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!

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!

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 Twitter, Facebook, 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!

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. 

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. 

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.

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.