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.

Monday, 19 January 2015

Quantifying pneumaticity

A few months ago I started talking about skeletal pneumaticity in pterosaurs and planned on following it up with this post on quantifying pneumaticity, but a few things got in the way, so here it is.

How do you quantify pneumaticity?

Most often in bones, and especially in the fossil record, pneumaticity is discussed on the basis of presence or absence, and documenting the location of pneumatic foramina. This is primarily done for taxonomic purposes, as the location of these foramina can be characteristic of the taxonomic group the pterosaur belongs in. Pat O'Connor started to look at quantifying pneumaticity in one way using what he called the Pneumaticity Index (PI), which was a way of comparing the number of pneumatic elements in different birds [1]. A PI of 1.00 indicates all potentially pneumatic elements of the bird's post cranial skeleton are pneumatised, and smaller numbers indicate fewer pneumatic elements. This allows for comparison of the number of pneumatised elements between taxa, but not the degree of pneumaticity between bones.

Air Space Proportion

Matt Wedel, a sauropod palaeontologist, does a lot of work on the pneumaticity in sauropod vertebrae and realised that there was no way of quantifying pneumaticity within a single bone. He proposed using the Air Space Proportion (ASP), a ratio of the cross-sectional area of the air-filled section compared to the total cross-sectional area [2]. From 0-1, an ASP closer to 1 indicates a bone that is mainly full of air, vs. closer to 0, which is mainly bone. He started doing this on sauropod vertebrae and comparing the ASP between different sauropods and different vertebrae. While Matt came up with the idea of ASP, several people in the past of used the K value (the ratio of the internal to outer diameter) to compare the bone thickness of different bird and pterosaur bones. In a tubular bone, ASP is roughly equal to K^2.

In 2012, Matt approached me after seeing a talk I gave on my MSc research on pterosaur bone mass and suggested that I look at ASP in pterosaurs using my CT scans. He had always been curious as to if it would change throughout the bone and if the cross-section of the bone would significantly change the ASP. I thought this was a good idea, and that it would also allow me to look at ASP in pterosaurs and see how it related to other animals.

Looking at CT scan slices at set intervals throughout several pterosaur bones, we found some interesting results. It turns out that ASP actually varies quite a lot throughout a bone, at least it does in pterosaur wing bones [3]. In fact, all pterosaur wing phalanges had high ASP values  at the ends of the bone (e.g. approximately 0.85 in NHMUK PV OR39411) and lower values in the shaft (e.g. approximately 0.71).
From Martin and Palmer [3]
This was not initially expected. Pterosaur bones are full of spongy trabecular bone in the ends, while the shafts are almost completely hollow with just cortical bone along the outsides, so at first glance you would expect less air in the ends. However, the ends are also expanded in diameter, the cortical thickness is extremely low and trabeculae are very small in thickness, while the shaft has higher cortical thickness, but a smaller diameter. The result of this is an increase in both air and bone at the ends, but proportionally more air. As most long bones in the fossil record are found broken in the shaft, it means that any estimates of pneumaticity of long bones using a shaft cross-section may be underestimating the values. It also means that single cross-sections of bones may not be accurately showing how pneumatic the bones are.

How do pterosaurs compare to other animals?

First of all, it's important to remember exactly what these numbers mean. If an ASP is 0.9, that means it 90% air, vs. an ASP of 0.1, or 10% air. Of the bones we looked at, they had average ASP values of 0.68-0.83, but the complete range was 0.56-0.88.
ASP values of pterosaur wing bones from Martin and Palmer [3]
This is significantly higher than the same bone and most others in a juvenile azhdarchid, similar to Pteranodon (calculated from K), and much higher than an unknown bone from a dsungaripteroid (from K). It's also higher than most birds, although these are all calculated from K values rather than ASPs. Finally, they are generally higher than sauropod vertebrae ASP, but there are some sauropods that have higher ASP values. This means that pterosaurs are among, if not THE, most pneumatic animals in the world.
ASP values of pterosaurs, birds, and sauropods from the literature in Martin and Palmer [2]
There is still a lot of work to be done on this. First of all, more bones need to be looked at as our study only included wing bones, and mostly wing phalanges. Next, more pterosaur taxa need to be studied. This is already underway and is showing some interesting results, so stay tuned! Finally, more groups need to be looked at, particularly birds. Do birds show the same patterns? Again, something that I am looking at! This work will be continued in my PhD in more detail, so more will come.

If you're interested, you can read more about this paper over at SVPOW where Matt Wedel summarised it. Also, the paper is published open access in Plos One, and can be read here.

Thanks to everyone who helped me along the way, especially Matt Wedel and Colin Palmer, and also Davide Foffa, Lorna Steel, Lauren Howard, Dave Martill, the staff at Muvis, Mike Habib, the Smithsonian staff, and Gareth Dyke. And of course to my other half Josh Silverstone :) 

References:
[1] O'connor 2004. Pulmonary pneumaticity in the postcranial skeleton of extant Aves: a case study examining Anseriformes. Journal of Morphology 261: 141-161.
[2] Wedel MJ (2005) Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates. In: Curry Rogers K, Wilson J, editors. The sauropods: evolution and paleobiology. Berkeley: University of California Press. 201–228
[3] Martin EG, Palmer C (2014) Air space proportion in pterosaur limb bones using computed tomography and its implications for previous estimates for pneumaticity. Plos One 9: e97159.

Monday, 8 December 2014

2014 - The year of pterosaur bonebeds

This post is part of the Science Borealis Blog Carnival discussing the most important science news in our fields. As a pterosaur palaeontologist, I've chosen to talk about pterosaur bonebeds - enjoy!

Pterosaurs (extinct flying reptiles that lived alongside the dinosaurs) are rare in the fossil record. Most species are known from a few specimens, and rarely found with more than one individual in one place. This is primarily because pterosaur bones are extremely fragile due to the thin-walled hollow nature of the bones caused by the respiratory system and pneumaticity. This is why it is so rare to find them together and why this year has been so important for pterosaur-related news. There was not one, but two pterosaur bonebeds reported in 2014: one in China, and one in Brazil.

What is a bonebed?


Pachyrhinosaurus bonebed in Alberta. The left image shows just how many people
 can work in one area as there are so many bones. The right shows how many
bones are found in one section. This bonebed is one of the highest concentrated
bonebeds in the world.
The first thing to understand why this is so important in palaeontology is to learn what a bonebed is. A bonebed is a geological deposit with many bones found throughout it. They are important in palaeontology for many reasons. First of all, and probably fairly obviously, they provide us with many specimens to study. Large accumulations of bones can provide us with a lot of information that single skeletons can't. If the bonebed is full of several species, it can be caused by something like quick sand that many different animals can get trapped in. If there is only one species, that can tell us that the animals were living in some kind of group that died in some kind of catastrophic event. For example, ceratopsian (horned dinosaur) bonebeds are common in North America, including PachyrhinosaurusCentrosaurus, and Styracosaurus. These have commonly been interpreted as herds of ceratopsians that have been caught in something like a flooded river. In addition to understanding things like social behaviour, it can also help us understand ontogenetic (developmental/age-related) changes and sexual differences. As herds consist of males and females, as well as all ages, these herd-accumulated bonebeds can be very important in understanding the biology of these extinct animals. 


As mentioned above, accumulations like this are extremely rare in pterosaurs. Before this year, only one had been found. This was from the Lower Cretaceous of Argentina, at a locality referred to as "Loma del Pterodaustro", named for the hundreds of specimens of the bizarre filter-feeding pterosaur Pterodaustro [1]. This locality provided information for this pterosaur from egg to adult. Unfortunately, the majority of this material is two-dimensionally flattened. Until this year, that was the only major pterosaur accumulation known.


Hamipterus - The Chinese Bonebed 

Large block showing several Hamipterus bones including
3 partial skulls (labeled sk). Scale bar = 10cm. Image from
Wang et al. [2]
The first pterosaur bonebed of 2014 came out in June describing a new species, Hamipterus tianshanensis [2]. This find was exciting for many reasons: it included specimens of all ages, several 3D preserved eggs, and evidence of sexual dimorphism. It represents an Early Cretaceous (100-120 million years ago) stream or lake deposit potentially formed by a storm, catastrophically killing all the animals at once and preserving them together. About 40 individuals (meaning identifiable individuals, not just bone fragments) have been removed from the locality, but the authors suggest there may be hundreds, making this a massive deposit. 


Hamipterus was a pteranodontoid pterosaur with teeth, a bony crest on the pre maxilla (the front part of the rostrum), and a wingspan of about 3.5 m. This crest changes throughout ontogeny (over its lifetime) and appears to be sexually dimorphic. Throughout its ontogeny, the rostrum (snout) and premaxillary crest becoming more robust. Crests and features that have some kind of sexually selective function become more prominent as the animal reaches sexual maturity, which is why these features are generally larger and more robust in older individuals. In Hamipterus, the crest also appears to represent a sexually dimorphic feature, with two different crest morphologies present in similarly sized skulls. Skulls tentatively described as males were larger and thicker with more strongly curved anterior portions, while "female" skulls have shorter crests without an anteriorly curved portion. Several skulls of both morphs were found and sex was tentatively assigned, although more information is needed to confirm these assignments such as difference in pelvis shape or presence of medullary bone. Finally, the other exciting thing about this find is the presence of five eggs, which doubles the total number of pterosaur eggs found in the fossil record. Even more exciting is that these eggs, like the rest of the fossils, are preserved in three dimensions, unlike the previous pterosaur eggs that were flattened. The morphology of the eggs confirms previous studies that have suggested pterosaur eggs were soft-shelled eggs, more similar to some snakes and lizards than modern birds. 
Hamipterus skulls: A and E represent "females", while B, D, and F represent
"males". C shows the outline of both female (lighter grey with dark lines) and
male (darker with white lines curving forwards) premaxillary crests. Image
from Wang et al. [2]

The presence of so many individuals and eggs lead the authors to suggest this was a nesting ground and that Hamipterus may have been gregarious, living (or at least nesting) in large flocks, much like some modern birds. 

This study was covered significantly in the media including the Guardian, Reuters, and CBC.


Caiuajara - The Brazilian Counterpart

After the announcement of Hamipterus, pterosaur specialists and other palaeontologists were very excited. Imagine our excitement when just 2 months later, in August, the massive Caiuajara (pronounced Kai-u-a-har-a, I believe) bonebed from Brazil was described [3]. This bonebed from the Late Cretaceous was found in the southwest part of Brazil, where pterosaur fossils were previously unknown. While Brazil has a lot of wonderfully preserved pterosaurs, they all come from the northeastern region. While the Hamipterus bonebed was from a water-logged area, Caiuajara dobruskii was found in a desert-lake deposit, the first time a pterosaur has been found in this kind of environment. 47 individuals have so far been identified from hundreds of bones, and there may be as many as a few hundred individuals present.
Block showing hundreds of Caiuajara bones with at least 14 partial skulls. Image from Manzig et al. [3]
Caiuajara was a tapejarid pterosaur, with a full grown wingspan of approximately 2.4 m, and was characterised by a ventrally deflected (curved down) front portion of the upper jaw, toothless jaws, and another premaxillary crest starting at the front of the rostrum and continuing towards the back of the skull. Tapejarid pterosaurs are known for their toothless jaws, thought to be used to eat fruit, and their large dorsally directed cranial crests. In the Caiuajara bonebed, skulls are present from all sizes, showing the ontogenetic trend in crest growth. It shows that as the animal got larger and reached sexual maturity, the size and shape of the crest changed, much like that seen in Hamipterus, only the crest of Caiuajara is much larger. Furthermore, the entire skeleton is known, even if bones cannot be attributed to specific individuals. 

The images above show the ontogenetic variation in Caiuajara dobruskii. The left image shows various skulls from the youngest and smallest (top left) all the way to the largest, oldest individual (bottom right). The image on the right is a very nice schematic drawing showing how the skull changes from the younger individuals (white) up to the oldest (dark red). Images are from Manzig et al. [3].

Like the Hamipterus bonebed, most of these fossils were preserved in 3D, allowing the scientists to understand information such as the actual morphology of the bones, and potentially the internal structure. The geologic bed has additional interesting information. 3-4 different accumulations were found, thought to be formed by separate events. This large accumulation, and the fact that there are a few independent events further supports the thought that some pterosaurs may have had some kind of gregarious behaviour, living together in a colony-like manner around an internal lake in the desert, rather than a fluke one-time occurrence. Furthermore, most pterosaur fossils are found are found in marine deposits, with few from inland terrestrial deposits, let alone deserts (only one found previously). This find has increased our understanding of pterosaur behaviour by adding another piece of evidence to the diversity of pterosaurs. They aren't all big pterosaurs swimming over the oceans and catching fish like is often portrayed.

This find also had a significant amount of media coverage including CBC and National Geographic

These two bonebeds have provided us with a lot of new information about pterosaurs. First of all, it suggests that pterosaurs may have been gregarious, living and nesting in groups (flocks?), much like modern birds. Whether or not this is a behaviour that they exhibit all year round, or just when nesting or mating is still unknown. While other pterosaurs are known from several ages and sizes, such as Pteranodon, Pterodactylus and Rhamphorhynchus, the ages and species are frequently debated, so ontogenetic sequences can be difficult. However, Caiuajara and Hamipterus provide us with 2 examples of true growth series from different, distantly related pterosaurs, which shows how they grew and how their biology changed over time. Furthermore, these bonebeds are so concentrated that they will continue to unearth a wealth of information about these pterosaurs. The next few years is going to be exciting to see what we learn from both of these!

And another bonus? Both of these studies are open access, so anyone can read about them. Check out the links below.


References:
1. Chiappe LM, Rivarola D, Romero E, Davila S, Codorniu L (1998) Recent Advances in the Paleontology of the Lower Cretaceous Lagarcito Formation (Parque Nacional Sierra de Las Quijadas, San Luis, Argentina). In Lower and Middle Cretaceous Terrestrial Ecosystems, New Mexico: Museum of Natural History and Science Bulletin Lucas SG, Kirkland JI, Estep JW, editors. 14: 187–192.

2. Wang X, Kellner AWA, Jiang S, Wang Q, Ma Y, Paidoula Y, Cheng X, Rodrigues T, Meng X, Zhang J, Li N, Zhou Z (2014) Sexually dimorphic tridimensionally preserved pterosaurs and their eggs from China. Current Biology 24: 1323-1330. (open access)
3. Manzig PC, Kellner AWA, Weinschütz LC, Fragoso CE, Vega CS, Guimarães GB, Godoy LC, Liccardo A, Ricetti JHZ, de Moura CC (2014) Discovery of a rare pterosaur bone bed in a Cretaceous desert with insights on ontogeny and behavior of flying reptiles. PLoS ONE 9: e100005. (open access)

Thursday, 20 November 2014

Pterosaurs of Stuttgart and Munich

As part of my PhD, and with the help of the Geological Association of London, I've been fortunate enough to go on several research trips to some museums in Germany including Tübingen, Karlsruhe, Stuttgart, and Munich. Stuttgart and Munich in particular have excellent pterosaur collections, including many historically significant specimens.

Stuttgart

The Staatsliches Museum für Naturkunde in Stuttgart (SMNS) is a large museum that houses one of the state collections of Baden-Württemberg (the other one being in Karlsruhe). The museum has a significant collection of material from the area, as well as some excellent material on display, but I'm only going to talk about some interesting pterosaur material. 

Campylognathoides
Campylognathoides zitteli was first found in 1858, from the Early Jurassic deposits of Württemberg. In 1893, a new specimen was discovered from the Holzmaden shale, and was named as a new genus and species, "Campylognathus zitteli", based on the specimen found below. It was later discovered that the genus was already in use for an insect, and so a new genus, Campylognathoides, was named in 1928.  
Type specimen SMNS 9787 of Campylognathoides zitteli
Austriadactylus
The type specimen of Austridactylus cristatus was found in the Alps of Austria, dating back to the Late Triassic. This is one of the earliest pterosaurs known so far as Triassic pterosaurs are extremely rare. They are also very poorly preserved, and Austriadactylus is a perfect example of this. Like many pterosaurs, it is completely crushed and incomplete, but some features can be seen. It has many primitive pterosaurian features including a long flexible tail (which lacks the stiffening rods seen in later pterosaurs) and heterodont teeth. 
Type specimen of Austridactylus cristatus SMNS 56342 

Line drawing of Austriadactylus cristatus from Dalla Vecchia et al. [1]
Miscellaneous
Also in the SMNS collections is some miscellaneous pterosaur material that shows some interesting features. Specifically, there are some 3D, beautifully preserved pterodactyloid fossils that show the internal structure of pterosaur bones, the delicate trabecular structure that existed in the heads, and the trabeculae that occur in the shafts.
Close ups of the internal structure of two pterosaur bones in the shaft (above) and head (below)

Munich

The Munich palaeontology collections exist in the Bayerisches Staatssammlung für Paläontologie ind Geologie (BSP), and are quite extensive, as shown by the large number of researchers there after the Society of Vertebrate Paleontology meeting in Berlin. It is especially great for pterosaurs, including numerous historically significant specimens, including the first ever pterosaur known to sciences, Pterodactylus antiquus. Unfortunately, that specimen is so valuable that it is kept out of prying eyes and is only accessible under specific permission, so I wasn't able to see it. However, that aside, there were many other significant specimens for me to see. 

 Aerodactylus
BSP AS V 29, type specimen of A. scolopaciceps
This genus has a complicated history. In 1860, a new species, "Pterodactylus scolopaciceps" was named by Meyer after being found in the Bavarian Solnhofen limestone from the Jurassic. This was later synonomised in 1883 with "P. kochi" which was thought to be a smaller species of Pterodactylus. However, over the years it has generally been agreed that "P. kochi" is just an ontogenetic stage of P. antiquus, meaning that they are just smaller, younger individuals. The original type specimen of "P. scolopaciceps" was more recently re-described as a new genus, Aerodactylus [2]. While all specimens of A. scolopaciceps are considered to be juvenile, it has been suggested there is enough of a difference to be a different genus.  
Beautifully preserved specimen of Aerodactylus
Close up of some details of the wing of Aerodactylus. Note the long slender pteroid bone, which is unique to pterosaurs
Germanodactylus
Germanodactylus cristatus was first described as a specimen of "P. kochi" by Pleininger in 1901 after being discovered in the Solnhofen lagerstätt, another Late Jurassic German pterosaur. It was then described as a new species of Pterodactylus, "P. cristatus". In 1964, a new genus Germanodactylus was named, and BSP 1892 IV 1 was named the type specimen of G. cristatus. The precise position of Germanodactylus within the Pterosauria has been debated, but it is definitely a pterodactyloid pterosaur. 
Type specimen of Germanodactylus cristatus, BSP 1892 IV 1
The Zittel Wing
By far, the most historically interesting specimen and biggest surprise for me came when I opened up a drawer and found the "Zittel Wing", a nearly complete Rhamphorhynchus wing. This wing was described by Alfred von Zittel in 1882. It was a significant find then, and to this day still represents one of, if not the best preserved wing membrane of a pterosaur. Nearly all the wing bones are complete, and the membrane is preserved from the tip of the wing finger (the elongated 4th finger) to underneath the humerus. It showed the width of the wing, as well as the actinofibrils, which are the strengthening fibres that provided the pterosaur wing with strength when they are overlain in criss-crossing layers. This was the first sign at how pterosaur wing membranes were formed.
The Zittel Wing
 3D ornithocheird wing bones!
For me, a highlight was looking at the 3D preserved specimens from the Early Cretaceous of Brazil. These were large pterosaurs, with wingspans of 5 m or so, and were part of the pterosaur revival of the 1970s to 1990s after being described in detail by Peter Wellnhofer. These bones are all very well preserved and have mainly been prepared out of the rock, meaning that you can pick them up, move them around, and really start to understand them. These were definitely the highlight for me!
Beautifully 3D preserved Santanadactylus spixi radius, ulna, and wing carpals.
Wing metacarpal with 3 other metacarpals from Santanadactylus pricei. Note the small pneumatic foramen (see previous post on pneumaticity for details) underneath the small finger metacarpals.
Those are my highlights from the natural history museums in Stuttgart and Munich. There were many more interesting specimens, and I could go on for ages about it, but I think I'll stop here!

References:
[1] Dalla Vecchia FM et al. 2002. A crested rhamphorhynchoid pterosaur from the Late Triassic of Austria. Journal of Vertebrate Paleontology 22: 196-199.
[2] Vidovic SU and Martill DM. 2014. Pterodactylus scolopaciceps Meyer, 1860 (Pterosauria, Pterodactyloidea) from the Upper Jurassic of Bavaria, Germany: the problem of cryptic pterosaur taxa in early ontogeny. PLoS ONE 9: e110646.