Dig for victory

In a previous post I showed what I think being a palaeontologist is all about, especially the point that palaeontologists are different from oryctologists. The first ones study changes of biodiversity through time, the second ones extract fossils (but again, both are far from exclusive).

Here is a short summary of  experience working at Upper Cretaceous excavation sites in the South of France (that’s around 80-65 million years old) namely in the Bellevue excavation site in Esperaza run by the Musée des Dinosaures.

First step is to find a place to dig.

Step 1.1: find something

Why along the road? It doesn’t have to be but it has two clear advantages: you can park your car next to it and it’s usually rich in fresh outcrops of rock (where you can find more fossils than in a crop field!).

Step 1.2: try again and again!

The second step, once you’ve decided that there might be something in the outcrop you’ve just explored, is to remove all the “annoying stuff”. To palaeontologists that obviously means all the wonderful fauna and flora and their associated environment (usually soil) that are growing above the potential fossiliferous site (how rude of them!).

Step 2: remove all the annoying stuff

Once you’ve removed the layer of living stuff, you can start the long and interesting part: hitting rocks with a hammer and a pike during the hottest days of summer.

Step 3: start hitting the rocks
Step 4: find something (hopefully!)

Finally, with a bit (a huge bit) of luck, you’ll find a fossil that was worth all this hassle.

Step 5.1: clean the fossil

Once you’ve found the fossil, the first step is to clean the surface facing you and start to build a trench around it in order to pour plaster over it and bring it to the lab. As you can see, paint brushes are useless here too: the hammer and the pike make ideal tools for the surrounding trench and an oyster knife and a smaller hammer do the cleaning jobs. Oh yeah, and a tube of glue. After around 80 million years, the bones get a bit fragile.

Step 5.2: clean the fossil… again!

The last step is to properly clean the fossil in the lab by removing it from all the surrounding rock. The best tools are mini pneumatic-drills and loads of patience. When all that is done, the palaeontologist can start to work on the fossil.

You can find more impressive pictures on the Musée des Dinosaures webpage.

Author: Thomas Guillerme, guillert[at]tcd.ie, @TGuillerme

Images: Thomas Guillerme and Sébastien Enault (with the kind authorisation of Jean Le Loeuff). Feature image: http://www.libraryofbirmingham.com/

What is(n’t) palaeontology like?


After rereading Sive’s excellent blog post on what is a zoologist or at least what is it like to study it, I remember having a slightly similar difficulty in explaining my background in palaeontology. Reactions range from: “Oh… Palaeontology? That’s like the origins of humans and stuff?” or “So you go on excavations and find ancient Roman pottery?” to “Bheuuh, want another beer?”. What frustrated me is that none of these reactions are correct but neither are they totally incorrect (especially the last one!).

Palaeontology is not archaeology

Most people that have only a vague idea of what palaeontology is are usually not big fans of Jurassic Park and don’t know Alan Grant so they usually associate palaeontology with Ross Geller or Indiana Jones. Being not a big fan of TV series, I don’t know whether Ross is a good representation of the reality of life as a palaeontologist but I know that Indiana is not. Not even a little bit. He’s an archaeologist. That might be a nerdy detail for some but to understand what palaeontology is about, it is important to understand the difference. Even though both archaeologists and palaeontologists study the past based on what they find in the ground (and in books!), the time scales involved make the two disciplines impossible to compare. Archaeologists are mainly interested in human culture (they might find animal bones but they are usually the fragments of crafted objects). In contrast, palaeontologists are interested in the remains of life that occurred before human civilisation. Therefore we have two very different time scales here: from years to centuries or, at a push, millennia for archaeologists and from hundreds to millions of millennia (or billion of years) for palaeontologists.

Palaeontology is not about excavations

Palaeontologists do not excavate fossils, that’s a job for Oryctologists. Okay, I’m being picky with the terms here but, again, the distinction is important. Most palaeontologists are also oryctologists, meaning that they go into the field and do excavations as the basis for their scientific work (yeah, in the end, that’s not a cliché, one of the nicest parts of the job is field work!). However, not all palaeontologists are oryctologists (even though most are) and many oryctologists are not palaeontologists. Again, palaeontology is not only about digging up fossils and putting them in museums (contrary to what this song suggests), it is about the study of changes that occurred on our planet through deep time (geography, climate, etc…) and how they affected living organisms (evolution, extinction, etc…).


While we’re on the subject of oryctology, there is a huge public misconception about excavations. Most people that have seen Jurassic Park might think that, in the 90’s, one could just go into the field armed with nothing but a paint brush and happily stumble across a complete Velociraptor (Deinonychus!) skeleton which just had to be cleaned out from the surrounding layers of dust. This scenario would certainly make palaeontology way more straightforward and easy but it would also mean that excavations would be just boring routines where a hoover would do a better job than a naively enthusiastic undergrad student!

Even though excavation techniques are at least as numerous as excavation sites, the paint brush must be one of the rarest tools. Personally, I’ve tried things like hammering a cliff with a pike, shoveling dust and blocks of stone, digging in solid clay with an oyster knife or sifting tons of bags of sediments after diluting it in acid in a lab. None of these activities are similar to the restful act of flicking away sand with a brush (but they’re still a lot of fun!).

Palaeontology is not dusty

The two points above are understandably confusing for the general public because of the Hollywood image of palaeontologists, depicted as “adventurers, not really serious, but entertaining” (to translate a quote from Eric Buffetaut’s book “À quoi servent les dinosaures?”). One might think that other scientists would have a better understanding of palaeontology. However, even if they generally understand the discipline and its implications better than the general public: “Paleontology has a reputation as a dry and dusty discipline, stymied by privileged access to fossil specimens that are interpreted with an eye of faith and used to evidence just-so stories of adaptive evolution” (Cunningham et al 2014).

Thankfully, however, the discipline that studies traces of evolution has not escaped evolution of its own. The “privileged access to fossil specimens” has been replaced by either huge online databases (just one example and one other among thousands) or accessible and well-curated collections. The “eye of faith” has been replaced by X-Ray tomography, Surface scanners and synchrotrons; and the “just-so stories” are now replaced by integrative studies leading to a new vision of the history of life

Palaeontology is… great

The differences between a nerdy “Indianajonesomorph” oryctologist that knows all of the dinosaurs’ names by heart and a realistic palaeontologist are what makes palaeontology so interesting. More than the taxonomy, taphonomy, comparative anatomy and cladistic tools that palaeontologists use, palaeontology is about the idea that everything is constantly changing and that we live in just one fleeting moment in the vast history of life.

However, I still like the image of the “adventurers, not really serious, but entertaining”… As long as palaeontologists don’t take this image seriously themselves!

Author: Thomas Guillerme, guillert[at]tcd.ie, @TGuillerme

Images: Wikicommons

Gould Mine


The career of Stephen Jay Gould eludes easy definition because of his prolific output in so many areas. Michael Shermer characterises him as a historian of science and scientific historian, popular scientist and scientific populariser.

The popular science writings of Stephen Jay Gould (20 of his 22 books and hundreds of articles) are responsible for making me want to study macroevolution. He said of his popular essays that they were intended “for professionals and lay readers alike”. We have already covered some aspects of science communication, like how to do it and which kind of scientists should engage in it. Gould wrote 479 academic papers during his career, so any thought of public outreach damaging one’s science certainly didn’t apply to him.

Let’s have a closer look at his academic legacy. Gould is well known for his theory of punctuated equilibrium co-written with Niles Eldredge. This fuelled the debate around ideas such as species selection and the mechanisms explaining macroevolutionary patterns.

Despite this being the work for which he is best remembered it represents a tiny fraction of his output. He actually published only 15 papers with this theory as a main topic, which represents only 3% of his academic work! As a comparison, he published more papers (17) on baseball!

His primary field was invertebrate palaeontology (he was the curator of Harvard’s Invertebrate palaeontology collections from 1973 to his death in 2002) but again, even his main focus in this area (on Cerion snails) represents only on one quarter of his work. Shermer describes him as being “no single-minded fossil digger or armchair theorizer.”

Actually, nearly one fifth of his massive scientific output is primarily focused on the history of science. Again, as Shermer says, he was a “Historian of Science and Scientific historian”.

So Gould should not be only remembered for his proposal of punctuated equilibrium. Gould published 169 papers in 23 last years of last century, which gives him an average number of publications in the history of science of 7.34 per year. To put it in the historical context of the field, the only names that have been more productive are Aristotle, Kant, Goethe and Newton.

It’s rare to see a scientist who divided opinion so much, hagiographies have been written about him but he’s also loathed. Look at these for contrasting views:

“In the field of evolutionary biology at large, Gould’s reputation is mud.”

“Steve is extremely bright, inventive. He thoroughly understands paleontology; he thoroughly understands evolutionary biology.”

I’ll leave it to the reader to find out where they stand on Gould for there is a lot of controversy to consume. I prefer to remember him through his essays on Natural History than through his few papers about punctuated equilibrium, better illustrating the “measure of a man” (that’s Shermer’s pun). His life illustrates how interdisciplinary studies exponentially increase scientific productivity: “Gould has used the history of science to reinforce his evolutionary theory (and vice versa)” writes Shermer. And that applies as much to punctuated equilibrium as to baseball!

Authors: Thomas Guillerme (guillert[at]tcd.ie, @TGuillerme) and Adam Kane (kanead[at]tcd.ie,@P1zPalu)

Image Source: Wikicommons

How Good is the Fossil Record?


One of the projects I’ve been working on recently has concerned diversity in the fossil record. In broad terms I’m looking at how diversity has changed over the last 540 million years, a period known as the Phanerozoic which starts at the Cambrian explosion and continues to this day. I want to try and understand what causes the periodic increases and decreases in diversity.

I’m not a palaeontologist, so this work has involved a massive learning curve in order to understand how we know what we know about the fossil record. What I’ve learned has led me to have an enormous respect for palaeontologists, but to also wonder whether some of the claims made on the basis of evidence from the fossil record may not be slightly overstated.

If we compared the fossil record to a court trial, I’d argue that the public perception is that the fossil record is rather like the court transcript: a full and complete record of the history of life on earth. Scientists outside the field of palaeontology probably understand that this is not true, and may liken it to more of a newspaper report on the trial: summarising, missing some details but the key facts are in place. The more I look into the fossil record, the more I think it seems like the hear-say testimony of an unreliable witness: heavily biased, missing important facts and giving probably erroneous information.

Before I get angry palaeontologists shouting at me I want to emphasise that that for short timescales or small areas I think the fossil record is brilliant and we can learn a lot about species turnover and ecosystem development. My concern comes from combining these short timescales and small areas and then using them to produce long timescale, global patterns of diversity. While it may seem like this is a sensible way to produce this data – who could possibly sample the entire earth for the entirety of the fossil record by themselves? – there are a number of so-called sampling biases that I feel make this approach potentially troubling. And while I have seen a great deal written about these biases and the efforts to reduce their effects, I have also seen research that makes me think these biases are impacting the data in ways we cannot predict.

So, after all that build-up, what are these biases? You’ll forgive me if I don’t discuss them all here, there are so many. Instead I’m going to split them into two groups and discuss these groups in very broad terms, focusing on the ones I think have the potentially biggest impacts on the patterns of diversity at the global scale. Proper palaeontologists have used a variety of different groupings, but I’ve grouped them into taphonomic biases and taxonomic biases. Taphonomy is the process of fossilisation but in this discussion it will also involve the process of the discovery of fossils. Taxonomy is the naming of species and there are a surprising number of biases that result from this seemingly simple process.

The most obvious taphonomic bias is that of the potential for fossilisation. It has been estimated that less than 10% of living species would end up in the fossil record and it would be heavily biased towards those organisms with bones or shells [1],. Many of the fossil diversity analyses are performed on molluscs as they have a good fossil record, so you might think that this would remove this problem. But the type of fossilisation affects how well an organism is preserved, if at all, and this affects molluscs just as much as other animals [2]. Plus, using molluscs assumes that they are a good model and representative of all organisms over all time which seems to be asserted without much evidence.

Another taphonomic bias is that of true sampling. At one end, not all environments are fossilised and at the other, not all fossil beds are studied by palaeontologists. In between, some fossil beds may be eroded over time and others may never reach the surface to be exposed for study. This leads to an effect called the ‘Pull of the Recent’ [3] whereby diversity increases towards the present day simply because there are more rocks available to study; the oldest ones have eroded, and the ones left are fewer in number the further from the present you go.

This sampling is not only biased in time, it is biased in space. There is a global trend in biodiversity, with highest levels at the equator and lowest at the poles, called the Latitudinal Diversity Gradient (LDG) [4]. This trend occurred throughout much, if not all, of the Phanerozoic and means comparisons of fossils between time periods must be from similar latitudes otherwise changes will say nothing about global diversity. While we may talk in terms of ‘global diversity’ it is often based on limited samples that may be predominantly from the tropics in one time period and temperate latitudes in another, yet this is rarely considered as a compounding factor when diversity is discussed.

Taxonomic biases are no less concerning. Naming fossils is more complex than naming living organisms, as the names must be based purely on the (potentially incomplete) skeleton. It is increasingly common to find living organisms that look identical but are genetically distinct species, and conversely organisms that look very different but are simply displaying phenotypic plasticity [5] yet fossils are named on the basis of their (potentially misleading) morphology which can significantly affect diversity estimates. Then there are problems of widespread fossils being given different names in different countries, or long-lived fossils being given different names in different geologic periods. Finally, there is the fundamental problem that the fossil record shows species evolving, and someone has to decide if and when a new species has formed and a new name applied. This will present itself in the data as an extinction and origination event, even when the population may not have changed in size or location.

These are just the very tip of an iceberg of biases. It may well be that palaeontologists have answers to all these biases and I have just failed to find the relevant literature. So far all I have found seems to be the claim (hope?) that all the biases will cancel each other out, leaving the true biological signal visible. I can’t be so certain. Indeed, my greatest fear is that the patterns of diversity are nothing more than the product of these biases and have little relation to the actual changes of diversity over the history of life on Earth. Reassurances to the contrary would be most welcome!

1. Nicol, D. (1977) The number of living animal species likely to be fossilised. Florida Scientist. 40, 135–139

2. Martill, D. M. (1998) Resolution of the fossil record: The fidelity of preservation. In The Adequacy of the Fossil Record (Donovan, S. K. and Paul, C. R. C., eds), pp. 55–74, John Wiley & Sons

3. Raup, D. M. (1972) Taxonomic diversity during the Phanerozoic. Science. 177, 1065–1071

4. Hillebrand, H. (2004) On the generality of the latitudinal diversity gradient. The American Naturalist. 163, 192–211

5. Bennett, K. D. (2013) Is the number of species on earth increasing or decreasing? Time, chaos and the origin of species. Palaeontology. in press,

Author and Picture Credit:

Sarah Hearne: hearnes[at]tcd.ie, @SarahVHearne

The Placental mammal saga; special summer double episode


As I wrote in a previous post last winter, O’Leary et al. added their oar into the Placental Mammal origins debate. For anyone who missed that episode, they argued, with the backing of masses of morphological data, that placental mammal orders appeared right after the extinction of non-avian dinosaurs (also known as the explosive model). This was in opposition to two other views based on DNA data which argue that placentals appeared way before (long-fuse model) or slightly before (short-fuse model) the Mexican dinosaurs had to deal with some meteorite… Again, have a look at this previous post criticizing O’Leary et al.’s paper and how they “forgot” to use (ignored?) state-of-the-art phylogenetic inference methods.

While I was away feeding mosquitoes in Finland – and wondering whether the lack of fishes for dinner was due to my poor fishing skills or the absence of fishes in the river – Science published two new episodes of the placental saga. Of the two, Springer et al. took the decision to properly criticize the methods of O’Leary et al.’s work. Amongst their detailed methods review, they particularly underlined the inaccuracy of O’Leary et al.’s explosive model; such a hypothesis would imply that the early placental mammals had a rate of molecular change similar to that of retroviruses. For over ten years it has been widely accepted that molecular rates (i.e. the number of DNA changes that are transmitted to descendants) vary among lineages through time. Knowing that, one can estimate these rates (or call it speed if you’re more comfortable with that) of evolution by calibrating phylogenetic trees with fossils. So, in this case, the amount of evolution needed to evolve from the late Cretaceous (~65 myr) non-placental mammals to the first placental mammals (~58 myr) has to be as high as evolutionary rates more characteristic of retroviruses to realistically explain this evolution.

Herein lies the eternal debate between palaeontologists and molecular biologists. The former base their estimations on the morphological changes they can see in the fossil record (even though some, as O’Leary et al. also include molecular data) while the latter calculate their evolutionary rate estimations on the molecular changes that they infer from living species’ DNA. Fundamentally, each method is valid but they are describing slightly different things ; palaeontologists infer the rates of changes between morphospecies (i.e. species that are separated based on their morphology) while molecular biologists study the rates of changes between surviving genetic pools (i.e. the populations leading to living species). My guess is that the true evolutionary history (i.e. the morphological and molecular changes of all the populations –fossils and living– through time) is to be found somewhere between these two approaches.

And that’s what I think O’Leary et al. demonstrated in their response to Springer et al.’s comments. Through a kind of a dodgy answer in reply to the technical points that Springer et al. underlined as the “retrovirusesomorph” rates, O’Leary’s team reran the analysis and found that yes, maybe the explosive model is not very realistic regarding the molecular data but neither is the long-fuse model regarding the palaeontological data. So which one should we choose? Hmmm, why not just go for the middle way with the short-fuse model? OK let’s do that – without calling it a short-fuse model though (they called it an “explosive model” in figure 2-B but to my mind at least, it’s getting closer to the short-fuse one).

So all that for what? Nobody can either deny O’Leary et al.’s amazing work nor claim that the long-fuse model is realistic; the consensual short-fuse model remains pretty well supported among both moderate palaeontologists and molecular biologists. However, I still cherish this paper because it shows how I think good science should always work; find the two extreme scenarios and then study the median one…


Thomas Guillerme: guillert[at]tcd.ie


Photo credit

Wikimedia commons

Dinosaurs are useless if they don’t go in trees!


I’d like to ask the question many paleontologists have to face when they (foolishly) venture out of their museum storage: “So you’re studying fossils right? But what will that bring to the people? A cure for AIDS?”. There are many possible answers from a punch in the face to more mature responses. But I was recently asking myself the question from a biologist’s point of view: “What can biologists really do with the fossil record?”. Well obviously, we can use it to recreate and understand the history of our planet (like in Nature last week) or to do use some nice methods in trying to understand ancient ecosystems. People even might feel lyrical and do some serious work on paleo-poetry! But all of these guys are paleontologists right? They live in their museums and only go out for a movie once every 10 years… How about the other biologists?

Think about it, when ever you’re studying any organism, it is obvious (thanks to this bearded ape) that they had a 3.5 billion year history behind them. Ignoring that might lead to a misunderstanding? As an example, I’d like to use my favorite PhD-presentation example: the crocodiles. When we talk about crocodiles, we automatically think about the few species of big lizard that live in rivers in the tropical/sub-tropical latitudes. But, after a quick look at the history of our planet, the only description that is more or less correct is “lizard” (archosaurians to be more precise). Crocodiles are composed of many species (8 genera today – soon to be 6 – but >70 in prehistoric times) that lived in rivers as much as in the sea, on the ground or even sometimes in trees and in tropical to temperate climates (remains of crocs were found in Normandy – France).

Well maybe that’s just because of this group. But if you think about it, many other groups have ecological or evolutionary features that becomes truly astonishing once you take into account their full history. For my PhD I decided, with Natalie, to look at this fun fact (life existed before yesterday and the people studying it don’t always focus on dinosaurs) through primates. My idea is to combine extant data based on DNA with extinct data based on morphology to have an integrative tree of all primate history. I agree that this sounds a bit too easy and naive, (the method is a bit more complex) and I’ll probably end up with something more humble. However I think the primates can be a good example to illustrate the point about the hidden diversity among extinct groups. The primate fossils are not dramatically different than the extant once (unlike crocs, there were no pelagic primates) but they still show some really interesting features, for the macroecology side, combined extant and extinct primates show massive variation in body mass in some groups (lemurs) but very few variations in others (tarsiers). Or on the macroevolution side, such an integrative tree could provide some further understanding to the old debate of primate origins! Well at least I hope so. For now I’m just comfortable with eating some burgers with a diet coke and a gun in a pickup truck while I’m scanning some primates in the Smithsonian Institution in Washington DC.

Thomas Guillerme: guillert[at]tcd.ie
Photo credit
Scott Hartman

Chronicle of a death foreseen


Why did Neanderthals go extinct while humans prospered? There are volumes full of speculations into the decline and fall of our burly cousin who last walked the Earth 30,000 years ago. Climate change may have reduced the large herbivores on which they depended for food. Humans may have inadvertently spread lethal diseases to them when we first came into contact. Perhaps the most sinister hypothesis is that we extirpated them in an ancient act of genocide (/speciescide?).

Researchers at Oxford now argue that Neanderthal orbit size gives us an insight into the reason for their downfall. They reason that, as Neanderthals had relatively larger eyes than humans, more of their brain was dedicated to visual systems. This was an adaptation to their habitats in the higher latitudes where light conditions were poorer. This came at a cost though because the evolved brain can’t be a master of all trades, there must be some tradeoff. In this case the authors propose that the Neanderthals suffered a reduction in their cognitive abilities.  This was significant because it meant that your average Neanderthal could deal with fewer social partners than a comparable human.

The impacts of this in the authors’ words, “First, assuming similar densities, the area covered by the Neanderthals’ extended communities would have been smaller than those of [humans]. Consequently, the Neanderthals’ ability to trade for exotic resources and artefacts would have been reduced, as would their capacity to gain access to foraging areas sufficiently distant to be unaffected by local scarcity. Furthermore, their ability to acquire and conserve innovations may have been limited as a result, and they may have been more vulnerable to demographic fluctuations, causing local population extinctions.”

But this proposal hasn’t gone unchallenged. Anthropologist Trenton Holliday says that by ignoring the relatively larger faces of Neanderthals the inferred larger visual brain region is mistaken. Another criticism comes from Virginia Hughes over at the Only Human blog. She points out that brains aren’t perfectly modular. So by comparing these idealised modules across species isn’t 100% informative. Perhaps Neanderthal brains were set up in a different way to process social information.

I think the visual system-cognition trade-off is something that could be easily explored in extant fauna. Think of related species that differ in latitude et voila a confirmatory or dissenting paper awaits.


Adam Kane: kanead[at]tcd.ie

Photo credit

wikimedia commons

You’re grounded!


Pterosaurs are the largest animals to have ever flown. Some species had wingspans exceeding 10 metres dwarfing the largest avian challenger. It must have been quite a sight to see one of these things blocking out the Mesozoic sun. But there have been niggling doubts about the ability of the larger representatives to fly. Will we have to re-evaluate our mental image of the Mesozoic and ground our pterosaurs?

Flight is no easy thing for an animal. It makes all sorts of demands on the physiology, morphology and ecology of the creature trying to take to the air for a living. With every added kilo a bit more lift has to be generated, for every extra wing flap more energy is required. Still, most pterosaurs look like they fit the bill. Their skeletons were heavily pneumatized and they had a hyper-elongated fourth finger from which they could support a membranous wing.

The problem arises when we look at the giant pterosaurs especially the Azhdarchidae family which houses the biggest species like Quetzalcoatlus northropi and Arambourgiania philadelphiae. One analysis gave a mass estimate of half a tonne for Quetzalcoatlus n., which would almost certainly render it flightless. Other researchers point to the terrestrial adaptations seen in this family and of course we can see many instances of birds who have become secondarily flightless. A size gap was pointed out where there exist small pterosaurs and giant ones but no intermediates which was said to mirror the pattern of flying birds and flightless ratites. Then there is the taphonomic bias seen in the fossil record whereby most of the Azhdarchid skeletons are found in terrestrial environments.

But not all palaeontologists are convinced by these arguments, pterosaur specialists Mark Witton and Michael Habib have taken each one of these lines of evidence to task and found them wanting.

Firstly, while most of the fossils have been found on land this doesn’t mean the animals were terrestrial, many bird species fly exclusively over land, so that bias is neither for nor against.

Secondly, the suggested size gap looks like an artefact in the fossil record which has been filled with intermediate forms.

Perhaps the most convincing piece of evidence in favour of flightlessness are the huge mass estimates. A half tonne reptile is going to struggle to get airborne. But this figure is beginning to look like an overestimate, the result of distorted fossils and inappropriate scaling techniques. A more lightweight figure of 240 kg looks to be more realistic when these biases are accounted for.

What of the terrestrial adaptations? Well, there is no issue with the animals being adept on the land while still being able to fly. Indeed the authors above argue that large Azhdarchids occupied the niche of modern day ground horn bills or storks both of which are well adapted to the land while still being able to fly.

In the end it looks like giant pterosaurs did take to the skies. Piecing together the mode of life of long extinct species is never easy but it’s not impossible.


Adam Kane: kanead[at]tcd.ie

Photo credit

Witton MP, Naish D (2008) A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. PLoS ONE 3(5): e2271. doi:10.1371/journal.pone.0002271