Two new theropods in November!

November's not quite done yet, and we've seen two important new theropod dinosaurs named this month alone. Both of these are scientifically significant, and both come from Utah, but they lived at different times and are from different groups. Here, I will briefly introduce you to these two new dinosaurs, Lythronax and Siats.

Siats meekororum
First up is Siats meekororum, from the Late Cretaceous [1]. It lived 98 million years ago, which makes it the youngest (geologically) known allosauroid (like Allosaurus) from North America. It's also the first time a dinosaur from the theropod group known as the neovenatorids has ever been found on this continent. Siats was a top predator, living long before tyrannosaurs, and may have been as much as 12m long. It is known from a single incomplete individual, that was skeletally immature, and about 9m long, suggesting a fully grown individual would have been longer. Siats helps to fill a 25 million year gap between larger North American predators like Acrocanthrosaurus and Tyrannosaurus, and palaeontologists were trying to understand why no large predator fossils had been found in between. They also found evidence of small bodied tyrannosauroids living alongside Siats, the first time these two groups have been found living together. We now know that there were large predatory theropods throughout the Cretaceous, and the presence of these other large predators likely prevented early success of they tyrannosaurs until after these allosauroids had disappeared. This was an important find by extending the evolutionary range of allosauroids, furthering our understanding of tyrannosaur evolution, and revealing a new coexistence between two groups of predators.

For a picture and another post on Siats, see Brian Switek's post here.

Lythronax argestes
The second big theropod news of November was Lythronax argestes, meaning 'southern king of gore' [2]. Lythronax is the oldest known tyrannosaurid known from a single adult individual with a partial skull and bits and pieces of the rest of the body. It would have been about 8m in length, and lived during the Late Cretaceous, about 80 million years ago. As there is a partial skull known, we know a bit about it's behaviour. Lythronax had a similar skull shape to Tyrannosaurus, with a short and narrow snout, wide back of skull, and forward-facing eyes allowing for depth perception, which is generally considered to be a characteristic of predators. This skull shape was thought to be a derived characteristic, but this find pushes the appearance of this skull shape back by several million years. It had large serrated teeth that were used for slicing through flesh, but also capable of crushing bones with its well built skull and jaw. Currently, Lythronax represents the largest predator from the ecosystem it lived in, which was cut off from the rest of North America from the Western Interior Seaway. This find has changed some of our understanding of tyrannosaur evolution as it has features that were not previously found so early, which has changed how we thought certain tyrannosaurs were related. Lythronax will be a very important find in the understanding of tyrannosaur evolution. 

For more details, check out Dave Hone's blog post in The Guardian about Lythronax, or download the paper itself, which is free and open access!

Pictures and skull reconstruction of Lythronax argestes from Loewen et al [2]

I hope you've enjoyed this short introduction to two important new theropod finds! These will both be very important in understanding theropod evolution in the future. 

References
1. Zanno and Makovicky. 2013. Neovenatorid theropods are apex predators in the Late Cretaceous of North America. Nature Communications 4.
2. Loewen et al. 2013. Tyrant dinosaur evolution tracks the rise and fall of Late Cretaceous oceans. PLoS ONE 8: e79420. --> Freely downloadable here doi:10.1371/journal.pone.0079420

Pleistocene Megafauna

In the past, we've been focusing on very old fossils, mainly from the Mesozoic. This week, we're going to talk about some fossils that are a bit younger, specifically, from the Ice Age. These animals are commonly referred to as the Pleistocene Megafauna, where the Pleistocene is the time period (epoch) that the most recent ice age occurred and these animals lived in (2.5 million to 11 700 years ago), and megafauna refers to the large size of these animals compared to what we see today. 

A number of these fossils are very well known, like mammoths, and sabre-toothed cats, but other ones are less well known. Although Albertan palaeontology tends to mainly be dinosaurs and similarly aged animals, there are actually a number of the Pleistocene megafauna fossils that can be found in Alberta. Relatives of modern animals like horses (from the genus Equus, the same genus as modern horses) and Bison are often found in Alberta, as well as mammoth fossils. Mammoth fossils can be found near Medicine Hat, as well as several places in western and northern Canada. Mammoths are extinct relatives of elephants that lived in colder habitats during the Ice Age. They are well known for often having long, curved tusks, which are found commonly in Canada. As mammoths lived in glacial environments, they can often are found mummified, so we know a lot about their biology.

Mammoth skeleton. Photo by WolfmanSF

Another example of a Pleistocene megafauna that lived in Alberta during the Ice Age was Jefferson's ground sloth, Megalonyx jeffersoni. This giant ground sloth measured 3 m long, and as much as 1 ton in weight. Shockingly, this is only medium sized among the giant ground sloths, but it's still significantly bigger than any sloths alive today. Its fossils are more rare than mammoths, but they can be found in Alberta, Saskatchewan, the Yukon, and NWT. Its peg-like teeth and plantigrade (flat) feet allowed the animal to reach up on its hindlimbs and pull leaves down from trees and break down the tough plant material. They also had long claws on the forelimbs probably used for stripping branches. 

Megalonyx skeleton. Photo by Daderot

Finally, who knew there were camels in Alberta? One species of camel, known as Yesterday's Camel, has also been found in Alberta.  It was over 2 m tall at the shoulders, and weighed 800 kg, and is thought to have been an opportunistic herbivore, meaning it would eat whatever plants it could find. The camelids, horses, and mastodons all went extinct in North America at approximately the same time as Clovis tools (early human tools) became common. This has lead to the belief that increased human activity in North America actually drove these animals to extinction as we started to hunt. This is also possibly the case for the disappearance of the Pleistocene megafauna from around the world.

There are many other megafauna found in Alberta, and around the world, but here was a brief overview and some examples from Alberta and western Canada. I hope you found this brief report interesting!

References
Jass, C.N., et al. 2011. Description of fossil muskoxen and relative abundance of Pleistocene megafauna in central Alberta. Canadian Journal of Earth Science 48: 793-800.

Marine Reptiles in Alberta

You may have noticed that there was no blog post last week. Sorry about that! That is because the writer of this blog (me - Liz) was busy last week starting a PhD at the University of Southampton in the United Kingdom. I was so busy last week I just didn't have a chance to write! But now we're back!

Although we've talked in passing about extinct marine reptiles in the past, it has never been in detail, which is why I decided that this week we would talk a bit about the sea creatures often found in Alberta. In order to talk about the marine reptile fossils found in Alberta, I think it's important to explain some of geological history of the region.

In the mid to Late Cretaceous, a large water body called the Western Interior Seaway ran through North America, connecting the Arctic Ocean to the Gulf of Mexico. This large seaway lasted for about 100 million years, and caused nearly the entire province of Alberta to be underwater. This large seaway allowed for many large and small marine animals to invade, including sharks, fish, and of course, large marine reptiles. 

Image of modern North America in the mid-Late Cretaceous, covered in seaways

Although there are many groups of marine animal fossils that have been found in Alberta, we are going to focus on the two groups of marine reptiles that have appeared. The first group is the plesiosaurs. Plesiosauroids are the long-necked marine reptiles in the group Plesiosauria. They differ from their close relatives, the pliosauroids, by (generally) having very long necks and small heads, while pliosauroids (generally) have short necks and large heads. As of 2012, nearly 30 plesiosaurid specimens had been found in western Canada, with just over half of them coming from Alberta [1]. Although not all are identifiable to genus or species, most of them are either from the family Elasmosauridae, which includes the plesiosauroids with the longest necks of all, or the Polycotylidae, which have shorter necks and closely resemble pliosaurs. Elasmosaurids from Alberta include Albertonectes (found near Lethbridge) and Wapuskanectes which was found in a Syncrude mine near Fort McMurray. Because the oil sands are marine deposits, it's quite common for marine fossils to be found in these mines. Trinacromerum (from Dinosaur Provincial Park) and Nichollsaura (also from near Fort McMurray) are some of the polycotylids found in Alberta. Plesiosaurs are also found in Saskatchewan, Manitoba, and occasionally in BC.

Artists impression of Albertonectes by Smokeybjb

Trinacromerum by Nobu Tamura

The second group of marine reptiles found in Alberta is the mosasaurs. Mosasaurs lived only in the Late Cretaceous, and were the dominant marine predators during this time. They were strong swimmers, and even better predators, reaching lengths from 3-18 m and having double-hinged jaws much like modern snakes, allowing them to open their mouths wide and swallow prey. Prognathodon, a rare, large-jawed mosasaur has been identified by a few specimens in Alberta, including one nearly complete specimen from near Lethbridge [2]. These were found by the Korite International, an ammolite mining company, while mining for ammolite. Another possible specimen was discovered in 2012 in a mine as well. Another mosasaur, Plioplatecarpus, which has proportionally larger eyes than other mosasaurs, was identified from an incomplete specimen found in southern Alberta.

Artists impression of Prognathodon

Plesiosaurs and mosasaurs are just two of the groups of marine fossil animals that have been found so far in Alberta. Other groups include fishes, sharks, and possibly pliosaurs as well. I hope this has given an insight into the non-terrestrial fossils that can be found in Alberta, and the kinds of marine reptiles often found!

References:
1. Kubo, T., et al. 2012. Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta. Journal of Vertebrate Paleontology 32: 557-572.
2. Konishi, T., et al. 2011. New exceptional specimens of Prognathodon overtoni (Squamata, Mosasauridae) from the Upper Campanian of Alberta, Canada, and the systematics and ecology of the genus. Journal of Vertebrate Paleontology 31: 1026-1046.

Dinosaurian Myths: Take 2

Last week, we introduced you to a few different dinosaur-related myths ("Brontosaurus, all dinos were big, and Triceratops is no more) that are particularly irksome in my opinion. This week, we're going to continue on this theme with three more common dinosaurian myths! Since last week was 1-3, this week will continue with 4-6.

4. All large, prehistoric reptiles were dinosaurs
This is one that I've touched on before at the very beginning of Mesozoic Mondays, when I explained, in detail, exactly what a dinosaur is, and for that matter, what isn't. Dinosaurs are a group of organisms united by a very specific suite of characters, not just a group of big, scaly creatures. In fact, all of those swimming, and flying things normally called dinosaurs in a kid's toy set or book are not even dinosaurs! The large, aquatic reptiles come from several distinct groups, not closely related to dinosaurs. These include ichthyosaurs, mosasaurs, plesiosaurs, pliosaurs, and many more. "What about those scaly flying creatures like a pterodactyl?" Nope, not dinosaurs either. These are pterosaurs, which are closely related to dinosaurs, but not actually in the Dinosauria. "Does that mean that not a single dinosaur swam or flew?" Absolutely not. Dinosaurs would have swam occasionally to get across water, and there is evidence some spent more time in the water than others. However, there are no fully aquatic dinos that evolved paddle-like limbs to swim around. These are just other prehistoric, and indeed Mesozoic reptiles. When it comes to flying, there are of course a whole suite of dinosaurs that flew: they are the dinos that evolved into birds, and in fact birds. "Ok fine, but what about those guys with the sails on their back that we always see in books? Those are dinosaurs, right?" you may be asking. And the answer is: nope, they lived even before the dinosaurs, and are ancestors to modern mammals. In fact, they are more closely related to you and I than to dinosaurs! So spread the word: not everything was a dino! 

5. Mammals outcompeted/were more fit than dinosaurs
This common myth comes in several different forms, but the general thought is that mammals were somehow more fit/better than dinosaurs  and therefore outcompeted them and that's why mammals survived and dinosaurs didn't. This is, of course, false on many different levels. First of all, while mammals were living at the same time as dinosaurs, they were substantially smaller (in general), and were not (also in general) capable of competing with dinosaurs for anything. Dinosaurs were widely successful, living in every ecological niche on land, while mammals were mainly filling the niche of small, scavenger-like creatures. When the meteor hit the Earth at the end of the Cretaceous, the wide scale environmental changes that ensued made it very hard on the dinosaurs, which in general required a large amount of food to survive. It was then that the mammals were able to truly expand into the niches left empty as the dinosaurs died, and then that mammals evolved into the diverse group they are today. While this myth is mainly false, there is a slight ring of truth to it in that mammals were better able to adapt to the changes once the meteor hit, than the larger dinosaurs. However, that does not mean that they were better in general, and they were not responsible for the demise of the dinos.

6. Stegosaurus (or other large dinosaurs) had a secondary brain in its hips.
Still, to this day, this boggles my mind whenever I hear it. In the 19th century, American palaeontologist Othniel Charles Marsh noticed that large dinosaurs often have big cavities in their hips. As this is associated with the area that the spinal cord passes through, he suggested that this cavity actually housed a second brain. Unfortunately, it's difficult to know exactly what this was for. Birds often do show a slight expansion of the spinal cord in this region to help regulate their limb movements, but this is hardly on the scale of a second brain. It's likely that this area actually housed something called a glycogen body, which is also seen in the hips of birds, and helps to store energy. 

Stegosaurus. Image by Nobu Tamura

I hope you enjoyed and learned a bit more about these common dinosaurian myths! If there's anything that you often wonder about in palaeontology, let me know, and I may discuss it in my next blog!

A Few Dinosaur Myths

This week, I'm going to tackle a few dinosaur-related myths that I find particularly irksome, or I think are important for people to understand are not true. So read-on to learn about some commonly discussed dinosaurian misconceptions!

1. All things "Brontosaurus"
This is less of a big thing now than it was throughout my childhood, as it seems that kids books are finally catching up with the science, but it is still around. Here's the deal: Brontosaurus does not exist. I know, you may need to take a seat, as many of you may have had a favourite dinosaur as a kid called Bronty. There's little that bugs me more than picking up a kids book or toy, looking at it, and discovering it's full of Brontosaurus labels. So whatever happened to Brontosaurus? Well if you've been following Mesozoic Mondays for a while, you'll remember that there are often problems with naming new species, and this is one of those instances. 

In 1877, well known American palaeontologist Othniel Charles Marsh named a new species, Apatosaurus ajax, from an incomplete, juvenile skeleton. A few years later, Marsh named a new, much larger (and more complete) skeleton, "Brontosaurus excelsus", mistakingly believing that it represented a new species. This name was cemented in the public's mind (the thunder lizard!), as it was the largest dinosaur ever discovered at that time. Unfortunately, as early as 1903, it had been suggested that these two species were actually the same, and as Apatosaurus was named first, it has priority, meaning every Brontosaurus you've actually read should be Apatosaurus. While scientists have been using Apatosaurus for more than 100 years, it's taken much longer to make it to the public, so spread the word! Tell your kids! No more Brontosaurus please!

Apatosaurus from Jurassic Forest

2. All dinosaurs were big
I'm not exactly sure where this idea comes from, but there seems to be a belief that all dinosaurs were these massive animals bigger than any animals alive today. While many of them were big, there were also just as many small dinosaurs, similar in size to modern animals. In general, an ecosystem wouldn't work if every animal was huge. You need little animals too to make the world go 'round!  In fact, part of why dinosaurs were so successful was that they were able to occupy many different niches with their wide range of sizes. Early dinosaurs like Eoraptor were small, weighing in at only 10 kg, while many derived, later dinosaurs were also small. And there were small dinosaurs in many groups too. There was Stegoceras, a 10 kg dome-headed (pachycephalosaurid) dinosaur from the Cretaceous of North America, or Anchiornis, a tiny pigeon-sized theropod from the Jurassic of China, and even Psittacosaurus, an early relative of the horned dinosaurs (ceratopsians) was only 20 kg. Not all dinos were the gigantic fearful animals from the movies!

Image showing the size of Anchiornis. Image by Serenthia

3. Triceratops is no more
This is something that came about the summer Jurassic Forest opened, and I remember very well how many people were asking us about this on the trails. Now this is more of a recent misconception, and probably is not really a myth as it's only been around for a few years, but it is a common misconception brought on by the media that really drives me crazy. This idea stems from some recent work by Jack Horner's lab, regarding the horned dinosaurs Triceratops and Torosaurus. The basic gist of it is that he believes that what we currently consider to be Triceratops is actually a sub-adult (therefore not fully grown) individual, and that the slightly larger Torosaurus actually represents the adult of this species. Most news stories picked this up by suggesting that Triceratops is no more... which is not correct. First of all, if this hypothesis is correct, they would still both be called Triceratops, only what we currently view as an adult Triceratops would not be the adult, but a subadult. They still look pretty similar, and it would still be Triceratops, but bigger! And the second, and very important thing to note, is that this may not be true. Not all researchers agree with this idea, and believe that Triceratops and Torosaurus are still distinct species. 

So, next time someone says "Triceratops doesn't exist", you know what to say!

Skulls of Triceratops and Torosaurus from Longrich and Field (2012)

So I hope you enjoyed (and more importantly, learned something!) this little introduction to dinosaur-related myths. Next week, we might continue on this topic with a few more common misconceptions! Stay tuned!

References:
Longrich NR, Field DJ (2012) Torosaurus Is Not Triceratops: Ontogeny in Chasmosaurine Ceratopsids as a Case Study in Dinosaur Taxonomy. PLoS ONE 7(2): e32623. doi:10.1371/journal.pone.0032623

Taphonomy

This week, we're going to talk about something that is arguably one of the most important things to understand in palaeontology: taphonomy. A basic definition of taphonomy is the study of everything that happens to an organism after it dies, and before we find the fossil millions of years later. 

Understanding taphonomy can give us many clues about the environment that an animal lived and died in. In particular, it can be very useful when it comes to studying bonebeds, geological deposits that are full of many bones. Here, I'll go through a step by step example of the things you can learn from bonebed taphonomy from the moment you find the bonebed, to the fine details you can find in a lab. 

When you first find a bonebed, there are several features that you notice first, like the number of bones, the number of taxa, how the bones are orientated, and how complete the skeletons are, which give us a wide range of information. The number of bones can obviously tell you how many animals are found there, while the number of taxa can tell you about how those animals came to be there. For example, bonebeds that consist of mainly one species, and all ranges of sizes are likely to be from a herd or pack of animals that all perished at one time in a catastrophic event. On the other hand, bonebeds with several taxa may be characteristic of something like a predator trap where many animals go (like a watering hole), and are then killed by predators, leaving several different kinds of bones over a long period of time. These are termed monotaxic (only one taxa present), multitaxic monodominant (more than one taxa, but there is primarily one), or multitaxic multidominant (more than one taxa, with more than one dominant taxa). 

The Edmontosaurus bonebed in Edmonton. An example of a multitaxic monodominant bonebed. Photo by Liz Martin.

Next, you might notice how the bones are orientated. Some bonebeds will show an obvious  orientation to the bones, which can tell us that the bones were transported by something like a river, that will orient the bones in the direction of the flow. By studying and mapping these bones, we can understand palaeoflow and something about the ancient rivers. Completeness and degree of articulation (whether the bones are joined together in the way that a skeleton normally is or jumbled up and separated) can tell us more about how those bones came to be in that place. A complete, articulated skeleton tells us that an animal died and was undisturbed after it died. Single, isolated bones mean that the skeleton was disturbed either during death (during an attack), or after death. Bonebeds full of disarticulated bones can tell us more about transport (as an animal carcass is transported by a river, it begins to come apart), or scavenging before fossilisation. 

Example of a map of a ceratopsian bonebed showing the orientation of different bones [1].

Finally, once all the bones have been mapped and palaeontologists have returned to the lab to look at the bones, they study another important aspect of taphonomy: the fine structure of the bone. Looking at the fine detail of the bone can reveal marks like insect borings, scratch marks, and bite marks, which can tell us more about how the animals came to be in that position. A devastating bite mark may show us how it died, or bites can show that the carcass was scavenged after it died, and in some cases, by what kind of animal. Scratches can show trample marks, or possible predatory marks with an animal scratching at a carcass to pull off meat. Insect borings can tell us about decomposers that may have infested the carcass after it died. All of these different pieces of information can be put together to understand more about how the animal(s) died, the environment that it lived in and much, much more. 

Possible beetle feeding traces on a Jurassic dinosaur Camptosaurus from the US [2].

Bite marks on a humerus of Saurolophus [3].

This has been a quick review of different aspects of taphonomy, and I hope you have learned a bit about what it can teach us. In the future, we'll talk more in detail about different aspects of taphonomy. Stay tuned!

References
1. Eberth, D. A., et al. 2007. A practical approach to the study of bonebeds. In Rogers, R. R. et al. (eds.) Bonebeds: Genetic Analysis, and Paleobiological Significance. pp 265-333.
2. Britt, B. B., et al. 2008. A suite of dermestid beetle traces on dinosaur bone from the Upper Jurassic Morisson Formation, Wyoming, USA. Ichnos 15: 59-71.
3. Hone, D. W. E., and Watabe, M. 2010. New information on scavenging and selective feeding behaviour of tyrannosaurids. Acta Palaeontologica Polonica 55: 627-634.
Background info:
Eberth, D. A., et al. 2007. A bonebeds database: classification, biases, and patterns of occurrence. In Rogers, R. R. et al. (eds.) Bonebeds: Genetic Analysis, and Paleobiological Significance. pp. 103-221.

Cladistics - How we understand relationships of animals

After writing this blog for a year, I've come across a number of terms that I've had to define as many non-biology people may not understand them. Then I thought maybe it would be a good idea to give a quick review of some of these and how they relate to palaeontology. So here goes...

The first important thing to understand is where modern taxonomy or classification of plants and animals comes from. The first important word is taxon. A taxon is a single group of animals. This group can be any group from species to phylum, depending on what is being talked about (for a review on the modern classification system of animals, check out our post 'Where do dinosaur names come from?'). So as an example, lets use Tyrannosaurus rex. It's classification is as follows:

Tyrannosaurus rex

Kingdom Animalia

Phylum Chordata

Class Reptilia

Order Dinosauria (this isn't completely accurate, but we will use it here as an example)

Family Tyrannosauridae

Genus Tyrannosaurus

Species Tyrannosaurus rex

In this case, taxon can refer to the species, genus, family, order, etc., as long as you are only referring to that one group. There are even subgroups, like subfamily, tribe, etc. and are also referred to as a taxon. If someone wanted to refer to a number of groups at once, we use the term taxa. That could be a number of genera (plural of genus) within a family, or something like that. 

The next important thing to talk about is cladistics, the main point of this post. Cladistics is a way of grouping organisms based on how many unique characteristics they share with each other. These characteristics must not be the ancestral state, or plesiomorphic, which means the character is retained from its ancestor. For example, most tetrapods have some type of front limb (like an arm or paddle), which is because fish have fins, and tetrapods evolved from fish. This character would therefore not be used to assess how closely related a tetrapod group is to another. In contrast, apomorphies, or derived characteristics are used to group closely related or separate distantly related organisms. To use the limb example again, snakes have lost their limbs, which is considered to be a derived characteristic. The loss of limbs could, therefore, be used in cladistics. 

As implied above, each character is coded into a character state using 0 as primitive, and 1-4 as derived. For example, using limbs again, an animal with front limbs would be coded as 0, as that is the basal state, whereas a snake would be coded as 1 for the derived state. This can become much more complicated where you could also have something like a state for a paddle-like limb for a swimming animal, and more. For a group of organisms and characters, you create a character matrix full of numbers (0-4 usually), which is then uploaded into a computer program like PAUP or TNT. Using a complex number of algorithms, these programs work out how closely or distantly related taxa are, and spit out a cladogram. Think of a cladogram as a kind of family tree, where the relationships between groups can be seen. 

An example of a character matrix for ceratopsian dinosaurs from Ryan et al. [1]. Each taxon has the same number of characters with states from 0-2. ? denotes where the state is unknown due to the lack of preservation, which is often the case in fossils.

An example of a cladogram made form the matrix above from Ryan et al. [1]. 

If the relationship is well supported and can be distinguished, there will be a branch of just 2 branches on each side. For example, you can see on the bottom that Chasmosaurus and Pentaceratops are split into two, suggesting these are very closely related, and well supported. In contrast, at the base of the "tree", you'll see that Protoceratops, Turanoceratops, Zuniceratops, and the large branch containing everything else are all coming off of the same line, meaning there isn't enough evidence to fully understand the relationship between those groups. A cladogram is made of clades, which can be any group of organisms that includes all descendants of a particular ancestor. For example, a clade may be the entire tree above, or could be the group in the middle that includes Centrosaurus, Coronosaurus, Styracosaurus and Spinops, or the small clade at the bottom with Chasmosaurus and Pentaceratops, and many many more. 

Another example of a cladogram for ceratopsians from Farke et al. [2]

Above is another representation of a cladogram, which may be more easy to understand. When comparing this one with the one from Ryan et al. [1]  you can see some differences. First of all, Protoceratops is no longer included in that group that was unresolved in the first one, however, Zuniceratops, Turanoceratops, and everything else is still not clear. Chasmosaurus and Pentaceratops still make up a group (seen towards the top) while Avaceratops, Albertaceratops, and the rest are now unresolved. 

The final term that I think is useful to talk about is 'sister groups'. When something is considered to be a sister group to something else, it means that these are closer to each other than anything else. It also means that these groups can swap places on the cladogram and it would not change the meaning. Looking at the above cladogram, Pachyrhinosaurus canadensis is sister to Pachyrhinosaurus lakustai. The group that includes both Pachyrhinosaurus species is in turn sister to Achelosaurus, and the group that includes all three is in turn sister to Einiosaurus, which makes that group sister to Rubeosaurus. That whole group is then sister to the group that includes Spinops, Styracosaurus, and Centrosaurus. In each of these sister groups, you could swivel the cladogram around and preserve the relationships, while showing them in a different order. 

Cladograms can be made of both morphological (as in the features you can see from looking at a skeleton or animal) or molecular (those that come from DNA studies). Of course in palaeontology, we are restricted to morphological studies as no DNA is present.

I know that might have been a bit complicated to wrap your head around, but I think it's a really important lesson to understanding palaeontological literature, and what some of these words mean! If you have any suggestions for next week's blog, let me know!

References

1. Ryan, M. J., et al. 2012. A new ceratopsid from the Foremost Formation (middle Campanian) of Alberta. Canadian Journal of Earth Science 49: 1251-1262.

2. Farke, A. A. et al. 2011. A new centrosaurine from the Late Cretaceous of Alberta, Canada, and the evolution of parietal ornamentation in horned dinosaurs. Acta Palaeontologica Polonica 56: 691-702. -> Available free online here.

Crown Group Mammals

Last week we introduced mammal evolution and discussed the earliest mammals and how they came to be. This week, we'll talk about crown group mammals, including some modern groups and when they evolved. In order to do that, we must first explain what is meant by "crown group". Crown group mammals include extant (still living today) mammals and their relatives, sharing a last common ancestor. 

Looking at the base of the cladogram (think of it as a kind of family tree) of crown mammals, we have monotremes. Monotremes are the most basal mammals alive today, and they include just five animals: one species of platypus, and four species of echidna. Very few monotreme fossils have been found, and the earliest are all from the Cretaceous of Australia. The earliest, Teinolophus, was already a fully evolved platypus, suggesting monotremes evolved earlier, possibly in the Jurassic. Monotremes are considered to be basal mammals because of many features, including the fact that they still lay eggs, unlike other mammals. 

The very strange duck-billed platypus. Image by Maksim

Moving up the "tree" we have a group of mammals called multituberculates. This fully extinct group is characterised by small rodent-like animals that have very distinct molars with tubercles. They lived from the Late Jurassic to the Oligocene (153-35 million years ago), and their position within Mammalia is often debated. Some scientists believe they are in this position, between monotremes and Theria (marsupials and placental mammals), while others don't agree that they are crown group mammals at all, and think they are more primitive than monotremes.

After a few minor extinct groups, we have the therians. This includes the two mammal groups we typically think of: the marsupials and placental mammals. Marsupials are the living representatives of Metatheria, which also include some fossil taxa. The first metatherian, Sinodelphys, lived during the Late Cretaceous of China, about 125 million years ago. Modern groups like opossums evolved during the Late Cretaceous, while diprotodonts (kangaroos, koalas, wallabies, etc.) first appeared in the fossil record during the Oligocene, about 25 million years ago. This is likely review for many people, but marsupials mainly differ from placental mammals in way of their reproduction. Marsupials do not have a placenta, and have very short gestational periods, causing them to "give birth" to very young, under developed offspring. The offspring are then kept in the mother's pouch, where they continue to develop for several months. 

Artists impression of Diprotodon, an extinct marsupial. Image by Nobumichi Tamura

Finally, this brings us to the Eutheria, and specifically, placental mammals. Fossils like Juramaia (160 million years ago) and Eomaia (125 million years ago) have been attributed to Eutheria, while other studies have suggested the earliest true eutherian is Maelestes that lived 91 million years ago. Relationships of modern placental mammals are messy, mainly due to the fact that studies based on physical characters do not agree with those based on molecular features and DNA. Some extant groups of interest include the Xenarthra (anteaters, tree sloths and armadillos) which evolved during the Late Cretaceous, Insectivora (including hedgehogs, moles, and are not to be confused with rodents) also in the Late Cretaceous, while rodents (mice, rats, squirrels, and porcupines) didn't evolve until the Paleocene (approximately 61 million years ago). Bats didn't appear until the Eocene (52 million years ago), with their evolution being fairly unclear as no transitional fossils have yet been found. The major groups of modern mammals all had started to evolve by the Miocene, 20 million years ago, with aardvarks being the last group to evolve. 

Fossil of Icaronycteris, the earliest known fossil of a bat. Image by Andrew Savedra

Skeleton of a modern bat, which is not significantly different from the early fossil bat above. Image by Mnolf. 

And I think that's about it for today on mammals. There are so many more groups of mammals, we could be talking about them for days! So I think this is it for now. Keep watching and maybe we'll touch on mammals a bit more soon!

Early Mammal Evolution

This week on Mesozoic Mondays, we're going to talk about early mammal evolution. Those of you who have been reading this blog since the beginning may remember our post on Dimetrodon, the early mammal relative. You may remember even further back to our post on What is a dinosaur, and about the importance of temporal fenestrae, or the holes in the back of the skull, throughout  the evolution of animals. Mammals are what we call synapsids, which are the group of animals that have just one temporal fenestra. As previously mentioned, Dimetrodon was also a synapsid, one of the earliest relatives of modern mammals. 

The very beginning of mammal evolution takes us back to the Carboniferous, when the first amniotes (animals with an amniotic egg) evolved into two separate lineages: the synapsids, which eventually give rise to mammals; and the sauropsid branch, which gave rise to lizards, snakes, dinosaurs and eventually birds. The first big group of synapsids were the pelycosaurs, like Dimetrodon. They were the largest land animals to live during the Early Permian, and gave rise to therapsids. Therapsids had larger temporal fenestrae, and included some very strange animals like dinocephalians, and the carnivorous gorgonopsids.

Struthiocephalus, a dinocephalian from the Permian

The gorgonopsid Arctops. Image by Nobumichi Tamura

Remembering back to the blog post on mass extinctions, you may remember that the largest mass extinction to have ever happened was at the Permian-Triassic boundary. Therapsids, like all groups, were very hard hit, but the cynodonts survived, and eventually gave rise to modern mammals. Cynodonts first evolved in the Late Permian, and have several mammal-like features including a reduction in the number of lower jaw bones (modern mammals have one bone while reptiles have many). They continued to evolve into the Triassic by further evolving precise occlusion of their teeth, the mammalian ear started to evolve, and their olfactory lobes increased in size to provide better sense of smell. 

Like all evolutionary transitions, the line between mammalian ancestors and true mammals can be hard to distinguish. Early mammals were small, typically the size of a rat or mouse. Their size, the environment they lived in, and delicate bones mean that they were not commonly preserved and are rarely found in the fossil record. Some of the earliest mammals, or mammaliaforms as some scientists call them, include the morganucodontids. These mouse-sized animals like Morganucodon were transitional between cynodonts and true mammals, seen by the lower jaws with two bones, and bony venomous spurs like modern monotremes (platypus and echidna). 

Morganucodon, a Late Triassic mammaliaform. Image by FunkMonk

Early mammals were evolving alongside dinosaurs, and therefore were restricted to ecological niches not occupied. They were generally small, and required little food and sustenance. Although mammals were typically thought of being "in the shadow" of dinosaurs throughout the Mesozoic, there is evidence that they were capable of defending themselves, and feeding on dinosaurs. 

That's all for the initial evolution of mammals, and we hope you've enjoyed it. Stay tuned for additional posts on further evolution of mammals, including the evidence we have of mammals defending themselves and feeding on dinosaurs!

Canadian Fossils

In one week, we celebrate Canada's 146th birthday. To celebrate, we will talk about some of the different fossil sites in the country. From west to east, here are some of them:

British Columbia
The Burgess Shale is one of the most famous fossil localities in the world. Located in Yoho National Park in the Rocky Mountains of British Columbia, this geologic formation dates back to the Cambrian, approximately 505 million years ago. The Burgess Shale was made famous by its exceptional preservation of soft body parts, which are not always well preserved. The Cambrian is the first geologic period that has significant numbers of clear animal fossils in it, and is often referred to as the Cambrian Explosion. Because of this, the Burgess Shale is particularly important in terms of early evolution of many animal groups. 

The Burgess Shale was first discovered in 1909, and has been well studied ever since. It is included in the Canadian Rocky Mountain Parks UNESCO World Heritage site, named in 1984. Because of the significance of this fossil site, it is very difficult to collect from or visit this location, with visitors only allowed on guided tours. It was deposited in an ocean setting, so all fossils are marine. There have been some well known fossils discovered here, like Marella (an early arthropod), Anomalocaris (an early arthropod relative), Hallucigenia (a bizarre spiny creature) and Pikaia (a possible early chordate, a group that includes vertebrates). 

Example of sizes of different organisms in the Burgess Shale. Image by Matt Martyniuk

Alberta
There are several excellent fossil sites in Alberta which we have discussed previously on this blog. For more information on those, check out our Palaeontology in Alberta post! 

Ontario
The Gunflint Chert in Ontario (and also in Minnesota) is an iron formation that was deposited about 1.9 BILLION years ago. In these rocks are tiny microfossils from stromatolites. These rocks were first studied in the 1950s and 60s and small spheres, rods, and filaments were determined to be single-celled organisms. This find kicked off the search for Precambrian microfossils.

Nova Scotia
The Joggins Fossil Cliffs of Nova Scotia are a famous Carboniferous fossil site from about 310 million years ago. The Carboniferous is often referred to as the 'Coal Age' due to the large number of fossilised trees that have been turned into coal. In particular, Joggins has a large number of complete and even upright trees that have been preserved, especially from the lycopodiphyte Sigillaria. In 1852, a great discovery was made when geologists found tetrapod fossils within an upright tree stem. The internal part of the tree had been eroded away, while the external bark was still in place, leaving a large hole for small animal bones to fall into and become fossilised. Further investigation revealed the earliest sauropsid (the group of amniotes that include reptiles, birds, dinosaurs and more) fossil ever found, Hylonomus. Other important fossils from Joggins Fossil Cliffs include Protoclepsydrops, an early synapsid that is older than Hylonomus, and small tetrapod trackways. 

Artists impression of Hylonomus by Nobumichi Tamura

Newfoundland and Labrador
Mistaken Point is found on a peninsula on the island of Newfoundland, and contains more Precambrian fossils, including some of the most diverse and well-preserved fossils from this time.  It contains what is most likely the oldest multi-cellular fossils from North America, the oldest deep water fossils and the oldest Ediacaran fossils in the world. They date back 575-560 million years. 

Nunavut
Although there aren't any truly fossiliferous sites in Nunavut, at least not like the ones we have mentioned previously, it is home to one of the most famous and important fossils ever discovered. In 2004, a group of palaeontologists discovered a partial skull sticking out of a cliff on Ellesmere Island. When they analysed it, they discovered it was an early tetrapod. This fossil, called Tiktaalik from the Devonian (375 million years ago), is an example of what we call a transition fossil. It shows the transition that palaeontologists refer to as "from fish to limbs". It's also what palaeontologists sometimes call a 'fish-er-pod', as in it has a combination of fish (e.g. gills and fins) and tetrapod (e.g. mobile neck and lungs) characteristics, as well as transitional features (e.g. half-fish, half-tetrapod limb bones and joints). Although there is only one of these fossils known, it has been extremely important in understanding the evolution of early tetrapods.

Artist's impression of Tiktaalik by Nobumichi Tamura

Although we only talked about a few localities, there are fossil localities all over the country, and in every province and territory! Unfortunately, if we talked about all of them, we would be hear for a while... So we hope you enjoyed these few examples of Canadian fossil localities. And have a great Canada Day next week! We will be open everyday next weekend from 9-7, and will have activities and special guests throughout the weekend. Visit our website for more details!

Colour in Fossils

Dinosaurs are always displayed as colourful, but how do we know what colour they were? The truth is, in most cases, we don't. In the typical depictions of scaly, reptilian dinosaurs, we can make educated guesses based on animals today, and the habitat of the dinosaur in question. For example, herbivorous animals that would need to hide from predators wouldn't be brightly coloured: they would be dull, earthy colours to allow them to fade into the background and hide from predators. Features that are used for some kind of display, like a crest, would likely have been brightly coloured, as it allows an even greater display. 

Caulkicephalus, a pterosaur from England illustrated with a bright blue and yellow crest. Copyright of Mark Witton

More recently, a new way of telling fossil colouration has been discovered. There are several forms of pigment in animals today, including melanin, carotenoids, luciferin, and more. Melanin is found in little packets called melanosomes, and is responsible for brown, black, and red colouration. These packets come in different shapes, for different colours. Eumelanin, responsible for brown-black colouring, is found in elongate sausage-shaped melanosomes, whereas pheomelanin, responsible for red or ginger colouring, is found in spherical melanosomes. They are very small structures, and can be seen using a Scanning Electron Microscope (SEM). This was first used in a fossil feather from the Lower Cretaceous [1], while the theropod Sinosauropteryx was the first dinosaur to have its colouration described by looking at melanosomes. The fossils showed a strange banding of the primitive feathers in a dark, and light pattern. When these different sections were analysed under SEM, pheomelanosomes were discovered in the darker banded areas, and no melanosomes (i.e. no pigment, and therefore white) were found in the lighter areas [2]. The authors suggested that to mean this animal had a tail banded in white and reddish colours in life. 

Since that first feathered dinosaur discovery, several other extinct feathered animals have been analysed using this method. This includes the four winged dinosaur Microraptor, and the possible early bird Anchiornis. In fact, one study on Microraptor has actually suggested that you can see iridescence from looking at the pattern of melanosomes within the fossils.

Artists impression of Anchiornis, colouration patterns known from fossilised feathers. Image by Nobuyuki Tamura.

 For anyone interested in more information about colouration in fossils and feathers, check out the blog Prehistoric Colours by a group at the University of Bristol in the UK. They are currently working on this issue and looking at different pigments found in fossils and how you can identify them. They are also working on identifying deformation in these structures in the fossil record. It's really neat research!

References:
1. Vinter, J., et al. 2008. The colour of fossil feathers. Biology Letters 4: 522-525.
2. Zhang, F., et al. 2010. Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds. Nature 463: 1075-1078.

Birds are Dinosaurs!

Did you know that birds are actually dinosaurs? 

This point is briefly mentioned in one of the very first Mesozoic Mondays post on saurischian dinosaurs, but little information on the subject is given. Here, I'm going to give a brief overview of the idea, what it means, and some of the evidence we have. 

The similarity between reptile skeletons and birds was noticed as early as the 1800s, with Thomas Huxley (one of the initial proponents of evolutionary theory) pointing out that the early bird Archaeopteryx showed transitional features between the two groups. He compared this fossil to dinosaurs that were known at the time, like Compsognathus, in great detail. However, his ideas were not widely accepted at the time. In the early 1900s, the issue was reviewed again, with Gerhard Heilmann (a Danish scientist) again concluding that theropod dinosaurs showed the most similarity to Archaeopteryx and other birds. However, no clavicles (collar bones) were known from dinosaur fossils, which in his mind meant that they could not be related as birds possess a fused clavicle called the furcula (or wishbone). Although the absence of clavicles does not rule out a relationship between the two (features can be lost and gained throughout evolution), we now know that theropods and possibly all saurischian dinosaurs did indeed possess a clavicle. The debate came around again in the 1960s when famous American palaeontologist John Ostrom named the dromaeosaur Deinonychus, and he noticed the similarities again between it and Archaeopteryx. Ostrom solidified the theory in palaeontology, and brought it to the front as the leading theory on the origin of birds.

Comparison of the hands and wrists of Deinonychus (left) and Archaeopteryx (right) shows the similarities between these two. Image copyright John Conway

Although there were major morphological similarities, there was still the major question of feathers. If Archaeopteryx, an early bird, showed fully developed flight feathers, where did they come from? Features do not just appear in animals fully formed: they need to evolve slowly and gradually. Finally, in the 1990's, several amazingly preserved bird fossils from the Early Cretaceous were found in a region of China, and in 1996, the first 'feathered' dinosaur was described. Sinosauropteryx was initially described as a bird (hence the -pteryx portion of the name, which means wing) [1]. Shortly after, however, its similarity to dinosaurs was discovered, and the importance of the fossil fully understood [2]. Although the skeleton itself is not remarkable in terms of dinosaurian anatomy, it is covered in tiny hair-like filaments from the head to to the tail. These filaments are thought to be 'protofeathers', an early evolutionary stage of feathers. 

Artists impression of Sinosauropteryx by Nobu Tamura. Note the patterned tail

Since Sinosauropteryx, numerous theropod dinosaur fossils have been found with filamentous feathers, mainly from China. These include Caudipteryx which has a cool tail fan, Velociraptor, Yutyrannus (an early tyrannosaur) and Microraptor, an odd 4-winged creature that may have been capable of flying, although this is debated. This means that more and more dinosaurs likely had some kind of feathers or filamentous covering, rather than the scaly appearance we see in the media. Look out for feathered T. rex in any scientifically accurate dinosaur portrayals! There is even some evidence that Psittacosaurus, an early relative of horned dinosaurs had some quills derived from early feathers, although this is controversial [3]. In addition to clarifying the story of bird evolution, these feathers can be useful in understanding colouration of these animals as well. Small structures called melanosomes, which house the colouration pigment melanin, can be preserved. This is where the striped pattern of the tail of Sinosauropteryx comes from. This will be described in more detail next week. 

Although the vast majority of palaeontologists now recognise the dinosaurian origin of birds, like all theories, there are a few holdouts that do not accept it. However, the evidence is overwhelming, and each issue that is brought forth by these people has been countered with fossil or developmental evidence. 

So what does this all mean? Birds are dinosaurs! As birds are directly descended from a group of theropod dinosaurs (the deinonychosaurs), they are considered to be dinosaurs in biological terms. Much in the same way that whales are mammals, as they share numerous characters with mammals, and evolved from terrestrial mammals, millions of years ago. 

I know this was a bit brief, but bird evolution is a topic we could talk about for hours. If you're interested in more, there are numerous websites that cover this topic in more detail!

References:

1. Ji, Q. and Ji, S. 1996. On the discovery of the earliest bird fossil in China (Sinosauropteryx gen. nov.) and the origin of birds. Chinese Geology 233: 30-33. 

2. Chen, P. et al.  1998. An exceptionally well-preserved theropod dinosaur from the Yixian Formation of China. Nature 391: 147-152.

3. Mayr, G. et al. 2002. Britle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus. Naturwissenschaften 89: 361-365.

Z is for Zupaysaurus

After 26 long weeks, we are now at the final dinosaur from our dinosaurian alphabet! This week, we bring you 'Z is for Zupaysaurus', a theropod from Argentina.

Zupaysaurus lived during the Late Triassic period, about 215 million years ago in northern Argentina. The name comes from the local Quechua word 'zupay' meaning devil. It was a medium-sized bipedal theropod, between 3 and 4 m in length, and weighed about 200 kg. It is known from one definitive specimen, which includes a nearly complete skull, vertebrae, and incomplete arms and legs [1]. In the original description, it was thought to have two parallel cranial crests, like those seen in Dilophosaurus. However, more recent analysis has suggested that these "crests" were simply bones that had been pushed up during deformation of the skull [2]. 

Artists impression of Zupaysaurus by FunkMonk

Like most theropods, Zupaysaurus was a carnivore. Most analyses suggest that it was a coelophysoid dinosaur, being closely related to the Antarctic theropod Cryolophosaurus, and was the first coelophysoid to be found in South America. It was found in the Los Colorados Formation of Argentina, which is thought to have been a floodplain. This formation is home to many sauropodomorph dinosaurs, like Riojasaurus, and many other tetrapods such as therapsids, pseudosuchians, and other archosaurs. In fact, it is one of the earliest known animal fossil assemblages that was dominated by dinosaurs!

And that is it for our dinosaurian alphabet! I hope everyone has enjoyed it. I'm looking for ideas of what to do for the blog in the future, so if anyone has anything they'd like to learn about, please let me know!

References
1. Arcucci, A. B., and Coria, R. A. 2003. A new Triassic carnivorous dinosaur from Argentina. Ameghiniana 40: 217-228. 
2. Ezcurra, M. C., and Novas, F. E. 2007. Phylogenetic relationships of the Triassic theropod Zupaysaurus rougieri from NW Argentina. Historical Biology 19: 35-72.

Y is for Yulong

Last week was our last dinosaur that was actually from Alberta. Now our second last dinosaur of the dinosaurian alphabet is a newly described theropod from China: Yulong. 

Yulong was described at the beginning of this year by a group of Chinese palaeontologists as well as well-known Canadian palaeontologist Philip Currie from the University of Alberta [1]. It comes from the Luanchuan County of Henan Province. Unfortunately, the exact age of the the formation is unknown, but it is likely from the Late Cretaceous based on the other animals that are found in this formation. The name Yulong is derived from the Chinese "Yu", the abbreviated name for Henan Province, and "long" meaning dragon. Only one species of Yulong is currently known, Yulong mini in reference to the fact that the specimens are very small. 

Photograph of 3 Yulong mini skulls (a-c) in right lateral view and d in right lateral view (from Lu et al. [1]). Note the scale bar showing how small these skulls are! 

Yulong was an oviraptorid dinosaur of approximately chicken size. Most oviraptorids are larger, and can reach sizes up to 8 m in length. Although Yulong is described as being chicken sized, it was likely larger as the fossils that have been found are all juveniles. Several specimens are known, including well preserved skeletons, skulls, and even a well preserved embryo coming from a nest of 26 eggs. A thin section through a rib showed no growth lines, suggesting the animal was not yet a year old when it died. 

That's it for Yulong as it's a fairly newly described species. Tune in next week for our final dinosaur of the alphabet to learn about a neat theropod from Argentina!

References:
1. Lu, J. et al. 2013. Chicken-sized oviraptorid dinosaurs from central China and their ontogenetic implications. Naturwissenschaften 100: 165-175.