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.

Dimetrodon

Dimetrodon is always in books on dinosaurs, often alongside dinosaurs and pterosaurs, as a big-scaly sail-backed reptile. Unfortunately, these books usually leave out an important fact: that Dimetrodon, along with pterosaurs, is not a dinosaur. If you've been out to Jurassic Forest and seen Dimetrodon, you likely already knew this. However, many of you were probably quite surprised to hear it. 

In order to first explain why our favourite sail-backed reptile is not a dinosaur, let's bring us back to one of the very first Mesozoic Mondays post on What is a dinosaur? Fortunately, this explanation is shorter than why pterosaurs were not dinosaurs. Remember back in the beginning when I was talking about holes in the back of the skull? The temporal fenestrae as we call them? Well if you remember, dinosaurs belonged to the group called the diapsids, which have two holes, one above and one below. Dimetrodon, on the other hand,belongs to the group called the synapsids, which have only one hole in the back of their skull. This is a very fundamental difference, and something that developed quite early in the evolution of tetrapods. 

Skull of Dimetrodon. The first hole on the left is the temporal fenestra, which distinguishes it as a synapsid.

Another problem with the books showing Dimetrodon walking alongside dinosaurs, is that they didn't actually live at the same time. Dimetrodon lived during the Permian Period, approximately 299-270 million years ago. It went extinct long before the first dinosaurs ever appeared, about 40 million years later. In fact, Dimetrodon is what some people would call a "mammal-like reptile", as mammals evolved from reptiles similar to it. This means that Dimetrodon is actually more closely related to us than it is to dinosaurs. Who would have thought??

Dinosaurs definitely weren't the only formidable predators around in the past. Long before the dinosaurs, Dimetrodon was terrorising the small animals with its long caniniform (canine-like) front teeth, and remarkably strong bite force. At up to 5 and half metres long and 250 kg, he could pack a punch. The sail-like structure on it's back also helped it be a faster predator. As Dimetrodon was an ectotherm, meaning its body temperature depended on its surroundings and could not be controlled internally, a way of helping to warm it up and cool it down is very handy. The sail on its back was actually formed by a highly vascularised (so it had lots of blood running through it) membrane stretched between elongated spines of its vertebrae. This membrane acted as a thermoregulator, increasing its temperature quickly when it went into the sun, and decreasing quickly in the shade. This allowed some control over its body temperature, which means it could be more active when it wanted to be. Reptiles are very slow and sluggish when it gets too cold, and this is a way of adapting to that. 

Dimetrodon. Image from Wikimedia Commons user DiBgd 

Dimetrodon fossils are most often found in the USA, but have also been found in Germany. These fossils come from areas that were wetlands during the Permian, suggesting it lived in something very much like Jurassic Forest, with lots of standing water and vegetation (albeit different vegetation). Those of you that have been to Jurassic Forest will know that our Dimetrodon hangs out by our small pond, surveying the water, much like he would have in the Permian, while hunting for fish! 

Palaeontology in Alberta

As most of you will already know, Alberta is a hotspot for palaeontology and fossils. This week, I'll be outlying a few of the places in Alberta that fossils can be found, as well as the kinds of fossils. Some of these I'm sure you will already be aware of, while some of them will come as quite a surprise! 

Dinosaurs

Of course, one of the most common group of fossils found in Alberta are dinosaurs. There are several localities in Alberta that have dinosaur fossils, and many different kinds of dinosaurs too. 

Dinosaur Provincial Park 

This is likely the most obvious place in Alberta to find dinosaur fossils. Dinosaur Provincial Park is located southwest of Drumheller, meaning that the Royal Tyrrell Museum of Palaeontology is not actually located within the park. Dinosaur Prov. Park is where palaeontologists like Dr. Phil Currie go each summer to find new bones. Individual bones are found, as well as nearly complete skeletons, and even large bonebeds. For example, there is a large Styracosaurus bonebed found here that provides evidence that these large herbivores moved in herds, like modern herbivores. 

Styracosaurus, a common ceratopsian found in Dinosaur Provincial Park

The fossils in Dinosaur Provincial Park are from the Late Cretaceous, approximately 77-74 million years ago. There are three terrestrial rock formations within the park, with the Foremost Formation being the oldest, then the Oldman Formation, and finally the Dinosaur Park Formation, while the youngest formation is the Bearpaw Formation, which is marine, and therefore does not have dinosaurs. Now bear with me, because there are a lot of examples from these formations. Found in all three terrestrial formations are animals like mammals (Pediomys), turtles (Adocus, Aspideretes), and crocodile relatives (Champsosaurus, Leidyosuchus). Dinosaurs commonly found in both the Dinosaur Park Formation and Oldman include Centrosaurus, Corythosaurus, Gryposaurus, Stegoceras, Gorgosaurus, Dromaeosaurus, Saurornitholestes, and Troodon. Many dinosaurs are found solely in the Dinosaur Park Formation, like Styracosaurus, Lambeosaurus, Edmontonia, Daspletosaurus, and Ornithomimus. There are also amphibians, birds, marine reptiles, the only pterosaur remains in Alberta (Quetzalcoatlus) and many more found here. Also interesting is that dinosaur egg shells have been within these formations. The list goes on and on... this is truly one of the best places in the world for dinosaur fossils and fossils of this age. The Bearpaw formation will be discussed later, with respect to non-dinosaur sites. 

The badlands of Dinosaur Provincial Park, showing the high amounts of erosion that make it such a good place to find fossils. Photo from Wikimedia Commons user Scorpion0422).

Horseshoe Canyon Formation

The Horseshoe Canyon Formation has outcrops in many areas of the province, including many outcrops in and near Drumheller, along the Red Deer River valley, and even within the city of Edmonton. Dinosaurs found in this formation include Daspletosaurus, Ornithomimus, Saurornitholestes, Troodon, Ankylosaurus, Euoplocephalus, Saurolophus, Pachyrhinosaurus, and at more than one location within the city of Edmonton, Edmontosaurus and Albertosaurus. There are also amphibians, mammals, and crocodile relatives found here. 

Some visible bones from the Edmontosaurus bonebed in Edmonton. Photograph by the author.

Grande Prairie Region

Although the area of Grande Prairie is not as productive for fossils as southern Alberta, there are two Pachyrhinosaurus bonebeds that have produced many fossils, as well as fossils from Saurornitholestes, Troodon, and some hadrosaurs. More finds in recent years have lead to the Pipestone Creek Dinosaur Initiative, and more recently, the Philip J. Currie Dinosaur Museum, which will hopefully lead to a new dinosaur museum in northern Alberta. You may have heard about these areas in the news lately, because unfortunately, someone has been vandalising fossil sites in this region and destroying fossils destined for the new museum. 

Other Sites

Other areas in Alberta that have provided dinosaur fossils include Lundebreck Falls, where the famous T. rex skeleton 'Black Beauty' is from; Dry Island Buffalo Jump Provincial Park, where an Albertosaurus bonebed was found; and Warner, Alberta, where 10 dinosaur eggs (possibly from Hypacrosaurus) were found. Another very interesting dinosaur found came from the Suncor Mine near Fort McMurray a few years ago, when a 3D preserved skeleton of an ankylosaur was found. This is especially interesting because these sediments are marine, suggesting the animal died, then was swept out to sea, where it was buried and preserved. 

Cast of 'Black Beauty' at the Royal Tyrrell Museum of Palaeontology. Photo from Flickr user subarcticmike.

Non-Dinosaur Sites

Although I've mainly focused on places were dinosaurs have been found, Alberta is also home to many non-dinosaur fossils. For example, marine reptiles are often found in Alberta, such as Albertonectes, which was found near Lethbridge. Ammolite, which is the shiny remains of fossilised ammonites, is mined near Lethbridge as well. Although ammolite in itself is a fossil, marine reptiles can also be found here, and a mosasaur was found in the mine earlier this year. Marine reptiles can also be found in the oil sands and regions in northern Alberta. There are also isolated cases of mammals, amphibians, reptiles, insects and more throughout the provinces, but it would take me forever to list them! 

Albertonectes fossil from Kubo et al. (2012). The neck is to the right (you can see it is broken), while the tail is to the left. 

References and links:

Kubo et al. (2012) Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta. Journal of Vertebrate Paleontology 32: 557-572.

The Paleobiology Database

Deep Alberta - A great book by John Acorn for anyone interested in dinosaurs in Alberta!

Invertebrates

Welcome to another Mesozoic Mondays blog from Jurassic Forest!  We're going to take a detour from our normal posts as our main blogger, Liz, is away (she is preparing for her thesis defense so wish her luck)!  My name is Kristina and I am another palaeontologist at Jurassic Forest.  Unlike Liz who studies large, flying reptiles, I study fossils that are very small.  Some of them are so small that you need a microscope to see them properly!  Another big difference between the animals that we study is that Liz studies animals that have backbones (vertebrae), and the ones I study do not.  These animals are called invertebrates, and they will be the topic of this week's Mesozoic Monday.

Jurassic invertebrate fossils!

Invertebrate animals have no vertebral column, no bones, and come in countless shapes and sizes.  They represent the most diverse groups of animals on the planet!  It would be impossible for me to give a complete representation of all invertebrates in a blog post, so I am just going to highlight some of the major groups and their evolutionary history.

The first evidence of multicellular animal life comes from fossils in the Ediacaran Period, about 600 - 545 million years ago.  Most of these fossils are from soft bodied creatures, somewhat like jellyfish.  These fossils represent soft bodied creatures that are very different from those seen today so classification of these animals is often very difficult.



Dickinsonia is a classic example of Ediacaran life

The first animals with hard parts appear in the fossil record during the Cambrian Period (about 542 million years ago).  This event is often referred to as the "Cambrian Explosion" because there was such a large radiation of life forms that appeared over a relatively short period of time ("relatively" in geologic terms means about 40 million years).  As well, animals with hard parts fossilize much more easily than soft bodied animals.  

Although most of the fossils from the Cambrian Explosion are very bizzare, most of them are clearly related to modern animal forms.  There are representatives from most major groups of animals, even vertebrates!  Pikaia is thought to be an ancestral form of vertebrate animals.  The most famous fossil site for animals from this event is the Burgess Shale in Yoho National Park, British Columbia.

Animals from the Burgess Shale (Top row: Anomalocaris, Opabinia; Bottom row: Hallucigenia, Wiwaxia, Pikaia), Image by: Matt Martyniuk

In the animal kingdom, there are many different categories of animals.  Vertebrate animals represent only one of these major categories!  The simplest form of animals are the sponges.  Even though they lack true tissue, they are considered animals because they have to eat food (they cannot make their own food like plants), and because they have sperm cells for reproduction.  Unlike other animals that have a digestive system, sponges feed by filtering water through the many pores in their bodies (hence their scientific name is Porifera).

Sponges are animals!

The next major group of animals are called the Cnidaria (pronounced "nye-DARE-ee-a").  They include the jellyfish, corals, and anenomes.  Unlike sponges, cnidarians have their cells organized into true tissues.  They also have special stinging cells, which is what makes some jellyfish so poisonous (please note that not all cnidarians are poisonous).

Anenomes are cnidarians

There are hundreds of different kinds of worms in the animal kingdom, which are usually organized into three major groups: the flatworms, segmented worms, and round worms.  These groups are incredibly diverse, but generally have a poor fossil record.

Worms, such as this tapeworm, can live almost everywhere, including your digestive system!

Molluscs are another incredibly diverse group of invertebrates.  They are one of the most abundant groups of animals in the fossil record and are characterized by a having a special muscle called the "foot".  They include animals such as clams, oysters, snails, slugs, octopi, squid, ammonites, and nautiloids.

Ammonites were one of the top predators in Mesozoic oceans! Photo by: Mike Peel.

By far, the largest, most diverse, and most abundant group of animals on the planet are the invertebrate group called the arthropods.  Arthropods are characterized by  having a hard exoskeleton which they shed (moult) as they grow, and a segmented body.  The arthropods include insects, crustaceans, arachnids, millipedes, centipedes, and a large extinct group called trilobites.

Trilobites first appear at the Cambrian Explosion, and are the only completely extinct group of arthropods.

The next group of invertebrates is one that most people have never heard of, but which were very important in the fossil record.  This group is called the lophophorates (pronounced "LOW-fo-FOUR-ate") and includes two major groups: brachiopods and bryozoans, both of which are still alive today.  They are characterized by a special feeding structure called the lophophore.  The lophophorates were incredibly diverse and abundant during the Paleozoic, but were largely replaced by molluscs during the Mesozoic.  This is the group that I study!

Brachiopods look like clams on the outside, but their internal anatomy is very different! Image by: Didier Descouens

The final major group of invertebrates are called the echinoderms (pronounced "eh-KYE-no-derms").  These animals are the closest relative of vertebrates because most have a special type of internal skeleton.  They are also characterized by a special body plan that has five sided symmetry.  Echinoderms include sea cucumbers, sea urchins, sand dollars, sea stars, brittle stars, sea daisies, crinoids, and an extinct group called the blastoids.

Crinoids are a cool group of echinoderms that are common in the fossil record!

While we are most familiar with vertebrate animals, there are way more invertebrates.  Beetles alone represent more than 28% of all living species of animals!  So for those of you out there that want to study palaeontology: don't forget that there is more that 600 million years of fossil record for you to choose from!  While dinosaurs are one of my favourite groups, there are countless plants, fungi, microfossils, and invertebrate fossils for us to study too.  That is what makes the science of palaeontology so awesome!

Fossils are awesome! Image by: Ghedoghedo 

 References:

Pearse, V., Pearse, J., Buchsbaum, M., and Buschsbaum, R., 1987, Living Invertebrates, Blackwell Scientific Publications, Palo Alto, CA, 848 pp.

http://www.ucmp.berkeley.edu/index.php - This website is a great resource for all things palaeontology and evolutionary biology.  Their invertebrates section is very good and includes some awesome diagrams and animations.
 

Pterosaurs!

This week, I'm going to talk about my personal favourites, and what I do my research on: pterosaurs! As mentioned in my previous post "What is a dinosaur", pterosaurs are flying reptiles that are closely related to dinosaurs (well, depending on who you talk to that is), but are not actually dinosaurs. As such, they are also not closely related to birds. They are a separate group all together that is entirely extinct, the last ones dying out at the same time as the non-avian dinosaurs. Pterosaur wings are different from both bird and bat wings. They are formed mainly from an elongated fourth digit (your ring finger), with a membrane from the end of that digit to its body. They have 3 tiny clawed fingers (digits I-III), as well as a bone only found in pterosaurs: the pteroid, which was likely responsible for controlling the leading edge of the wing membrane. 

Diagram of a pterosaur wing from Wikimedia Commons user ArthurWeasley

Pterosaur evolution is a bit hard to understand because they appear quite suddenly in the fossil record as fully flying pterosaurs during the Triassic. In terms of morphology (the form of the animal), pterosaurs can be divided into two groups: the rhamphorhynchoids, and the pterodactyloids. 

Rhamphorhynchoids

Rhamphorhynchoids are the smaller, more primitive pterosaurs. The had short necks, long tails, and more basic body plans. Dimorphodon comes from the UK. It had a wingspan of 1.2 m, a huge head (20 cm), and long curved claws, suggesting it was a good climber. 

The Early Jurassic pterosaur Dimorphodon 

Another interesting rhamphorhynchoid is Anurognathus, which means 'frog-jaw', for its distinctly froggy jaw. It comes from the amazing Upper Jurassic Solnhofen limestone in Germany, which is known for the amazingly preserved fossils found within. Unlike other rhamphorhynchoids, Anurognathus had a very short tail and a short, squat skull. 

Anurognathus

Rhamphorhynchus

Of course, there is also Rhamphorhynchus, which gives the group its name. Also from southern Germany, England, Switzerland, Africa and maybe the US,  this is one of the most commonly found pterosaur fossils. It has a long tail with a diamond-shaped vane at the end, and lots of pointy teeth used to catch prey. 

Other important or interesting rhamphorhynchoids include Sordes and Jeholopterus, which have shown that pterosaurs were covered in a hair-like material called pycnofibres, and Darwinopterus, which has features from both rhamphorhychoids (characters of the body and wings, like a long tail) and pterodactyloids (characters of the neck and skull, like a crest). This shows that pterodactyloids evolved from rhamphorhynchoids. What a great find! 

Darwinopterus

Pterodactyloids

Pterodactyloids generally include the more well known pterosaurs like Pteranodon, which had no teeth, and flew over the seas and oceans, swooping down to catch fish. They also had large crests, which are different between males and females, suggesting they could be used for sexual displays. These are some of the larger pterosaurs, with the wingspan reaching 7 m. 

A male Pteranodon in front with a large, colourful crest, while a female rests behind, with a smaller crest

Another odd pterodactyloid pterosaur is Pterodaustro, which belongs to a group of pterosaurs known as the 'comb-mouths'. This is because Pterodaustro and its relatives look kind of like a baleen whale. They have over 1000 long, peg-like teeth on their curved lower jaw that they could use to filter small animals out of the water with. 

Pterodaustro from the Early Cretaceous of Argentina

Of course, we can't forget about Quetzalcoatlus, the largest flying animal to have ever lived. This guy was enormous. With a wingspan of about 10-12 m, it is by far the hugest thing to fly. Of course, this has lead to debate about whether or not it was actually capable of flying, but that is for a different day. Unlike the other toothless pterosaurs, this guy may have hunted on land using a 'terrestrial stalking' method, picking up small dinosaurs or other animals as it goes (see Witton and Naish 2008 for details if you're interested). 

Quetzalcoatlus shown using the 'terrestrial stalking'
method eating small sauropod dinosaurs

Size comparison between Quetzalcoatlus, an
average sized person, and a giraffe

Other well-known pterodactyloids include the ornithocheirids Ornithocheirus, and Anhanguera, and the crested Tupandactylus, Tapejara, and Tupuxuara, which all had an enormous crest on their skulls. 

Tupuxuara

Tapejara

 Some important things about pterosaurs to point out. First of all, they are not all toothless. In fact they are far from it as you should have learned. Two groups lost their teeth, the pteranodontids like Pteranodon, and the azhdarchids like Quetzalcoatlus. Another interesting thing about pterosaurs is the debate over where the membrane attached. There are currently three theories: it attached to its ankle, thigh, or hip. There are arguments for all of them, and it's not yet clear which one it was, or if it was different in each pterosaur. Finally, you may have noticed that in all the pterosaurs depicted on the ground, they were not moving around bipedally on their back legs, but quadrupedally using digits I-III to support themselves, while the wing is tucked upwards. This is well supported by pterosaur trackways. Related to this, is the theory that pterosaurs took off not like birds, but by launching themselves quadrupedally, mainly using their forelimbs to produce enough energy to get them off the ground (Habib 2008). A video of this can be seen here. 

UPDATE 3/9:
After I got some feedback about the blog, I found something out that I slightly mis-represented. According to Mark Witton, the membrane attachment issue is much more 'solved' than what I suggested. There is no fossil evidence for the hip-based membrane attachment, and it is highly unlikely that the thigh/knee attachment is correct thanks to another look at the key fossil of Pterodactylus that supported this idea. This leaves the ankle attachment as the only valid thought left. Many different specimens and species show a distal hindlimb attachment in the fossils, so this is most likely it. Thanks Mark for letting me know!

I think pterosaurs are pretty cool. If anyone has any questions about them, please let me know! One last thing I'd like to mention. The majority of these images came from Mark Witton, with permission. Thanks so much for letting me use your pretty pictures Mark! Also, this means that if someone wants to use these images, you need to ask Mark. He's a pretty nice guy and will probably say yes, but they are his and you need permission, so please don't steal them!

References and interesting sites

Habib MB (2008) Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana Reihe B 28: 159-166

WittonMP, Naish D (2008) A reappraisal of azhdarchid pterosaur functional morphologyand paleoecology. PLoS One 3: e2271

Pterosaur.net - Great website for anyone interested in pterosaurs to take a look at. It's run by palaeontologists that work on or specialise in pterosaurs. It has info on their evolution, anatomy, biology, basically everything you want to know!

Mark Witton's images at Flickr and his website - Dr. Witton is a pterosaur palaeontologist as well as a palaeoartist, which means that his images are all scientifically accurate! Definitely take a look at what he's done, but if you want to reproduce or use anything, make sure you ask him because they are all copyrighted!
Musings of a clumsy palaeontologist - specifically, the post on pterosaur mass if you're interested!
Update: Also check out Dave Hone's recent post on pterosaurs. Great read for people not familiar with pterosaurs!

Ornithischians

After a week long hiatus, Mesozoic Mondays is back! Last time, we were explaining what the saurischian dinosaurs were. This week, we will describe the second large group of dinosaurs, the ornithischians. For a review of the difference between the Saurischia (lizard-hipped) and Ornithischia (bird-hipped) dinosaurs, view the Mesozoic Mondays post on the saurischians. 

Most herbivorous dinosaurs are ornithischians, and basically all ornithischians are herbivorous. The early ornithischians look superficially similar to early saurischians, but they evolved later. The earliest ornithischians include dinosaurs like Pisanosaurus from the Late Triassic of South America and Eocursor from South Africa, which lived about 210 million years ago. 

Eocursor,an early ornithischian. (Image from Wikimedia Commons user ArthurWeasley)

Ornithischians are divided into three main groups: the thyreophorans, ornithopods and marginocephalians. What a mouthful! Thyreophorans are the 'shield-bearers', also known as the armoured dinosaurs like ankylosaurs and stegosaurs. They evolved in the early Jurassic and lived right up until the non-avian dinosaurs went extinct at the end of the Cretaceous. Ankylosaurs are divided into 2 groups: the ankylosaurids like Euoplocephalus which have large tail clubs to protect themselves, and the nodosaurids like Edmontonia, which do not have tail clubs. Both groups are characterised by the heavy amount of armour that covers their head, back, and tail to protect them. They are likely the best protected dinosaurs from predation. The stegosaurs include the well known Stegosaurus, as well as other dinosaurs with alternating rows of plates and spikes. Other stegosaurs include the Chinese Huayangosaurus and Tuojiangosaurus. 

Huayangosaurus (image from Wikimedia Commons user ArthurWeasley)

The ornithopods are a very large group. Ornithopod means 'bird foot', with respect to the three-toed feet found in most of these dinosaurs. Although there are many kinds of ornithopods, the main group is the iguanodontians, which includes the hadrosaurids, or 'duck-billed' dinosaurs. The most famous iguanodontid is Iguanodon, which is known for its large thumb spike and is found in Europe. Hadrosaurids are generally divided into two groups: the crested (lambeosaurine) hadrosaurids like Parasaurolophus and Lambeosaurus, and the non-crested (hadrosaurine or saurolophine) ones such as Edmontosaurus. The crests of lambeosaurine hadrosaurids were likely used like a resonating chamber to make sound and to communicate. Hadrosaurids were one of the most successful groups of ornithischians in the Late Cretaceous and lived in Asia, Europe and North America.

Iguanodontian heads (left column then right column): Ouranosaurus, Muttaburrasaurus, Corythosaurus, Lambeosaurus magnicristatus and Lambeosaurus lambei. (image from Wikimedia Commons user FunkMonk)

The final group of ornithischians is the marginocephalians, which are the 'fringe heads'. This group includes the dinosaurs that have some kind of fringe or frill on their skull margin like the pachycephalosaurs and ceratopsians. Pachycephalosaurs, or 'thick-headed lizards' include the very large Pachycephalosaurus, and the small Stegoceras. They may have evolved during the Early Cretaceous, but primarily lived during the Late Cretaceous. Some pachycephalosaurs may have been omnivorous, eating insects as well as plants. Some palaeontologists believe they used their heads to head-butt each other, possibly as a mating display, while others believe that would have resulted in concussions or possibly even broken necks. They argue that pachycephalosaurs were more well suited to flank-butting, where it's a bit more fleshy. 

Skull of Pachycephalosaurus from Wikimedia Commons user  Dudo

The ceratopsians are arguably the most recognisable dinosaurs: the horned dinosaurs. They are an interesting group because they actually have a separate bone on the front of their mouth that makes up the bottom part of their tooth-less beak: the rostrum. No other group of dinosaurs (or animal for that matter) has this bone. Although they are generally known as being horned, not all ceratopsians had horned. Early ceratopsians like Psittacosaurus were bipedal, had no horns and lived during the Early Cretaceous. Recently, a specimen was found that showed barb-like filaments on the tail of Psittacosaurus. Late Cretaceous ceratopsians reached an amazing level of diversity from the three-horned Triceratops, to the spiky Styracosaurus, to the bony boss-covered Pachyrhinosaurus. Although their skulls are very diverse, the rest of their body morphology is fairly common throughout the group. They were all large, quadrupedal, herbivorous dinosaurs. 

Psittacosaurus (image from Wikimedia Commons user ArthurWeasley)

Ceratopsian skull diversity. Some genera include Styracosaurus (bottom left), Centrosaurus (right of Styracosaurus), Achelosaurus (?) (top right of left section), Chasmosaurus (centre), Kosmoceratops (just to the right of center on the bottom with 2 large horns), and Triceratops (?) (top right). Image from Wikimedia Commons from Flickr user Magnus Manske.

Ornithischian fossils are very common in Alberta, especially hadrosaurids and ceratopsians. For a list of some dinosaurs found just in Dinosaur Provincial Park, go here. There are many other places in Alberta where you can find ornithischian dinosaurs including near Grande Prairie (Pachyrhinosaurus, hadrosaurids and more), and right here in the city of Edmonton (Edmontosaurus and more)!

Ornithischians at Jurassic Forest:
Ankylosaurus
Corythosaurus
Edmontosaurus
Hadrosaurus
Iguanodon
Maiasaura
Pachycephalosaurus
Pachyrhinosaurus
Parasaurolophus
Stegosaurus
Styracosaurus
Triceratops

References:
Most of the stuff from this week came from my brain, but some good sites to check out include:
The Paleobiology Database - this site is run by palaeontologists and is a good place to get information on things like dates classification, and where fossils are found. It is a bit technical though.
http://palaeo.gly.bris.ac.uk/communication/boulton/evolution.html