Monday, 22 June 2015

Palaeontology in Canada

A few weeks ago I had the opportunity to attend the Canadian Society of Vertebrate Paleontology meeting in Kelowna, BC. It was a fantastic meeting full of Canadians, and people working in Canada on vertebrate palaeo including some of the fields brightest minds. We had 2 full days devoted to talks and posters, ranging from fish to mammals and everything in between – lots of dinosaurs, marine reptiles, pterosaurs (from me of course), ichnology (fossil trackways), crocodiles, teeth, macroevolution, and the list goes on. I won’t discuss the research presented as much of it is currently unpublished, in prep or in press, but I can tell you that there is a lot of awesome stuff coming out of Canada in palaeontology right now.

In the last talk, David Evans from the Royal Ontario Museum talked about how we’re in another “golden age” of dinosaur discovery in Canada, and I think this is an important and interesting idea. He had a neat graph that showed new dinosaur species named over time, and we’re currently on a strong upward trend even when comparing to the early 1900’s when dinosaur hunting in Canada was getting going with the likes of Barnum Brown, Lawrence Lambe and more.

Of course this is something that can be said with the entire world, with new fossil-rich areas being found in China, Brazil, Africa, etc. However, I think it’s important to highlight and remind people just how significant Canada is in understanding the history of the Earth and in palaeontology. We have numerous world famous fossil sites representing almost animals from the earliest existence up to the most recent fossils, from vertebrates to invertebrates to plants, and several very important sites from coast to coast. There are too many to list, but here are a handful of sites or significant fossil finds from Canada that are extremely important in understanding the past and how our world came to be how it is today.
  1. The Burgess Shale – I’m sure most of you have heard of this - up in the Rocky Mountains of Yoho National Park, British Columbia, an exquisite fossiliferous area represents some of the earliest recognizable animals from the Middle Cambrian, from a time known as the Cambrian Explosion. This period represents a time of significant evolution, and these fossils show us what the Cambrian seas would have looked like, with some of the first vertebrates like Pikaia, and numerous arthropods like Hallucinogenia (named because it is so weird you just must be hallucinating), and Anomalocaris. The reason this is so significant is that these animals are known almost exclusively from soft tissues, which are difficult to preserve in the fossil record. Yet here, thousands of soft-bodied organisms are preserved that give us a window into an early stage of evolution in many animal groups. Recognised for it’s importance, the Burgess Shale is part of the Canadian Rocky Mountain Parks UNESCO World Heritage Site named in 1984.
    Anomalocaris reconstruction by Nobu Tamura
  2. Dinosaur Provincial Park – And of course I have to talk about this as well. Dinosaur Provincial Park (DPP) is located in southern Alberta, and is also a UNESCO World Heritage Site, known for – you guessed it – dinosaur fossils. From the Late Cretaceous, this area is one of (if not THE) best place in the world to view the ecosystems from this time period. Not just dinosaurs are found here, but also turtles, pterosaurs, crocodilians, mammals, plants, and more. Basically anything you would expect to be in that kind of ecosystem is represented, from big animals like T. rex and Triceratops to smaller dinos like Saurornitholestes (although the smaller the animal the less common they are). Dinosaurs have been coming out of DPP for well over 100 years, and with the continued field work of groups like Phil Currie and the University of Alberta, David Evans at the Royal Ontario Museum, and of course the Royal Tyrrell Museum in Drumheller where most of the material is housed, it’s not going to stop anytime soon. If you want to hear more about the dinosaurs in Alberta and DPP, check out my Palaeocast episode with Phil Currie.
    Hoodoos in Dinosaur Provincial Park. Photo by Joanne Merriam
  3. Ellesmere Island – Up in the frozen north of Nunavut lies a large island where several fossils have been found. While not traditionally thought of as a fantastic place to look for fossils, northern Canada has yielded a significant number of things like plesiosaurs, dinosaurs, and from Ellesmere Island – Tiktaalik. Tiktaalik is an amazing fossil, what we might call a “transition fossil”. From the Late Devonian period, long before dinosaurs when animals were just starting to colonise the land, Tiktaalik shows a perfect ocean to land transition, somewhere between a water-dwelling fish and a land-dwelling tetrapod (four-legged animals). It had fish gills, scales, and fins, but a mobile neck and pectoral girdle, ribs, and lungs of a tetrapod, as well as many bones and joints that lie somewhere in between. It is a true mosaic of features and just might be somewhere in the middle of fish and tetrapod, which has led to the term “fishapod”.
    Reconstruction of Tiktaalik by Obsidian Soul.
    Tiktaalik fossil from Ellesmere Island. Image by Eduard Solà.
  4. Carboniferous of Nova Scotia – There are two sites in Nova Scotia, both dating to different parts of the Carboniferous Period that deserve a mention. The first one is the oldest of the two sites, found at Blue Beach. This is not publicly or scientifically well known, but represents an important period in tetrapod evolution, as it represents part of a time period known as ‘Romer’s Gap’. During the Early Carboniferous, there are a conspicuously low number of tetrapod fossils or sites bearing these known from around the world, leading palaeontologists to wonder what happened during this time. Is this actually a gap where few tetrapods existed? Or is it some kind of bias preventing them from being preserved or found? Well thanks to some fossils recently described from Blue Beach, we are starting to understand this period a bit better, and the evidence is suggesting the gap is not a real gap in tetrapod evolution
  5. Hylonomus by Nobu Tamura
    • Later on in the Carboniferous brings us to Joggins Fossil Cliffs. Here fossils of tetrapods, fish, and much more are found, often within fossilized "tree" stumps (actually a club moss or lycopodiphyte Sigillaria, which is a tree-like plant). This area was a lush, forested swampland 310 million years ago, from the so-called "Coal Age", known for the large number of coal seams produced by the coalified. The trees are preserved in situ, meaning they are in their life position, standing upright. Often, these trees are hollowed out, and vertebrate fossils are found within the tree trunks, including amphibians and some of the earliest reptiles, including Hylonomus, the first indisputable reptile from fairly complete remains, and Archaeothyris and Protoclepsydrops, the earliest synapsid reptiles.
  6. Mistaken Point, Newfoundland – Here we have fossils from the earliest of animal evolution, the Ediacaran. These rocks date from the Precambrian, approximately 550 million years old. Mistaken Point has some of the most diverse and well-preserved fossil assemblages from this time period, an important time in organism evolution on Earth. The fossils consist of imprints of soft-bodied organisms, unlike anything alive today, typically of frond-like and leafy forms with or without stalks, some with branching network-like forms, and others more like spindle-shapes with pointed ends. The exact affinities of these fossils are still poorly understood and heavily studied, but it is difficult when they are so unlike anything today or even other fossils. This is definitely an important locality in understanding the history of our planet.
    The 'spindle-shaped' fossil Fractofusus from Mistaken Point
    (Image by MistakenPoint)
Of course this is not it for important Canadian fossil localities. From East to West, North to South, every province and territory has it’s share: the Peace Region of northeast BC is known from some of the best ichnological finds with dinosaur, bird, and more footprints, as well as body fossils from the Late Cretaceous of the small islands of Denman and Hornby; Alberta has some fantastic palaeobotany sites such as Joffre Bridge of Paleocene age as well as amazing ammonites that have been preserved in such a way that the gemstone ‘ammolite’ is a favourite in jewelry; Saskatchewan has it’s share of Late Cretaceous dinosaur and marine vertebrate finds, as well as some mammal fossils from the Cypress Hills Formation; Manitoba is home to the Pierre Shale Formation, a marine formation known for many marine fossils including the Tylosaurus, a mosasaur, including 'Bruce' who is the largest mosasaur on display in the world at 13 m long; Ontario is home to the Gunflint Chert, an early Proterozoic (approx. 1.8 billion years old) site with some of the earliest fossils of cyanobacteria; Migwasha National Park in Quebec is home to more Devonian aged fossils including fish that are thought to be ancestral to tetrapods, and well preserved plant spores; Prince Edward Island was recently in the news for a new find, the only reptile known from the specific time period 300 million years ago; the Yukon is best known for it's Pleistocene Ice-Age fossil mammal sites including mammoths; and finally the Northwest Territories has a number of Paleozoic sites with marine invertebrate fauna such as brachiopods, trilobites, corals, and also marine vertebrates like acanthodian fishes. 

Canada is full of fossils, and is very important palaeontologically speaking for a number of different plant and animal groups, ages, and evolutionary questions. This is by far not a comprehensive list, but just a few examples of what Canada has to offer in palaeontology. Let me know of any other famous ones I’ve missed – I’m always interested in hearing about Canadian palaeo and I’m sure there are some out there I haven’t heard of…

Tuesday, 9 June 2015

Predation traces in the fossil record

Traditional palaeontology as we think of it consists of finding bones, shells, etc., and describing them and mounting the skeletons in a museum to look at. However, most of the actual science is looking at things like behaviour. From looking at bones, how can we infer the animal’s behaviour? And more than that, how can we figure out things like predation and interactions between different animals?

Of course, your average bone isn’t going to tell you this kind of information, but bones with bite traces can start to give us these hints. Bite traces on bones can tell us that the animal was attacked, and in what way. If the bone shows evidence of healing, then the animal was obviously attacked while it was still alive and survived the attack. However, if there is no evidence of healing (and this is substantially more common), then the animal was dead. Whether or not it was a fatal blow where the animal was attacked and died, or whether it was dead for some time before being chewed on can be harder to tell.

Bite traces on Late Cretaceous dinosaur bones showing
serrated marks. From Jacobsen and Bromley (2009).
Majungatholus tooth showing denticles and bite traces
showing denticle marks. From Rogers et al. (2003).
Different kinds of bites can leave different traces on the bone, as well as different kinds of teeth. Fine detailed analysis can help us understand exactly how these marks were made, and by what kind of animal. For example, teeth with denticles (small tooth-like projections) can often leave drag traces from the denticles on the bone after biting and dragging, which can only be made by denticles or serrated teeth. Many theropod dinosaurs have denticles, including tyrannosaurs, dromeosaurs, troodontids, etc. Conversely, many crocodilians do not have denticles or serrated tooth, but rather have a simple cone-shaped tooth, so the lack of serration traces can suggest this kind of predator (but does not necessarily mean that). Additionally, different bite traces can indicate different behaviours such as gnawing. Mammalian gnawing leaves very distinct traces on the bones that are not produced by other means. This has been seen in Late Cretaceous dinosaur bones that were gnawed on by multituberculate mammals. Bite traces can range from punctures (when the tooth breaks through the bone cortex) and pits (a single vertical bite with no cortical breakage), to scores and drags, caused when the animal bits and drags its teeth across the bone.
Multituberculate gnaw traces on several Late
Cretaceous bones. From Longrich and
Ryan (2010). 

Unfortunately, determining the exact predator can be extremely difficult, if not impossible in many cases. Generally we can narrow it down to “theropod”, “crocodile”, “mammal”, or other broad categories like that. If you’re in an area where there are very few theropod predators for example, than you can make a reasonable assumption that that is what caused it. Or if you have other evidence, like for example numerous shed teeth from a tyrannosaur like Albertosaurus, then it’s not unreasonable to assume that bite traces may be due to Albertosaurus.

However, there are cases where the predator can be identified. One example of where the predator is clear is a beautifully preserved azhdarchid pterosaur from Alberta. The animal consists of a partial skeleton (7 bones to be exact) with wing, leg, and vertebrae present. The coolest part of this is that one of the long bones has several bite traces on the shaft on one end (Currie and Jacobsen 1995). This alone would not be enough to identify the cultprit. However, conveniently, it also has a partial tooth still embedded in the bone. This tooth can be identified as a dromaeosaurid tooth. The only dromaeosaurid known from this time in this area of the world is Saurornitholestes, which is pretty well known from teeth and a few skeletal remains in Dinosaur Provincial Park, Alberta, where this pterosaur was found. It’s a pretty cool specimen, especially considering how rare pterosaur remains are in Alberta. To find one with bite traces and a tooth is pretty cool! Teeth are not infrequently embedded in bone, and this has happened in other pterosaur remains, as well as dinosaurs and many other extinct animals.

Azhdarchid pterosaur long bone with tooth embedded (right side, bottom of the bone). Image by Liz Martin. 
Close up of pterosaur bone with tooth emedded and bite traces visible. Image by Liz Martin
The nature of the bite can also tell us about the nature of the animal making the traces. Most bite traces found in the fossil record are typical of scavenging. They show no evidence of healing, and are often found in areas that wouldn't typically be covered in bites if it were something like live inter or intra-specific competition such as the ends of bones. However, there are also bite traces in the fossil record that show evidence of healing. A tyrannosaur (Daspletosaurus) shows evidence of several healed bites on its skull, leading the authors to believe this was some kind of intra-specific competition with other Daspletosaurus (Hone and Tanke 2015).

Examples of dermestid mandible marks on
Jurassic Camptosaurus bones. From Britt
et al. (2008).
Of course predation traces are not restricted to vertebrates. They are commonly found on things like ammonites, which were often predated on by mosasaurs in the Cretaceous oceans. And of course predation traces or scars are not limited to being caused by vertebrates. Many invertebrates are capable of scarring bones and shells. Dermestid beetles are well known today for decomposing flesh and cleaning of skeletons, but they can also leave traces on the bones, and have been found in dinosaur fossils. Molluscs are known for using their "thorny tongue" or radula to scrape away shells in order to get inside the shell at the animal living inside. These bore-holes are common in modern shells and frequently seen in the fossil record as well. Sometimes these borings are stopped partway through the shell, and considered "unsuccessful", while they are often termed "successful" as the hole goes through the shell to the unsuspecting clam or oyster within.

In addition to predation traces, there are also several other kinds of marks that can be found on a specimen, including trample traces, transport marks (abrasion, etc.), and other kinds of breakage indicators. This leads to the field of taphonomy, which is basically everything that has happened to an animal from the time it dies to when it is discovered by a palaeontologist. These things tell us about the environment it lived in and aspects of its preservation, and is much to wide of a topic to discuss here. Maybe next time!

Determining the different marks or traces on fossil bones, where they came from, and what other animal may have caused them can be extremely difficult, despite the fact that these marks can be extremely common in the fossil record.

NOTE: Since posting this, Lothar Vallon has pointed out that there is a specific scientific definition for the use of marks vs. trace, in case anyone is wondering why I use trace in most places and mark in others. You can see his comment below!

Britt, BB, et al. 2008. A suite of dermestid beetle traces on dinosaur bone from the Upper Jurassic Morrison Formation, Wyoming, USA. Ichnos 15: 59-71.
Currie, PJ, and Jacobsen, AR. 1995. An azhdarchid pterosaur eaten by a velociraptorine theropod. Canadian Journal of Earth Sciences 32: 922-925.
Hone, DWE, and Tanke, DH. 2015. Pre- and postmortem tyrannosaurus bite marks on the remains of Daspletosaurus (Tyrannosaurinae: Theropoda) from Dinosaur Provincial Park, Alberta, Canada. PeerJ 3: e885.
Jacobsen, AR, and Bromley, RG. 2009. New ichnotaxa based on tooth impressions on dinosaur and whale bones. Geological Quarterly 53: 373-382.
Longrich, NR, and Ryan, MJ. 2010. Mammalian tooth marks on the bones of dinosaurs and other Late Cretaceous vertebrates. Palaeontology 53: 703-709.
Rogers, RR, et al. 2003. Cannibalism in the Madagascan dinosaur Majungatholus atopus. Nature 422: 515-518.