Monday, 25 March 2013

R is for Richardoestesia

Last week, we discussed the giant pterosaur, Quetzalcoatlus. This week, we're back to dinosaurs from Alberta, with 'R is for Richardoestesia', which is the only dinosaur from Alberta that starts with 'R'.

Richardoestesia was a medium-sized theropod that lived mainly in the Late Cretaceous (76-75 million years ago) of North America. The holotype, a pair of lower jaws, was found by well known Canadian palaeontologist Charles Sternberg in Dinosaur Provincial Park in 1917. However, it remained un-named until 1924, when Charles Gilmore named a new genus Chirostenotes, and referred the jaws to this new genus. However, the rest of the skeleton of Chirostenotes was obviously from an oviraptorsaur, and this jaw was not, again leaving these jaws nameless. In 1990, Phil Currie and two colleagues named a new species Richardoestesia gilmorei, with these jaws as the holotype. The genus name comes from Richard Estes, to honour his significant research in small vertebrates in the Cretaceous, while the specific epithet honours Charles Gilmore, for his attempt to name it in 1924. These jaws are long and slender, with relatively small, finely serrated teeth having a whopping 5-6 denticles per mm. This high density of serrations is what distinguishes Richardoestesia from other genera. Although the holotype is actually represented by immature teeth, there are many, many mature shed teeth from older individuals in the fossil record [1]
Photo showing the serrations and examples of teeth from Richardoestesia gilmorei (left) and R. isosceles (right) from Larson and Currie [1]. Scale bar = 1mm.
Unfortunately, because Richardoestesia is known primarily from teeth, there is very little known about this dinosaur. Based on the size of the teeth, it is estimated to be a medium-sized theropod, around 100 kg. The teeth also tell us that it was a coelurosaur (which is a very broad group of dinosaurs), and that it was a carnivore based on the serrations. In fact, it was possibly a piscivore (fish-eater), at least this has been suggested for R. isosceles [2]. While Richardoestesia-like teeth have been reported from several other formations, a recent study has suggested that many of these teeth are significantly different from each other (7 different morphotypes), and that they may represent different species [1]. This study suggests that R. gilmorei is only definitely known from the Dinosaur Park Formation, and that it is distinctly different from  R. isosceles. This study was actually very important as it suggested that the number of small theropod dinosaurs in the Late Cretaceous of North America had been greatly underestimated. Previously, the lack of small-sized theropods was not fully understood as other contemporaneous ecosystems had several, while North America did not. While others tried to explain this lack, Larson and Currie looked at over 1100 fossil teeth from this area and suggested that it is possible to separate out species just from teeth, which brought the number of possible small theropod species in western North America to 23. 

Although there wasn't a lot to say about Richardoestesia as an animal, I hope this gave a bit of an insight into some of the challenges that palaeontologists face when it comes to fossils. I also hope that it revealed some of the painstaking methods that some palaeontologists go through to find information. 1100 dinosaur teeth! Wow!

Next week we'll be talking about another dinosaur from Alberta, but I haven't decided which one yet. Hadrosaur or theropod? Let me know which one I should do! 

References
1. Larson, D.W., and Currie, P.J. 2013. Multivariate analyses of small theropod dinosaur teeth and implications for paleoecological turnover through time. PLoS ONE 8: e54329. doi:10.1371/journal.pone.0054329
2. Sankey, J.T. 2001. Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas. Journal of Paleontology 75: 208-215.

Monday, 18 March 2013

Q is for Quetzalcoatlus

As there are no dinosaurs from Alberta that start with 'Q', we are going to talk about an animal that may have lived in Alberta, although there are no confirmed fossils. Quetzalcoatlus was a giant pterosaur that lived in North America during the Late Cretaceous (70-65 million years ago). Remember that pterosaurs are not dinosaurs, contrary to popular belief. The name comes from the Mesoamerican feathered serpent god Quetzalcoatl. 

Quetzalcoatlus is famous for being the largest pterosaur known from decent remains. There are two different morphs, a smaller one with a wingspan of about 6 m, and a larger one with an estimated wingspan of 10-12 m. That's about the length of a yellow bus. Can you imagine an animal with wings the size of a yellow bus?! The first fossils were found in Texas and consisted of a partial wing of the large morph, while other partial specimens from Montana have been found of the smaller morph, including partial skulls. Pterosaur fossils are extremely rare in Alberta, however, one large neck vertebra found in Dinosaur Provincial Park may be from Quetzalcoatlus based on size and some distinctive features [1]. Another partial skeleton with tooth marks and an embedded tooth from Saurornitholestes, a small theropod, is from an azhdarchid pterosaur, the group that Quetzalcoatlus belongs to [2]. Quetzalcoatlus had a large skull with a toothless pointed beak and a small crest. Like other pterodactyloid pterosaurs, it had only a short tail. 
Skeletal replica/reconstruction of Quetzalcoatlus. Photo by Liz Martin
Their fragmentary remains and strange morphology have made it difficult to fully understand this animal. Many studies have looked at whether or not Quetzalcoatlus was capable of flying, and a feature most important with respect to flight capabilities: how much did it weigh? Unfortunately, this is a very difficult question to answer. Mass estimates for the large morph have ranged from75 to 544 kg, which is a huge difference. Although 75 kg certainly would have been light enough to fly, it is not physically possible to have an animal that size weigh so little. On the other hand, 544 kg surely would have prevented the animal from flying, which begs the question - why did they have such large wings? More recent estimates have suggested a mass around 250 kg which, according to different studies, may or may not have allowed it to fly. For a more detailed explanation on the mass estimates, check out these posts by pterosaur palaeontology student Liz Martin here and here. More recently, a study has suggested that large azhdarchid pterosaurs like Quetzalcoatlus were well adapted to life on land, and moved around on land, feeding by "terrestrial-stalking", but would have been capable of taking off and flying as well [3]
Artists impression of the 'terrestrial-stalking' feeding method of Quetzalcoatlus. Image copyright of Mark Witton [3].
Although some studies have suggested that Quetzalcoatlus fed by skimming the water for fish, this idea is unlikely for several reasons. These include the fact that the fossils are found 100's of km from the nearest palaeo-coastline, and that their skulls and necks lack features required for skim-feeding, like a doubly re-inforced jaw joint found in modern skimmers [3]. In terms of flight, some studies have suggested Quetzalcoatlus was flightless, while others have shown it may have been capable of flying 1000's of km, much like a modern albatross. In this case, it would have used a short burst of energy, followed by large amounts of thermal soaring, relying on the wind and thermals to carry them. 

This is currently an exciting time for pterosaur research, and many people are looking at these animals, especially with respect to their biomechanics. There should be lots of interesting information and debates in the next few years! It is also interesting to note that Quetzalcoatlus was recently featured on a special edition Canadian quarter, the second in a series of prehistoric creatures. The image was made by a fantastic palaeo-artist Julius Csotonyi. This coin sold out rapidly, so I hope you got yours!
New 'glow-in-the-dark' special edition Canadian quarter featuring Quetzalcoatlus
Hopefully you enjoyed this post about Quetzalcoatlus, the huge pterosaur from North America. Watch for us next week when we talk about a small theropod dinosaur from Alberta!

References:
1. Currie, P.J., and Russell, D.A. 1982. A giant pterosaur (Reptilia: Archosauria) from the Judith River (Oldman) Formation of Alberta. Canadian Journal of Earth Sciences 19: 894-897.
2. Currie, P.J., and Jacobsen, A.R. 1995. An azhdarchid pterosaur eaten by a velociraptorine theropod. Canadian Journal of Earth Sciences 32: 922-925.
3. Witton, M.P., and Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE 3: e2271. Freely downloadable here

Monday, 11 March 2013

P is for Pachycephalosaurus

This week in our Albertan dinosaurian alphabet, we are going to talk about the (debatable) Albertan dinosaur Pachycephalosaurus. It lived during the Late Cretaceous (70-65 million years ago) of western North America, and specimens have been found in Montana, Wyoming, and possibly Alberta. The name means "thick-headed lizard", in reference to the very thick (up to 25 cm) domed skull found in these dinosaurs. One possible specimen has been found in Alberta, and has been referred to from the British Museum of Natural History. However, this record is very dubious [1]. This means that this dinosaur may not be found in Alberta after all. Because of this, I'll go through a short description of Pachycephalosaurus, why it's interesting, then talk about some similar ones that are found in Alberta. 

Strangely enough, this dinosaur is known only from portions of the skull: no postcranial remains have been found, meaning most of its body information comes from other closely related species. The skull is much larger than other related species, suggesting it stood as tall as 1.5 m high (with it's head leaning forward), a length of 4.5 m, and weighing 450 kg. Pachycephalosaurus has a very distinctive skull that makes this dinosaur famous. As mentioned previously, it had an extremely thick skull (up to 25 cm) that had a smooth dome-shape to it. At the back of the skull were several bony spikes and knobs, which are also found around the sides and even on its face. Like other pachycephalosaurids, it had sharp leaf-shaped teeth that would have been successful at eating tough fibrous plants, insects, and seeds. 
Artists impression of Pachycephalosaurus by Nobu Tamura
Pachycephalosaurus is perhaps most famous for what it may have done with its hard, domed head. Originally, it was thought that pachycephalosaurs used their round heads to smash into each others' heads, much like bighorn sheep or musk oxen today. This is the idea that has been picked up by popular media, and in fact appears in many books and movies. However, more recent studies have suggested that this would have been impossible. For example, one study suggests that the amount of force this would create would collapse the skull roof, which would obviously cause problems with the brain, although another study has suggested this is not the case [2-3]. Furthermore, the neck vertebrae are unable to lock in a straight position, which would result in a very unstable structure during collisions. Finally, the smooth, rounded surface of the dome would result in glancing blows, rather than direct contact with each other, which would be of further danger to the animal. Although these animals were likely not butting their heads against each other, they were likely using these thick skulls to butt something softer like the flank of other animals. This could have been used to intimidate another individual in something like a mating competition. 

So what about pachycephalosaurids from Alberta? First of all, a nearly complete specimen of Stegoceras was found in southern Alberta, and is actually housed at the University of Alberta. It was much smaller than Pachycephalosaurus, at 2 m long and weighing only an estimated 60 kg. Another possible Albertan pachycephalosaurid is Stygimoloch, which is found primarily in the US with a possible find in Alberta. It is smaller than Pachycephalosaurus, and has much pointier spikes sticking off of its skull. Some authors believe that Stygimoloch, along with another pachycephalosaur Dracorex (which has a species named after the Hogwarts castle from Harry Potter) actually represent a growth series with Pachycephalosaurus being the adult [4]. In fact, some of you may remember Dr. Jack Horner talking about this 2 summers ago at Jurassic Forest! 
Proposed growth series of Pachycephalosaurus. (G, H) represent the youngest in the series, Dracorex; (E, F) represent an incomplete specimen of Stygimoloch, slightly older; and the top two rows are specimens previously attributed to Pachycephalosaurus. Image from Horner and Goodwin [4].
I hope you enjoyed learning about this interesting dinosaur. Next week, we'll be on Q, which will bring us another non-Albertan dinosaur. 

Other 'P' dinosaurs from Alberta:
Prismatoolithus - a dinosaur egg genus
Prosaurolophus - a hadrosaur 
Parasaurolophus - a hadrosaur
Pachyrhinosaurus - a ceratopsian
Prenoceratops - a ceratopsian
Panoplosaurus - an ankylosaur

References:
1. Ryan, M.J., and Russell, A.P. 2001. Dinosaurs of Alberta. In D.H. Tanke and K. Carpenter eds. Mesozoic Vertebrate Life. Indiana University Press.
2. Carpenter, K. 1997. Agonistic behaviour in pachycephalosaurs (Ornithischia, Dinosauria); a new look at head-butting behaviour. Rocky Mountain Geology 32: 19-25.
3. Snively, E., and Cox, A. 2008. Structural mechanics of pachycephalosaur crania permitted head-butting behaviour. Palaeontologia Electronica 11: 3A. Freely downloadable here
4. Horner, J.R., and Goodwin, M.B. 2009. Extreme cranial ontogeny in the Upper Cretaceous dinosaur Pachycephalosaurus. PLoS ONE 4: e7626. Freely downloadable here

Monday, 4 March 2013

O is for Ornithomimus

Last week we talked about a plesiosaur, Nichollssaura, but this week we're back to dinosaurs, with 'O is for Ornithomimus'. 

Ornithomimus was a theropod dinosaur that lived during the Late Cretaceous (75-66 million years ago) of western North America, including Alberta and Saskatchewan, as well as several states in the USA. The name means 'bird-mimic', and it was named in 1890 by Othniel Charles Marsh, one of the great American fossil hunters. Ornithomimids are characterised by 3-toed feet, long necks, and birdlike elongated, toothless beaks, hence the name 'bird-mimic'. They were bipedal, walking on the two hindlimbs, and were likely fast runners. Ornithomimus had longer, more slender forelimbs than other ornithomimids and have been estimated to be 3.8 m long and 170 kg (O. edmontonicus). Evidence of feathers has been found on several specimens (including the first ever definite dinosaur feathers from Alberta), and one study suggested that Ornithomimus was covered in pennaceous feathers throughout its life [1]. They also suggested that wing-like structures were only found in adults, and may be because these are used for a mating display. Although most theropods were carnivorous, the body of this dinosaur suggests it may have been largely herbivorous. Its large eyes tell us it had good vision, and may have used that great vision to catch small mammals or lizards to supplement its diet. 
A nearly complete (missing only a small portion at the end of the tail) of Ornithomimus from the Royal Tyrrell Museum of Palaeontology. Photo by Sebastian Bergman.

Currently, the number of valid species for Ornithomimus is debated. The type species, O. velox, is still valid, while O. edmontonicus is considered by some to be Dromiceiomimus, while other studies have suggested that there is no distinction between Dromiceiomimus and Ornithomimus, and that O. edmontonicus is a valid species [2]All in all, the taxonomic (as in how many species, and what is actually Ornithomimus) history has been very complicated. 

That's it for the bird-mimic. Next week, we'll move on to an interesting thick-skulled dinosaur! Stay tuned for more!

Other 'O' dinosaurs from Alberta:
Possibly Orodromeus, but that is unconfirmed

References:
1. Zelenitsky, D.K., et al. 2012. Feathered non-avian dinosaurs from North America provide insight into wing origins. Science 338: 510. Can be downloaded as a PDF here.
2. Mackovicky, et al. 2004. Ornithomimosauria. In Weishampel, Dodson, and Osmolska (eds.), The Dinosauria Second Edition. University of California Press. 861 pages.
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