Monday, 6 October 2014

Introduction to pterosaur skeletal pneumaticity

In my last post, I talked about the “lightweight” skeleton of birds, and a bit about the possible myth that birds evolved lightweight skeletons in order to fly. I discussed the fact that birds have light skeletons because of their respiratory system which invades and hollows out the bony tissue, filling many bones with air rather than marrow (especially the vertebral column, but also the appendicular skeleton in the wings).

As mentioned, this feature is unique to birds today, but was also found in their ancestral theropods, as well as in the necks of the large-bodied sauropods, and of course in pterosaurs. Pterosaur pneumaticity is something that has been discussed a fair bit in the literature as it is believed to be a key feature that allowed pterosaurs to reach their large sizes. While many animals of cranial pneumaticity (including humans – we have sinuses throughout our skulls that are full of air), the presence of pneumaticity in the postcranial skeleton is much more rare. For brevity, if I talk about pneumaticity here, I mean postcranial skeletal pneumaticity!

It appears that all pterosaurs had some aspect of postcranial skeletal pneumaticity, with evidence of it in the axial skeleton of the Triassic pterosaurs Raeticodactylus and Eudimorphodon [1]. This can be identified by the presence of pneumatic foramina, small holes that go into the bone cavity where the respiratory system would enter the bone through structures called diverticulae. To identify these as pneumatic features rather than nutrient foramina, we can look at modern bird bones and see how these features differ. In the earliest pterosaurs, only the axial skeleton can explicitly be described as pneumatic: several pneumatic foramina have been identified in the cervical vertebrae, ribs and dorsal vertebrae.
Pneumatic foramina (PF) in a modern swan humerus (A and B), and a goose cervical vertebra. From O'Connor [2]
Pneumatic openings in the dorsal vertebrae of Dimorphodon [1]

Pneumaticity seems to be found in all groups of pterosaurs. Thus far, no specimen unequivocally lacks pneumatisation, and those that are thought to lack it are more likely crushed or destroyed [1]. As we move further up into the derived pterosaurs, the pterodactyloids, pneumaticity becomes much more interesting in my opinion. While the early pterosaurs had only cranial and axial pneumaticity, most pterodactyloids have some degree of appendicular pneumaticity in their wings as well.

Scapulacoracoid of Montanazhdarcho showing
 a pneumatic foramen (pf). From McGowen et al. [3].
Many of the wing elements were pneumatic. The scapulacoracoid (the bone that articulates with the vertebral column and the humerus at the glenoid fossa) in many species is pneumatic (e.g. Montanazhdarcho, Anhanguera, Pteranodon). Pterodactyloid humeri and first wing phalanges (the biggest bone in the wing of a pterosaur) show the highest degree of pneumaticity. The number and location of pneumatic foramina can differentiate different groups, but in general, pterodactyloids have foramina on the proximal end of their humeri. For example, these have been found in Tapejara [4], Montanazhdarco [3], Pteranodon [5], Anhanguera [6], etc. The air sacs would enter the humerus proximally near the glenoid, and leave the humerus at the distal end where the humerus articulates with the radius and ulna.
Tapejara humerus showing pneumatic foramina on the proximal end. From Eck et al. [4]
Distal end of a Pteranodon humerus with pneumatic foramen. From Bennett [5]

While there isn’t as much documented evidence for pneumatisation in the radius and ulna, it has been reported in the ulna and radius of Pteranodon [5]. There is also significant pneumatisation of the carpals (the bones that articulate between the metacarpals and phalanges to make the pterosaur wrist). This is seen in the proximal carpals (e.g. Montanazhdarcho) and fused syncarpals and preaxial carpals of Pteranodon. Even small bones like the pteroid have pneumatic foramina in Pteranodon [5]. This pattern of extensive pneumatisation in the wings of Pteranodon continues, with nearly every element showing some kind of evidence of pneumatisation.
Pneumatic foramina in the proximal carpal of
Montanazhdarcho. From McGowen et al. [3]

Finally, the wing finger of pterodactyloid pterosaurs shows extensive pneumatisation, especially the first phalanx. In Pteranodon, the pneumatisation occurs all the way down to the 4th wing phalanx. The 1st wing phalanx is also pneumatic in Tapejara, Anhanguera and more.
PFO - Pneumatic foramen in the first wing phalanx of
Anhanguera. From Kellner and Tomida [6]
This should have shown you that there is evidence of skeletal pneumaticity throughout the axial skeleton and the wings of pterosaurs, meaning that air sacs existed all the way down the wing in at least pterodactyloid pterosaurs. This indicates that they had a very efficient respiratory system which allowed for respiration all the way down the wings. This is more than what is found in modern birds, which are primarily pneumatic only in the axial skeleton and a few elements in the wings. Very few birds have distal pneumatic elements [2].
Pneumatic openings in the wing phalanges of Pteranodon.From Bennett [5]
Pulmonary air sac system in Anhanguera: lungs (orange),
cervical (green), abdominal (blue), abdominal (grey) and
wing diverticular system (light blue). From Claessens et al. [7]
Detailed studies of the pneumatic system of pterosaurs has suggested that number of different pulmonary air sacs existed. It is thought that derived pterosaurs had lungs as well as cervical, abdominal, and thoracic air sacs. They also had an air sac or diverticular system that went into their wings. 

While we've been talking about pterosaurs that show pneumaticity, there are also some that have very little. Dsungaripterids, for example, are quite derived pterodactyloids, but they have virtually no post cranial skeletal pneumaticity. In fact, they have extremely thick-walled bones. This makes them a bit strange, but this is a topic for the future!



Pneumaticity can also be quantified using Air Space Proportion (ASP). Pterosaurs have varying degrees of pneumaticity within the bones with relation to the size of the air sacs, which I will talk about in the next post.  

References
[1] Butler et al. 2009. Postcranial skeletal pneumaticity and air-sacs in the earliest pterosaurs. Biology Letters 5: 557-560.
[2] O'connor 2004. Pulmonary pneumaticity in the postcranial skeleton of extant Aves: a case study examining Anseriformes. Journal of Morphology 261: 141-161.
[3] McGowen et al. 2002. Description of Montanazhdarcho minor, an azhdarchid pterosaur from the Two Medicine Formation (Campanian) of Montana. PaleoBios 22: 1-9.
[4] Eck et al. 2011. On the osteology of Tapejara wellnhoferi KELLNER 1989 and the first occurrence of a multiple specimen assemblage from the Santana Formation, Araripe Basin, NE-Brazil. Swiss Journal of Palaeontology 130: 277-296.
[5] Bennett 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Palaeontographica Abteilung A 260:1-112.
[6] Kellner and Tomida 2000. Description of a new species of Anhangueridae (Pterodactyloidea) with comments on the pterosaur fauna from the Santana Formation (Aptian-Albian), northeastern Brazil. National Science Museum Monographs 17: ix-137.

Tuesday, 16 September 2014

The evolution of the "lightweight" skeleton of birds

We often read in the literature, or hear it in popular science shows that birds are able to fly because of their lightweight skeleton, but is this really true?

There are several aspects surrounding this issue that I am going to try to discuss. I'll talk about where the idea of the lightweight skeleton comes from, whether or not it actually is the case, and whether this feature truly evolved to allow them to fly.

First of all, where does the idea of a lightweight skeleton in birds come from? This comes from the fact that many bird bones are hollow. Unlike mammal bones which have generally thick walled bones filled with marrow, bird bones are commonly filled with air. This is related to their breathing system and the intake of oxygen. In mammals, this is done primarily in the lungs, but also the trachea, bronchi, and diaphragm. Birds, however, have very different respiratory systems. They have air sacs in addition to lungs which is significantly more efficient than the typical mammalian system. These air sacs act in a manner similar to bellows which allow for air to be pushed through uni-directionally. This allows for consistent movement of the oxygenated air in one direction, which prevents the mixture of oxygenated and de-oxygenated air. Another unique feature related to the avian respiratory system is that the air sacs have diverticulae, finger-like projections that invade/hollow out the bones. This commonly occurs in the arm/wing bones of birds, and occurs at varying degrees of pneumatisation (air within the bones) throughout the wing [1].
From O'Connor [1]
O'Connor [1] found that the pneumaticity index (the number of elements pneumatised in the skeleton) varies throughout birds with heavier birds such as swans and geese having higher degrees of pneumaticity. If heavier flying birds have more pneumatic skeletons, then it stands to reason that they need pneumaticity to lighten the bones, right?

Well maybe... but there's much more to this topic than originally thought. A few studies have suggested that birds don't have that light of skeletons after all. First, Prange et al. [2] compared the dried skeletal mass of birds and mammals to their body mass and found that the relationships were remarkably similar in these phylogenetically distant groups. It was always assumed that the skeleton of birds was lighter than those of similarly sized mammals, but this seems to suggest that bird skeletons are just as heavy as mammal bones for a similar size.


Left (top), the body mass - skeletal mass relationship found in birds, compared to the same relationship in mammals (left bottom). The regression was found to be very similar in both. From Prange et al. [2]

Now I've spent a lot of time looking at this relationship and discussing it with people and I always thought there something a bit off with the conclusions, but never could fully put my finger on it. However, Matt Wedel (a sauropod palaeontologist and expert on pneumaticity) very correctly pointed out that by weighing the dry skeletal mass of the mammals, the authors had essentially artificially pneumatised the mammal bones. While the actual bone     itself may not be heavier in mammals, it most certainly would be in a living animal when the bone would be filled with marrow, unlike the hollow air-filled bird bones. This means that the relationship may not be that shocking after all when compared with mammals. Interestingly enough, when marrow is accounted for, small rodents appear to have similar soft tissue mass - skeletal mass proportions to birds, while bats have a heavier skeleton for a given amount of soft tissue [3].

The graph to the right shows soft tissue mass - skeletal mass relationships in passerine birds (black squares), and rodents (grey diamonds) and bats (white circles) which have had 15% of the dried skeletal mass added to it to account for marrow. From Dumont [3]. 

More interestingly, Dumont [3] found that the actual bone density in birds and bats was higher than those found in the similarly sized rodents. While the bony material is less, the density appears to be slightly higher.

But how do density and pneumaticity affect the bone? Here is where I believe this all comes together. Both density and pneumaticity have the same effect as both the pneumaticity and density increase, so does the bone's stiffness and strength. Bone density is proportional to stiffness and strength, and the shape affects stiffness. Hollow bones follow the same principles as a an I-beam. If you look at any construction site, you'll see that the beams used for major load bearing parts are I-shaped (that's why they're called I-beams). This is because bending results in high stress in the areas located furthest from the neutral axis. Material must be concentrated along these areas of high stress (the horizontal portions of the I), whereas less material is needed along the neutral axis (the central portion between the two horizontal axes). This is the same principle seen in hollow bones. The neutral axis is the central hollow shaft of the bone, where little stress occurs, whereas the bone is concentrated towards the outside, where the stresses occur. A perfectly circular hollow cylinder will be stiff in all directions, unlike an I-beam which is easier to bend one way than the other. However, the details of the direction of stiffness in bones is an entirely too complicated topic for now, and I will likely discuss later in a different post.


Right: image from Dumont [3] showing how density, and the shape of the bone relate to stiffness and strength.

For now, the important thing is this: birds have hollow bones which make them more stiff.

Now the title of this post is the evolution of the lightweight skeleton of birds, and I haven't talked at all about evolution yet. So where does evolution come in, you might ask? Well I think, and I'm not alone in thinking this, that the hollow pneumatic skeleton of birds (and in fact pterosaurs, the extinct flying reptiles I study) evolved not purely as a weight-decreasing method, but likely in a more complicated intertwined way of increasing strength, decreasing weight, and improving the respiratory system while flying. This is certainly not a novel idea, but it's about time this idea of the hollow bird skeleton evolving purely as a means to decrease mass be put to rest. I've seen it several times on "science" shows, and it's brought up constantly in the media. It's not all about mass reduction, but likely a complicated number of things that affect each other.

In the future, I'll talk a bit about the pneumaticity in pterosaurs, as that's part of my PhD so look forward to that!

References:
1. O'Connor, P. M. 2004. Pulmonary pneumaticity in the postcranial skeleton of extant Aves: a case study examining Anseriformes. Journal of Morphology 261: 141-161.
2. Prange, H. D., et al. 1979. Scaling of skeletal mass to body mass in birds and mammals. The American Naturalist 113: 103-122.
3. Dumont, E. R. 2010. Bone density and the lightweight skeleton of birds. Proceedings of the Royal Society B 277: 2193-2198.

Tuesday, 9 September 2014

North American Summer

As I mentioned previously, my summer was billed to be a pretty busy time, and indeed it was. I am now back in the UK, and back at work, but I'll talk a bit about my trip to North America looking at pterosaurs and digging for dinosaurs.

My trip to North America started out in Los Angeles, where I spent 4 days working at the LA County Museum of Natural History (LACM) with one of my supervisors, Mike Habib. I had a great week looking through material, mainly of Pteranodon, but also some casts of Pterodaustro, and a Nyctosaurus. The museum has a decent amount of material, including part of a very large skull which is on display, and also a few partial or nearly complete wings, which I really enjoyed. I also was fortunate to have arrived just after they had prepared a new specimen (I say new, but they actually received it in the '60s, but it was only recently opened up and prepared), which was very exciting. It was a really cool specimen, but I am not sure if I'm allowed to talk about it too much yet, so maybe later. We spent a lot of time looking at the wings for evidence of pneumaticity, which is one of my interests as you will know if you've read my previous posts. Unfortunately, as many of you may know, Pteranodon and Nyctosaurus are both almost completely flattened, which means that finding pneumatic foramina can be extremely difficult.
Pteranodon display at the LACM. Note the absolutely massive partial skull on the bottom right.
I also got to go to the Page Museum where the La Brea tar pits are, and got to go behind the barriers and see some material actually being excavated which was pretty cool. Probably my favourite part of that museum was looking at the birds, particularly the teratorns, that have come out of the tar pits. Standing there for some time while Mike pointed out features like pneumatic foramina, the tank-like nature of the teratorns, and other cool things was a big highlight for me.
Not a great picture, but here's a complete skeleton of a Teratornis at the Page Museum. I was amazed by the tank-like stature of it compared to more typical gracile birds.
The best part of the summer for me was spent doing 2 weeks of field work in Alberta, Canada, near Grande Prairie, where I got to work on a dig with Phil Currie's lab, in conjunction with the 'soon-to-be-open' Philip J. Currie Dinosaur Museum. We were working mainly at the Pipestone Creek bone bed, which is an almost completely monotaxic (one group of animals) Pachyrhinosaurus bone bed located near the town of Wembley. This site is 73 million years old, and may represent the most abundant bone bed from the Late Cretaceous (or one of the most fossiliferous bone beds anywhere!), with between 30-100 bones found per square metre! While only a small portion has been excavated to date, it's estimated that the bone bed takes up over two football (American football) fields in size. It's likely that over 1000 Pachyrhinosaurus (a ceratopsian dinosaur distantly related to Triceratops) died here, possibly in a flood. While over 99% of the bones found here are Pachyrhinosaurus, there are tyrannosaur teeth, and very rarely some theropod bones.
The area of the bone bed we exposed this summer was found underneath the tarp, which we laid down each night to keep it dry. You can see the massive hill behind that we had to climb with our buckets of matrix (dirt/rock) after uncovering the fossils.
Palaeontologists and volunteers hard at work uncovering Pachyrhinosaurus fossils.
The bones found here are all disarticulated and jumbled up, rather than nicely articulated, complete skeletons. This indicates that the skeletons were broken apart before buried and fossilised. The animals were likely scavenged by large and small predators alike as their bodies rotted and the carcasses lay exposed after dying after the flood. The large number of shed tyrannosaur teeth indicates this, as tyrannosaurs like Albertosaurus lost and replaced their teeth constantly, like modern sharks.

This site was initially excavated by the Royal Tyrrell Museum of Palaeontology in the 80s when Phil Currie was still working there after being told about the site in the 70s. After moving to the University of Alberta, he realised that the remains represented a new species of Pachyrhinosaurus, and named it Pachyrhinosaurus lakustai, after the science teacher (Al Lakusta) that found the site. Dr. Currie and the U of A team have continued to work at this site each summer. Now that a permanent palaeontology museum with palaeontologists like Matthew Vavrek has started up in the area, the U of A team will likely scaled down their work there and let the new museum take over. While it has been worked on for many years, there is still lots of new information coming out of the bone bed, and lots to be learned!
Some Pachyrhinosaurus fossils as they were being uncovered. The large top one near the feet is a fairly complete rib that continued to go underneath several other bones which can barely be made out.
The grid square - an important palaeontological tool. This allows for all bones found to be mapped so the orientation can be analysed later. This allows us to better understand patterns in orientation related to things like palaeo-river flow.
I was also able to spend some time at another bone bed that is found along the Wapiti River. This site is much smaller, and located on the side of a cliff/steep hill, which poses some interesting problems with access and specimen collection. The material found here is interesting though because while it is Pachyrhinosaurus, it's unclear exactly what species it is, since the material is found in extremely hard and difficult to prepare iron nodules. This makes it challenging to figure out exactly what is going on, as it may not represent the same time period as the Pipestone Creek bone bed.
The Wapiti River bone bed - what a wonderful view!
Another fun thing about being there when I was, was it was the official ribbon cutting ceremony of the Philip J. Currie Dinosaur Museum, named for my old supervisor that I was doing field work. This meant that we were host to a number of celebrities over the final week, including Dan Aykroyd and family, Fran Drescher, and the Canadian Tenors. We also got to go to the Dinosaur Ball, which is an annual event to raise money for the museum.
Some of us and Dan Aykroyd! I'm on the right

Tuesday, 8 July 2014

Italy, Germany, and Pterosaurs, oh my!

As promised, here's another post about what's happening in my research life. In my last post, I mentioned that I was going to have a crazy busy summer of travelling. Well that has indeed started...

First off, I went to Italy for my first European Association of Vertebrate Palaeontologist's meeting. I went a few days early to visit a friend, where we went to see some dinosaur footprints at Lavini di Marco near Lake Garda. It was a wonderful site with theropod, sauropod, and ornithopod footprints. This site is dated to the Early Jurassic, and were uncovered by a rock slide. The prints are meant to represent Camptosaurus and Dilophosaurus, and a few others not identified to genus. There was another surface that supposedly had trackways going up it, but despite spending about 20 minutes looking, we did not see any...
Ornithopod trackways at Lavini di Marco

Single theropod footprint at Lavini di Marco
Next up was EAVP in Turin. As I mentioned, this was my first time at the meeting. I enjoyed the conference, as it gave me a chance to speak to some researchers from outside of the UK, including other pterosaur workers. The conference was great. I presented some of the preliminary work I've done in my PhD and did in my MSc on pterosaur bone mass and pneumaticity. I enjoyed the relaxed, but still scientific and interesting nature of the conference, and would think about attending again. Next year it is going to be in Poland, but I don't think I will be able to attend unfortunately. 

From Turin, I started my pterosaur adventures in Germany, first heading to Tübingen, then to Karlsruhe. Tübingen was a beautiful city, and had a few interesting pterosaurs as well. The first day consisted of looking at mainly flattened remains of Cycnorhamphus, Dorygnathus and Rhamphorhynchus, but they were interesting historical specimens with a some possibilities for cortical thickness measurements, including the type specimen of Cycnorhamphus suevicus (below).

On the second day, we discovered a forgotten specimen on loan to Tübingen, which made me very excited. They have a 3D dsungaripterid from China, described as Lonchognathosaurus, but thought to be a junior synonym of Dsungaripterus. Anyone who knows pterosaurs understands why this is exciting for me looking at biomechanics and mass - while most pterosaurs are known for having extremely thin-walled bones (mm to sub- mm in places), dsungaripterids have much thicker bones, reaching several mm in size. Fortunately for me, most of the bones were broken, which allowed me to look into the bones and get some good estimates of thickness. Hurray!

My next, and final stop was the Staatliches Museum Für Naturkunde, Karlsruhe, where I was greeted at the museum by this guy:

That made me sure I was in the right place! I was actually welcomed by Dino Frey, who wonderfully hosted me for 3 days while I browsed through collections. The museum in Karlsruhe is a fantastic place with great displays, including a vivarium full of fishes, amphibians, and reptiles. They're currently in the process of building a much larger one as well which will include live coral, large snakes, and more. I was lucky enough to get a quick tour through the future exhibit. I'd like to go back when it's done! They also have a great section upstairs on flying animals, including birds and pterosaurs, with many unique original fossils, like the type specimen of Ludodactylus.
Type specimen of Ludodactylus sibbicki with the "killer" leaf stuck in it's jaw. Sorry for the crappy picture...
The other great thing about Karlsruhe is the pterosaur replicas. You've already seen the one sitting outside, but the one I love is the full-size Quetzalcoatlus northropi replica they have hanging from the roof. Now if you know anything about pterosaurs, you know that that is a feat. This is one of, if not the biggest pterosaur known yet, with a wingspan of 11-12 m. And they have one, fleshed out, covered in pycnofibres and all, hanging from the roof. It's quite a sight from beneath where you can get a glimpse of it from another part of the museum. It is a remarkable thing...

I was told that it took 3 days to install, and it came in 3 pieces. You can also see a little Rhamphorhynchus sticking out of the top left. The best thing about Karlsruhe, of course, was the fact that I got to borrow a bunch of specimens to CT scan back in Southampton. I am so happy for this opportunity and looking forward to what I'll find!

This weekend, I'm off to North America, starting with LA. Let the jet-setting continue!

Sunday, 8 June 2014

PhD Happenings

So it's been a while since I got around to posting on my blog... I've now been working at my PhD for 9 months (holy crap I can't believe it's been that long), and it is going well so far. 

I got my first paper officially published about a month ago on air space proportion (ASP) in pterosaurs. I'll talk a bit more about that soon and cover the details of the paper, but it's looking at quantifying pneumaticity (air sacs in bones) in pterosaurs using CT scans. Basically, degree of pneumaticity changes throughout the bone (at least it does in pterosaurs, and it probably does in other things), which is something you can't tell unless you look at the entire bone, which most fossil studies don't do. This might affect how we use pneumaticity to understand certain aspects of biomechanics. If you're interested, the paper is open access and freely available from Plos One here. Full reference is:

Martin EG, Palmer C (2014) Air Space Proportion in Pterosaur Limb Bones Using Computed Tomography and Its Implications for Previous Estimates of Pneumaticity. PLoS ONE 9(5): e97159. doi:10.1371/journal.pone.0097159

For what it's worth - I would recommend publishing in Plos One to anyone looking to get something dealt with quickly. My paper was accepted in 2 months, published in 3, which is much more than I can say for my actual first accepted manuscript which will see a year between acceptance and publication, and no advanced online publication (which I guess isn't even that bad compared to other horror stories I've heard). They were great to deal with, and everyone involved was just really good. I enjoyed it!


This project was something I started thanks to Matt Wedel, and plan on continuing to look at in my PhD, along with bone mass and flight mechanics of pterosaurs, mainly using CT scans. I've already got a bit more data on both bone mass and ASP that I'll be presenting later this month at the European Association of Vertebrate Palaeontology annual meeting in Italy. After that, I'm heading to Germany to do some museum visits and bring back a load of specimens that are generously being loaned for CT scanning. Anyone who knows my research and has read my blog probably knows by know that I am a big fan of CT. I can't stress enough how awesome CT stuff is. If you have material (especially pterosaur or bird because I'm biased), scan it! I know it's expensive, but if you have the means to do it, there is so much you can do with CT scans. Then, share them with me. Ha, just kidding (well not really...).

What else is happening, you might ask? Well it turns out, quite a lot. We hosted Progressive Palaeontology a few weeks ago, a conference for early career palaeontologists (mainly students), here in Southampton, which I helped to organise. It turned out to be a pretty big success with more abstracts being submitted than ever before. We had a good (but rather wet and cold) trip to the Isle of Wight where we found some ankylosaur armour and neat foot casts. 
Iguanodontid foot cast from the Isle of Wight. Photo by Rosie Sheward.
I'm also going to be helping out with organising the semi-annual pterosaur conference Flugsaurier 2015 in Portsmouth (Aug 26-30, 2015), and SVPCA 2015 here in Southampton (Aug. 29-Sept. 3/4, 2015). It'll be a busy year of conference preparation I think! Really it's just a busy year all together... In about a month I'm heading to LA to spend a week with one of my supervisors, Mike Habib. From there, I head home to Canada for a few weeks, where I'll get to go to Grande Prairie and do some fieldwork at a Pachyrhinosaurus bone bed with my old group. I'm super excited to get to do this and spend some time with the Currie lab. Then it's off to SVPCA in York in September, and SVP in Berlin in November, interspersed with research trips to numerous museums.

Basically, I've got a lot going on right now. I'm currently working on 3 manuscripts on completely different things, only 1 of which related to my PhD. Things are a bit hectic and showing no signs of slowing down... Watch this space for more news!

Oh ya, also, I got married! Future publications and things will be Elizabeth Martin-Silverstone. I've finally made the decision to hyphenate, which has been a long and stressful decision, believe me. But I've made it, it's done, so that's what it'll be from now on!

Until next time...

Thursday, 24 October 2013

Preprint For Accepted Papers

It has finally happened. My first paper has been accepted! Look forward to seeing "A novel method of estimating pterosaur bone mass using computed tomography scans" published in the Journal of Vertebrate Palaeontology sometime next year. *sigh* I was (perhaps naively) hoping for the paper to be published soon, but hey, it's now officially "In Press", which means I can put it on my CV! Super excited about that.

I'm thinking about putting it somewhere on a preprint server like PeerJ, or ArXiv. Does anyone have any advice about this? Or know anything about it? If a paper has been accepted, and copy edited, but isn't going to be officially published for a while, is it ok to put it somewhere like this? Do journals have policies against this? I'd appreciate any information or advice, because I'm not sure what I should do! I need to run any ideas past the other author as well, but I wanted to have all the info first.

EDIT: Since posting this, I have found out that preprint is not an option for JVP. Unfortunately, it looks like I'm just going to have to wait and get it out there the old fashioned way instead. I'm a bit annoyed that the journal says the average time from acceptance to publication is 3 months on their website, but since being accepted, I have been told it's more like 8 months. Gr.

BUT because I can, here it is:
Martin, E. G., and Palmer, C. In Press. A novel method of estimating pterosaur bone mass using computed tomography scans. Journal of Vertebrate Paleontology.

EDIT 2: Since I'm not allowed to put it online anywhere and it won't be published for a while, here is the abstract for a talk I gave on the same topic at SVPCA 2012. If anyone wants to know more about it, let me know!

A novel approach to estimating pterosaur bone mass using CT scans 
Elizabeth Martin & Colin Palmer 
University of Bristol 

Body mass estimation in extinct animals can provide information about ecology and biomechanics of the animal and is vital for flying animals as it determines its ability to take off, land, and indeed, fly. However, existing mass estimation methods for pterosaurs produce a wide range of values, especially in the larger animals. This hinders our understanding of their flight capabilities and indicates a need for a more accurate method for estimating body mass. A novel approach has been developed that uses CT scans of pterosaur wing bones to determine the volume of bone material and thus the bone mass. Results show much larger masses for some bones than previous methods, which indicates that a reassessment of methods for estimating total mass in pterosaurs is required. 

Sunday, 15 September 2013

The Amazing Galapagos

This is a little bit late, but life has taken over for the last month and a half and I haven't had a chance to write. So finally, here it is: my amazing trip to the Galapagos. 

First, some background and history on the Galapagos. The Galapagos Islands are a chain of volcanic islands about 1000 km off the coast of Ecuador, in the Pacific Ocean. The islands are part of Ecuador, and were made famous when Charles Darwin, the English naturalist travelled there. In 1831-1832, he joined a voyage on the HMS Beagle, which brought him to the Galapagos Islands, where his studies of the plants and animals, and especially the finches, led to his theory of natural selection in his 1859 book "On the Origin of Species".

Now, our amazing trip. The majority of the islands are uninhabited, and protected. This means that there are no cars, hotels, or anything on most of the islands; just nature. Each day, the cruise ship we were on was anchored at sea, and we took boats of 16 to the island we were seeing. We had a morning island visit, then back to the ship for lunch, then another excursion in the afternoon.
Map of the Galapagos Islands
Highlights: Espanola Island
What a cutie! Sleeping Galapagos sea lion (Image by Liz Martin)
Our first day on the islands was a truly amazing experience. We started at Gardner Bay, on Espanola Island, which is a very calm bay, with hundreds of sea lions. As there are no natural land predators on the islands, and the animals are well protected, they have little reason to fear people. As such, they are often very curious, especially the sea lions. When you get on the islands, you're supposed to stay far away from the animals, but this can be hard with the sea lions, especially the young ones, as they are extremely friendly and curious. They will walk right up to you, and chase you around, and as long as they aren't the bull males, they are relatively harmless. The Galapagos sea lion (Zalophus wollebaeki) breeds almost exclusively on the Galapagos Islands, but also on another single Ecuadorian island, and they are found throughout the Galapagos. We wandered around the bay for an hour or so, watching the sea lions, and also got our first view of marine iguanas. After walking, we got to go snorkelling for the first time, which was absolutely amazing. If I thought sea lions were friendly on land, I was in for a surprise for what happened in the water. The sea lions will swim right up to you, even at your face, and at the last minute they turn and swim underneath you. They have so much fun with people in the water, it was absolutely amazing. Definitely one of my favourite experiences on the trip.

The afternoon excursion was also a big highlight for me. We went on a long hike, and saw numerous animals. First, there were hundreds of marine iguanas, which I will talk about later. The main highlight of the afternoon for me was Punta Suarez, where many bird species nest. We saw the amazing blue-footed boobies (which are common throughout the Galapagos), Nazca boobies, Galapagos hawks, and my favourite, waved albatrosses. This was the only time we saw albatrosses, and they truly were magnificent. The waved albatross (Phoebastria irrorata) are basically endemic to the Galapagos, although there are a few pairs that nest on the Ecuadorian Island of Isla de la Plata. We were fortunate enough to witness their courtship behaviours, which consists of a bizarre dance where they repeat their movements over and over while they rock back and forth, stick their heads down to the ground, open their beaks wide, and more. When they finally choose a mate, waved albatrosses mate for life. We also got to see one albatross take off, which was a bit awkward, as these animals are fairly large, with a wingspan of about 2.3 m, and they do a kind of waddling/running take off. I sat for as long as I could watching them soar over the cliff. I spent a lot of time imagining them as pterosaurs (of course), and they were absolutely majestic. It was very hard to leave this place
Part of a waved albatross mating dance. Image by Liz Martin
Highlights: Floreana Island
A frigatebird with a baby turtle in its mouth. Photo by Liz Martin
The morning of Floreana Island started out with a walk to a bay. When we looked into the water, we realised that this bay was full of stingrays. We could stand at the end of the water and the waves would bring them towards us, as many as 10, just sitting in the water. The other interesting thing on this bay was that there was a green sea turtle nest. We weren't able to go up to the nesting site as it is off limits, but we could see the tracks from where the females had gone up and laid the eggs. Green sea turtles (Chelonia mydas) are known from both the Pacific and Atlantic oceans, and they lay clutches of 70-100 eggs. This nest had apparently recently hatched, as we knew there were many baby sea turtles, trying to get out of this nest. How did we know this if we couldn't see them? Well, we had the very fortunate/unfortunate (depending on who you ask) sight of a frigatebird swooping down and trying to eat these baby turtles. We watched several attempts, as it would swoop down, miss, and go back up, circling until it would try again. Finally, we watched as it managed to pick up one baby turtle, and fly away. As sad as it was for the turtle, it was a perfect example of "the circle of life", and just shows why they lay so many eggs. We were told that of 100 eggs, only 10 would successfully make it to the water, and of those 10, only 2-3 would survive until maturity. After that, we got to go snorkelling again, where we swam with a sea turtle!

Highlights: Isabela Island
Note the small vestigial wings on the flightless cormorant.
 Photo by Liz Martin
Isabela Island is the largest island in the Galapagos. It is formed from five separate volcanoes, all but one still active, and much of our walk was over old lava flows. Here we saw flamingoes, more blue-footed boobies, flightless cormorants, marine iguanas, and sea lions. No one really knows how the flamingoes on the Galapagos got there, as they are not strong flyers, and the islands are 1000 km from the mainland. There are only about  500 nesting pairs here. In a small in-land lagoon, we also saw some white-tipped reef sharks, which had come in through an underground system of cracks through the lava. The main highlight for me was the flightless cormorants, the only truly aquatic, flightless bird other than penguins. While penguins have evolved flipper-like wings to "fly" underwater, the flightless cormorant (Phalacrocorax harrisi) has extremely reduced wings and extensively webbed and powerful feet. These vestigial wings are used only to assist in balancing while they hop around rocks, while they propel through the water with their feet. This species is found only on the Galapagos Islands. We also got our first view of the Galapagos penguin (Spheniscus mendiculus), the northernmost species of penguin.
Galapagos penguin. Photo by Josh Silverstone
In the afternoon, we got to see our first glimpse of both the land iguanas, and giant tortoises. While marine iguanas are black, land iguanas (Conolophus subcristatus) are brightly coloured. Different islands have different subspecies with different sizes and colours, but they are primarily yellow, red, and orange.
A land iguana. Photo by Liz Martin
Highlights: Fernandina and Isabela Islands
One of the many "piles" of marine iguanas we encountered.
Photo by Liz Martin.
At Fernandina, we saw another large colony of marine iguanas. Marine iguanas are very interesting. The marine iguana (Amblyrhynchus cristatus) is endemic to the Galapagos, and is the only truly marine lizard in the world. They are black, in order to better take in the sunlight to allow them to warm up. They feed solely in the water on algae, and spend about half an hour a day diving into the water to feed, and the rest of the day basking in the sun to warm up from the cold water. To help with warming up, they are normally found in large clusters, sometimes with hundreds of iguanas in one place. We also stumbled upon several bones: a reconstructed whale skeleton with a dolphin skull, and some sea lion skulls, which of course I had great fun inspecting. After the walk, I got to partake in a deep water snorkel, where we saw some more sea turtles, fish, and numerous invertebrates along the coast.

Off the cost of Isabela for the first and only time, we saw a fur seal! Unfortunately, I don't have a great picture of it, but we watched a mother and young fur seal playing with the zodiac. The Galapagos fur seal (Arctocephalus galapagoensis) is endemic to the Galapagos, and is the smallest of the fur seals. They are currently endangered, as they were nearly hunted to extinction in the past.

Highlights: Santa Cruz Island
A dome-shaped giant tortoise in the wild. Photo by Liz Martin
On our last day, we spent time on the populated island of Santa Cruz. First, we went to the Charles Darwin Research Station, where they focus on breeding tortoises, and numerous other research projects to help protect the life in the Galapagos. We also got to go to the highlands, where we were able to see giant tortoises in the wild. The giant tortoise (Geochelone elephantopus) is found on a few tropical islands in the world, and as many as 11 subspecies exist in the Galapagos, with different subspecies on different islands or regions of islands. These subspecies and populations have little to no interaction with each other, and are morphologically distinct, with many people believing they are on their way to becoming separate species. Already, there are two distinct morphotypes: saddle-back, and dome-shaped shells. Unfortunately, many of the subspecies are in decline or have become extinct, which is why the Charles Darwin Research Station is focusing much of their efforts on tortoise conservation.
Lava lizard from Espanola island. Photo by Liz Martin

Other highlights
Being on the Galapagos in general was absolutely amazing, and there were a few things that I can't pick as being a specific highlight of a day or island. Mainly, these include some great examples of evolution and adaptation. There are seven species of endemic lava lizards in the Galapagos, with one species present on 10 islands, and the other 6 being restricted to single islands. They are generally very colourful, with females being more colourful than males, and differ morphologically from island to island.
Some of Darwin's finches. Photo by Liz Martin

Of course as a biologist, seeing Darwin's finches was always amazing. Unfortunately, I'm not able to identify them at all, but was able to see the slight differences in beaks that lead Darwin to his theory of natural selection. They are spread throughout the islands, with 13 species in total.

Swimming blue-footed booby. Photo by Liz Martin
And finally, although I won't talk about them in detail because there are discussed quite heavily in many aspects of biology, seeing blue-footed boobies was of course great. We were fortunate enough to see one of their famous mating dances, watch them fly, dive into the water to feed, and swim along the surface. These birds are truly magnificent, and their feet really are bright blue!


Blue-footed booby. Photo by Liz Martin
The biggest highlight of all was just being on these islands, barely touched and disturbed by humans, and seeing the nature first hand. Seeing the different populations of animals on different islands, and how these animals differ and adapt from island to island was amazing. Even the plants have adapted to different pressures, responding to birds that feed on their leaves. I would highly recommend to anyone, especially anyone interested in evolutionary biology to take advantage if they ever get a chance to go there. I hope you've enjoyed my account of my trip, and more importantly, that you've learned something you didn't know before!

Background info:
While some of the information in this post came from the book Galapagos Wildlife by David Horwell and Pete Oxford, most of it actually came from the brilliant guides we had along the way. The naturalists really know what they're talking about, and they were a never-ending source of information about the islands, the wildlife, and more! Thanks to them for teaching me what they knew.