Earliest theropod abdominal air sacs?

Skeletal pneumaticity is the presence of air within bones of animals. This is typically in the presence of sinuses (think of your face and your achey sinuses during a cold, caused by a build up of pressure in the air spaces), or in birds, when the respiratory system projects part of itself into the bones to invade and hollow them, typically seen in in many avian vertebrae and wing bones. In birds, their respiratory system is more advanced than those in mammals, with air flow being separated between oxygenated (the air breathed in), and de-oxygenated (used air being breathed out), while mammal respiration is less efficient mixing both oxygenated and de-oxygenated air.  For more background on pneumaticity and post cranial pneumaticity, check out my previous post on pterosaur pneumaticity (and the lightweight skeleton of birds.

In addition to birds, postcranial pneumaticity is commonly found in some animals in the fossil record, including pterosaurs, and non-avian dinosaurs. Sauropods often have highly pneumatised vertebrae, thought the help keep them light and facilitate movement of their massive necks, while some theropods have pneumatic vertebrae and even postcranial elements in some species. Traditional studies on pneumaticity have used just visual methods to identify pneumatic foramina and determine if elements are pneumatic, but more recently, scientists have started using CT scans to look inside the bones and determine if they are pneumatic. This allows us to see through any matrix present, and see where the foremen leads to, without destroying the specimen.

The presence of pneumaticity in theropod dinosaurs was originally thought to be something leading towards birds, as the efficient respiratory system is believed to be what allows birds to be so successful, allowing for better breathing during flight. However, the exact timing of the bird-like respiratory system has been unclear and controversial. A new study, lead by Akinobu Watanabe from the American Museum of Natural History, and published in PLOS ONE, looked at the presence of postcranial pneumaticity in Archaeornithomimus and other ornithomimosaur dinosaurs, a group of theropods not directly on the branch to modern birds. Using CT scans, they were able to show that Archaeornithomimus had pneumatic cervical (neck), dorsal (back), and caudal (tail) vertebrae, but there was no unequivocal evidence of pneumatic sacral vertebrae, although there were some possible pneumatic fossae. Watanabe et al. (2015) also looked at other ornithomimosaurs to look at the evolution of pneumaticity in this group, but unfortunately these specimens were studied without CT scans. They found that the cervical vertebrae of Nqwebasaurus (basal ornithomimosaur), Pelecanimimus, Gallimimus and Ornithomimus showed evidence of pneumaticity, while the dorsal vertebrae of Gallimimus are also pneumatic. They suggest that the sacrum of Gallimimus is also pneumatic, but without CT scans showing precisely where these foramina are going, it's hard to be sure.

Cervical vertebrae and CT images taken at specific points of Archaeornithomimus (Watanabe et al. 2015)

Now the important part of the paper - what does is mean for the evolution of pneumaticity in ornithomimosaurs? Compared to several other groups of non-avian theropods, ornithomimosaurs are less pneumatic. Basal members are less pneumatic (with just their cervical and possibly dorsal vertebrae showing evidence), while more derived members Archaeornithomimus, Gallimimus, and Deinocheirus may have independently evolved higher levels of pneumaticity, which is especially evident in Deinocheirus. Additionally, the presence of a pneumatic hiatus, or an area where the vertebrae appear not to be pneumatised between two sections that are, suggest the presence of distinct air sacs. In the case of Archaeornithomimus, the dorsal and caudal vertebrae are pneumatised, while the sacral are not, suggesting that ornithomimosaurs may have had distinct abdominal air sacs, the evolution of which has been contentious in theropods. If this is the case, this represents the earliest appearance of abdominal air sacs in coelurosaurian dinosaurs. The authors suggest that this may mean that pneumatic hiatuses have been missed before, without the use of CT revealing other pneumatic features.

This paper highlights the need for CT scans in fossil data, and the numerous questions that still exist in understanding the evolution of post cranial pneumaticity in birds, dinosaurs, and of course in my favourites - pterosaurs. As postcranial pneumaticity evolved in all of these groups, several questions about their evolution exist. Derived pterodactyloid pterosaurs appear to have had abdominal air sacs as well, so did they evolve first in a common ornithodiran ancestor, and were subsequently lost by ornithischian dinosaurs and other pterosaurs? Or did they evolve in a basal saurischian ancestor and pterosaurs separately? Or possibly they evolved several different times? We still don't know the answer.

Reference:
Watanabe A, et al. (2015) Vertebral Pneumaticity in the Ornithomimosaur Archaeornithomimus (Dinosauria: Theropoda) Revealed by Computed Tomography Imaging and Reappraisal of Axial Pneumaticity in Ornithomimosauria. PLoS ONE 10(12): e0145168. doi:10.1371/journal.pone.0145168

Where to publish?

As a student, choosing where to publish your next paper is extremely important in order to showcase your research and build your reputation. Perspective employers look at the journals you publish in to rate your research and decide how employable you are, which makes it very stressful making the decision.

So how do you decide? This is something I really struggle with. On one hand, I believe in the Open Access movement, and think that papers should be open and not behind a paywall. I also agree with the thought that impact factor is fundamentally flawed, and doesn't necessarily say anything about the quality of research. Often papers published in the highest impact journals are not the best scientifically, but are "sexy", so they make it in, while extremely important and excellent science gets published in lower impact journals because they may not be as sexy. While I don't feel the need to chase for higher impact factors, the more I talk to senior academics and post doctoral researchers, the more I am told that it is still important. Everything I've heard about getting a job later is that employers look at the journals you have published in, even if they maybe shouldn't.

I'm looking for a bit of advice, combined with giving a bit of my own, from what I've been told after talking to other people. Of course in palaeontology there are a few journals specifically for the topic, such as the Journal of Vertebrate Paleontology, Palaeontology, Acta Palaeontologica Polonica, and more. These are typically good for descriptions of new taxa, new localities, and more specifically palaeontology-related topics. Other journals such as Biology Letters, Proceedings of the Royal Society B, Journal of Anatomy, Journal of Evolutionary Biology are good for papers that have a wider interest than just palaeontology. Then there are open access journals such as PeerJ and Plos One that allow you to publish any aspect of palaeontology that you want, including a lot of data and supplementary material, which is extremely useful. For me, I think about what I'm trying to publish (do I have a lot of data? Is it strictly palaeontological, or is there a wider use for my work? Is it ground-breaking, or just a bit more data to add to an already painted picture?), the reputation of the the journals (more so than impact factor), and personal experiences with specific journals of myself or people I know.

I have a paper that I'm getting ready to submit, that is not sexy, but has some important data. I was planning on submitting it to a Canadian journal that is not high impact, but is well respected and they like publishing palaeo papers. Then I was going to submit it to a new journal, which is completely open (free to submit, and free to access), but after talking to some senior academics (including the editor of the new journal), I was encouraged that as a student I should not submit to any journals that are new and do not have impact factors yet. So my question is, what about submitting to new journals that are published by well known publishers like the Royal Society or Canadian Science Publishing?

What other advice to people have when deciding what journal to submit to? Especially keeping in mind that I'm a student and have a lot of things to think about... And advice for lots of other people reading as well!

And don't forget to do the survey!I've teamed up with Science Borealis, Dr. Paige Jarreau from Louisiana State University and 20 other Canadian science bloggers, to conduct a broad survey of Canadian science blog readers. Together we are trying to find out who reads science blogs in Canada, where they come from, whether Canadian-specific content is important to them and where they go for trustworthy, accurate science news and information. Your feedback will also help me learn more about my own blog readers. If you complete the survey, you will be entered to win a prize, and be given a high resolution science photograph.

It only takes 5 minutes to complete the survey. Begin here: http://bit.ly/ScienceBorealisSurvey

Dimetrodon is Bathygnathus? Or Bathygnathus is Dimetrodon?

While the west of Canada is known for Late Cretaceous dinosaur fossils, the east has a number of Paleozoic outcrops with some early terrestrial tetrapods. In 1845, before Canada was even a country, a fossil of an upper jaw and some teeth was found on Prince Edward Island, and was first described in 1854. As the second ever vertebrate fossil to be found in Canada, this specimen has had an interesting history.

It was first identified as an extinct 'saurian', then as a dinosaur, followed by a theriodont, and finally correctly identified as a sphenacodontid, a group of early synapsids (a group of tetrapods with no temporal fenestra, or holes, in their skulls, consisting of mammals today) which includes the famous extinct sail-backed reptile Dimetrodon grandis. It hails from the Lower Permian, 283-290 million years ago, and was called Bathygnathus borealis. The fragmentary nature of the fossil made it difficult to determine the exact affinities of this specimen. Over the years it has been studied by a number of people, and similarities have been identified with Dimetrodon, Sphenacodon, and Ctenospondylus, but the similarities have never been major enough to warrant an official change. That is, until now.

ANSP 9524 - type specimen of 'Bathygnathus' borealis (Brink et al. 2015)

Dr. Kristin Brink worked on Dimetrodon and similar animals during her PhD research at the University of Toronto (Mississauga) and studied the specimen which is now housed at the Academy of Natural Sciences in Philadelphia. Primarily working on tooth of these similar animals, she was able to study the specimen using CT scans and compare it to other sphenacodontids[1]. She re-described the specimen and underwent phylogenetic analysis and found some interesting results, including that dental characters appear to be extremely important in sphenacodontid taxonomy. Based on phylogenetic analysis of morphological characters, Dr. Brink found that 'Bathygnathus' borealis appeared as a sister taxa to Dimetrodon grandis, and nestled within 3 species of Dimetrodon.

Cladogram showing position of 'Bathygnathus' borealis (Brink et al. 2015)

'Bathygnathus' borealis has the same tooth count, denticles, and tooth roots as Dimetrodon grandis, characters only found  in D. grandis. Brink et al. (2015) concluded that 'Bathygnathus' borealis was actually Dimetrodon borealis, making this specimen the first and only Dimetrodon in Canada.

The interesting and very important thing about this paper is related to the the rules of taxonomic nomenclature and priority. Bathygnathus borealis was named 20 years before Dimetrodon, meaning that by the law of priority, Bathygnathus should have priority and replace Dimetrodon. However, Dimetrodon is a well known and very famous fossil and no one wants to lose that name. Exceptions are occasionally made when there is a strong reason to retain initial names, and they have started a case with the International Commission of Zoological Nomenclature (ICZN), the group responsible for taxonomic names and problems like this. If they succeed, we won't lose Dimetrodon, but gain a new species of 'Dimetrodon' borealis!

And don't forget to do the survey! I've teamed up with Science Borealis, Dr. Paige Jarreau from Louisiana State University and 20 other Canadian science bloggers, to conduct a broad survey of Canadian science blog readers. Together we are trying to find out who reads science blogs in Canada, where they come from, whether Canadian-specific content is important to them and where they go for trustworthy, accurate science news and information. Your feedback will also help me learn more about my own blog readers. If you complete the survey, you will be entered to win a prize, and be given a high resolution science photograph.

It only take 5 minutes to complete the survey. Begin here: http://bit.ly/ScienceBorealisSurvey
References
Brink KS, Maddin HC, Evans DC, and Reisz RR. 2015. Re-evaluation of the historic Canadian fossil Bathygnathus borealis from the Early Permian of Prince Edward Island. Canadian Journal of Earth Sciences 52: 1109-1120.

Survey time! Please take part :)

To my readers...

I've teamed up with Science Borealis, Dr. Paige Jarreau from Louisiana State University and 20 other Canadian science bloggers, to conduct a broad survey of Canadian science blog readers. Together we are trying to find out who reads science blogs in Canada, where they come from, whether Canadian-specific content is important to them and where they go for trustworthy, accurate science news and information. Your feedback will also help me learn more about my own blog readers.

It only take 5 minutes to complete the survey. Begin here: http://bit.ly/ScienceBorealisSurvey

If you complete the survey you will be entered to win one of eleven prizes! A $50 Chapters Gift Card, a $20 surprise gift card, 3 Science Borealis T-shirts and 6 Surprise Gifts! PLUS everyone who completes the survey will receive a free hi-resolution science photograph from Paige's Photography!  

It's a great chance for me to get feedback on who is reading my blog, and for Dr. Jarreau to get more detailed feedback about Canadian science blogs in general, but of course, you don't need to be Canadian to take part. Please take the time to fill out the survey, and you may even win a prize!

FYI I'm registered with Science Borealis as Liz Martin-Silverstone, so that is probably the name to use when they ask.

Thanks to all in advance!
Liz

To self-fund a PhD or not? That is the question...

I am a (partially) self-funded PhD student. As such, prospective PhD students often ask me if I would recommend going into a PhD without secure funding, which is a bit of a complicated issue. Doing a PhD self-funded has it's ups and downs, and pros and cons, which I'm going to try to summarise here, as it's something I think a lot about.

To start, I'll explain my situation a bit. As many of you know, I'm a PhD student at the University of Southampton in the UK, however, I'm originally from Canada, which complicates things. I have just started my 3rd year of a 3-4 year PhD on pterosaur biomechanics. As I'm not from the UK, yet doing a PhD here in the UK, funding has always been difficult. Before starting at Southampton, I had intended on doing a PhD at the University of Bristol, where I did my MSc. Unfortunately, I was unable to secure any funding, and was looking at the prospect of ending up approximately £80000 in debt at the end, assuming I would be unsuccessful of finding any funding (which, indeed, was an unlikely event). With this daunting prospect, I decided to try for a PhD at the University of Southampton, where my now supervisor was confident I would secure something. After interviewing fairly well, I ended up being given an offer that was suggested to be quite good for an international student: the graduate school would cover half of my tuition, and I would receive a Research Training Support Grant (RTSG) of an unknown amount (at least £1100 per year), and I would be responsible for the rest. No stipend, still responsible for about £9000 a year of tuition, and a lower RTSG than students funded through research councils like NERC. 

Seeming like a much better offer than nothing, I accepted, confident I would eventually manage to find some more funding. At the end of my first year, I successfully was granted an NSERC award from the Canadian science funding agency, a hearty sum of $21000 CAD per year. My supervisor was also able to secure some additional research funding for me in order to cover my CT scans (of course I chose a project that isn't cheap), and I've since managed to get some funding from external sources to cover travel or research trips (thanks to the Palaeontological Association and Geological Society of London, and one of my supervisors - Mike Habib). However, I have applied for far more than that (nearly 20 if I counted correctly, since my MSc, and I'm not telling you how many were successful). In fact I don't know of any other PhD student that has applied to the same number of grants/scholarships/awards as I have, and while I have definitely improved over time, it's still just as depressing when you get that "sorry, you weren't selected" letter. The reality is that as an international student, even if the university covers half of my tuition, I'm still responsible for £9000 a year in fees, which is barely covered by my Canadian scholarship, and I have nothing to cover my living expenses. In fact, if it wasn't for my husband's PhD funding (and now job) and some help from both of our fathers (thanks Dad and dad-in-law!), we never would have been able to make it work. 

This sounds pretty unpleasant and unappealing, so what are the pros of doing it on your own? There aren't a lot of advantages, but I would argue that there are some major ones. First of all, you don't have the same kind of pressure to finish. In the UK, PhD's are funded for 3 years, with the possibility of extending it to 3.5, but rarely 4. As I've started my 3rd year, this means most of my friends are aiming to finish by the end of this year, or the middle of next year. I, however, don't have that rush. I've been surviving without my living expenses being covered for 2.5 years now, and an extra year isn't going to kill me. I am able to focus on the problem at hand without massively stressing over getting it done by this time next year. The other advantage is that I don't have a funding agency breathing down my neck, directing my research. Because I am self funded, the project is more-or-less up to me. Of course my supervisors give me suggestions and help, but what I do and where I go with it is more up to me than those who have been given funding for specific projects. These two major advantages of left me pretty happy with my PhD project and where I'm going.

However, would I recommend it? Not unless you have something to fall back and catch you if you can't find funding. Don't go into it expecting to find full funding in your first year, especially if you're not from the country you're doing your PhD in. So many funding bodies don't provide funding to people from outside the UK/EU, and they don't give funding for tuition or living expenses. It's pretty easy to find funding to cover conferences or research expenses, but a lot harder to help out with your dinner and to put a roof about your head. 

There are also a lot of problems that pop up and that you wouldn't expect, and I can think of 2 examples of things that have happened to me. First of all, it makes the possibility of extensions a bit terrifying. If something happens to you and you need to suspend your PhD, you can get an extension to go beyond the normal 4 year limit. It may seem like a good offer, but it's a bit of a trojan horse - if you don't have funding, and are barely living day-to-day, that extra few months may kill you financially, and there is no funding agency to ask for help, even if it would help your project. Another problem I've had is funding for Open Access. I am a big proponent of Open Access publications. However, did you know that in the UK universities will only cover the fees if you are funded by a UK research council? I didn't... I've been able to get fee waivers for both of my papers published with PLOS ONE, but it wasn't easy. And I don't have the money to throw around for a PeerJ subscription either. It makes it just that little bit harder to do than for people who can just ask their uni to pay.

So, my advice? Don't start a self-funded PhD unless you know that you can finance it yourself if need-be. Everyone assumes they'll find funding later on, but it's really hard to get once you start. You might get lucky and get some, or you might not, so be aware of that before you start. And to supervisors and academics: for the love of all of us self-funded students, don't promise money that you don't have! I've heard countless stories of people starting with the promise of funding from supervisors that just doesn't appear. If you want a student that badly, find money for them without lying or promising something you don't have, even if you're doing it out of the goodness of your heart and are positive you will find money. Sometimes, you don't, so don't say it until it's in your hands! It's much harder to realise a year into a PhD that you can't afford it when no funding appears than to just hold off in the first place and wait for secure funding. And finally, if you're going to do it, make sure it is something that you truly want to work on and that you are happy with. Don't pay to do a PhD that you will end up hating. It is absolutely not worth it.

After posting this, I realised that I should really add this: I am fortunate because I am not fully self funded, but I know a number of people that are, with varying degrees of support. While I have some tuition covered, I still pay more than anyone else I know for a PhD (with the exception of one other self-funded person I know). Other people have fees waived, but less RTSG, and some still pay fees, or have no RTSG, or both, but none with a stipend. There are varying branches to the self-funded tree. and I can only truly comment on the one I am on: I have a fairly large amount of funding, but not nearly enough to cover my fees or living costs.

Any other self-funded PhD's out there who have comments, please leave them! I'd love to hear other people's opinions.

Skeletal mass in birds

I've spent a lot of time on this blog rambling about estimating mass in extinct animals, including talking about the "lightweight" skeleton in birds, pterosaur bone mass, and the likelihood of giant pterosaurs weighing as low as 70 kg. Now I'm going to talk a bit more about this problem, specifically looking at the relationship between skeletal mass and total body mass in birds, the topic of my most recent paper.

In 1979, a paper came out looking at the relationship between skeletal mass and total body mass in birds, which was remarkably similar to that same relationship in mammals [1]. Since the two groups had such a similar relationship, the same was to estimate the total body mass in pterosaurs, after estimating the skeletal mass using simple geometric methods [2]. Because mammals and birds are so different and far apart in the evolutionary tree, it was thought that a similar relationship between the two meant that other animals like pterosaurs would share a similar relationship. Of course, I'm interested in pterosaur mass, so these methods are interesting to me.

During my MSc, my supervisor Colin Palmer and I looked at the original 1979 study a bit closer and found some slight problems with it. First of all, while they sampled a large number of bird taxa, each species average skeletal and body mass was determined from just 1-6 individuals, with most of them being just a single individual. How can they know this is a normal average weight? Additionally, the original data were presented in a log-log scale, showing a nice tight relationship with little variability. However, when the data were plotted on a linear scale, significant variability could be seen. This made us more interested in the topic.

When I started my PhD, my supervisor Gareth Dyke told me about a big dataset that his friend Gary Kaiser had meticulously collected on over 700 bird specimens from the Royal British Columbia Museum, which included total body mass and skeletal mass for over 400 individuals from 79 species. This dataset has more individuals than the original, but fewer species, meaning we had 1-30 individuals for each species, giving us a much better picture of average mass and variation within a species. With some help from an undergraduate student Ria McCann, and a lot of stats help from Orsi Vincze, we started to look at this dataset and saw some pretty interesting patterns, which we recently published in PLOS ONE [3]. First of all, our new dataset turned out to result in a pretty similar relationship to the original study, which was good news. We also found that there was even more variability within our dataset than the original study, which isn't surprising with a large number of individuals per species. For example within a single species, the rhinoceros auklet, total body mass varied from 0.4-0.6 kg (approximately 33%), while skeletal mass were varied by almost a factor of two. At a total body mass of about 470-490 g, the measured skeletons weighed in from 26 g to 34 g. This is a large range for a single species. Total body mass ranged from just 256 g, up to 616 g.

Variation in body mass and skeletal mass in the rhinoceros auklet.

Of course, that range could be due to age, and we thought it may be possible that age would affect these relationships. Unfortunately, it can be difficult to determine age of a bird if it is found dead (as most of these specimens were), so the only age classes we could determine was whether the bird was within it's hatchling year, or above that. However, we found no statistical difference between the two groups, suggesting that this feature does not change ontogenetically, which was a bit surprising. We also looked at males vs. females, as it was suggested that this could change things. We know that female birds regulate the amount of calcium in their bones depending on what cycle of egg-laying they are in, as they use the calcium from their eggs to make the hard shells. Again, however, we found no statistical differences between the two groups.

Sexual variation between male (blue) and female (red) birds

One thing I was most looking forward to testing was if there were any differences between different flight modes. Birds that fly in different ways having different body set ups with slightly different morphological adaptations, like longer, more slender wings for birds that soar. But are their skeletons built differently? For example, do birds that spend more time on ground, so-called 'burst-adapted' birds like pheasants and ptarmigans, have more robust skeletons that are maybe less 'light-weight' than traditional bird skeletons? Well at least between the 3 main flight modes we tested (soaring, continuous-flapping, and flap-gliding), they are not different. Unfortunately, we didn't have a large enough sample size of burst-adapted flyers to see if they were statistically different. I'd like to look at this more as my hunch is they will be different. I'd also be interested in seeing how passerines would be different, as passerines use a type of flying that is referred to as intermittent-bounding, where they kind of hop through the air with intermittent periods of flapping and not. Our new data set didn't have any passerines in it, which is fairly uncommon since they make up a large number of modern bird species.

Different flight modes - blue = soaring, red = flap-gliding, green = continuous flapping.

But why is this important? Well going back to the original question about mass estimation, we found that these results were correlated with phylogeny. This means that for a group of modern birds, like Neornithes, this relationship holds true. However, as you move further from this group, the relationship is going to be less and less supported. So moving into groups with no modern representatives like enantiornithine birds, which are significantly different from modern birds, or non-avian theropod dinosaurs, this relationship is going to be less accurate. Finally, moving all the way to pterosaurs, which are the sister group to dinosaurs, this relationship may not yield an accurate result, which is something that we hinted to in my first paper on pterosaur bone mass estimation [4].

I think that using the more traditional methods of volumetric mass estimation is likely to be more accurate for pterosaurs, for this reason, rather than using skeletal correlates as is becoming more common. Unfortunately, that requires more complete skeletons and a lot more work. Pterosaurs have no modern analogues or close relatives, suggesting that skeletal correlates are not going to work. Jon Tennant wrote a great post on this paper as well over at PLOS Paleo if you want to take a look!

Another thing I'd like to point it is the dataset we used. Gary Kaiser and Carl Jonsson collected a large amount of data on these specimens, including measurements of various skeletal elements, most of which we didn't use in this study. We know that a lot more information can be used from this dataset and many more interesting studies can use it, and we have posted the data up on the PLOS One website as supplementary material. We hope that someone can use the data for more in-depth studies like this! Please share if you know someone who could use it!

References:
1. Prange HD et al. 1979. Scaling of skeletal mass to body mass in birds and mammals. American Naturalist 113: 103-122.
2. Witton MP. 2008. A new approach to determining pterosaur body mass an its implications for pterosaur flight. ZittelianaB 28: 143-158.
3. Martin-Silverstone E, Vincze O, McCann R, Jonsson CHW, Palmer C, Kaiser G, Dyke G. 2015. Exploring the relationship between skeletal mass and total body mass in birds. PLOS ONE 10: e0141794.
4. Martin EG and Palmer C. 2014. A novel method of estimating pterosaur skeletal mass using computed tomography scans. Journal of Vertebrate Paleontology 34: 1466-1469.

Exceptionally preserved Early Cretaceous mammal

There's an ongoing theme/belief in vertebrate palaeontology that if you want to work on Mesozoic mammals, you have to like teeth. This stems from the fact that a large number of early mammal or mammaliaform fossils are actually teeth, and the different species, genera, or even families are primarily distinguished from each other due to the features of their different teeth, and in particular their molars. This can be related to their exact dental formula (i.e. how many incisors, canines, premolars and molars they have), the number of cusps found on specific teeth, etc. In fact, many names of species or families come from the teeth: Morganucodon, one of the best known early mammals means "Glamorgan tooth", from the Vale of Glamorgan in Wales where it was first found, identified first by a tooth; and eutriconodonts have three ("tri") cones or cusps ("con") on their teeth, while many more end with "dont" or "don" or "dens", all different ways to say teeth.

This is not to say that these animals are known only from teeth. Morganucodon for example is known from many bones. Unfortunately, in the area of Wales where they are commonly found, the skeletons are all broken up and the bones are often broken, and always separated from each other (disarticulated), making it difficult to do more studies with them. However, once in a while, a very well preserved Mesozoic mammal pops up, which is where Spinolestes xenarthrosus comes in. Described this week in Nature by Thomas Martin and colleagues, this new mammal is very interesting.

Fossil of Spinolestes xenarthrosus from Martin et al. (2015).

Spinolestes xenarthrosus is a newly described eutriconodont mammal from the Early Cretaceous of Spain. The skeleton reveals a variety of functional features, suggesting Spinolestes was a proficient mover on land, and may have dug into the ground when necessary, but not necessarily adapted for this kind of lifestyle as it lacks the dental and skeletal characters typically associated with animals that habitually live underground. It had vertebrae similar to those found in xenarthrans (anteaters, armadillos and sloths), a condition that it evolved convergently (meaning the existence of this feature in both groups is not due to shared ancestry, but rather it evolved twice). While these are all interesting features, what is the most remarkable about this specimen is the soft tissue and integumentary structure preserved.

Spinolestes, amazingly, has a number of organs preserved including the outer ear, and possible lung, and liver tissue. The authors have even identified the presence of a muscular diaphragm. Spinolestes is characterized by having a mane containing long “guard hairs” along the neck and shoulder region, and longer hairs along the middle of the back and tail, making a hairy crest along the midline of the animal, while the rest of the body is covered in more typical shorter, soft underfur. In addition to these hairs, it also had “protospines” along the back of the hip-region, which are larger than hairs and formed by several smaller hair-like filaments merging together, similar to how spines are formed in modern mammals like hedgehogs. These features in combination show that mammals evolved this covering of a softer undercoat, denser and thicker guard hairs, and stiffer spines already in the Early Cretaceous, relatively early on in mammal evolution, a feature that is still seen in mammals today.

Lifelike reconstruction of Spinolestes xenarthrosus by Oscar Sanisidro

Martin T, Marugán-Lobón J, Vullo R, Martín-Abad H, Luo Z, Buscalioni AD. 2015. A Cretaceous eutriconodont and integument evolution in early mammals. Nature 526: 380-384.