Monday, 29 February 2016

How old is that dinosaur?

One important aspect of palaeontology is identifying the age of the specimen we are describing. Exact age is generally not possible to know, but relative age (e.g. hatchling, juvenile, sub-adult or adult) can often be worked out using a number of different techniques. It can be important in taxonomy (we try not to name new species off of juveniles unless they are clearly different), understanding growth (how did that big dinosaur make it to that size?) and also aspects of ecology and evolution of the group.

However, telling what age it is can be difficult, and in fact, different methods can give different signals. This question was addressed in a new study by Hone et al. (2016), using dinosaurs as an example. So how do you tell what ontogenetic (age-class) stage the fossil in question is from? There are a number of different methods we can use, some of which are described in this paper. At first glance, relative age can often be determined if there are any structures present that are typical of sexual display structures (i.e. crests, horns, and frills). The more developed these are, the older the animal is. Relative size is also often a good indicator - chances are the larger individuals of a species are going to be older than the smaller one, without other features indicating sexual dimorphism, sexual immaturity, etc. Fusion of elements can also be used, such as relative fusion of skull bones or the neural arch of vertebrae since fusion of bone typically occurs later on in an animal's life, when the animal is no longer growing rapidly. Rapid growth can also be looked at in detail through histological sampling of bone tissue, and general bone texture can also give an idea of the relative age of the fossil.
From Hone et al. 2016

But what happens if you have a species that appears to be osteologically or skeletally immature - it has unfused bones or is still rapidly growing - but has a well developed crest and is of large size? This brings in another issue all together - the difference between skeletal maturity and reproductive maturity. Hone et al. (2016) suggest that in palaeontology, we tend to under-age our material. Non-avian dinosaurs were typically described as juvenile or sub-adult when they may have in fact been sexually mature. In the modern world, we consider animals to be adults when they reach sexual maturity (aside from our own species, which we make up our own rules for). A dinosaur can be a sexually mature adult before attaining all of the features that define its species.

Hone et al. (2016) suggest that when trying to age a fossil, overlapping criteria is needed. In order to be sure of your identification, use as many of the ageing techniques as possible. This is not a surprise, nor is it particularly new as science works best when you get the same answer using different methods. However, this is particularly difficult in palaeontology. The specimen may be particularly incomplete or poorly preserved, making things like size, sexual features, or bone fusion difficult to determine. Or, this may be the only specimen you have of that species, which makes determining relative size compared to others impossible.

Even with these problems, it's true that we do probably need to do better at our definitions. There are a number of definitions of growth stages out there, and they are a bit 'wish-washy' sometimes. They also suggest re-defining the words "adult", "subadult", "juvenile" and "embryo" when it comes to dinosaurs, creating a new standard going forward. Unfortunately though, we are as good as our samples, and there isn't a whole lot we can do about the state of the fossils we find!

Hone, DWE, Farke, AA, and Wedel, MJ. 2016. Ontogeny and the fossil record: what, if anything, is an adult dinosaur? Biology Letters 12: 20150947.

Monday, 15 February 2016

Why should we fund palaeontology?

There has been a disturbing trend in the last few years by government funding organisations to both decrease the amount of funding for science, and to put more of a focus on funding science with obvious applications or money-making outcomes. Last year, the Government of Canada announced a new federal budget that emphasised science funding on projects that are joint with industry and applied research. This pulls money away from pure science and research which was already losing money over the years. There is a possibility that that may change now that Canada has a new, science-friendly government, but nothing is going to happen immediately. Moving to the US, just this week it was announced that NSF (National Science Foundation) grants would require "national interest", and they would only back things that they deemed to fit this category, mainly things like improving health or defence, or anything else that specifically and clearly benefits the people. Now I'm hearing rumblings that NERC, the Natural Environment Research Council of the UK is moving into the "applied science" category, and decreasing funding for pure science (although I haven't seen an official article saying this, just general agreement amongst scientists).

In particular, as a palaeontologist, this is problematic. Palaeontologists constantly struggle to emphasise to the public why our science is important. There are 2 aspects of palaeontology that can easily be considered 'applicable' or 'important' that first come to mind - fossil fuel exploration and climate studies, both of which use a lot of fossils, and have clear applications today. But most people don't understand why things like finding new dinosaurs or modelling pterosaur flight or understanding how feathers evolved is something they should be paying for. To the majority of these government funding agencies, palaeontology is not worth funding because they can't come up with an application for how many dinosaurs existed during the Jurassic.

However, there are several reasons why I would argue palaeontology is important. Just a few of them are discussed below:

  1. First of all, palaeontology and the study of fossils is what has led to a significant amount of modern knowledge, like understanding extinction and evolution. If scientists in the 1800's had not started to wonder about these large bones that were nothing like any modern animals that kept being found, our understanding of these may be completely different. 
  2. In terms of extinction, it's especially important in our understanding of extinction events - what animals can survive massive environmental changes like bolide impacts or significant temperature changes? How does this affect us in the future? To a non-scientist, looking at the species present in the Late Cretaceous before the bolide impact may seem useless, but to us, we see an opportunity to understand how the world change in these big events.
  3. Understanding the past helps us understand the present and maybe get an idea of the future. This may sound like complete crap to some people, but it is true. We constantly use animals and plants today to get inspiration for useful things today (e.g. gecko foot adhesion, velcro from barbs on plants, or research on spider silk properties). But modern organisms are just a small fraction of the number that have existed since the first multi-cellular organisms, and fossils provide us with a large number of features or morphologies that we can't see today. It is possible to use fossils for these kinds of applications as well, from looking at modern hydrodynamics questions by using fish and plesiosaurs, to flight questions using pterosaur wing structure
  4. Kids (and adults) love palaeontology. Some might consider this is a bit of a soft reason, but I think it's still important. Palaeontology (in particular, dinosaurs) get kids (and adults!) into science. They get people's imagination going, and they get people, especially kids thinking. It's hard to get your child to read a particle physics book, but get them to sit down with a book on dinosaurs, and they have no idea that the whole time you're teaching them science. It encourages them to understand evolution, extinction, biology, biomechanics, and a number of interesting aspects of science, while also encouraging their creative side with drawings, story-telling, etc.
There are several more we could discuss of course. A big one being that palaeontology (and all aspects of science really) are just interesting, and therefore shouldn't be any less funded than other sciences. Understanding our history and the Earth isn't any less important than detecting a Higgs boson or building a quantum computer. Primarily, I think one of the main reasons for the importance of continuing palaeontology-based research is that we can't predict what will be important. Who knows what next dinosaur find is going to be important in 20, 50, or 100 years? Some things we learned 200 years ago are still significant today. And some fossils we discovered 100 years ago are now being studied in a different light for different purposes. When you go out on a fossil dig, there is no guarantee you are going to find something at all, let alone something amazing, but if we stopped going out all together, we would certainly never find anything. If we stopped studying fossils, who knows what we would miss? As we get more sophisticated technologies, palaeontology is constantly evolving. We can now study things like the colour of fossils by looking at small cells previously undetectable, the internal structure of fossils using CT scans, and details of animal locomotion using sophisticated computer modelling techniques. Who knows what we will develop next and what we will learn from it? 

People tend to think there are no relevant applications to (especially vertebrate) palaeontology, but I completely disagree. There are several applications, and who knows what we will find later. I don't think anyone predicted 200 years ago when the first pterosaur was found that they would be look at to make flight suits one day. What's next? 

Sarah Werning did a great post on this same topic a few years ago if you want to read some more. And keep the ideas coming if you think there is something else I forgot to mention.

Thursday, 11 February 2016

Misidentified fossils - Turtle edition

My initial title for this blog was "Things that people thought were interesting fossils but turned out to be turtles". Of course, I don't mean that, I just have had a particularly frustrating few months reading the same undergraduate projects on turtle evolution, so they are not my favourite at the moment.... However... in the last few years, their bones seem to be popping up as being identified as other animals, which is something I found a bit amusing.

Mistaken identity 1 - the Flying turtle

The first time I became aware of this was something that I was actually involved in, and a case known to pterosaur workers as the "flying turtle". Last year, a new pterosaur was named from the Maastrichtian Transylvanian Basin of Romania, where I've had the opportunity to work. This pterosaur was heralded as being an "out of place, out of time" pterosaur [1]. Described as 'Thalassodromeus sebesensis', from the Oarda de Jos locality, near the town of Sebes, this was the first Thalassodromeus specimen found outside Gondwana, the southern supercontinent present during the Mesozoic after Pangaea broke up. This was described in the paper as an extremely important find - not only did it massively increase the geographic distribution of this genus (the only other specimens are known from South America), but it also more than doubled the temporal range of the group, giving it an additional 42 million years, where no thalassodromine fossils had been found. The discovery of this genus in Romania was thought to suggest it was a forest-dwelling animal, and gave evidence for the endemic island fauna of the Hateg Island during the Late Cretaceous. The authors also made some extraordinary claims about muscle attachments and soft tissue crests that could have been used as a rudder in flight, an idea that has always been contentious (and generally not accepted) by pterosaur workers and aerodynamicists alike. Therefore, this creature was exceptionally interesting.

The problems began when looking at the fossil itself. Known from just one small, thin, sheet-like bone, 'Thalassodromeus sebesensis' is not the most convincing pterosaur fossil. It was described as being part of the crest, yet no pictures are provided showing how it would have sat in the animal. Looking at the pictures, I still can't see how this is supposed to be any type of crest, and I can't quite put it on a pterosaur skull. When the paper came out, it was immediately scrutinised by pterosaur workers from around the world, me included. No one was convinced (even non-pterosaur workers were suspicious) by the pterosaurian identity of the specimen, let alone the extraordinary claims of the Laurasian Thalassodromeus that used it's head as a rudder. What did we think it was? A turtle. To be exact - part of the plastron of Kallokibotion, a Maastrichtian turtle commonly found in Romania. And this was agreed on by a number of turtle workers as well, not just pterosaurologists (as Mark Witton would say). We published this response not long after the initial paper came out [2], which was swiftly responded to in turn. The initial authors still disagree with us, but I don't know anyone else who thinks it's a pterosaur, so that's ok. If you want to read more about this story, you can check out Mark Witton's blog post, which he wrote when our paper came out, as well as his follow-up on the response to our paper, which was quite controversial... 
Above: plastron of Kallokibotion, with outline showing where the 'Thalassodromeus sebesensis' (Below) specimen would fit from Dyke et al. 2015. 

Mistaken identity 2 - Giant raptors!

Ok to be fair, this one isn't the entire specimen, just a little bit of it, and it doesn't change the story really. At the end of last year, a new species of giant dromeosaur was described from the Hell Creek Formation of Montana - Dakotaraptor steini [3]. This find was significant as it was the first giant raptor from the Hell Creek Formation during the Late Cretaceous, and it had clear evidence of feather quill knobs on the ulna, the first direct evidence of feathers on the forelimbs of large dromaeosaurids. The existence of feathers on the forelimbs of a giant obviously not-flying dinosaur further supports the thought that feathers did not evolve specifically for flight, which some people have argued in the past. The new species was described from a partial associated skeleton and some additional material, including much of the forelimb, some hindlimb elements, some vertebrae, and the furculae, AKA the wishbones.

Now the difference with this find is that it was named from a significant amount of material, and most of it is just fine. However, it's now been shown (just a few days ago by Victoria Arbour and colleagues) that the so-called "wishbones" of Dakotaraptor steini are actually part of the entoplastron of a trionychid turtle [4]. To be fair, looking at both papers, I can see how these could have been confused, especially since I don't work with turtles. Fortunately, in this case the initial authors appear to accept their mistake in an article written by Ed Yong. This is science at it's best! Science works better when we can admit our mistakes and move on.

Figure 1 from Arbour et al. 2015 showing where the entoplastron is found in trionychid turtles (A-D), and the "furculae" in question of Dakotaraptor (E-G).

Of course there are lots of examples of fossils being misidentified. It's bound to happen when you're dealing with often fragmentary or distorted material, but these two examples of turtles mistaken for some extinct reptiles within the same year stuck with me. I've been asking for other examples, and apparently some other things like T. rex and ankylosaur bones have been misidentified as turtles in the past (thanks Dean Lomax for sharing that), and even lungfish tooth plates were thought to be turtle shell (thanks to Graeme Lloyd for that), but I wasn't able to find any information about any of those. The interesting thing is that those are examples of people thinking they were turtles because they had never seen anatomy like that (these are from before dinosaurs and lungfish were properly understood), while the recent examples are actually turtles that are described as something else. The important thing to remember is that this is not uncommon. It happens to lots of people. The best way to avoid this is to avoid describing particularly fragmentary or poorly preserved material, and to avoid naming things if you aren't sure, as that is much less likely to be a big deal. But we are palaeontologists who like name things...

Anyone have any other examples of things that are actually turtles? Or other amusing fossil mixups you want to share?

Since the original post, I've had a few other examples pointed out to me. David Evans showed me an example of some turtle phalanges originally described as troodontid pedal phalanges from Mexico, which were the only troodontid fossils known from the Cerro del Pueblo Formation, leaving no known troodontid material from this formation (see Evans et al. 2014). I was also reminded of one of the big examples of dinosaurs being mistakenly identified as turtles - Therizinosaurus cheloniformis (thanks to Logan Orlowski for pointing it out in the comments below). This bizarre dinosaur is known for it's large claws (almost 1m long), which were originally thought to belong to a turtle-like reptile. With only the arms known, it was thought that the claws would have been just for something like harvesting seaweed in the oceans. However, we now know this is a dinosaur, and the species name cheloniformis comes from this misinterpretation, meaning 'turtle-formed'.

1. Grellet-Tinner, G. and Codrea, V.A. 2015. Thalassodromeus sebesensis, an out of place and out of time Gondwana tapejarid pterosaur. Gondwana Research 27: 1673-1679.
2. Dyke, G. et al. 2015. 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/ Gondwana Research 27: 1680-1682.
3. DePalma, R.A., et al. 2015. The first giant raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation. Paleontological Contributions 14: 1-16.
4. Arbour, V.M., et al. 2015. The furculae of the dromeosaurid dinosaur Dakotaraptor steini are trionychid turtle entoplastra. PeerJ 4:e1691.