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 ;)

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.