Posts Tagged 'evolution'



Issues on understanding evolution

A couple of things intersected over the last week or so that have had me thinking a bit more about evolution and how it’s presented. More specifically, I’ve increasingly noticed a phenomenon that seems to get little attention and might be worth a bit more consideration. In short, there do seem to be a good number of people who, for whatever reason, are really quite happy with the concept of evolution as a whole (species arise, natural selection happens, common ancestry etc.) but seem to profoundly misunderstand how and why it works.

It’s perhaps understandable that a lot of focus goes into winning over the people who don’t accept that evolution even exists, but we should not ignore those who are happy enough with the idea, but actually don’t understand it at all well. After all, they might well be vulnerable to misinformation or further misunderstandings, when in fact they should be the kind of people who would be resistant to such things. I’ve heard or come across all sorts of basic mistakes and misunderstandings like the idea that evolution is directed (or has some predetermined outcome), that mankind is all but inevitable, that evolution occurs at the individual level, that X is the exact and direct ancestor of Y and so on.

All of these things are the kinds of fallacies that creationists use to undermine evolution or promote confusion about how it really operates, yet these are also errors made by those who have no problem with the concept. While these mistakes are not ignored when it comes to public outreach in science, I do wonder if in part, we are paying too little attention to a sizable number of people who would benefit from knowing more and having a better understanding and appreciation of evolution, and likely be interested in learning more. We’re not talking about deep and complex evolutionary theory, merely some fairly basic concepts that should be easy and simple enough to explain quickly and effectively, the question is, are we doing that for the people who need it?

 

Variation and selection

Well hey, another little leftover from the Carnegie I should have mentioned before.

There are of course a multitude of ways of presenting ideas in museum exhibits. This one is not only well done (showing the natural variation present in a selection of specimens of one species alongside male and female differences and by extension a little of the diversity and variation seen between species) but has a little resonance for me as it combines two other displays I have seen and commented on before. Tokyo has a nice cabinet showing the diversity seen in a single species (mentioned here, but not shown I’m afraid) and Oxford commented on the diversity of beetles with this lovely effort.

In all three cases the message is simple, but a profoundly important part of biology as a whole and the mechanics of evolution specifically. Communicating that quickly, effectively, simply but with maximum impact and interest is a real challenge and whoever came up with these various cabinets deserves much credit for having done so.

Intraspecific variation

There have been a couple of posts on here before on this subject. A good long time ago now I put up a post on intraspecific variation and the implications for taxonomy, and I also had a post on variation in coat colour in deer. Fine though that was, colour is not the best example to use when talking about vertebrate palaeontology, some kind of nice osteological feature is what you really want.

And here is one – horns of the addax, taken at Marwell zoo. Horns can be notoriously screwy in captive animals and you can see whole herds of things like bongo with barely a one having the ‘normal’ horn shape for the species. While that effect is probably a bit at play here you can see variation in the curvature of the horns between the different animals, not to mention the one with a really screwy (and presumably trimmed) horn.

Plus, well, I like addax and hadn’t managed to include them in the zoo review.

The giant, feathered tyrannosaur Yutyrannus huali

So perhaps inevitably the fossil beds of Liaoning in China have coughed up yet another fascinating feathered dinosaur. Yutyrannus huali (which translates as the ‘beautiful feathered tyrant’) is big – as big as some of the Late Cretaceous tyrannosaurines with the largest specimen being around 9 m long and estimated to have weighted close to 1.5 tons. In short, this was big. And feathered. While they are not brilliantly preserved, they are clearly present in places and directly associated with the skeleton as should be expected.

There are a few interesting things about this and I’ll go over them in turn, though as ever the first port of call should really be the paper for the real nitty gritty. First off, the specimens themselves – there are three of them, so this is already a well known animal, and two are basically complete. There’s a lot of anatomy right there and yes, I have to confess, rather more than some other tyrannosaurs I could mention. Indeed two of them are preserved together, as a pair, which nicely hints at least (well, I’m going to say so) at the possibility of sociality (theropods being more social than previously suggested, how interesting?).  Multiple specimens are always great and animals this size being preserved at all are quite rare in the Jehol, so it’s pretty impressive we have three of them. They are also preserved in that psuedo-3D manner I mentioned the other day so there’s really quite a bit of detail there and they are not badly crushed or mashed (as you can see in the pictures below).

Now it is of course already known that tyrannosaurs were feathered, with the basal Dilong being preserved with feathers. The question is of course, did the bigger ones like T. rex have them? There’s been suggestions that they didn’t as they could overheat and there are hints of scaly, feather-less skin from impressions refereed to Tyrannosaurus. So while at least some tyrannosaurs certainly had feathers, and large ones certainly could have done, this is definitive evidence that they genuinely did. The size issue is of course interesting since indeed, very large animals tend to reduce insulation to avoid overheating (elephants, rhinos, hippos etc. are not that hairy and indeed elephants can struggle to keep cool). The obvious exception being animals that live(d) in cold climates like mammoths, and the researchers note that actually the environment Yutyrannus lived in was likely rather cooler on average than that occupied by a number of later tyrannosaurs, so this may indeed have helped them stay warm.

Below are some pictures of the various fossils. While you’ve probably seen a number of these before on all the other sides my insider contacts means I’ve been sent a few to use which were neither in the paper nor press release. So there’s something novel here for everyone, even if it’s not in the text.

Top image by Brian Choo (used with permission) and the rest courtesy of Xu Xing and colleagues.

Xu, X. et al. 2012. A gigantic feathered dinosaur from the Lower Cretaceous of China. Nature. doi:10.1038/nature10906

Heads and tails – Microraptor feathers

From Li et al., 2012

Much has been said about the recent Science paper reporting on the possibility, or perhaps rather probability, that Microraptor had iridescent feathers. So much so awesome, but there are, for me, other interesting things that are buried in the supplementary data to the paper that I’ve not seen mentioned so far (not that I have widely read coverage of the paper, I mostly just read the paper).

First off, as seen above, the idea that things like Microraptor and others (Anchiornis being the most obvious candidate) had some little crest of feathers on the head. As shown by the X-ray, pigeons have a very similar arrangement of feathers and yet it’s simply part of the natural contours of the feathers and their position. Basically the feathers really are preserved as they were in life, and that this isn’t anything odd or expanded but that the shape of the head (with feathers) would be very modern bird-like.

Secondly, the tail was noted to have two rather elongate streamers in the midline and this looked familiar but I couldn’t place my finger on it. Now I have it, it is, for me, really quite similar to what you see in European magpies. There’s an obvious tail fan there, but in the middle, the feathers are rather longer, though not *that* exaggerated. Given the implications for signalling advocated in the paper, I’d be intrigued to know if people have looked at these feathers alone in magpies and how they are used or if birds are affected socially when they are trimmed or absent – could be something there to look at one day.

From Li et al., 2012

Li, et al. Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science 9 March 2012: 1215-1219.DOI:10.1126/science.1213780

Arctometatarsal origins

A comment on my recent post about alvarezsaur arctometatarsals made me realise there was a bit more scope for talking about this issue of the origins of this structure. Arctometatarsalian pedes are known in tyrannosaurs, troodontids, alvarezsaurs, ornithomimids and oviraptorosaurs. In other words a pretty big selection of derived theropods have at least some taxa with this condition.

This begs the obvious question of whether or not this is homologous? After all, this could easily plot on a cladogram as originating before the tyrannosaurs and being maintained throughout the derived theropods only to be lost in therizinosaurs and droimaeosaurs + birds. However, there are two good reasons to think that this convergence and not homology with the characteristic being acquired multiple times.

First off are the details of the actual pes. Although obviously we would expect different lineages to adapt and modify such a structure independently, there are some very clear differences between quite how the middle metarsal is pinched and in which way by which of the surrounding elements. It’s subjective of course but they do look quite different in form.

Secondly and more importantly, the character is not shared by all of the taxa in those various groups and especially not basal forms. Early tyrannosauroids like Dilong and Guanlong don’t have it, nor does the basal alvarezsauroid Haplocheirus, and it’s not present in at least some early troodontids, ornithomimids or oviraptorosaurs. So it is not a simple plot of acquisition before tyrannosaurs and occasional lost, but instead more parsimonious to infer that it has been gained independently multiple times (each with a slightly different form) than been lost multiple times in all those basal forms (i.e. lost in each of Guanlong and Dilong and any other tyrannosaurs or even lost at the base and then acquired again) and been modified repeatedly along each lineage.

What has drive this convergence is likely the benefits of such a structure. Work on the functional morphology of such a foot suggests that it increases running efficiency and may also provide increased turning ability. In short, this is a feature of active runners, something that certainly matches at least some other anatomical specialisations seen a number of these groups.

Bits of Archaeopteryx

What’s a bit more Archaeopteryx between friends eh? After the ‘clearing house’ that was the last two posts, I’ve since found yet more photos of specimens that I have never used. This is the generally somewhat horrible to be honest Burgermeister-Mueller specimen, though while the head and body of this one are not great, as you can see here, the hands and feet are actually pretty good (though my pictures could be better).

Berlin Archaeopteryx

I have managed to get decent pictures of nearly every Archaeopteryx specimen on here at one time or another. For those who have missed out, there’s Daiting, Eichstaett, London, Bergermeister-Mueller, Thermopolis, the ‘new’ specimen, the ‘chicken wing’ (and a couple of others), and various ones in UV. One that has done badly as it were, is Berlin. The most famous of the lot and to date all I have shown is a grainy old image from when the leg feathers were still present. Finally though, here is a good quality photo of the whole thing.

Sadly for me, it’s not because I have been back to Berlin where this is now permanently on public display, but comes courtesy of Heinrich Mallison who kindly took this for me.

 

Guest Post: Dinosaurs and the latitudinal biodiversity gradient

Today Phil Mannion returns to the Musings with a guest post on his recent paper on dinosaur diversity patterns and their relationships to latitude. Take it away Phil:

The presence of a latitudinal biodiversity gradient (LBG), whereby species richness is highest in the tropics and declines polewards, is a pervasive pattern affecting the majority of life on Earth today, and was recognised by early naturalists such as Charles Darwin and Alexander von Humboldt (whose foundation coincidentally partly supported the research outlined below). Despite its near ubiquity (on both land and in the sea), the causes of the gradient are less well established, with numerous hypotheses proposed over the last fifty or so years. Most of these have been refuted, leaving climate and the distribution of area as the two most likely causes. Understanding the cause and evolution of the gradient is vital to predicting biodiversity loss driven by present-day climate change and explaining geographical variation in biodiversity; as such the fossil record offers a unique perspective on this issue.

Previous work investigating the deep time LBG focused on marine invertebrates – these studies tended to find support for a modern type pattern throughout the Phanerozoic (approximately the last 530 million years). Little prior work has been carried out on terrestrial species, but the few studies to look at the deep time LBG on land found no evidence for a modern pattern until after the Eocene (approximately 30 mya).

Along with colleagues from the UK (Roger Benson, Paul Upchurch, Richard Butler and Paul Barrett) and USA (Matt Carrano), we looked at the LBG in Mesozoic dinosaurs (including birds). Using a number of different methods to mediate for sampling biases in the fossil record, we found no evidence for a modern type pattern at any point in the 160 million year evolutionary history of Mesozoic dinosaurs; instead we found dinosaur diversity to peak at palaeotemperate latitudes (30-60° North and South). The consistency of this result across analyses for different time slices indicates that this pattern is not controlled by climatic fluctuations – evidence suggests that the climatic gradient was “flatter” in the Mesozoic than today (i.e. there was less of a difference in temperature between tropical and temperate regions) – but was instead driven by the amount of available land area in latitudinal belts.

Residual dinosaur diversity after controlling for sampling, plotted against non-marine area (NM area) and palaeogeographical reconstructions for the Late Triassic (bottom), Jurassic (middle) and Cretaceous (top). From Mannion et al., 2012

Given that living birds conform to the modern day pattern, a significant change must have occurred at some point in the last 65 million years. Evidence from molecular phylogeny (and work on fossil insects) suggests that this change occurred at the end of the Eocene (34 mya), following the strengthening of the climatic gradient and an increase in seasonality. As such, there is no evidence for a modern type LBG on land before the last 30 million years.

Mannion, P. D., Benson, R. J. B., Upchurch, P., Butler, R. J., Carrano, M. T. and Barrett, P. M. 2012 (Published online). A temperate palaeodiversity peak in Mesozoic dinosaurs and evidence for Late Cretaceous geographical partitioning. Global Ecology and Biogeography, doi: 10.1111/j.1466-8238.2011.00735.x

Mutual sexual selection in dinosaurs and pterosaurs

As of last night my latest paper has come out, coauthored with Darren Naish and Innes Cuthill. Those with access to the journal Lethaia can get it here. Believe it or not I’ve been juggling with the idea as to whether or not to blog about this for quite some time. This is, I think, the most significant paper that I’ve produced and it’s the product of literally years of work (though at least part of that was as a result of very difficult editors and referees at various times, this was started back in 2007!) and I’m really rather proud of it.
Then why not blog it? Well the short answer is that this is a long and complex paper and it ultimately deals with a huge range of difficult issues (and not in the length we’d have liked, it had to be cut down severely to fit the journal and we still incurred page charges). It touches at various times on pterosaurs, sauropod body size, various ornithischian lineages, theropod sociality, the origins of feathers among other themes. All of this means that it’s very hard to blog about and cover the salient points for a non-expert audience without writing thousands upon thousands of words and, well, I did that for the paper.

This is obviously counterintuitive for a blog that is effectively about science communication, but I can’t do everything all the time (I certainly haven’t blogged all of my papers of the last few years). Moreover, in my experience, a paper like this which rather stomps a bit over some much cherished hypotheses of people tends to attract huge number of comments along the lines of “but what about *this* contrived example!” which I can assure you gets very annoying when people won’t let it drop.

None of this means I *won’t* be blogging it at length. But I know it’s likely to be covered a bit elsewhere on the web and thus it’ll look odd that I’m not doing it right away and it seemed sensible to provide an explanation up front. What I will at least talk about it mutual sexual selection – it’s right there in the title and the abstract and is, I suspect, a concept unfamiliar to most, perhaps nearly all, readers. it is after all, something almost entirely absent from the literature on dinosaurs and pterosaurs, Darren and I could only find two other references to it ever and one of those was what we put into the Taylor et al. paper on sauropod necks and the other sprang from Portsmouth. So it’s something that’s only really just coming into the literature.

Sexual selection is probably familiar – the idea that some traits are selected for by the opposite sex and can drive the development of bight colours, crests. displays and all manner of other things. The obvious one that’s endlessly used is the train of a peacock, that makes the male look very different to the drab female. This is typically coupled with sexual dimorphism (again, like the peacock) where the male is bigger than the female and has the extra ornaments etc. and males compete for females, with the best ornaments males advertising their fitness through the size and quality of their fitness (though in some cases like jacanas, this is reversed with bigger females).

So far, so simple. Mutual sexual selection is simply an extension of this into both genders. Both males *and* females are ornamented (or rather, have sexually selected traits) and just as males are competing with other males for the best females, so too the females are competing with each other for the best males. This means that dimorphism is limited or even absent – both genders having such traits. This is in fact, well known for quite a number of bird species and the number of papers on the subject in living species is increasing in leaps and bounds.

In the paper we hypothesis that this may have been common in the ornithodirans. It explains (potentially) quite a lot and solves a couple of previous paradoxes about crests evolution and development. Critically it means that you *don’t need* dimorphism of a feature for it to be sexually selected – both genders can have a crest and it can still be a sexually selected feature. This needs testing, this paper does little more than lay out all the conceptual issues and evolutionary biology and ecology behind the hypothesis, but at the same time, I think we do have some pretty good support for our ideas.

But as ever, what really needs to happen is for you to go and read the paper! And yes, I do have a PDF if you want it.

 

HONE, D. W., NAISH, D. and CUTHILL, I. C. (2011), Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs?. Lethaia. doi: 10.1111/j.1502-3931.2011.00300.x

Psittacosaurus again

Psittacosaurus is a genus that has had much coverage on the Musings if only becuase there are so many specimens floating around. However, while I’ve at least made mention of it, the most important specimen had not really featured here before and so here it is (well a cast). This is the famous / infamous ‘filamentous’ specimen that was purported to show an ornithischian with something close to protofeathers. It caused a storm of controversy, partly because of the apparently illegal acquisition of the specimen and also because it was far from clear if these were filaments or not. Obviously the appearance of Tianyulong went a very long way to convincing people that this was likely for real and not just the remnants of a plant, what with that being an ornithischian covered in them. This remains then a most important and much understudied specimen – would kinda help if it turned up – anyone know where it is?

The horse (of course)

Sometime ago I covered the fantastic series of whale skeletons in the Tokyo Museum and how useful they were to show such a classic evolutionary series as forms adapt and change from an ancestral animal to one far more familiar to people that exists today. The Carnegie has a different version, but one no less often used in text books and websites to illustrate evolution, the origins of the modern horse. Here are a selection of skeletons and with some excellent signs pointing out key transitions etc. and showing how various features have changed. This is rather less dramatic than the changes undergone by whales of course, but then the increased familiarity of the subject makes it perhaps the better study. Either way, it’s great to see.

Incidentally, I’ll be talking museum signs and displays over the next few days. The Carnegie (yes, still) had a plethora of excellent signs and many of them covering things I’ve discussed before and so I want to revel in their excellence and make note of it all. More to come therefore, but in the meantime, here’s a couple of previous posts about museum signs and the like which might be of interest, and especially the comments in the first one:

Signs

An inordinate fondness….

National Museum of Science and Nature

The practice of palaeontolgoy encapsulated


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