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

Chirostenotes

Corythosaurus

Centrosaurus

Coronosaurus

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. 

5. McDonald, AT. 2011. A subadult specimen of Rubeosaurus ovatus (Dinosauria: Ceratopsidae), with observations on other ceratopsids from the Two Medicine Formation. PLoS ONE 6(8): e22710. 

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.

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.