Sunday, 30 December 2012

2012 in Review

This week we are going to take a break from our A-Z of Dinosaurs from Alberta to do a quick review of this last year. We'll summarise a palaeontology-related story from each month of the year, with a focus on Alberta and dinosaurs. 

January:
We start off the year with a non-dinosaur/non-Alberta find. In January, a very cool invertebrate fossil study was presented from the Burgess Shale in British Columbia. This strange flower-like animal called Siphusauctum lived on the bottom of the ocean more than 500 million years ago, during the Cambrian period [1]. It was likely a filter feeder, allowing its food to pass through openings in its tulip-like top, and catching it with comb-like elements. It attached to the ocean floor with a long stalk and holdfast, and was topped with a tulip-shaped calyx (cup-like structure). You can read more about this find here.
Siphusauctum (Copyright Marianne  Collins)

February:
February brought us back to a cool dinosaur study from an Alberta researcher, Dr. Phil Bell, the palaeontologist for the future Philip J. Currie Dinosaur Museum in northern Alberta. For the first time ever, Dr. Bell was able to determine that dinosaur skin can be used to tell the difference between species [2]. He found that dinosaur skin from the duck-billed dinosaur (AKA a hadrosaur) Saurolophus was different between Asian and North American specimens. He looked at fossils from southern Alberta and Mongolia and found that they had significant differences in their skin. Dinosaur skin had previously never been used as an identifiable feature in different species. Another very cool find from this study is that he was able to see how the scales changed in different regions of the body, and in some cases with interesting patterns. To learn more about this study, read this press release from the Philip J. Currie Dinosaur Museum. 

March:
The month of March started with word of a cool fossil found in an ammolite mine near Lethbridge. Ammolite is a gemstone produced from the shells of ammonites, large marine fossils. Other marine animals have been found in this mine, including a large mosasaur skeleton dating back about 74 million years ago. It was apparently scavenged by some kind of shark with the body being dismantled and several teeth found with the skeleton. Mosasaurs were large, ferocious ocean predators during the Cretaceous period. This particular one was likely about 4 m long. We'll look forward to hearing more about this specimen in the future! You can check out a picture of this as it's being prepared on the Royal Tyrrell Museum of Palaeontology's Facebook page.

April:
April brings us two interesting Alberta-related palaeontology stories. First of all, well-known Canadian palaeontologist and specialist on Albertan dinosaurs Dr. Philip Currie was honoured for his passion with an Explorers Club Medal. Although actually awarded in March, most press articles on the subject came later when Dr. Currie was back in Edmonton. This prestigious medal is given for exceptional work and research in the physical, natural, and biological sciences. Previous winners of this award include Sir Edmund Hillary, Neil Armstrong, and Roy Chapman Andrews. Read more about the award here.
Another interesting dinosaur-related story from April comes courtesy of the Royal Canadian Mint when they announced a glow-in-the-dark quarter with an image of Pachyrhinosaurus lakustai on it. P. lakustai fossils are found in northern Alberta near Grande Prairie, in a large bonebed with thousands of bones. This image was designed by Julius Csotonyi, a well known palaeoartist. Unfortunately, they only produced a limited number of these coins, and have all been sold out! More on this story here.
Pachyrhinosaurus lakustai coin (Copyright Royal Canadian Mint)

May:
Right at the beginning of May, we heard of a new marine reptile from Alberta, aptly named Albertonectes [3]. This new species was an elasmosaurid plesiosaur, which are known for their exceptionally long necks, and this animal was no exception. The total length comes in at about 11 m, and the majority of that is in fact its neck. This fossil is about 70 million years old and is a pretty neat find! For more information about Albertonectes and other elasmosaurs see this blog post.

June:
The notable story for palaeontology in June is actually one that spans several months, with an important event occurring in June. In May 2012, a nearly complete Tarbosaurus skeleton went on auction at an American auction house. Few details were released on the fossil, but it did state that it was found in the Gobi Desert. This is a big problem because Tarbosaurus remains are found in large quantities in Mongolia, and more rarely in China, and that's it. Many palaeontologists got involved and interested in this case because Mongolia has very strict fossil laws, and it is illegal to export fossils from Mongolia, especially for private sales, meaning that this skeleton was removed from the country illegally. The sale went ahead, with the remarkable fossil going for nearly $1 million USD. Now we get to June. After this was brought up by several palaeontologists, and in fact the Mongolian president himself, two well known palaeontologists (including Dr. Philip Currie who has worked on numerous Mongolian fossils) inspected the fossil and concluded that it was in fact from Mongolia (they can tell from the colour of the bones and sediments found in the bones). Once this was determined, the American government took an unprecedented step and seized the skeleton from the auction house in June. Despite several attempts to get the fossil back, continue with the sale and plead innocence, the fossil dealer who had sold it to the auction house recently pleaded guilty to illegally importing this and several other skeletons from Mongolia and China, and is now faces 19 years in prison for his crimes. You might ask why this is such a big deal. Palaeontologists will tell you several reasons, but mainly because it encourages fossil poaching which results in specimens being broken, lost to science (they tend to go to private collections) and most importantly, they are removed from the surrounding rock which means a lot of valuable information is lost. For more information on this, there are several blog posts by palaeontologists and writers including Brian SwitekVictoria Arbour, and me (my personal blog) as well as several news articles! 

July:
Unfortunately, July started with an story that did not have such a good ending. We heard the devastating story of a priceless, well preserved duck-billed dinosaur (hadrosaur) fossil being destroyed in near Grande Prairie. In June, the fossil was discovered by Dr. Phil Bell and some people from the University of Alberta. They were not able to remove the skeleton from the ground immediately, so they re-buried it, only to return a few weeks later to find it destroyed. Several bones had been taken, damaged or destroyed, with pieces scattered around the site. Because of the quality of this fossil, it had been slated as a possible major exhibit at the museum once it is built. However, the few bits that were left were barely salvageable, leaving Dr. Bell heartbroken. More on this from CBC here and here.
Image showing some destroyed bones (From CBC article, image by Phil Bell)

August:
In August, a huge Triceratops skeleton was unearthed near Drumheller, not far from the Royal Tyrrell Museum, which was a pretty convenient find for them! It took several days for them to take the 2000 kg animal out of the ground. The fossils were discovered by a former museum employee who recognised the bones after they were exposed due to erosion, and date back to about 65 million years ago. What's particularly exciting about this is that despite Triceratops being a well known dinosaur, its fossils are relatively uncommon in Alberta, in comparison to surrounding Montana and Saskatchewan fossils. More information can be found from CBC

September:
Another marine reptile was found, this time near Grande Prairie by a 72 year old farmer. The 80 million year old plesiosaur was identified by Dr. Phil Bell who recognised the large vertebrae and knew instantly that they were not from dinosaurs. This particular plesiosaur was a smaller one, probably reaching only 2-3 m in length (compared to the long 11-12 m ones known). Many marine fossils can be found in Alberta from that time period because Alberta was covered by what was known as the Western Interior Seaway - a huge sea that went from northern Canada all the way to the Gulf of Mexico. These fossils will eventually make a display at the Philip J. Currie Dinosaur Museum, and may be a new species. 

October:
October was a very exciting month for palaeontology in Alberta, as a new paper came out with the first ever undebatable occurrence of dinosaur feathers in North America, coming out of Dinosaur Provincial Park in southern Alberta [4]. This came a year after dinosaur feathers were reportedly found in amber from Alberta. These feathers, however, are unquestionably dinosaurian in nature as they came attached to dinosaur fossils. In fact three separate Ornithomimus skeletons showed these feathers, and the authors have interesting insights into the evolution of feathers. They found filaments in both juveniles and adults, but wing-like structures only in the adults. This suggests that these wing-like structures were only being used in some kind of reproductive behaviour like showing off to other individuals. This find is also the first ever find of feathers in course sandstone, rather than the fine-grained sediments typical of feather finds in China and Germany. More information on this can be found in CBC, but be wary of some mistakes in the article! These are not the oldest feathered dinosaurs ever found, as suggested. 

November:
This month we had another new dinosaur named from Alberta, this time a ceratopsian or horned dinosaur. The new dinosaur is called Xenoceratops which literally means 'alien horned-face', in reference to its somewhat alien appearance for the time [5]. The bones had actually been collected over 50 years ago, but were previously left unstudied. This dinosaur is the oldest large horned dinosaur found so far in Canada, and shows that even the oldest ones had distinct horns and obvious morphological diversity. Xenoceratops would have weighed in at more than 2 tons, and reached a length of 6 m, making this a huge horned dinosaur. We just keep discovering new dinosaurs in Alberta all the time! For more information, check out the press release from the NRC Research Press here
Xenoceratops, Copyright of Julius Csotonyi
December:
Right at the end of the year, we heard that the Philip J. Currie Dinosaur Museum, set to be located just west of Grande Prairie, got the last bit of money it needed to go ahead. This means that they can finally start breaking ground on the new dinosaur museum! They will start construction in the spring, and plan to be open to the public in the summer of 2014. Construction plans will start in January, and we're looking forward to seeing what the museum is going to look like. This new museum further cements Alberta's reputation as being an excellent place for palaeontology! More information can be found in their monthly newsletter here.

So that's our summer of palaeontology-related excitement from Alberta and the world in 2012. We at Jurassic Forest hope everyone had an excellent 2012, and has an even better 2013. We are looking forward to an excellent season beginning this April, and hope we can see you! Happy 2013 everyone!

References:
1. O'Brien, LJ, and Caron, J-B. 2012. A new stalked filter-feeder from the Middle Cambrian Burgess Shale, British Columbia, Canada. Plos One 7: e29233. Open access, can be downloaded here.
2. Bell, PR. 2012. Standardized terminology and potential taxonomic utility for hadrosaurid skin impressions: a case study for Saurolophus from Canada and Mongolia. Plos One 7: e31295. Open access, can be downloaded here.
3. Kubo, T, et al. 2012. Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta. Journal of Vertebrate Paleontology 32: 557-573. NOT open access, but can be found here.
4. Zelenitsky, DK., et al. 2012. Feathered non-avian dinosaurs from North America provide insight into wing origins. Science 338: 510-514. NOT open access, but can be found here.
5. Ryan, MJ., et al. 2012. A new ceratopsid from the Foremost Formation (middle Campanian) of Alberta. Canadian Journal of Earth Sciences 49: 1251-1262. Open access, can be downloaded here

Monday, 17 December 2012

F is for Falcarius, which is not from Alberta

For our next post in the Albertan dinosaur alphabet, we come to the letter F. Unfortunately, there are no dinosaurs from Alberta that start with 'F', so we are going to talk about one from the US called Falcarius. Falcarius is a very strange dinosaur from the Early Cretaceous (about 130-125 million years ago) of Utah. Its name means 'sickle-cutter' in Latin, and describes the large claws on its long arms. Falcarius was a kind of theropod called a therizinosaur, which are very strange looking dinosaurs with long necks, wide bodies, and bipedal (walking on two legs) stance. This dinosaur is found from two bonebed locations in Utah, with possibly thousands of individuals being found here. 
Artists rendition of Falcarius by Michael Skrepnick, courtesy of University of Utah
Falcarius was much smaller than the later therizinosaurs at about 4 m long, 1.2 m tall, and weighing in at 100 kg. The bonebeds contain juveniles and adult individuals, with the smallest juvenile being just 0.5 m long. Therizinosaurs are known for being a group of herbivorous theropods, and Falcarius is no exception with its small, leaf-shaped teeth good for chewing vegetation. Although no feathers have been found on this dinosaur, closely related dinosaurs like Beipiaosaurus from China have well preserved feathers which suggests Falcarius did as well. 

This dinosaur is thought to be a "missing link" between the carnivorous theropods and the very strange therizinosaurids. These later therizinosaurids are often compared to large ground sloths with their huge torsos, likely roaming the ground for vegetation. Therizinosaurids also had large claws that reached up to a metre in length! 
Nothronychus, a derived therizinosaurid from the US. Image by Wikimedia user DinoGuy2
Update:
Since originally posting this, a new paper has come out which shows the structure of the brain of Falcarius and other therizinosaurs [1]. Remember back in September when we talked about how palaeontologists can use CT scans to better understand extinct animals? Well this is another great example of what CT scans can show us, and what they can tell us about the animal. They found that Falcarius and other therizinosaurs like Erlikosaurus and Nothronychus had well developed sensory abilities, especially with respect to smelling and hearing. A well developed sense of smell is normally found in carnivorous dinosaurs, while these animals were herbivorous or omnivorous. Since these herbivores had a great sense of smell, they suspect they were using it to track down plants with particularly smelly flowers or fruits. This is especially likely as they also found that therizinosaurs did not have a good sense of vision, so they needed to rely on smell and hearing to find food and avoid predators

Next week we'll be back to dinosaurs from Alberta with the letter 'G'. If you have any Albertan dinosaurs that start with 'G' that you'd like to hear about, let us know!

References:
1 Lautenschlager, S, et al. 2012. The endocranial anatomy of Therizinosauria and its implications for sensory and cognitive function. PloS One 7: e52289.
Also check out Brian Switek's blog on this paper for more information here

Monday, 10 December 2012

E is for Edmontonia

Last week, we talked about the large theropod Daspletosaurus. Continuing through the Alberta dinosaur alphabet brings us to the letter 'E', and 'E is for Edmontonia', an armoured dinosaur from the Late Cretaceous. Edmontonia was named after the Edmonton Formation, a rock formation that is now known as the Horseshoe Canyon Formation, and is found in Alberta, where this dinosaur was first found. Edmontonia fossils can be found in Alberta, Saskatchewan, and the US, and it lived approximately 76-70 million years ago. 
Edmontonia was an armoured dinosaur, also known as an ankylosaur, and was covered in large bony plates called osteoderms. These plates provided a lot of protection from predators, as they covered most of its head, neck, back, and tail. However, the underside is unprotected, leaving itself vulnerable if it could be flipped over. Some of these osteoderms were modified into spikes (as seen around the shoulder area). Edmontonia stood about 2 m high and 6.5 m long, making it a pretty sturdy dinosaur, often compared to a tank. Unlike some other well known armoured dinosaurs, Edmontonia did not have a tail club on the end of its tail, meaning it was not able to defend itself by smashing the club into incoming predators. Instead, it could potentially use the spikes on its shoulders to intimidate a predator, and they could also use them in self defence. The shoulder spikes may have also been used in territory disputes between males. This dino wouldn't have been an easy one to eat!

Other 'E' Dinosaurs from Alberta:
Euoplocephalus
Edmontosaurus
Eotriceratops

Monday, 3 December 2012

D is for Daspletosaurus!

Next up in our 'A-Z of Dinosaurs from Alberta' series is the ferocious theropod Daspletosaurus (pronounced 'dass-PLEE-tuh-SAWR-us). Daspletosaurus is a large tyrannosaur found in Alberta and the US, and its name means 'frightful lizard', which I'm pretty sure I don't need to explain. It lived about 77-74 million years ago, close to 10 million years before its more famous relative, T. rex. Although it was likely an apex predator, Daspletosaurus was small for a tyrannosaurid at 2500 kg and 8-9 m long. It's hard to imagine that being considered small! Like other tyrannosaurids, its skull was huge, at about 1 m in length, and it had very short arms with two fingers (although it may have had the longest arms compared to the rest of its body of any tyrannosaur). Unlike other tyrannosaurids, Daspletosaurus has distinct crests around its eyes [1]. 
Currently, just one species is known: Daspletosaurus torosus. However, it is likely that there are more species that are yet to be described including one from Dinosaur Provincial Park here in Alberta [1]. 
Unfortunately, the exact position of Daspletosaurus within the Tyrannosauridae is not clear, especially with these undescribed species. It has been suggested that Daspletosaurus is actually the most closely related dinosaur to Tyrannosaurus (or to the Tyrannosaurus + Tarbosaurus group) [2]. 
Artists impression of Daspletosaurus torosus by Steveoc 86
Daspletosaurus lived alongside another tyrannosaurid, Gorgosaurus. The existence of two large predators, and in fact two tyrannosaurids together is a rare occurrence. In order for both to survive in the same region, they likely had some type of niche partitioning (separation of their ecological positions), either by living in different environments, preying on different animals, being active at different times, or maybe even being separated geographically. Several studies have aimed to answer this, but there is no clear explanation yet. It also lived alongside dinosaurs like Centrosaurus, and likely preyed on large ceratopsians and hadrosaurs. There is even some evidence that Daspletosaurus lived in social groups, or maybe hunted in groups, which is also seen in the tyrannosaurid Albertosaurus
A Daspletosaurus eating a ceratopsian. Image credit to Dmitry Bogdanov
Several daspletosaurs have been found in Alberta, and well known Canadian palaeontologist Philip Currie (currently of the University of Alberta) has worked on this dinosaur before. In fact, during the last field season, the Currie lab was able to remove a very well preserved Daspletosaurus from southern Alberta, which is currently being prepared at the University of Alberta! 

Other 'D' dinosaurs from Alberta
Dromaeosaurus
Dyoplosaurus 

References:
1. Currie, PJ. 2003. Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada. Acta Palaeontologica Polonica 48: 191-226. Download here
2. Carr, TD., Williamson, TE., and Schwimmer, DR. 2005. A new genus and species of tyrannosauroid from the Late Cretaceous (Middle Campanian) Demopolis Formation of Alabama. Journal of Vertebrate Paleontology 25: 119-143.
More information can be found at the Saurian blog on Daspletosaurus

Monday, 26 November 2012

C is for Chasmosaurus!

The third instalment in our 'A-Z of Dinosaurs in Alberta' brings us to the letter C: C is for Chasmosaurus. Chasmosaurus is a ceratopsian dinosaur from the Late Cretaceous (about 75 million years ago) of North America. It was named by well known Canadian palaeontologist Lawrence Lambe in 1914. Its fossils are found mainly in Alberta, but may also be found in Montana and possibly New Mexico. The name means 'opening lizard', in reference to the large fenestrae or openings in the frill of this dinosaur. 
Image of Chasmosaurus belli showing the large openings in the frill. Image from FunkMonk, Wikimedia Commons.
Chasmosaurus was an average sized ceratopsian dinosaur, at about 5-6 m in length and weighing 3600 kg. It is well known with most of the skeleton having been found. In general, the body of ceratopsians is not very distinct, while the skull is what makes the difference between different genera and species. In the case of Chasmosaurus, it has a small horn on it's nose, and small horns above its eyes, along with the large holes in the frill. In some specimens, show ossifications on the frill called epoccipitals, which are commonly found in ceratopsians. Along with all other ceratopsians, it was a herbivore, using its large battery of teeth to break down tough plant material. Two species are known, Chasmosaurus belli, and Chasmosaurus russelli. One specimen of C. russelli actually showed traces of fossilised skin, which is a remarkable find. Chasmosaurus is a very commonly found dinosaur in southern Alberta, and it was one of the earlier dinosaurs to be named as well. 
Artists impression of Chasmosaurus from ArthurWeasley (Wikimedia Commons)
That's it for Chasmosaurus. Next week, we'll have a large theropod for the letter D!

Other Dinosaurs that start with 'C' from Alberta


Monday, 19 November 2012

B is for "Brachyceratops"

To continue with our 'A-Z of Dinosaurs from Alberta', we have B is for "Brachyceratops" this week. You will notice that "Brachyceratops" is surrounded by quotation marks. This indicates that the name is not valid, which will be explained here. 

"Brachyceratops" was named in 1914 from some partial skeletons found in Montana [1]. The name means 'short-horned face', because it has an abbreviated face compared to other ceratopsians. It comes from the Upper Cretaceous, approximately 75 million years ago. It is characterised by its short face, small horns over its eyes (supraorbital horns), and small size. It has also been found in Alberta [2].
"Brachyceratops". Image from Wikimedia Commons (Nobu Tamura)
Unfortunately, the characteristics that were used to differentiate it from other species are also characteristic of juvenile ceratopsians, specifically centrosaurine ceratopsians [3]. It is found in areas where other ceratopsians like Einiosaurus and Achelusaurus are found, and may represent juveniles of these genera, while one specimen has been identified as a juvenile Rubeosaurus [3,4,5]. Because of this, "Brachyceratops" has been classified as a nomen dubium, or 'dubious name', and is not generally considered to be a valid genus of dinosaur, as all specimens are juveniles of other ceratopsian dinosaurs. It can be difficult to determine which dinosaur the juvenile belongs to, but it seems that "Brachyceratops" may represent different ceratopsian juveniles. 
Rubeosaurus from McDonald [5].
Other B dinosaurs from Alberta
There are no other non-avian dinosaurs starting with B from Alberta, but there is one bird called Baptornis.

Stay tuned for next week: C is for Chasmosaurus!

References:
1. Gilmore, CW. 1914. A new ceratopsian dinosaur from the Upper Cretaceous of Montana, with not on Hypacrosaurus. Smithsonian Miscellaneous Collections 63(3): 1-10.
2. Russell, LW. 1934. Fauna of the upper Milk River Beds, southern Alberta. Transactions of the Royal Society of Canada, series 3 4(29): 115-128.
3. Sampson, SD, Ryan, MJ, and Tanke, DH. 1997. Craniofacial ontogeny in centrosaurine dinosaurs (Ornithischia: Ceratopsidae): taxonomic and behavioral implications. 
4. Ryan, MJ, Holmes, R, and Russell, AP. 2007. A revision of the late Campanian centrosaurine ceratopsid genus Styracosaurus from the Western Interior of North America. Journal of Vertebrate Paleontology 27: 944-962. 

Monday, 12 November 2012

A-Z of Dinosaurs in Alberta: A is for Albertonykus

Today we are going to start a series called the A-Z of Dinosaurs in Alberta. This series will take 26 weeks, a week for each letter of the alphabet, and will take us all the way to April 2013 when we will open for the 2013 season. The idea for this series came from Brian Switek, a science writer that focuses on palaeontology. He is currently doing his own A-Z of dinosaurs on his Smithsonian blog 'Dinosaur Tracking', and he agreed to let us use his idea. 

Each week, we will introduce a new dinosaur from Alberta that starts with the letter of the alphabet in question. Now there are plenty of dinosaurs from Alberta, but there are a few letters with no dinosaurs found here. For these letters, I will discuss a different dinosaur from around the world. Now, let's get started with 'A'!


A is for Albertonykus

Albertonykus is a small theropod dinosaur found in southern Alberta. Named in 2009 by Nick Longrich (previously of the University of Calgary, now at the Yale Peabody Museum) and Philip Currie (University of Alberta), it's a relatively new dinosaur from Alberta. It's name means 'Alberta-claw', in reference to it's many claws. It is known from a variety of bones from at least two individuals including a a left ulna (lower arm bone), right tibia (lower leg bone), end of left tibia, and several hand and foot bones. Most of the bones are found in a single bone bed in Dry Island Buffalo Jump Provincial Park, which is known as the Albertosaurus bone bed, as the remains are dominated by Albertosaurus. So far, all Albertonykus remains have been found in Alberta.

Artists impression of Albertonykus borealis. Image from Wikimedia Commons user Karkemish
There is one species of Albertonykus known, Albertonykus borealis. It is a small theropod, an alvarezsaur, from the Late Cretaceous, living approximately 70 million years ago. Although it's remains are quite partial, it was likely about 1 m long, with quite small, reduced forelimbs, which is common among alvarezsaurs. Like other alvarezsaurs, it is thought that Albertonykus was an insectivore, feeding primarily on small insects like termites. It could have used it's forelimbs to claw at wood, getting at the termites within the trees. 

Classification

Dinosauria
      Saurischia
           Theropoda
                 Maniraptora
                       Alvarezsauridae
                             Albertonykus

Other A-dinosaurs from Alberta

Albertosaurus, Anchiceratops, Ankylosaurus, Arrhinoceratops, and Atrociraptor

Reference

Longrich, N. R., and Currie, P. J. 2009. Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: implications for the systematics and ecology of the Alvarezsauridae. Cretaceous Research 30: 239-252.

Monday, 5 November 2012

The end of the dinosaurs

For the last two weeks, we've been talking about mass extinctions (part 1 and part 2), and last week we introduced the Cretaceous-Palaeogene (AKA Cretaceous-Tertiary, K-T, or K-Pg) extinction. Of course this is the most famous mass extinction because this is the one that caused the end of the dinosaurs. This week, we'll go into the K-Pg mass extinction in a bit more detail. 

The impact hypothesis


This is the most strongly supported hypothesis for what caused the mass extinction, and is generally supported by the majority of palaeontologists and scientists. At the very least, the occurrence of the impact is supported, although some people still debate whether it caused the extinction. How did this hypothesis come to be? It's actually quite an interesting story. In 1980, a team of scientists including physicists, geologists and chemists suggested that the extinction was caused by an impact from an extra terrestrial object (Alvarez et al. 1980). They found that the sediments at this time contained much larger amounts of an element called iridium than either before or after. Iridium is a very rare find on Earth, but is found in high concentration in meteors and asteroids. This led them to believe that an extra terrestrial impact occurred at the time of the extinction, and therefore caused the extinction. They predicted that object that collided with Earth would have been about 10 km in diameter, and would have caused a crater over 100 km wide. They also predicted that it would have hit the ocean, and caused large amounts of highly pressured sediment to be ejected into the atmosphere. They were able to identify very fine sediment and clay from this time that could be explained by a large amount of sediment being kicked up into the atmosphere and slowly settling. The catch: they did not have the crater. 

At this point, some people thought the idea was a good one, but many people thought they were totally on the wrong track. Iridium can be caused from volcanic eruptions, and after all, they didn't have a crater. Then, in 1991, a crater was identified with a diameter of 180 km that is partially on the Yucutan Peninsula, but mainly in the Gulf of Mexico (Hildebrand et al. 1991). It was identified from studying sediment core samples that had been retrieved in oil exploration. This crater is called the Chicxulub crater, and appears to match the time of the K-Pg extinction. 
Results of a NASA topography study showing the shape of the Chicxulub crater

How does an impact cause a mass extinction?

There are several different stages of an impact that can cause extinction. First of all, any animals living close to the impact would have died instantly either by the impact itself, or by the high amount of pressure and subsequent shockwave. As the impact was partially in water, huge tsunamis would have occurred, wiping out anything living close to the coastline. The biggest problem, however, comes from the dust ejected into the atmosphere. It's hypothesized that such a large amount of sediment was ejected into the atmosphere that it would have blocked out the sunlight. This was further made worse by gas and aerosols going into the atmosphere and absorbing sunlight before it could reach the Earth. This may have occurred for up to 10 years, which means that anything that relies on photosynthesis (plants and small animals like phytoplankton) would die. Of course this causes a chain reaction, since herbivores would then die from starvation, and eventually carnivores would also die. It also may have caused global fires and acid rain. 
Artists impression of some pterosaurs flying by the impact, which eventually would cause their extinction

Volcanism as a cause

The leading alternative hypothesis of the K-Pg extinction stems from a huge volcanic eruption that occurred in what is now India, in what is called the Deccan Traps. There is an extremely large amount of basalt, a type of rock formed by lava, that can be found in this area. It is thought to have been caused by constant volcanic eruptions occurring from about 68 to 65 million years ago. It's thought that this could have caused similar problems to the impact, injecting large amounts of aerosols into the atmosphere. It also may have greatly increased the amount of carbon dioxide into the air, which may have had a greenhouse effect and caused global warming. 
Picture of the Deccan Traps near Mumbai. Image from Wikimedia Commons (user Nichalp)

What really happened?

There is some debate that dinosaurs were already dying out before the end of the Cretaceous, and that the impact just finished them off. Other people suggest that the impact occurred earlier and could not have caused the extinction. Finally, some people think it most likely was caused by a combination of the impact and volcanism. Either way, the Earth was particularly volatile at this point in time and wouldn't have been a great place to live!

References and Links
University of California Berkeley - The Great Mystery
Alvarez, L.W. et al. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208: 1095-1108.
Hildebrand, A.R. et al. 1991. Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucutan Peninsula, Mexico. Geology 19: 867-871.

Monday, 29 October 2012

Mass Extinctions (part 2)

Last week, we introduced mass extinctions by explaining what they are, some keys to surviving extinction, and then describing the first three mass extinctions in Earth's history: the end-Ordovician, the Late Devonian, and the end-Permian. This week, we will talk about the last 2 major mass extinctions, and some other events that were major, but not considered to be huge mass extinctions. 

The Big Five mass extinctions continued:
4. The Triassic-Jurassic extinction event - This extinction event occurred at the boundary between the Triassic and Jurassic periods, approximately 200 million years ago. It affected both life on land and in the sea, with twenty percent of all marine families being lost, and many on land as well. Animals affected on land include many therapsids, large reptiles (non-dinosaurian archosaurs), and large amphibians. The extinction of these large animals allowed for the dinosaurs to really evolve and take over the landscape, filling the ecological niches left open by the extinct animals. Like most other mass extinction events, the cause is not clear. Possible causes include climate change resulting in sea-level changes or ocean acidification, an asteroid impact, or large volcanic eruptions. Of all of the mass extinctions, the Triassic-Jurassic extinction event is probably ranked fifth in terms of extinction rate. 
Smilosuchus was a phytosaur, a group of reptiles that went extinct in the end-Triassic extinction. Image from Wikimedia Commons user ArthurWeasley.
5. The Cretaceous-Palaeogene mass extinction - Also known as the Cretaceous-Tertiary extinction, or K-T/K-Pg for short, this is the most famous mass extinction to ever occur, although it is not the largest. It marks the end of the Cretaceous period, approximately 65 million years ago. In addition to the extinction of non-avian dinosaurs and pterosaurs, large marine reptiles like mosasaurs and plesiosaurs also went extinct, as well as many plants and invertebrates like ammonites. It affected both animals on land and in the oceans, with a total of 65-70% of all species going extinct, making it the second (or third) largest extinction event in Earth's history. This mass extinction is the only one that the cause is most likely known. It was almost definitely caused by a meteor impact in the Gulf of Mexico, although there is some evidence that it was caused by increased volcanic eruptions in what is now India. To learn more about the Cretaceous-Palaeogene extinction, check out Mesozoic Mondays next week.
Artists rendering of the bolide impact that likely caused the Cretaceous-Palaeogene extinction
Other lesser extinction events have occurred throughout history, during the Precambrian, Cambrian, Silurian, Carboniferous, Permian, Jurassic, Cretaceous, and Neogene. The last extinction event occurred during the Quaternary, and resulted in the extinctions of the large megafauna that existed. Only large animals were affected, so it is not considered to be a true mass extinction, although animals all over the world went extinct. Several events occurred during the Quaternary extinctions, and cause has been attributed to over hunting by humans, climate change, disease, predation, or a swarm of comets. As you can see, it can be very difficult to determine the cause of these mass extinctions. 
Large megafauna like the mammoths went extinct during the Quaternary. Image from Plos Biology credit Mauricio Anton.
Now you have seen a summary of what a mass extinction is, the Big Five extinction events in Earth's history, and some other extinctions. Next week, we will talk about the Cretaceous-Tertiary extinction in detail!

Tuesday, 23 October 2012

Mass Extinctions (Part 1)

Throughout geological time, several mass extinctions have taken place, significantly changing the makeup of plants and animals over time. This post will be talking about mass extinctions, what they are, what causes them, and some examples, followed by another post next week. 

The first question to ask is 'what exactly is a mass extinction'? A mass extinction (also known as an extinction event) is a time when levels of extinction are much higher than normal background levels for a large number of groups, and is not limited to one group or one environment. Mass extinctions are widespread: the have global affects, and they result in a large decrease in diversity and abundance in microscopic and macroscopic life. 

No organism is immune to extinction, but there are characters that can help one survive a mass extinction. Organisms that are widespread are more likely to survive, as they are often more flexible and able to live in different environments. For example, if an animal is found only in a specific environment and a certain area of the world, and that area has a massive fire, then that animal will most likely die. Another thing that helps is numbers. If there are many of the animal, they are more likely to survive. For more details on what helps an animal survive a mass extinction, check out UK palaeontologist Dave Hone's post "How to survive mass extinction.

In the past, there have been several mass extinctions. In palaeontology, we refer to the "Big Five" mass extinctions. This week, we will talk about the first 3: 
Graph showing number of families of animals over time, indicating the 5 major mass extinctions. Image from UMass.
1. The Ordovocian extinction event - occurred at the end of the Ordovician, about 443 million years ago. It was characterised by 2 peaks of extinctions separated by as much as a million years. As the Ordovician is quite early in the evolution of life on land, most life was still in the ocean, and therefore it was marine life that suffered, including a large number of brachiopods and bryozoans. More than 60% of all marine invertebrates went extinct, and as much as 85% of all life, making it the second (or possibly third) most deadly mass extinction of all time. Although the immediate cause is difficult to determine, it seems to have been caused by a decrease in temperature worldwide, resulting in glaciation and fall of sea level. 
Diorama of typical Ordovician life before the extinction. Image from Wikimedia Commons
2. The Late Devonian mass extinction - This likely occurred as a series of events (2 or more) and the event as a whole was approximately 360 million years ago at the end of the Devonian period. Again, primarily marine life was affected, with shallow seas being particularly deadly. Approximately 75% of all life died, including nearly all the corals, which had previously colonised much of the Earth's sea, producing large reef systems. Again, the cause of this extinction is not clear, with theories including a bolide (extraterrestrial) impact, sea level changes, and lack of oxygen in the oceans. This is the least deadly mass extinction.
Typical Devonian ocean life. Image credit: University of Michigan University of Paleontology
3. The Permian mass extinction - The Permian mass extinction occurred at the end of the Permian and the end of the Paleozoic, approximately 250 million years ago. This event is also known as the Permian-Triassic event, as it separates the Permian from the Triassic, the first period in which dinosaurs occur. This is by far the largest mass extinction event in history. It's estimated that as many as 96% of all marine species and 70% of terrestrial species went extinct at this time. This caused a major faunal turnover, with many new groups appearing in the Triassic to exploit the areas left empty by all of the animals that went extinct. Several causes have been proposed including a large release of methane gas, large fires, huge volcanic eruptions, bolide impacts, and sea level changes, although it is likely a result of several different events. Whatever the cause, this is definitely the most catastrophic event that has happened on Earth. Trilobites, foraminiferans, brachiopods, and ammonites suffered substantially, with trilobites going extinct completely. On land, many mammal-like therapsids as well as other reptiles and amphibians died out. 
Trilobite fossil from the Permian of Russia. Image from the Carnegie Institute for Science
Next week, we will continue talking about mass extinctions, including a description of the final two: the end Triassic extinction, and the end Cretaceous extinction, which is the end of the dinosaurs! 

Links:
For more information, check out the BBC Nature website on mass extinctions!

Monday, 15 October 2012

2012 season in summary

As you all should know, yesterday Jurassic Forest closed its doors for the final time in 2012, capping off the 2012 season. This week on Mesozoic Mondays we wanted to just give a quick summary of the last year and thank everyone who helped make it a success. 

We opened up at the end of April this year, and saw a great two months of school trips. We had many first-timers, and several repeats from last year, which made the school season great. We had all ages from Kindergarten to high school, doing both our 'self guided' basic packages, but mainly taking advantage of our curriculum based All-Inclusive packages. If you're looking for somewhere to bring your school this year, check out our Educational Resource Area of our website. 

As summer rolled in, we welcomed many corporate family events, birthday parties, and special events. Highlights from special events include Dr. Phil Currie and Dr. Eva Koppelhus from the University of Alberta talking about their dinosaur hunting trip to Antarctica, and Dinosaur George who gave one of his always-entertaining talks on dinosaurs. 
Dr. Phil Currie giving a talk on dinosaurs and field work in Alberta
Dinosaur George in front of a very packed crowd for one of his several shows
Of course, this year also featured many talks from local PhD students on pterosaurs and dinosaurs, as well as many visitors from the Royal Alberta Museum, like Peter Heule (the "bug guy"). We also had another visit from the Grande Prairie Regional College, who brought out some real fossils to show off and talk about the finds in the region, plus Dr. Phil Bell from the not-yet-built Philip J. Currie Dinosaur Museum in Grande Prairie. Of course we also had some local reptile, amphibian, bat, fish, and plant experts out. All-in-all, a pretty eventful year for special events! We're already thinking about events for next year, so if anyone has any ideas or suggestions, we'd love to hear them. 

Of course, we can't forget to mention that we welcomed two brand new dinosaurs into the park! Well technically, we welcomed one Troodon, and three Pachyrhinosaurus, but who's counting? We had another great day with some helicopter dino-landings to bring in the Pachyrhinosaurus', and the new dinos were definitely a success. Both dinosaurs are commonly found in Alberta, and Pachyrhinosaurus is especially well known from the Grande Prairie region, and Dinosaur Provincial Park. 
One Pachyrhinosaurus flying through the air!
As summer ended and fall began, we had more school trips to cap off the year. This year was a great year at Jurassic Forest and we already can't wait for next year. Unfortunately, the dinos need to have a break for the winter since they are pretty tired from the long season. 

We may be closed to the public, but we are still pretty busy already planning next year. We have some great new ideas, so watch TwitterFacebook, and sign up for our newsletter for more details throughout the next few months! Our E-store is also available for any dino-related Christmas (or other) gifts you may want to purchase, and you can always give us a call at 780-470-2446 for more information! Also, Mesozoic Mondays will be continuing, although it may be less often than weekly. Keep checking for more details!

We hope everyone had a great year this year, and can't wait for the 2013 season! See you all in April!

Monday, 8 October 2012

Where do dinosaur names come from?

Have you ever wondered where a dinosaur gets its name from? Why is it called T. rex sometimes, and Tyrannosaurus rex other times? This week, a little crash course on what we call taxonomy, specifically, the Linnaean taxonomic system, which is what biologists (and palaeontologists) use today. 

To start, a basic lesson on the different groups that we classify animals into. It's a hierarchical system, with all animals being grouped from the top (Kingdom) to the bottom (Species) with the classification as follows:
Kingdom
Phylum
Class
Order
Family
Genus
Species

All animals belong to the Kingdom Animalia, while according to some classifications, dinosaurs are in the Order Dinosauria, and pterosaurs are Order Pterosauria. All dinosaurs are further grouped into families like the Hadrosauridae (duck-billed dinosaurs), Ceratopsidae (horned dinosaurs) and Tyrannosauridae (tyrannosaurs). Families are distinguished by ending in -idae, and in common language, -id (e.g. a hadrosaurid). According to the Linnaean classification system (named for Carl Linnaeus, who invented the system in 1735), the scientific names from Kingdom to Genus should be capitalised when the full name is used. Genus (genera plural) names should be capitalised AND italicised when in print, while species names should always be in lower case and italicised.

Now the genus name is usually what we use to identify dinosaurs. Genus names are used to describe the dinosaur as well, usually with a descriptive feature, or where it was found, or sometimes named after someone, in either Latin or Greek primarily. A species name is used to describe that specific species. There can be many species in one genus, and species are defined by a group of animals that cannot interbreed with other animals to make fertile offspring. In palaeontology, this is difficult because we can't tell from fossils if animals were capable of interbreeding. We make assumptions based on how the animals look. 

As mentioned before, genus names are usually what we use to identify fossils like dinosaurs and pterosaurs. A perfect example of that is Tyrannosaurus. The genus is Tyrannosaurus, while the entire species is called Tyrannosaurus rex, which can be shortened to T. rex. Tyrannosaurus means 'tyrant-lizard' while rex is Latin for king, making it the 'tyrant-lizard king'. Genera that describe certain features about the dinosaur include Dilophosaurus (two-crested lizard), and Centrosaurus (pointed lizard), while others are named for people (e.g. Lambeosaurus for Canadian palaeontologist Lawrence Lambe) or where they are found (e.g. Albertosaurus for Alberta).  

All modern animals have scientific names with genus and species, in addition to their common names. Humans are Homo sapiens, the lynx is Lynx canadensis, and the moose is Alces alces. 

Monday, 1 October 2012

Palaeontology is a Real Science Part 3: Using Geology to Understand Fossils

One of the most important things for palaeontologists to understand is geology. Being able to understand basic geological principles can help a palaeontologist in many ways. It can help determine the kind of sediments that the fossils are found in, which can tell us the environment the animal was living in, or how the animal died. 

Most fossils are found in marine sediments, as water preserves animals the best by quickly cutting off the oxygen supply to the animal which allows for better preservation. Marine sediments can be identified easily and there are several different kinds. Very quiet water from a lagoon or lake is typified by very fine sediments that usually take a long time to settle in a quiet lake. Rocks from this kind of environment often have fossils that are some of the best preserved, lying at the bottom of the lake, undisturbed. A great example of these types of sediments are in shales, and the Solnhofen limestone in Germany. Black shales are typical of anoxia (lack of oxygen) from quiet oceans or lakes. One example of that is the Burgess Shale, in Yoho National Park in BC. 
Marrella a typical Burgess Shale fossil (image from Wikimedia Commons user  PurpleHz)
The Solnhofen limestone in Germany is a type of Konservat-Lagerstaette from the Jurassic that is a lagoon deposit. It preserves some exceptional fossils of fish, crustaceans, insects, and even pterosaurs. The quiet, salty nature of the lagoon made oxygen rare and preservation potential very high. 
An example of an ophiuroid (also known as a brittle star) from the Solnhofen of Germany (image from Wikimedia Commons user UlrichStill) 
Sediments can also show when the fossils have been deposited by something like a river or floodplain. In the case of bone beds, they are often found jumbled up with bones all over the place, overlaying each other. Analysis of the sediments can reveal details about what caused the animals to die and fall apart to the point that they are found. In southern Alberta, there is a Centrosaurus bone bed. By analysing the sediments found along with the bones, it was determined that a herd had tried to cross a flooded river and had drowned. The bodies were swept down-river, while their bodies came apart in the river, separating their bones and eventually resulting in the bones settling together in a jumbled nature. The direction that the bones are facing can also tell us the direction of the stream or river that carried the bones. 
Photo from an Edmontosaurus bonebed showing jumbled nature of dinosaur bones in bone beds. Photo copyright of Liz Martin
Fossils in China are often found in sandstone, typical of animals buried in a sandstorm. These fossils are often preserved in 3-dimensions and show the animals caught in the sandstorm and in their natural positions. 

There are lots of other sedimentological and geological details that can be useful to palaeontologists to help understand the environment or even the cause of death for the animals. 

Monday, 24 September 2012

Palaeontology is a Real Science Part 2: Using CT Scans

This week, we'll continue on with our theme of "palaeontology is a real science" by talking about how palaeontologists use computed tomography (CT) to view and analyse fossils. Many of you have probably heard of CT scans in terms of medicine. The basis of this technique is that it uses x-rays to produce cross-sectional tomographic images ('slices') of the area of the body in question. These slices can then be studied for abnormalities such as tumours, as it can show some soft tissue as well. If several x-rays are taken around an axis of rotation, the slices can be put together to form a 3-dimensional model of the structure in question, showing the internal and external structure. 
Example of CT slices from the base of the skull (top left) to the top of the head (top right)
In palaeontology, CT scans can be very useful. First of all, they allow analysis of a bone if it is still in the rock. In some cases, a bone cannot be completely removed from the rock because of preservation, or in cases where the original geometry of the rock needs to be retained like an egg or several specimens in a single section that show interesting behaviour. In these cases, CT can be very useful to see the full structure of the bone, and what else is in the rock. 
Example of a dinosaur egg as a whole, and showing the internal structure after CT scanning (Balanoff et al. 2008)
In addition to allowing you to see the full external structure, it also allows visualisation of the internal structure of the bone. One especially cool aspect of CT scans is that it allows for the reconstruction of soft tissue, such as the brain. Because brains are incased in a braincase of bone, CT scans of the braincase can show the shape and structure of brains from extinct animals. This has been done in a number of fossils, including dinosaurs (e.g. Spinophorosaurus) and pterosaurs (e.g. Anhanguera). There is a palaeontology lab in the USA run by Dr. Larry Witmer that does many of these studies, and has produced endocasts (the casts made from the braincase) for several extinct animals. 
Example of a braincase from the sauropod dinosaur Spinophorosaurus  from Knoll et al. 2012. To see a 3D animation, go here
Related to reconstructing brain cases, CT scans can allow us to see structures within the bones like replacement teeth, or the roots of teeth. This can help to determine things like tooth replacement patterns in extinct animals. 
Example of the teeth and bone from the right dentary (lower jaw) of the small dinosaur Fruitadens from Butler et al. 2012
The third main way that CT scans are used in palaeontology is to create a 3D model of the skull or bones, often using a relatively new strategy of analysing fossils called Finite Element Analysis (FEA). Now for any engineers out there, you will know that FEA has been around for a long time. It's used by engineers to determine areas of high stress and strain in things like bridges and buildings. This method can also be used in fossils to see where the areas of high stress and strain in a dinosaur's skull might be. This method was used by Arbour and Currie (2012) to determine different taphonomic (what happens to an animal after it dies and becomes fossilised) pressures necessary to cause the deformation seen in an anylosaur dinosaur. The models created from CT scans can also be used to determine muscle attachment points and therefore aid in muscle reconstruction (see our previous post on muscle reconstruction in fossils). 
Finite Element Analysis on the skull of the ankylosaur dinosaur Minotaurasaurus showing areas of low (blue) and high (red/white) stress (Arbour and Currie 2012).
Hopefully you now understand a very useful piece of technology for palaeontologists, and how we can better understand fossils using CT scans. 

Links:
If you're interested in learning more about CT scans and palaeontology, check out the University of Bristol page on CT in palaeontology.
For more cool stuff from the Witmer Lab, check out their website, especially looking at projects and 3D visualization.

Open Access (freely accessible) References:
Arbour, V. M., and Currie, P. J. (2012) Analyzing taphonomic deformation of ankylosaur skulls using retrodeformation and Finite Element Analysis. PloS One e39323.
Butler, R. J. et al. (2012) Anatomy and cranial functional morphology of the small-bodied dinosaur Fruitadens haagarorum from the Upper Jurassic of the USA. PloS One e31556.
Knoll, F., et al. (2012) The braincase of the basal sauropod dinosaur Spinophorosaurus and 3D reconstructions of the cranial endocast and inner ear. PloS One e30060.

References (not Open Access):
Balanoff A. M., et al. (2008) Digital preparation of a probable neoceratopsian preserved within an egg, with comments on microstructural anatomy of ornithischian eggshells. Naturwissenschaften 95: 493-500.

Monday, 17 September 2012

Palaeontology is Real Science Part 1: Muscle reconstruction

This week's Mesozoic Mondays post is going to be a bit different from usual. Since working at Jurassic Forest, I've been amazed by how many people don't consider palaeontology to be a real science, and how surprised they are to see a speaker talk about their research. In particular, I remember one set of parents who were engineers, that came to watch a particularly technical talk on theropod tail muscles. After the talk, the father said "I had no idea so much science was involved in palaeontology"! In response to this, I'm going to do a few posts based on this, showing some of the different scientific techniques palaeontologists use in their research. It's not all digging and assembling skeletons you know! 

To continue with the topic mentioned above, I'm going to talk a bit about muscular reconstruction first. It may sound trivial, but reconstructing fossil muscles is extremely important to understand how an extinct animal was able to move, and it's also very difficult to do correctly. There are two important pieces of information needed to reconstruct fossil muscles. The first, is something called the extant phylogenetic bracket (Witmer 1995). To first understand this, you must understand phylogenies. A phylogeny is something like an evolutionary family tree that shows how different groups of animals are related to each other, based on different features that the animals share, or new derived features. By using living animals (extant) that 'bracket' the extinct form in question on either side, an idea of how the muscle may have appeared in the bracketed animal may be possible. This is by assuming the theory of parsimony, that it is more likely that if something is present before and after, it is most likely also present in the evolutionary middle, rather than losing the feature and re-evolving it. I know, it's a bit complicated! For a good explanation of phylogenetic bracketing, check out the Wikipedia page, which is quite good and full of examples. One example is that theropod dinosaurs are bracketed between crocodiles, their closest living relatives that evolved before dinosaurs, and birds, which of course evolved from dinosaurs. Anything present in both crocodiles and birds was likely present in theropods, whereas something that is not present in either probably wasn't in theropods.
Example of a cladogram showing the phylogenetic relationships of modern reptiles (including birds).  An example of extant phylogenetic bracketing is also seen. The four-chambered heart is present in both crocodilians and birds, and therefore most likely present in dinosaurs. Image from Palaeos.com

Now, once you know what the animals look like that evolved before and after the animal in question, the next key is to look at muscle scars. For this, I'm going to use a paper by Persons and Currie (2011a) from the University of Alberta as an example, as it is open access, so anyone can download it if they would like. By looking at the caudal (tail) vertebrae of the theropod dinosaurs Carnotaurus and Aucosaurus, muscle attachment sites can be viewed. By combining muscle attachment sites with the phylogenetic bracket, it's possible to determine what muscles attach where, and possibly how big they were. Persons and Currie (2011b) used a combination of both methods by dissecting modern caimans to understand their musculature in order to reconstruct the tail musculature of Tyrannosaurus. Although still controversial, this new muscle reconstruction suggested that Tyrannosaurus was a pretty fast guy, using large muscles that ran from its tail to its leg to run. Pretty cool stuff coming out of the University of Alberta! You may have guessed by now that it was actually a talk by Scott Persons that spurned the "paleontology is a real science" discussion. 
Caudal vertebra of Aucosaurus showing a sequence of muscle scars from the ischiocaudalis and caudofemoralis muscles. (Persons and Currie 2011a)
That was an introduction into how palaeontologists can reconstruct muscles from bones, and hopefully it taught you something you didn't know! Muscle reconstruction is really quite important in order to understand some aspects of behaviour and locomotion, as seen in the study of Tyrannosaurus. If it was really as fast as suggested, he was definitely an active hunter rather than a scavenger like some people suggest. Of course, this isn't an easy thing to do since most fossils are incomplete, and it can be difficult to see things like muscle scars. It can also be difficult to determine the phylogenetic position of an extinct animal, and changing the position can greatly change the reconstruction. That being said, this is a very common method used in palaeontology, and it's very important to understand the anatomy and muscular systems of living animals in order to better understand extinct animals!

References:
a Persons, W.S., and Currie, P.J. 2011. Dinosaur speed demon: the caudal musculature of Carnotaurus sastrei and implications for the evolution of South American abelisaurids. PlosOne 6: e25763. --> Freely available online, so take a look if you're interested!
b Persons, W.S., and Currie, P.J. 2011. The tail of Tyrannosaurus: reassessing the size and locomotive importance of the M. caudofemoralis in non-avian theropods. The Anatomical Record 294: 1442-1461. --> unfortunately not open access.
Witmer, L.M. 1995. The extant phylogenetic bracket and the importance of reconstructing soft tissues in fossils. In: Thomason, J (ed.) Functional Morphology in Vertebrate Paleontology. pp. 19-33. Cambridge University Press.