2009. Estimating the effects of the rock record on pterosaur diversity patterns: implications for hypotheses of bird/pterosaur competitive replacement. Paleobiology 35: 432-446.
3. Benson R. B. J. et al. 2014. Competition and constraint drove Cope's Rule in the evolution of giant flying reptiles. Nature Communications 5: 3567. 
4. Vremir, M. et al. 2015.A medium-sized robust-necked azhdarchid pterosaur (Pterodactyloidea: Azhdarchidae) from the Maastrichtian of Pui (Haţeg Basin, Transylvania, Romania). American Museum Novitates 3827: 1-16.
5. Agnolin F. L. and Verrichio D. 2012. Systematic reinterpretation of Piksi barbarulna Varricchio, 2002 from the Two Medicine Formation (Upper Cretaceous) of Western USA (Montana) as a pterosaur rather than a bird. Geodiversitas 34:883-894.

Tuesday, 17 March 2015

Bring azhdarchids down to the ground

Last week, palaeontologist Mike Taylor (of SVPOW) brought up a very good point on twitter:
And many of us whole-heartedly agree. Flying models of azhdarchid pterosaurs are what typically grace museums, if they appear at all. These are impressive, but also often missed. For example, at the AMNH pterosaur exhibit on that ended earlier this year, there was a giant fleshed out azhdarchid model on the ceiling. The problem? It was in a room with lots of things that people were more interested in, and hardly anyone actually looked up and saw it. Even once you do see it, it's hard to really understand how big it is, and that it is really a model of a real, flying animal.
Full-sized flying azhdarchid model at the State Museum of Natural History, Karlsruhe
An azhdarchid pterosaur standing to attention with a giraffe
and human for scale. Image copyright Mark Witton.
However, if you stand an animal on the ground next to something they are used to seeing (or even better, where they can stand next to it), the scale suddenly becomes a lot more clear and it's much easier to be amazed by the size. Take Mark Witton's iconic azhdarchid with giraffe for scale - it allows us to really appreciate how big these animals were. I think everyone would agree that a giraffe is a very tall animal, and the biggest azhdarchids were just as tall. Tell me that isn't impressive! Pterosaurs don't always need to be depicted with their wings outstretched and flying. They were equally as impressive on the ground walking around on all fours. Additionally, depicting a pterosaur on the ground teaches people that pterosaurs were actually quadrupedal animals. They were not walking around on their hind limbs like birds, and like many old depictions show. They walked with their wing finger bent up behind them and their hand down on the ground as shown in the image above. We know this is true thanks to the anatomy combined with a number of trackways attributed to pterosaurs that clearly show 2 different sets of prints: a hind limb set and a forelimb set. Bringing those pterosaurs down to the ground both reiterates how large they were, AND teaches people something about their biology. What could be wrong with that?

I can personally attest to how impressive a standing floor mount of an azhdarchid can be, and what it can do. I've always been interested in palaeontology, but was never sure exactly what I wanted to study. That was until I went to France in 2009 on a family trip during my undergraduate degree. I had heard about a small but interesting natural history museum in Esperaza, and we decided to check it out. Here I saw my first (and only) azhdarchid floor mount, and was instantly amazed. I'm not sure how long I stood there, but  I can tell you that I spent probably 20 minutes looking at this thing from different angles in awe. That was the moment that I decided I wanted to study pterosaurs, and it was that instant that made me ask the question "how did these large animals fly?". And to top it off, that mount isn't even showing the azhdarchid standing to full height. It's sprawling quite a bit, and should be even taller.
The Quetzalcoatlus standing skeletal mount in Esperaza (sorry the picture isn't great!)
While they are frequently depicted in palaeoart down on the ground, they are so rarely shown this way in museums. I wholeheartedly agree with Mike Taylor and Mark Witton about this - bring azhdarchids down to the ground! Let people stand beside them and look up at them. It's the best way to truly show how big the animal is. It's what I owe my current love for pterosaurs to!

- Thanks to Mike Taylor and Mark Witton for the idea, and Ben Miller and Joe Hancock for the blog post encouragement!

Monday, 9 March 2015

AMNH Pterosaur Exhibit

From April 5 to January 4 the American Museum of Natural History in New York (AMNH) had a special exhibit called "Pterosaurs: Flight in the Age of Dinosaurs". I was lucky enough to make it to see the exhibit over the final weekend while I was on a research trip to see the collections.

The exhibit was curated by the AMNH palaeontology curator Dr. Mark Norell, and Brazilian pterosaur expert Dr. Alexander Kellner, with some help from Dr. Mike Habib, a palaeontology and flight expert (and one of my many supervisors). It included fossils from all over the world, and was generally very well done in my opinion, encompassing some controversies in pterosaur palaeontology, old and new ideas, and some of the most recent studies and finds. It was also accompanied with a fantastic gift shop including a very-well illustrated book based on the exhibit.
The front of the book, featuring a Tupandactylus.
Back cover featuring an assortment of pterosaurs.
Dsungaripterus skeleton
It started in the same way as most exhibits with a background of pterosaur research, explanation of what pterosaurs are, and an overview of their diversity. They discussed pterosaur locomotion, including some fossils of footprints and various things. The exhibit was full of life-size skeletal models of pterosaurs that hung over top of you as you went along, which was a really cool addition, including Dsungaripterus shown here.

It was starting at about this point in the exhibit that I started getting really excited. First of all, there were some really well done (and also simple) educational displays explaining features like the wing structure in pterosaurs (vs. birds and bats) and the hollow aspect of the bones. Of course anyone who has read my blog before and seen my posts on pneumaticity in pterosaurs and birds will guess that I like hollow bones. I enjoyed the explanations and diagrams on the hollow bones and the comparison of pterosaur bones to airplane wings with the trabeculae acting as struts (see image below). However, there is some evidence that the trabeculae in the shaft actually didn't do a lot in terms of strengthening the bone and preventing bending or torsion, but still a cool analogy.
The next room of the exhibit focused on the flight capabilities of pterosaurs, and included a number of flight games that allowed people to stand in front of a camera and pretend to be a pterosaurs. It was entertaining to watch the kids flap around and try to be a pterosaur while the pterosaur on-screen mimicked what you did. They included flying, taking off, taking off from water, picking up fish from water, chasing insects, etc. The unfortunate thing about these videos is that they were so distracting to the kids that most of them failed to notice the giant life-size model of Quetzalcoatlus northropi suspended from the ceiling above. It was so big (and the lighting was so poor and I forgot my flash) that I didn't get a picture, but it was impressive. Along with it was a replica of the humerus, just to show how big it really was.
Quetzalcoatlus northropi humerus replica
The rest of the exhibit focused on looking at the different sizes, shapes, and possible functions of the cranial crest, followed by a special focus on the Araripe Basin of Brazil where a large number of exceptional pterosaur fossils (and much more) come from. 

The highlights of the exhibit for me included:
The "Dark-wing" Rhamphorhynchus
1. The "Dark-wing" Rhamphorhynchus - Anyone who works on pterosaurs knows this fossil as one of the best preserved, three-dimensional Rhamphorhynchus fossils from the Solnhofen in Germany. The best part of this fossil, however, is that it also preserves a large amount of soft tissue, and is the fossil that gave us the first true insight into the internal structure of the wing membrane. It is a truly wonderful fossil, and is actually owned by a private fossil collector in Germany, so is rarely seen on display. This was the first time the specimen had been on display outside of Germany, and it was a joy to see. I was hoping to be able to examine it after the exhibit was done, however, that was not possible.
AMNH 22555 - Anhanguera santanae
2. AMNH 22555, one of the best preserved specimens of Anhanguera santanae - This specimen is a beautifully preserved skeleton including the head, neck, much of the pectoral girdle (but unfortunately only bits and pieces of the wing), trunk, pelvic girdle, and some of the legs. It shows very well how weird the body proportions of pterosaurs can be with a massive head, long neck, small trunk, and tiny pelvis. It's especially interesting to me for several reasons: a) it was described by pterosaur legend Peter Wellnhofer; b) It is 3-D and therefore much of the original structure can be determined; and c) I have had the opportunity to view CT scans of it thanks to Pat O'Connor, who previously scanned the specimen. After the exhibit finished, I also was lucky enough to examine it up close in collections for several days. 
Romanian pterosaur bones. Top right is a syncarpal
(wrist bone), and bottom left is a cervical (neck)
3. Romanian pterosaurs - At the very end of the exhibit, where many people walked past thinking it was not interesting, was a small display on the "next big thing" in pterosaur palaeontology, including 2 casts of giant Romanian pterosaur bones. This is interesting to me first of all because my research group in Southampton does field work in Romania where these bones are found and is involved with these studies (and I was lucky enough to have one of those bones placed in front of my by my supervisor early in my PhD), but also because as a pterosaur palaeontologist any giant pterosaur bones are interesting to me. I was also happy to see an image by my friend and great palaeo-artist Mark Witton in the case, showing Romanian pterosaur Hatzegopteryx. There is some great stuff coming out of Romania, and I'm looking forward to heading back at the end of the month. Maybe we'll find more! 

Of course with any exhibit, and with a pterosaur one in particular, there are going to be some things I'm unhappy with. There were 3 I can think of, but they have annoyed me quite a bit. These are:
Goofy looking Nyctosaurus with a fleshy crest.
1. The constant depiction of Nyctosaurus with a fleshy sail-like head crest - In the portion of the exhibit on head crests, there is a replica of the famous crested Nyctosaurus skull. Along with this is a portion of text that read "Most scientists think these bony prongs were connected by soft tissue... Some think they could have remained bare, like deer antlers". I was quite surprised when I read this, and immediately consulted with fellow pterosaur-palaeontologist Dave Hone, and we agreed that we didn't know anyone that still thought there was soft tissue. In fact, there is no evidence to suggest that there was soft tissue on their crest... Every image of Nyctosaurus in the exhibit was reconstructed to have a giant, awkward sail on it's head!
2. Discussion of skim-feeding - This isn't particularly surprising as there are a number of people that support this, but there is also a significant amount of evidence that says they were not able to do this. Dip-feeding, yes. Skim-feeding, no. I haven't looked at it empirically, but I can just think mentally that once a pterosaur opened it's mouth in the water there would be so much drag that it wouldn't be very good for the animal's jaw. I know that Darren Naish and Mark Witton have looked at this a lot, and it seems to make sense that they couldn't feed that way. However, there was no discussion of these problems or other views, not entirely surprisingly.
3. "Dawndraco" cast - This bit has annoyed me for a few reasons. First of all, there is much debate about the validity of this species. Despite this, there was a massive cast and focus on the species, and no mention of the other viewpoints. This leads me to my next problem with it, which you may be familiar with if you read my post on fossil casts. It's a minor problem, but it still annoys me... The original of this specimen is housed at the University of Alberta, my old university. The specimen on display at the AMNH was a cast of the original. Despite other casts in the exhibit correctly stating that they were casts, this specimen said it was the original skeleton. And to frustrate me even more, the specimen number was incorrect! This specimen has a history of being incorrectly referred to in the literature, despite being one of the best pteranodontid specimens in existence. Give credit to the correct institutions, label specimens correctly, and don't say it's an original when it isn't... I'm sure it was an honest mistake, but how can so many "honest mistakes" come with one specimen?!

So there's my take on the AMNH pterosaur exhibit. Anyone who wants to know more about it can go to their website where there are videos to watch and some more information. I wish I could have posted this in time to recommend people to go, but unfortunately, I only got to see it on the last day... However, I get to enjoy it again each time I have a shot or make a drink from this awesome shot glass: