Friday, 24 July 2015

Spinal cords of extinct animals

This is something I've become a bit interested in recently while looking at a number of pterosaur vertebrae and thought that I'd discuss it a bit here.

Looking at the nervous system of extinct animals is something that has been fairly common in palaeontology. We are frequently interested in looking at the endocranium (the part of the skull where the brain sits) in order to reconstruct the brain of extinct animals, which can tell us much about how that animal behaved. It's fairly well documented that the endocranium preserves the shape of different parts of the brain, and can therefore be reconstructed with some kind of accuracy.

But what about the rest of the nervous system? The other major part of the nervous system, of course, is the spinal cord, which transmits all that information that is important to the rest of your body to and from the brain. Plus, there's a complicated network of nerves as well. While most focus in palaeontology is on the brain, is there anything we can say about the spinal cord?
Spinal columns of an alligator and human showing the relationship between the spinal cord, nerves, plexus location, and vertebrae. From Giffin 1995a.
For this, of course you need to look at the vertebrae. But how much can you say really from the vertebrae? While it's been sometime since this has been looked at, there is some information you can gain from looking at the vertebrae, and specifically the size of the neural canal. Emily Buchholtz (Giffin) pioneered this field in the 1990's by looking at the spinal column of several living groups and comparing them to fossils. She found that the neural canal and spinal cord area were well correlated, allowing for the size of one to predict the other, useful for fossils.
From Giffin 1995b
This allows for more accurate reconstruction and visualisation of the spinal cord, and then leads to the next question of how we can better understand some things like behaviour. Buchholtz also suggested that through a standardised measurement of the neural canal area throughout the vertebral column, you can interpret some kind of behaviour or locomotory patterns. By plotting this standardised area throughout the vertebral column, she noticed that the area increased in areas of the vertebral column where the limbs would have been. This is not particularly surprising as you would expect that the spinal cord would need to increase in size in order for nerves to start and run into the limbs, and many nerves would be going into the limbs at this point. What's interesting though is that she found that different locomotory strategies revealed unique patterns in the neural canal morphology.
Bird standardised spinal cord area. Columba and Turdus are both flying birds, while Struthio is an ostrich (Giffin 1995b)
Lizard standardised spinal cord area (Giffin 1995b)
 Birds have different locomotory patterns, but flying birds rely heavily on both their legs and their wings. Their legs are important in take off, while their wings obviously are important in flight. In flying birds, you can see that both the wings (first peak) and legs (second peak) show higher spinal cord area, while the ostrich (Struthio) has low area at the wings, and high at the legs. Ostriches barely use their vestigial wings, and certainly don't use them to fly, so they do not need heavy innervation, hence the lower amounts. Birds also have higher peaks in general than those seen in lizards (bottom graph). In general, the lizards have higher canal area in the front limbs than the hind limbs, but not by very much. Again, you can see that as both limbs are used heavily in locomotion, both limbs show high peaks in canal area, but there is a slightly higher peak for the front limbs.

Unfortunately, trying to do this in fossils is more difficult. As fossils are so often found incomplete, fragmentary, and poorly preserved, this can be hard to study. Buchholtz did try to do this with some dinosaurs (Allosaurus and Saurornitholestes), but as you can see from the graph below, it's a lot noisier and not as clear as the modern animals. She also tried it with some fossil crocodilians, which seemed to work a bit better, indicating that Leidyosuchus may have used the back legs substantially.
Dinosaur standardised neural canal area. From Giffin 1995b
Crocodilian standardised neural canal area. From Giffin 1995b
Of course most of this requires some kind of complete or semi-complete vertebral column well enough preserved so you can see the neural canal, and disarticulated so you can do these measurements. With the advent of CT scanning, and the easier way of looking at the internal structures of fossils even if they are in matrix or articulated, this is something that might be more possible now. Maybe there is information we can learn even with just partial vertebral columns? Can we learn anything about an animal's locomotory capabilities this way?

I'm very interested in people's thoughts on these methods and approaches. It hasn't been used or worked on since the 1990's, and I don't know if that's because it fell out of favour for particular reasons, was not received well in the scientific community, or just that no one bothered to look at it more. I've seen it referred to in books, and never negatively, but I find it odd that no one has tried to use it again.

References
Giffin, E.B. 1995a. Functional interpretation of spinal anatomy in living and fossil amniotes. In: Thomason, J. (ed.) Functional morphology in vertebrate paleontology. Cambridge University Press. pp. 235-248.
Giffin, E.B. 1995b. Postcranial paleoneurology of the Diapsida. Journal of Zoology 235: 389-410.

Wednesday, 15 July 2015

Hatzegopteryx and friends

Throughout this blog I have alluded to and mentioned giant pterosaurs, but I've never actually described them or discussed them properly. As previously mentioned, pterosaurs included the largest animals to ever take to the air, and these large pterosaurs are not just one-off weird things. Animals with wingspans of 5-8m are fairly common in the Cretaceous with the large ornithocheirid pterosaurs of Brazil, including Ornithocheirus and Tropeognathus, and of course one of the most famous pterosaurs of all, Pteranodon from the Kansas chalk deposited from the Western Interior Seaway.

The true giants, however, are the azhdarchids, the most common (if not only) pterosaurs in the latest Cretaceous. Although some azhdarchids were of smaller size (2.5-3 m in Montanazhdarcho and Eurazhdarcho), they also reach absurd sizes of 10-12m wingspans. In contrast, the largest living flying birds (the wandering albatross) had wingspans of approximately 3m (but as much as 3.5m), while the largest extinct flying bird, Pelagornis [1], had a wingspan of 8-9 m. These giant pterosaurs in comparison would have rivalled airplanes with their wingspans, and reached as high as a giraffe when standing.
Giant azhdarchid Arambourgiania with a giraffe and human for scale. Image copyright Mark Witton.
So how many giant pterosaurs were there? So far, there are 3 described species of giant pterosaur: Hatzegopteryx thambena [2] from Romania, Arambourgiania philadelphia [3] from Jordan, and arguably the most famous of the three Quetzalcoatlus northropi [4] from the USA. Unfortunately, these are all currently known from pretty fragmentary remains, but there's just enough to get an idea of what kind of things these animals were up to, and how big they really were. 


Hatzegopteryx

The proximal humerus fragment of Hatzegopteryx [5].
Scale bar is 10 cm.
The first one I'll talk about is the one I'm most familiar with - Hatzegopteryx thambena. Hatzegopteryx was first described in 2002 by Eric Buffetaut and colleagues, from a portion of the skull, humerus, and femur. The skull and humerus came from the Vălioara locality, and the femur from Tustea of the Haţeg Basin of Romania. These localities are terrestrial deposits, deposited during the Maastrichtian (latest Cretaceous) in an area that was then full of small islands. The skull portions consist of part of the and occipital region. Only the proximal (closest to the body) part of the humerus (upper arm bone) is preserved, and it is massive, measuring over 16 cm in it's widest part, and shows a large unwarped deltopectoral crest, which helps in the identification of the group of pterosaurs it belong to (this means it is not an ornithocherioid). The deltopectoral crest is large, and represents the area where the large flight muscles would attach.
Undescribed giant azhdarchid cervical (neck)
vertebra from Romania [7].
Although only known from a few fragmentary remains, much can be determined about this animal and it's size, by scaling up other more complete azhdarchids such as Montanazhdarcho. Original estimates suggested this animal has a wingspan of 12-15 m, but more conservative recent estimates suggest it had a wingspan of 10-11 m [5]. Even at just 11 m wingspans, this animal would have been terrifying. As mentioned in a previous post, the palaeoecology of this region is interesting. Hatzegopteryx appears to be the largest carnivore and predator of the Late Cretaceous of Romania. This has lead people to suggest that Hatzegopteryx would have preyed on small dinosaurs, termed the 'terrestrial stalking' hypothesis [6]. Islands limit the amount of resources available for animals, and typically result in island dwarfism. Pterosaurs, however, would not have had this restriction as they could have flown from island to island. Additional remains from Romania that are currently being described suggest that there may have been other giant pterosaurs, and further Hatzegopteryx-like material has been found. Unfortunately, the lack of overlapping material between specimens makes it difficult to determine if they are the same species or different ones.

Arambourgiania

Arambourgiania philadelphiae is probably the least well known and recognisable of the giant pterosaurs, although it was described first. First described by French palaeontologist Camille Arambourg as "Titanopteryx" philadelphiae in 1959  [3], it was later redescribed as Arambourgiania philadelphiae by Nesov in 1987, as Titanopteryx was already taken as the name of a beetle. Arambourgiania was originally described from a single partial cervical vertebra, which at the time was described as a metacarpal, but later recognised as a cervical vertebra [8,9]. All of the material comes from the Maastrichtian of Jordan, and additional material including a wing phalanx fragment and a cervical vertebra. Additional specimens exist from other museums that have been undescribed or referred to including the Natural History Museum of London. The best estimate for a wingspan of Arambourgiania philadelphiae is similar to Hatzegopteryx with 10.5m being the estimated greatest wingspan possible [5]

Quetzalcoatlus northropi

Giant Q. northropi humerus (b, c), and
smaller Quetzalcoatlus sp. humerus (d)
and cervical vertebra (a) [4]
Quetzalcoatlus northropi, on the other hand, is probably the best known or at least most popular in the media of the giant pterosaurs. From the Maastrichtian of Texas, only a few bones of Q. northropi have been described in the literature. The genus Quetzalcoatlus is known from 2 size morphs: a smaller one generally referred to as Quetzalcoatlus sp., and the giant Q. northropi. First described in 1975 by graduate student Douglas Lawson, Q. northropi is known from a fragmentary wing (humerus, carpals, phalanges), with just the humerus figured in the original description [4]. Approximately 40 km away, a number of much smaller specimens were found and described as the same genus, but a different unnamed species, hence Quetzalcoatlus sp. In total, and at the time of original description in 1975, the material existing for Quetzalcoatlus consisted of four wings, a neck, hind limbs, and the lower jaw. Frustratingly, no more of this material has been described. It represents the best known giant azhdarchid, but it has never been properly described in the literature, although there is hope that this may happen soon. 

The lack of description for Quetzalcoatlus is particularly frustrating as it means that additional material from North America cannot be properly described. For example, there is large azhdarchid material from Alberta that is thought to represent at least Quetzalcoatlus sp., and possibly even Quetzalcoatlus northropi. However, until these specimens are properly described, it's unknown if this is the case. Subsequently, a lot of this material is not properly described and people are just waiting for the other material to be described. Hopefully that will come though!

While only 3 species of giant pterosaur are currently known, they seem to not have been restricted to one area as they are known from Europe, the Middle East, and North America. Hopefully more material will be found and described with ongoing studies in Romania and North America especially, and new species may pop up!

Terrestrially stalking Hatzegopteryx preying on small sauropods in Romania [6]

References:
1. Ksepka, D. 2014. Flight performance of the largest volant bird. PNAS 111: 10624-10629.
2. Burretaut, E., et al. 2002. A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften 89: 180-184. 
3. Arambourg, C. 1959. Titanopteryx philadelphiae nov. gen., nov. sp., ptérosaurien géant . Notes et Mémoires sur le Moyen-Orient 7: 229-234.
4. Lawson, D. A. 1975. Pterosaur from the latest Cretaceous of west Texas: discovery of the largest flying creature. Science 187: 947-948.
7. Vremir, M. 2010. New faunal elements from the late Cretaceous (Maastrichtian) continental deposits of Sebes area (Transylvania). Terra Sebus, Acta Musei Sabesiensis 2: 635-684.
8. Martill, D. M., et al. 1998. Discovery of the holotype of the giant pterosaur Titanopteryx philadelphiae Arambourg, 1959 and the status of Arambourgiania and Quetzalcoatlus. Neues Jahrbuch für Geologie und Paläontologie Abhandungen 207: 57-76.
9. Frey, E., and Martill, D. M. 1996. A reappraisal of Arambourgiania (Pterosauria, Pterodactyloidea): one of the world's largest flying animals. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 199: 221-247.

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!

References
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.

Thursday, 23 April 2015

Fossils and Geology

A few weeks ago, I was demonstrating on a geology field course in Wales. It was fantastic for several reasons - I had a great time, it was out on the coast of Wales mostly on the coast, and more importantly, it reminded me of my love for geology. It's been a while since I've done some geology, about 6 years to be exact, and I really enjoyed looking at rock types, folds, faults, and all those other fun things.

One of the other things I remembered on the trip was the occasional animosity that is seen between geologists and palaeontologists. I remember in my undergrad geology classes how geologists would rant about how they hated palaeontology and fossils, and vice versa for palaeontologists regarding rocks and geology. Then in Wales, one of the lead staff members would make a face each time we found a fossil or discussed them. While I will admit to preferring fossils over rocks (obviously, I'm a palaeontologist...), there is one important thing to remember: palaeontology and geology NEED each other. And palaeontology especially would not exist without geology.

To start with the obvious side, fossils are basically rocks made of bones, shells, soft tissue, etc. of long dead animals or plants. The process of fossilisation means that the organic material is literally replaced over time with rock and mineral. This is done primarily by highly-mineralised pore water in the ground and sediment. As an animal dies and is buried by sediment, highly mineralised water flows through the sediments and around the dead body, and over time, the minerals in the water will replace the tissues of the body, primarily the hard tissue. Soft tissue is generally decayed and broken down, while the hard tissues of bone and teeth remain replaced as rock. Being able to tell what type of rock now makes up the fossils can be important in figuring out the environment that the fossil was deposited in. Even more important is that the rocks surrounding the fossils can contain clues about how the animal died and the environment in which it lived. For example ripples in sandstone tell us there was a current, while fine laminated sediment like mudstone tells us that the animal died in a quiet low-energy environment like a lake or lagoon where fine sediments settled over a long period of time to the bottom. The presence of specific minerals can tell us things as well. Pyrite is formed in low-oxygen environments, so pyritised fossils mean a low-oxygen environment like the bottom of a deep ocean. Having a background in geology can definitely help in understanding palaeontology, specifically in order to understand the environment that the plant or animal was living in.

On the other hand, palaeontology and fossils can tell us specific things about the environment and geology of an area. There are fossils called Index Fossils, which are fossils that lived for a very little amount of time, and a specific time. They are obviously identifiable, and the fact that they are only found at very specific times means that when they are found, we know exactly what time period those fossils come from. Additionally, fossils can be helpful in determining geological structures like bedding planes. Sedimentary rocks are deposited in layers called beds. These layers are deposited as horizontal beds as sediments fall from lakes or rivers, for example. Through geological processes, these beds can be folded, faulted and overturned, making it difficult to tell which way is up and what has happened geologically speaking. This is where fossils, and in particular trace fossils can come in to help clear up some of the problems. If an animal is walking around on the bottom of the ocean or lake, the footprints or traces will be on a single bedding plane. If preserved and fossilised, these traces can tell us which way was "up" on the bed when it was deposited. This can help us understand what geological processes have happened in the past in terms of folding and faulting.
Trilobite trace fossil from Wales. This showed at this particular locality that the bedding planes here were nearly vertical, and allow us to see that there was some significant folding in this area, specifically an an anticline in the bay where this was found.
So as you can see, geologists need palaeontologists, and palaeontologists need geologists. Or even better, it's important for geologists and palaeontologists to learn about each others subject. So here it is - palaeontologists: stop hating on geology and rocks! You need it! And now geologists: fossils aren't so bad, and they teach us things every day! We need each other, so stop with all the malice.

Tuesday, 14 April 2015

Late Cretaceous of Romania

For the last 2 weeks, I have been on fieldwork in Transylvania (western Romania) with the University of Southampton Vertebrate Palaeontology group. This is part of a long-term project between several groups including British, American, and Romanian organisations looking at the vertebrate palaeontology of this area. This is the 3rd year this Easter trip has run, and was the biggest yet (25 strong at it's largest!).

The area was first recognised as being an important vertebrate palaeontology location by Baron Franz Nopsca, the Hungarian aristocrat and palaeontologist of the late 1800's and early 1900's who is widely thought to be the kickstarter of palaeontology in the region.

Geological Setting

When mentioning fieldwork in Romania, and in particular Transylvania, most people think of vampires, castles and mountains, and have no idea about the palaeontological significance (or even topography) of the region. While there are outcrops of many ages, the areas that we are interested in are of Late Cretaceous (Maastrichtian) age, deposited approximately 72-66 million years ago. This is the last time period of the Cretaceous, culminating in the end Cretaceous extinction 66 million years ago that saw the extinction of pterosaurs, non-avian dinosaurs, and many more. There are the Carpathian mountains, and also several plateaus and rivers where much of the fossils come from.

In particular, there are 2 areas of interest in Transylvania that yield Maastrichtian deposits - the lesser known sedimentary Transylvanian Basin in the area of Sebeş and Alba Iulia, and the famous Haţeg Basin to the southwest. During the Late Cretaceous, this area was characterised by an island environment, and is represented by both terrestrial and marine deposits in the area, with the younger terrestrial/continental deposits overlying the older marine sediments. Numerous islands were found in this area of the world, with Haţeg Island being one of the major islands. 

Palaeontology of the Area

Transylvanian Basin

Râpa Roşie
There are numerous sites in the Transylvanian Basin that have yielded vertebrate remains, and many different groups of animals have been found. At the river site Sebeş-Glod the theropod Balaur bondoc was found[1], which has an interesting double sickle-clawed foot and has proven to be highly controversial in it's placement among theropods. Balaur was a small theropod estimated at just 1.5m in length from an incomplete skeleton unfortunately lacking a skull. Also from Glod is the azhdarchid pterosaur Eurazhdarcho, which had a wingspan of around 3m and is known from an incomplete skeleton as well with no skull[2]. Further finds include additional dinosaurs (Zalmoxes, titanosaurid sauropods), turtles, crocodylomorphs, and more. At Petreşti (also a river site) a number of fossils have been found including pterosaurs and the ornithopod dinosaur Zalmoxes[3]. A productive site at Lancrăm has produced fossils of numerous groups including primarily titanosaurs (Magyarosaurus) and ornithopods (Telmatosaurus and Zalmoxes), but also turtles and crocodylomorphs[4]. Oarda de Jos is another river locality that may have represented a bird breeding colony[5], but also includes turtles, amphibians, fish, lizards, crocodylomophs, dinosaurs and mammals [4]. While it has been suggested that pterosaur material has been found here, this was actually a misidentified turtle [6-7]. The final site I will highlight from the Transylvanian Basin is that of Râpa Roşie, the "Red Ravine". This is a breathtaking site that reminds me of the badlands of southern Alberta, but with massive imposing red cliffs. Vertebrate fossils from here include crocodylomorphs like Allodaposuchus, turtles, azhdarchid pterosaurs, titanosaurid sauropods, ornithopods (both Telmatosaurus and Zalmoxes), ankylosaurs, and theropods[4]. In the Transylvanian Basin alone there are numerous vertebrate groups represented from several fossil-bearing localities showing just how rich this region is, and this is just a snapshot of all the localities! 
The foot of Balaur bondoc from Csiki et al. [1]

Haţeg Basin

Vadu
Sînpetru sandstone











While the Transylvanian Basin is certainly fossiliferous, the Haţeg Basin is the more famous of the two, and arguably even more fossil-rich. The first site to discuss is near the town of Sînpetru (or Sânpetru sometimes), and is the stratotype of the Sînpetru Formation. This is now a protected site so no hammering or digging is allowed, but you can still go and take a look to see if anything is there on the surface. Here, several dinosaur, crocodile, turtle and mammal fossils have been found. Not far from Sînpetru is the river site of Vadu, which is set in the middle of the basin with the Carpathian Mountains on all sides. This is a very shallow river with fossils consisting of birds, dinosaurs, crocodylomorphs and much more. Another interesting site is Tustea, which is best known for a large number of dinosaur eggs, including egg clutches, which are thought to be from the ornithopod dinosaur Telmatosaurus or the titanosaurid Magyarosaurus due to the presence of their fossils in this region as well. Additionally, turtle, crocodylomorph, mammal, and pterosaur fossils have also been found here, one of the most famous perhaps being that of the giant pterosaur Hatzegopteryx thambena, which was described first from here and another site Vălioara[8]. Finally one of the most active sites in recent years is that of the Barbat River at Pui. Numerous dinosaur fossils have been found here including the ornithopods Telmatosaurus and Zalmoxes, pterosaur fossils like the recently described short-necked azhdarchid vertebra[9], turtles (e.g. Kallokibotion), crocodylomorphs, mammals, and more. 
Artists impression of a short-necked azhdarchid pterosaur based on a cervical vertebra from the Barbat River described by Vremir et al. [9]. Image copyright Mark Witton.

 Interpretations and observations

Little Magyarosaurus being tormented by a flock of
Hatzegopteryx - a possible use of terrestrial stalking. Image
copyright Mark Witton.
Interpreting the palaeoecology and palaeobiology of different animals in this region has been a heavily debated and hot topic in palaeontology over the last few decades. Island dwarfism is a process that applies today to animals living on islands where their size is limited and over many generations animals get smaller and smaller as their resources are limited. Nopsca first suggested this was what had happened on Haţeg Island in the Late Cretaceous since most of the dinosaurs in particular are significantly smaller than their contemporaries in other parts of the world. For example, Magyarosaurus was a titanosaurid sauropod dinosaur, a kind of large long-necked dinosaur. Unlike what we are used to seeing as the giant long-necked dinosaurs like Apatosaurus, this dinosaur was less than 2m tall. Additionally the ankylosaur Struthiosaurus is smaller than other members of its group. Currently, very few theropod remains are known, and the best known is that of Balaur, which is similar in size to a small chicken at approximately 50 cm high and 2 m long. With theropods being so rare, what would the main predator in such an environment be? Well one thought is that the giant pterosaur Hatzegopteryx terrorised the land animals as the major predator[10]. With this animal being by far the largest found so far, this is a well supported theory. These points all suggest that the Late Cretaceous islands of Romania were a strange and dangerous place to live.

New finds?

 
Corvin Castle in Hunedoara
Barbat River in the snow
Unfortunately I can't reveal too much about our trip yet as there are publications imminent and forthcoming, but I will say that we had a very productive year. We visited a number of sites in both the Transylvanian and Haţeg Basins, and found a lot of bone. Some highlights include some pterosaur material (both cranial and postcranial), a partial ornithopod dinosaur skeleton, and some additional bits and bobs. We had a great time wading through rivers, getting snowed on, checking out little museums, and some of us even got to go see a castle (although not the famous Dracula castle, it's still an awesome castle). 

Keep following for news on the new finds as they become available. I'll update when we have more news!

Special thanks to Prospectiuni and the National Geographic Society for funding for this trip. Without them, this trip would not be possible!








References
1. Csiki, Z., et al. 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. PNAS 107: 15357-15361.
3. Vremir, M., et al. 2014. Petreşti-Arini — An important but ephemeral Upper Cretaceous continental vertebrate site in the southwestern Transylvanian Basin, Romania. Cretaceous Research 49: 13-38.


4. Vremir, M. 2010. New faunal elements from the Late Cretaceous (Maastrichtian) continental deposits of Sebeş area (Transylvania). Terra Sebus. Act Musei Sabesiensis 2: 635-684.


5. Dyke, GJ., et al. 2014. A drowned Mesozoic bird breeding colony from the Late Cretaceous of Transylvania. Naturwissenschaften 99: 435-442.
6. Grellet-Tinner, G., and Codrea, VA. In Press. Thalassodromeus sebesensis, an out of place and out of time Gondwana tapejarid pterosaur. Gondwana Research. In Press - online July 2014.
7. Dyke, GJ., et al. In Press. Thalassodromeus sebesensis — A new name for an old turtle. Comment on "Thalassodromeus sebesensis, an out of place and out of time Gondwana tapejarid pterosaur", Grellet-Tinner and Codrea (online July 2014 DOI 10.1016/j.gr.2014.06.002). Gondwana Research. In Press - online August 2014.
8. Buffetaut, E., et al. 2003. Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (western Romania). Geological Society, London, Special Publications 217: 91-104.
9. Vremir, M., et al. 2015. A medium-sized robust-necked azhdarchid pterosaur (Pterodactyloidea: Azhdarchidae) from the Maastrichtian of Pui (Haţeg Basin, Transylvania, Romania). American Museum Noviciates 3827:1-16.