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!

References
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 (HaĊ£eg 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)
vertebra.
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:

Friday, 27 February 2015

Fossil casts are not "fake"

After the news story a few weeks ago about the replacement Dippy the Diplodocus at the Natural History in London with a blue whale skeleton, there has been a lot of talk in the media and palaeontology community. I'm not going to go into why Dippy should or shouldn't be replaced, as it has been covered by numerous palaeontologists and news sites (for example, palaeontologist Steve Brusatte and HuffPost Technical Editor Michael Randle argue it's a good thing, while others like palaeontologist Mike Taylor disagree with the idea), but I will talk about another thing that has come up since then. One thing that a lot of non-palaeontologists have been saying is “oh well it was fake anyways” since it was made up of replica bones rather than real fossils. This is something that really bugs me.

I’m not sure why this has been picked up so much recently that casts and replicas are just “fake”. First of all, fake is something that is made with the intent to deceive. Fake money is meant to replace real money, or fake designer purses are meant to look like the real ones they imitate so people don’t know you have a fake. A replica or cast of a fossil is not meant to deceive. That is not the purpose. Any signs about the specimen will (or at least should) state whether the specimen is a skeleton, cast, or composite. No one is trying to trick you! You just have to read the signs!

The next important point is how these casts are made. Fossil casts are made from real fossils. There are many ways of making them, and I’m no expert so I won’t discuss that here. What I know is that people who make fossil casts, especially good ones, is that they put A LOT of effort into making them look as accurate and real as possible. They are most often made from some kind of mould that is made from the fossil using something like silicone or rubber. After that, plaster or something else hard is poured into the mould which allows for the exact structure of the original to be seen. Finally, the cast is painted and coloured in a way that matches the original specimen. When done properly and well, these casts look almost identical to the original fossil and only close examination by experts will reveal it as a cast. The best cast I have seen was of the pterosaur “Dawndraco” (or Pteranodon if you prefer) in the American Museum of Natural History (AMNH) pterosaur exhibit that ended in January. Just 2 weeks before I had seen the original at the University of Alberta, and was so convinced by the cast that I actually emailed the people who made it to confirm that it was indeed a cast (it wasn’t labeled as a cast, naughty AMNH!). Only because I knew it was not original was I able to spot the signs, but it was hard. The important thing to note here is that they are not just “fake” fossils that are made from someone’s head. These are (usually) skilled professionals who are basing their model off of a real fossil, and it is meant to look as close as possible to the original.
Original specimen of "Dawndraco kanzai", a pteranodontid from Kansas. Original housed at the University of Alberta
Cast of "Dawndraco kanzai" on display in the pterosaur special exhibit at the American Museum of Natural History
It's a bit hard to tell from the pictures as the lighting and angle is different, but I can tell you that they looked incredibly similar and the cast looked very real.

The final point to make with this is why museums have casts, especially as their large centre pieces. There are 2 reasons for this. First of all, fossils are rare. Despite what you may think by seeing all these fantastic fossils in museums, they are exceedingly rare. Not every museum has the money to buy a real fossil, or the ability to go out into the field and dig up their own, so they have to rely on casts. If not for casts, very few people would be able to see the specimens. Additionally, if fossils are rare, beautiful, complete fossils that look like Dippy are exceptionally rare. Most often fossils are found with bones missing, or smashed. Fossil replicas and casts allow for these missing bits to be filled in from other partial skeletons, which is what we call a composite skeleton. These can be made from skeletons that are incomplete so some bones are real, some are not. And of course, when we do find one of those exceptionally rare complete or near-complete fossils, casts allow us to share them with the world and show other people. And finally, fossils are of course extremely fragile. It can be very difficult to mount a skeleton in a way that isn't going to damage the specimen, especially if they are fragile. For this reason, museums will sometimes put the cast on display, and keep the original specimen in the collections in order to preserve it. Does it make it any less amazing? Personally, I don't think so. I'd rather know that the original is being conserved and properly looked after than see it on display in a museum. 


Fossil casts are not “just a fake”. They are replicas of rare and uncommon treasures. Without casts, most of the world would not be able to see these treasures. Dippy, for example, comes from the Morrison Formation of the USA originally. The likelihood of the Natural History Museum in London getting it’s hands on a complete skeleton of a large sauropod from the USA is pretty unlikely. So what would you prefer, no dinosaur at all? Or an exact replica of a real one that existed on another continent, allowing you to wonder in awe?

Thursday, 19 February 2015

People-snatching pterosaurs

I'm sure by now everyone has seen the recent Jurassic World trailer and palaeontologists and dinosaur fans alike have been salivating over it. The paleontological community is mostly in uproar over the scientific inaccuracies, mainly related to the lack of feathers on the theropod dinosaurs (for a few examples see Brian Switek here, Mark Witton, etc), but there have also been a few other comments about some problems with the creatures seen in the movies.

Of course for me, I notice how poorly done the pterosaurs are with respect to their contemporaneous dinosaurian relatives (remember, pterosaurs aren't dinosaurs!). I think Mark Witton put it the best:
I'm not going to go into the general inaccuracies of the pterosaurs (e.g. they should be covered in fibres, more meaty, etc), but I will talk about this problem of people-snatching pterosaurs. This is something that goes back quite far in Hollywood and dinosaur-related movies. There is always an image of a large pterosaur (typically Pteranodon) swooping down and picking up a person and flying away.
Nice grainy image of the Pteranodon flying away with a poor, unsuspecting woman in Jurassic World
Painting of a Peregrine falcon by John Gerrard
Keulemans. Notice the foot on the front bird and
how it is grasping the branch. 
THIS WAS NOT POSSIBLE!

Drawing of a Golden Eagle foot by Lydekker (1895)
showing the 4-digit structure of the foot.
There are several reasons for this, and I'm going to demonstrate this by comparing them with birds. In order to pick something up like that, you need some kind of grasping foot. Anyone who has had any type of raptor (as in the bird raptors - hawks, eagles, etc.) sit on their arm knows what this feels like. Their feet have 3 forward-facing clawed toes, and one reversed digit, known as the reversed hallux that faces backwards, allowing for a 4 digit grasping claw. This is what allows birds to perch on a branch, as they are able to grasp the branch to prevent themselves from falling off. This is also what allows these kinds of birds to pick up their prey as they swoop down. An important thing to note about that is that their prey is typically quite a bit smaller than they are (e.g. mice, rabbits, fish, etc.), although some of the larger birds have been known to kill bigger animals such as deer, antelope, etc. However, if a bird does this, it doesn't fly off with the prey, but rather will kill it and eat it in place. If it's going to fly off with it, it'll go for something much smaller. Another key bit of information with birds that do this - they have strongly muscled legs. Birds take off with their legs, and in comparison have very muscly feet and legs.

With that in mind, let's think about pterosaur feet. Pterosaurs have slender, weakly muscled feet. While the earlier non-pterodactyloids had 4 long, slender clawed digits that would have been flat on the ground during walking (in a plantigrade posture), the 5th digit was still elongated but did not touch the ground when walking (but was also not reversed as seen in birds). In more derived pterodactyloids, the 5th digit is almost entirely lost. None of these digits are reversed like in birds, and do not show the grasping structure as is typically shown in movies. Furthermore, pterosaur legs are weakly muscled, with most of their musculature occurring in the wings. They simply would not have had the musculature present to grasp prey in the same way that birds do.
Drawing of pterosaur hindlimbs from Witton (2013). A represents a pterodactyloid hindlimb (Anhanguera) with the nearly missing digit V, while B shows a non-pterodacctyloid (Rhamphorhynchus) with an elongated (but not clawed) digit V. 
The final "nail in the coffin" so-to-speak about people-snatching pterosaurs is the problem of weight. As I mentioned above, birds pick up small prey, typically much smaller than their body mass. Pterosaurs, however, are depicted picking up children or full grown humans. As it's typically Pteranodon being represented this way, we'll look at them. A large Pteranodon had a wingspan of about 6 m, and weighed probably somewhere around 35 kg if you go with the heavier estimates that I tend to favour from Witton (2008). The woman shown above that was carried off quite easily by a Pteranodon was probably somewhere around 60 kg at least. That means that it would have had to have been capable of carrying something and flying off with more than double it's initial mass. Considering there are already debates about if large pterosaurs were capable of flight (ok this isn't normally debated in Pteranodon, but I'm trying to prove a point!) there is no way it could fly if it was suddenly responsible for flying off with an additional 60 kg. Flight is hard enough as it is, and that additional mass would make it impossible. Then when you consider that 35 kg is a heavy estimate, moving do the lighter estimates and more "shrink-wrapped" pterosaurs to quote Witton, there is just no way.

So next time you see a pterosaur flying off with a person in tow in any kind of movie/tv show/etc., remember that it just couldn't happen. If pterosaurs were alive today, that would not be a concern we would have to deal with!

Special thanks to Tony Martin for giving me the idea for this post!

References:
Witton, MP (2008) A new approach to determining pterosaur body mass and its implications for pterosaur flight. Zitteliana B28: 143-158.
Witton, MP (2013) Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press, Princeton, USA. 304 pages. 

Saturday, 14 February 2015

Pterosaurs are not dinosaurs!

This post isn't the kind of post I normally do, but it stems from a conversation I had with someone at Science Borealis when they shared my Canadian pterosaur post and incorrectly called them dinosaurs. Being a pterosaur palaeontologist, this is something that I deal with constantly, the misconception that pterosaurs are 'flying dinosaurs'. I am going to try to explain why this is scientifically inaccurate.

The first thing to understand is that both the terms "dinosaur" and "pterosaur" are scientific terms with specific definitions and meanings, just like a mammal, reptile, or fish. All of these are scientific names that are used within the common tongue, but hold specific scientific definitions. Dinosaur stems from Dinosauria, the name of the group that includes all dinosaurs, while pterosaur represents a member of the Pterosauria or Pterosauromorpha. There is a tendency in popular culture to call any large extinct animal, particularly if it lived during the Mesozoic, a dinosaur. Unfortunately, this is incorrect. Pterosaurs were not dinosaurs, marine reptiles (like plesiosaurs, ichthyosaurs, and mosasaurs) were not dinosaurs, and neither was Dimetrodon, that weird sail-backed reptile from the Permian. In fact it's more closely related to you and I than it is to dinosaurs as it is a mammal-like reptile. To learn more about that, you can go to a blog I previously wrote for Jurassic Forest called Mesozoic Musings.

So how are pterosaurs and dinosaurs related, if at all? 

Pterosaurs and dinosaurs are closely related, meaning they share a number of features, but are still distinct groups, or clades as we call them in biology. They both belong to a group called the Archosauria, which includes crocodilians, dinosaurs (including birds, as they evolved from dinosaurs and therefore are dinosaurs by definition), and pterosaurs. Archosaurs share a number of characteristics including an antorbital fenestra (a hole in the skull in front of the eye) and teeth set in sockets. However, early in archosaurian evolution there was a split between crocodilians and their close relatives (the crurotarsans or pseudosuchians) and birds and their closest relatives, including dinosaurs and pterosaurs (known as the avemetatarsalians). Avemetatarsalia is a mouthful, but it's pretty easy to break down. Basically this group is united by a bird-like ankle, among other features. Within this group is another group called the Ornithodira, which means bird-neck, again uniting the group with features of the neck that are bird-like, and includes both pterosaurs and dinosaurs.

So now we know that pterosaurs and dinosaurs are united by a number of features including (but not limited to) an antorbital fenestra in the skull, teeth set in sockets and a bird-like structure of both the ankle and neck.
Cladogram from Nesbitt (2011) showing the relationships in the Archosauria, including the Avemetatarsalia, Ornithodira, Pterosauromorpha (including pterosaurs and their close relatives) and the Dinosauromorpha.

What features separate pterosaurs and dinosaurs?

There are a large number of features that distinguish each group, and they are very different anatomically, but I will only mention some of the major ones, specifically features that pterosaurs have and dinosaurs do not. Pterosaurs are highly modified for flight, and right now, we don't fully understand how they evolved. Several of the features that distinguish them from dinosaurs and other animals are related to this. The two most obvious features include:
1.  An elongated 4th digit (finger) to which a flight membrane attached. Pterosaurs have lost their fifth digit (their pinky finger), but have an extremely long 4th finger. Imagine you had no pinky, but a ring finger that was longer than the rest of your arm. These is a feature unique to pterosaurs, and found in all pterosaurs. 
2. Possession of a pteroid bone. In the pterosaur wrist, an additional bone is present called the pteroid.  This bone points most likely antero-medially (forward and into the middle in flight) and likely controlled the position of the wing membrane in between the wrist and the body. This bone is not found in any other animal.
Drawing of the wing of the pterosaur "Santanadactylus pricei" showing the elongated 4th finger and pteroid bone. Image from Witton (2013), redrawn from Wellnhofer (1991).
There are a number of other anatomical features that separate pterosaurs from dinosaurs that are unrelated to the wing, including several features in the skull (e.g. their skull is very long with respect to their vertebral column), vertebrae (e.g. their neck vertebrae are long compared to other vertebrae), and legs. In total, there are at least 13 characters that unite the Pterosauromorpha, that are not found in combination or at all in dinosaurs. 

Hopefully this has shown why palaeontologists cringe whenever someone calls a pterosaur a flying dinosaur. To quote Brian Switek's article on the same topic, "calling a pterosaur a dinosaur is an error of the same order of magnitude as saying that our species is a marsupial". So next time you talk about a pterosaur, or write an article about one, please don't call them a dinosaur! 

References
Nesbitt, SJ (2011) The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pages.
Wellnhofer, P (1991) Weitere Pterosaurierfunde aus der Santana-FOrmation (Apt) der Chapada do Araripe, Brasilien. Palaeontographica 215: 43-101.
Witton MP (2013) Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press, Princeton, USA. 304 pages. 

Friday, 6 February 2015

Canadian pterosaurs

It's pretty common knowledge that Canada is rich in fossils, and particularly well known for both the Cambrian Burgess Shale in the Rocky Mountains of British Columbia, and of course the Late Cretaceous dinosaur-bearing formations of southern Alberta. Additionally, marine fossils from a bit earlier in the Cretaceous are found from when Alberta was covered by the Western Interior Seaway, including fish, sharks, and marine reptiles. The Late Cretaceous formations are most famous for dinosaurs, but also preserve plants, mammals, turtles, other reptiles, and pretty much everything you would expect to find in the ecosystem. They also exist all over the province with body fossils round in all corners, while footprints and trackways are commonly found in the northwest and into British Columbia. If you're interested in learning more about the dinosaurs of Alberta, check out this Palaeocast interview I did with Dr. Phil Currie of the University of Alberta.

But what about the pterosaurs?

But we're not interested in the dinosaurs of Alberta. They are well documented, and we know they are common, but what about pterosaurs? In a Late Cretaceous environment full of dinosaurs, we would expect pterosaurs to be found as well. Other similarly aged formations around the world have pterosaurs, so Canada should too. In the slightly older marine sediments, pterosaurs such as Pteranodon and Nyctosaurus are found commonly (at least Pteranodon is) in the US, where the sediments come from the same Western Interior Seaway as found in Alberta. Pteranodon is the best known pterosaur by number, with thousands of Pteranodon fossils found so far from the chalk formations of Kansas. Moving into the latest Cretaceous where the dinosaur fossils dominate, similarly aged formations frequently uncover azhdarchid pterosaurs, specifically large ones. In the Hatzeg basin of Romania, Eurazhdarcho represents a smaller azhdarchid, while Hatzegpteryx is a massive 10-11m wingspan pterosaur, and pterosaur fossils are relatively common. Moving southeast, there's the giant Arambourgiania from Jordan (pictured below), and then into Texas we have the best known Quetzalcoatlus, both a smaller form, and the giant Q. northropi.
The giant pterosaur Arambourgiania with a giraffe and human for scale. Image copyright Mark Witton.

Alberta pterosaurs

Knowing that similarly-aged rocks all over the world produce pterosaur fossils, we would expect to find them in Alberta. However, while they do exist, they are very uncommon. The first pterosaur found in Canada was a partial first wing-finger phalanx from the Oldman Formation of Alberta described in 1972[1]. It was a pretty unexciting find (at least in terms of the material present), and represented a pterosaur with a wingspan of around 3.5 m. 10 years later, a long bone shaft and cervical (neck) vertebra were found and attributed to the giant pterosaur from Texas, Quetzalcoatlus[2]. However, more recently the long bone shaft has been interpreted as a possible elongated cervical vertebra, as they are very long and can look like long bones if the ends have been broken off [3].
The first pterosaur from Canada - a first wing phalanx from the Oldman Formation in Alberta. Image from Russell (1972).
An incomplete cervical vertebra in dorsal view of cf. Quetzalcoatlus. Image from Currie and Russell (1982).
So far, there is only one partial associated skeleton that likely represents a single animal and consists of a cervical vertebra, rib, humerus, pteroid, metacarpals III and IV and a tibia (TMP 92.83) [3-4]. This is thought to have a wingspan of about 5 m, corresponding with the smaller Quetzalcoatlus from Texas. One of the interesting features of this specimen is that the tibia has a velociraptorine tooth embedded in it, likely from the dinosaur Saurornitholestes, thought to be a result of scavenging [4].
Tibia of TMP 92.83 showing bite marks (a, b, c) and an embedded velociraptorine tooth (d). Image from Currie and Jacobsen (1994).
Right humerus of TMP 92.83. Image from Godfrey and Currie (2005).
Distal end of a non-azhdarchid wing
metacarpal from the Oldman Formation.
Image from Currie and Padian (1983).
A few other fragmentary isolated bits have been found including several cervical vertebrae, a few wing bones (humeri, metacarpals, wing phalanges, etc.), and some leg bones (femora, tibiae, and a metatarsal). The majority of the specimens are thought to be azhdarchids, with smaller bones possibly representing Montanazhdarcho and larger ones being similar to Quetzalcoatlus. However, there are a few that seem to represent a species other than an azhdarchid. This is represented by two partial wing (4th) metacarpals, one of which was originally described as a tibia [5], but is clearly a metacarpal. These distal metacarpals closely resemble the ornithocheiroid pterosaurs Santanadactylus and Pteranodon, suggesting maybe some ornithocheiroids were present in Alberta as well [3]. Unfortunately with so few and fragmentary remains, we don't know for sure. Also unfortunate is the lack of skull material from Alberta, with no cranial specimens reported so far.


Pterosaur track from the Wapiti Formation of
northwest Alberta. Image from Bell et al. (2014).
Of course body fossils aren't the only fossils we find. There is one reported footprint from a pterosaur from northern Alberta, southwest of Grande Prairie near the Wapiti River. This print is interpreted as a right manus (hand) print from a large pterosaur, estimated at 7.7 m wingspan [6]. It is currently the largest pterosaur print known from North America. Unfortunately, as it is an isolated print with no associated bones it is not possible to assign it to a group, but has tentatively been assigned to the ichnospecies (what we call specific types of trace fossils) Haenamichnus. Additionally, similarly large pterosaur tracks have been found in the Alaskan Cantwell Formation possibly of similar age to the Wapiti Formation in Alberta.

Other Canadian pterosaurs

Of course this post is about pterosaurs in Canada, not just Alberta. So is there any evidence of pterosaurs in the rest of Canada? Well the short answer is there is very little. I mentioned above that no cranial material had been found of pterosaurs in Alberta, so imagine how excited we were in 2010 when the anterior portion of an upper jaw was described of a new pterosaur Gwawinopterus (which I think is an awesome name) from Hornby Island in British Columbia. It was interpreted as an istiodactylid pterosaur from the Upper Cretaceous, but was based on a fairly unimpressive specimen from a nodule with a lot of teeth and not much else to see [7]. Unfortunately, that specimen has consequently been reinterpreted as a fish [8], so there is still no known pterosaurian cranial material from Canada. 
Image of "Gwawinopterus", now known to be a saurodontid fish rather than a pterosaur. Image from Arbour and Currie 2010.
While "Gwawinopterus" may not be a pterosaur, there is still a limited amount of evidence of pterosaurs from Hornby Island, which is currently being worked on [9]. The other potential place that would be a prime candidate for finding pterosaurs in Canada would be Saskatchewan. However, to my knowledge, no evidence of pterosaurs has ever come out of the province. If anyone knows differently, please let me know!

Why are they so uncommon?

Now that we've gone through the relatively desolate pterosaur fossil record of Canada, we can start to think of why this is the case. There is no reason to believe that pterosaurs were not present in these ecosystems as we know that they existed (sometimes in large number) in similar ages and environments around the world, and we have a number of their fossils from Alberta, even if they are rare and fragmentary. The answer then must be in pterosaurs themselves. Anyone who works on pterosaurs knows how uncommon they are in the fossil record, and how notoriously poorly preserved they can be. There are a few examples of pterosaur bone beds, but these are extremely uncommon and you can read about them in one of my previous posts if you're interested. The main reason for this is their hollow bones. You may recall that pterosaur bones are typically extremely thin-walled, and their bones are mostly full of air, a product of their respiratory system which we call pneumaticity. This, unsurprisingly, makes their bones extremely fragile and not as commonly fossilised as their contemporaries. The fact that birds are also uncommon in the fossil record of Alberta, and share this feature of highly pneumatic skeletons, may support this. It may just be that the environment of the Late Cretaceous of Alberta was not receptive to the fossilisation of extremely fragile pterosaur bones. 

Of course we'll keep looking, and maybe we'll find a pterosaur bonebed in Dinosaur Provincial Park... If anyone knows of any pterosaurs lying around from Canada that haven't been described, please get in touch! I'm always looking for things to procrastinate my PhD a bit more ;)

References:
1. Russell, DA. 1972. A pterosaur from the Oldman Formation (Cretaceous) of Alberta. Canadian Journal of Earth Sciences 9: 1338-1340.
2. Currie, PJ and Russell, DA. 1982. A giant pterosaur (Reptilia:Archosauria) from the Judith River (Oldman) Formation of Alberta. Canadian Journal of Earth Sciences 19: 894-897.
3. Godfrey, SJ and Currie, PJ. 2005. Pterosaurs. In Currie, PJ & Koppelhus EB (eds): Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Indiana University Press, Bloomington, 292-311.
4. Currie, PJ and Jacobsen, AR. 1994. An azhdarchid pterosaur eaten by a velociraptorine theropod. Canadian Journal of Earth Sciences 32: 922-925. 
5. Currie, PJ and Padian, K. 1983. A new pterosaur record from the Judith River (Oldman)Formation of Alberta. Journal of Paleontology 57: 599-600.
6. Bell, PR, Fanti ,F, and Sissons, R. 2013. A possible pterosaur manus track fro the Late Cretaceous of Alberta. Lethaia 46: 274-279.
7. Arbour, VM and Currie, PJ. 2010. An istiodactylid pterosaur from the Upper Cretaceous Nanaimo Group, Hornby Island, British Columbia, Canada. Canadian Journal of Earth Sciences 48: 63-69.
8. Vullo, R, Buffetaut, E, and Everhart, MJ. 2012. Reappraisal of Gwawinopterus beardi from the Late Cretaceous of Canada: a saurodontid fish, not a pterosaur. Journal of Vertebrate Paleontology 32: 1198-1201. 
9. Arbour, VM and Currie, PJ. 2010. An istiodactylid pterosaur from the Nanaimo Group, Vancouver Island, British Columbia, Canada. In Flugsaurier 2010: Third International Symposium on Pterosaurs abstract book. Acta Geoscientica Sinica 31, Supp. 1: 3.