Monday, 24 June 2013

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
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! 

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. 

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!

Monday, 10 June 2013

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!

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.

Monday, 3 June 2013

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!

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.