Posts Tagged 'taxonomy'



Taxonomy never stops

It’s hard to tell if this is a misconception about taxonomy as it never seems to even be mentioned conceptually, but I suspect it is one, or at least is never even thought about. Taxonomy quite simply does not stop with the naming of a new species. While this is perhaps the most obvious, and arguably most important, aspect getting a new species named is just the start. Now I’m sure that most readers by now will be familiar with the various arguments about whether or not individual species are valid and genuinely different and the issues caused by different species concepts.

However, the recent post on the problem with undiagnostic types masks a more serious issue. Even the best type specimen and a good solid description and diagnosis is often only the start of a species’ taxonomic identity and work for the taxonomist. Taxonomy never really stops.

We’ll keep things overly simple but imagine we find a new species of a brand new mammalian family. It’s some kind of carnivoran with blue fur and giant fangs. That makes it nice and easy to diagnose – blue, big fangs. Then another new species turns up with is also blue and has no fangs, each is clearly different. But what happens now if we get a light blue one with no fangs and a darker blue one with fangs. These are still different, but our original definitions need to shift to take this new information into account. We can’t just go with ‘blue’ but need ‘light blue’ and ‘medium blue’ and ‘dark blue’. So not only do we need to be careful with the descriptions of our new species, but we also have to revise the definition of the original ones too. So even if they are valid taxa and have good descriptions and types, our definitions need to be corrected in the light of new information. Discovery of alternate colour morphs, tooth variation, other new species etc. will only add the need for more refinements.

And this is why taxonomy never stops. All that new information from ontogeny, variation, new analyses (DNA, interbreeding, behaviour etc.) will help to redefine and refine a species’ identity, and new discoveries of new taxa will complicate this further. All of this must be weaved together correctly and that takes time, skill and a good understanding of the situation. Some surprisingly famous species have poor or out of date or problematic definitions and these only get more complicated as time goes on. Calling something Linheraptor or Limusaurus and everyone agreeing it is new is really the start, not the end.

Typical Type Problems

Returning to the theme of Archaeopteryx in its 150th anniversary it seemed a good opportunity to mention type specimens. I’ve generally steered clear of these in the past since I suspect most readers have a general idea of how things work and what types actually are and because I really didn’t want to sink deep into the depths of lectotypes and so on. However, there is a more common problem that Archaeopteryx can illustrate well so let’s crack on with that.

Type specimens in general are given special recognition in taxonomic work – these are if you like the ‘definitive’ specimens: the ones that stand out as being the recognised ‘identity’ of a species. As discussed in the ‘morphological species concept’ post, species can have several different definitions and there are various ways of defining things. In order to make sure everyone is talking about exactly the same thing, type specimens are erected to provide that literal physical basis of identity. Among types, the holotype is the most important. This single specimen is the one and all references to species identification should ultimately come back to the holotype.

For most of biology this is fine. You go out and find a new bird species say, collect some specimens, sort through them and when you describe it you name a holotype and maybe a few paratypes or whatever. You have the luxury of a whole set of specimens to pick through and can make sure your holotype really is typical and complete and contains every bit of information you think in should.

In palaeontology of course you generally don’t get a choice. Even if you are lucky enough to discover multiple specimens when finding something destined to be a new species, it’s unlikely that you’ll get a single and nice complete adult animal in good condition. Holotypes are almost inevitably incomplete, or crushed, or have key parts not clearly visible or who knows what and of course some are really based on very little material indeed – as little as a single bone. There’s nothing wrong with this really since if that’s all you have, that’s all you have. You can’t assume you’ll ever find another specimen of the same species (and that may not be any better than what you have already) so you have to go with what’s there and if it’s distinct and diagnosable then it should be named.

However, things can be distinct and diagnosable at the time and later loose that title as new discoveries show that what had appeared to be unique turn out to be common. On occasion though things can be pretty much undiagnostic to begin with. Enter Archaeopteryx stage left.

When it was first named, Archaeopteryx was just a feather (photo here on Pick and Scalpel). For all the famous specimens that attract all the attention, the original name was erected for a single bit of integument. Now arguably this was diagnostic in that there were no such things as Mesozoic birds at the time. I’m inclined to disagree with this since a separation of time and space is helpful to help separate out species, but hardly concrete evidence of genuine difference. In any case the rapid discovery of ‘real’ specimens of Archaeopteryx, and other birds, means that the feather is undiagnostic. There’s not really anything there that can be genuinely shown to be different to any other fossil feathers, or indeed those of many living birds. As a side problem, not only is the feather not diagnostic, but it’s also the holotype specimen.

That actually means that in theory at least, we don’t know what Archaeopteryx is. Or to be more specific, we don’t have an official holotype that is diagnostic. In practice of course we have important and complete specimens like those of London and Berlin that everyone accepts are members of this species and are distinct and diagnostic, so while this does need to be sorted out (and indeed the wheels are very much in motion on this) it’s not a huge problem. But it does provide an obvious illustration of these problems. I doubt there’s anyone reading this who doesn’t have a good mental image of what Archy really is, but I doubt that is just a single small feather, though technically, it should be.

My thanks to Paul Barrett for some info and fact checking on the status of the feather as holotype, Paul is part of the petition to get the London specimen designated as the new holotype.

The imminent death of taxonomy

I’ve commented before on the slow and painful death of taxonomy in science and the issues this is likely to bring in the long run. Fortunately it seems that this is finally starting to be picked up in the wider world and that this may get a little attention. Case in point being this rather good article on the subject which I can highly recommend (thanks to Taissa Rodrigues for flagging it up).

The only thing I’d add is that they seem to have overlooked what, for me, is the biggest problem. Species are inherently hard to identify and sort out properly. And so while an absence of taxonomists does mean we can loose species without knowing they exist or have real problems understanding biodiversity and conservation, the real issue is far more fundamental. If you do not know what a given species is, or it is not defined properly then *any* research based on that in any way is fundamentally undermined. You simply can’t practice biological research effectively if your most basic unit of study is questionable. Try doing a phylogenetic or ecological analysis when it’s not certain which specimens in your lab belong to species A or B, or even Q. Taxonomy is the absolute bedrock of biology and without it, the foundations of our research are going to be awfully shaky.

 

 

‘Pterodactylus’

This is Pterodactylus. Well, it was. It’s now called Scaphognathus and for those who know, it’s really not even very close to Pterodactylus as pterosaurs go (for a start, it’s a non-pterodactyloid) with a positive hatful of characters that clearly separate the two.

Of course taxonomic revisions are a constant theme of palaeontology, but this would seem to be a rather extreme case. Part of this of course is down to the age of the original specimen (the photo above is of a cast), consistent taxonomy is hardly at a peak now, so back in the early 1830s, dramatic lumping of this kind can hardly be considered a huge sin in hindsight. However, this is also a good demonstration of a far more common issue in biology as a whole: the more data you have, the harder it can be to sort out your taxonomy as previously distinctive characters can turn out to be less useful that originally thought.

Consider the pterosaurs. When the original Pterodactylus specimen turned up, it was obviously completely different to anything else then known. You could instantly distinguish it from any other vertebrate by the wing finger alone, let alone anything else in the skeleton. It was then perhaps not a surprise that the next few pterosaurs to appear, like Scaphognathus, despite some obvious differences, were put into Pterodactylus based on their even more obvious similarities  – these were, after all, obviously pterosaurs. However, once it became clear that there were some important differences, as well and the similarities, then thinks like Dimorphodon and Scaphognathus were separated out into their own genera. This is an extreme example, but the principle is the same and constantly resurfaces.

Even the best taxonomic work and definitions can eventually crumble under the weight of new data, and if the original was also based on rather poor material or what turned out to have little going for it apart from characters that are no longer unique, then still more problems will inevitably arise. Thus what this ultimately boils down to is the fact that taxonomy is always going to be an ongoing process. Not only does every new taxon need to be described and diagnosed, but a large part of the time, this has a knock-on effect meaning that other things now also need to be revised or redefined as a result of the new information. As I have lamented before, taxonomy as a field, both in biology and palaeontology seems to be every dwindling as money is funnelled into for ‘sexy’ subjects, despite basic taxonomy being the absolute foundation of all biological research and this underappreciated field can only cause problems if this trend continues.

Introducing Bentonyx

Very longtime readers will know that one of my first papers (and indeed posts) was on the rhynchosaur Fodonyx. Rhynchosaurs are archosauromorphs – reptiles that lie just outside the archosaurs and thus this representes one of the Musings’ rare departure from that group despite this being a totally artificial and near-random name anyway). Anyway, the erection of the name Fodonyx was based around a new skull and some other postcranial material that was recovered from several sites around the south of England. The paper was originally part of my PhD thesis, and my supervisor, Mike Benton, helped nurture it to publication.

Mike is well known in the palaeo community and the University of Bristol (mostly through Mike) has handled a huge number of people through their masters, PhDs or postdocs to the point that there seems to be someone just about anywhere if you look. I know of people working in or are from Australia, France, Germany, China, Japan, the US, Canada, Spain, Italy, Ireland, the Netherlands, South Africa, Mexico, Brazil, and beyond. Mike is also perhaps the world expert on rhynchosaurs and worked on them for his PhD under Alick Walker. There are really quite a few of these critters in the UK and despite having a global distribution, the UK has been a bit of a centre for rhynchosaur research as a result.

Back in January of 2009, Darren Naish wrote this on his blog, while talking about rhynchosaurs in general “Someone should definitely name a rhynchosaur taxon Bentonyx one day. Alas poor Mike, at the moment his only patronym is the procolophonoid Kapes bentoni”. Mike for all his plaudits has done rather badly for taxa (palaeo greats generally get something named after them at some point and generally by one of their students). This rang bells in my ears as I had had similar thoughts myself, but knew I’d probably never go back to rhynchosaurs. So I did the next best thing and mailed Adam Yates and Max Langer – old colleagues and ‘Bentonites’ who work in South Africa and Brazil respectively where rhynchosaurs are often found. I mentioned that this was a good idea and if either of them happened across a new rhynchosaur then naming it after Mike was the obvious way to go.

Max replied promptly with one of those ‘funny you should mention it’ e-mails. He and his PhD student Felipe Montefeltro had been looking at Fodonyx and thought that actually the separate skull might belong to a new genus. Max took on the challenge and roped in most of the world’s few rhynchosaur researchers and together we produced a paper, out today, naming the animal after Mike. Bentonyx is now a new genus of British rhynchosaur honoring Mike Benton.

Oddly enough this is the name Darren first proposed. While he can take all the glory, the name was arrived at by chance. I’d only suggested we name it for Mike and had never mentioned his proposed name, nor do I think the others had read Darren’s piece and in any case it was months before we thought about a name properly. We actually sent through quite a few possibilities and actually Bentonyx was a bit of a last-minute decision and I think it’s probably little more than a happy coincidence and the fact that the name just sounds right (a much under appreciated part of taxonomy).

There’s really not too much to add to this since this is more about taxonomy than much else since the critical specimen (the skull) was described in some detail not long ago (by me, obviously). Still max added some revisions and indeed new reconstructions of the skull and a new analysis in the paper of Devon taxa shows the difference of this new genus from the others.

Really all I can say is thanks again to Darren for the original idea, thanks to Max for letting me in on the paper, and thanks to Mike for all his hard work and time in getting me (and so many others) to where we are now. And of course, hello to Bentonyx.

Langer, M.C., Montefeltro, F.C., Hone, D.W.E., Whatley, R. & Schultz, C.R.  ON FODONYX SPENCERI AND A NEW RHYNCHOSAUR FROM THE MIDDLE TRIASSIC OF DEVON. Journal of Vertebrate Paleontology 30(6):1884–1888

All at sea

Sauropod fans will probably be regular readers of SV-POW! and might have spotted the recent posts here and here on the sort-of-but-not-quite paper by a group working on some privately collected material. There are all kinds of issues about the rights and wrongs of collecting material like this and producing papers on material that is privately held and indeed a paper that is privately published and apparently un-reviewed. All of this aside (and not that it is not important) for me the real issue is the proposal in the manuscript that pretty much every sauropod in the Morrison (thinks like Amphicoelias, Diplodocus, Apatosaurus and many others) are ALL just a single species.

Now this is perhaps silly at best, and what it does (if this paper gets published) is create as huge problem that simply should not exist. As I have said repeatedly on here, publishing a paper is about style and attitude, not qualifications. However, inevitably, those people without formal training (or a limited amount) in academia and palaeontology are more likely to make bigger mistakes.

Issues of all kinds, but especially taxonomic ones, can be a massive headache for mainstream research. Such problems are incredibly easy to create and very hard to fix. One solution (often adopted by those wishing to skirt around such papers) is to simply ignore it. Don’t refer to the work or cite it (or at least the problematic issues). I don’t like this as it is, I think, intellectually dishonest to ignore the work when you know it exists (however bad, or complex). The alternative is though, I admit, little better. To fix these problems can involve the creation of a long and difficult paper which will take a huge amount of time but achieve little other than restoring the status quo. Whichever person ends up taking on the responsibility will lose quality research time to get back to the status quo and produce something that few people will read or cite.

Take the example here, assuming it is published with the ideas as stated. One would have to establish that the new taxon is not synonymous with every other sauropod in the Morrison and  reestablish all the existing genera and demonstrate that these are genuine and not just the result of variation or sexual dimorphism or ontogeny. Obviously much of this has gone before, but restating it the context of a new taxon makes it awkward and it’s all utterly unnecessary.

This is not to pick on the paper in question (enough people are doing that) but to make a point. Science is there to make progress and create understanding. There are ways of doing this from dabbling in the shallows to diving deep where far from land. However, one should work from one to the other. Picking your spot and hurling yourself out into the unknown without the requisite experience or training means those that have it have to come and rescue you and one should not be surprised if they find the job onerous, unnecessary, tedious and annoying. They want to explore the depths of understanding, not try and drag your embarrassing mess back shore and throw it up on the beach so it can’t bother the others. It’s not their job, but they’ll do it. But you are wasting their time if they do save you, and cluttering the view with your rubbish if they just let it sink to the bottom.

The obvious solution? Don’t do it. Just because it looks fun and easy doesn’t mean that it is and learning that will make it better for everyone. Sadly I can cite a few examples of people whose only response to this kind of this is to jump back in even further out than last time but hopefully a few might learn the lessons of others and take the steps to get it right having seen this one flounder.

Synonymy

I’ve covered a fair bit of taxonomy on here before, though there it lots more to come. However, I though it worth starting with synonymy since it’s pretty common in archosaur palaeontology and has led to a few misconceptions in the past. Synonymy is basically the practice of putting two or more names together as a single taxon because they are all the same thing but have multiple names.

Continue reading ‘Synonymy’

Taxonomy of the kind I still see too much of

Abstract:
Here we report a new dinosaur Nomen dubium (gen. et. sp. nov.) based on a very incomplete specimen with most of the important parts missing and the rest badly prepared, preserved, damaged or all three, including all the parts that have critical characters for the placement of this taxon in the clade we say it belongs to. It comes from the very vaguely defined beds of uncertain age of some incredibly large and unspecific region which we clearly got from a fossil dealer but won’t admit to. Nomen dubium can be diagnosed by the following characters that we will repeat in full in the paper but we want to put here to flesh out the abstract: absence of a key element that could easily just be missing given how incomplete the fossil is, the absence of a key character that is equally probably just broken because the bone is so badly damaged, and some ridiculously unhelpful and non-diagnostic character like the length of the femur and the number of gastralia, we do include one proper character but it’s not diagnostic of the taxon so much as saurischians / reptiles / tetrapods so is useless. This new genus is placed in the family Wastebasketoidea because it is really poorly defined so we can cram anything we want in there even though all the other members are from a different continent and are 50 million years younger. Finally we conclude with some pretty meaningless statement like the fact that this adds to the diversity of the area (like it could do anything else, though of course that point is dripping with irony given the appalling definition presented here that clearly means this isn’t new) or that it was an important part of the terrestrial ecosystem or some other pointlessly obvious and uninformative sentence.

……………………………………….
I’m not the only one who keeps seeing these am I? And I’m not the only one who is worried he’s actually produced something like this either, right?

Relative relatives

The subject of relatives has been bouncing around my brain of late. The statements, ‘the gorilla, a relative of modern humans’ and ‘the salmon, a relative of modern humans’ are both true, but one is perhaps more true than the other. Obviously all things alive today are relatives at some very deep and very ancient level. As far as we know and can tell, life only originated once on Earth and if you go back far enough fungi, trees, people, dinosaurs, bacteria and viruses have some form of common ancestor somewhere, not to mention all the things in between. However, there are of course, relatives and then there are relatives – relativity is all relative.

It’s clear that humans are more closely related to gorillas than they are to deer, closer to deer than to salmon, and closer to salmon than spiders, but they are still all related. Move in though, or move to an unfamiliar group and that becomes trickier – are beetles closer to flies or mantids, are spiders closer to weevils or centipedes? Unless you have a pretty good grasp of the detailed phylogeny to hand or some clear qualifiers any statements about relationships rapidly, or even instantly, become fuzzy to the point of being irrelevant.

You do see this at its worst in the media (big surprise) but I am sympathetic here. When trying to communicate the idea that some groups or species are closely related to others, aimed at an uninformed audience and avoiding technicalities and illustrations it becomes very tricky very fast. =I’ve also seen a fair amount of tired internet discussions along the lines of ‘Velociraptor isn’t related to Tyrannosaurs at all’. OK the ‘at all’ we can allow as conversational hyperbole, and of course tyrannosaurs and dromaeosaurs (within the theropods) are quite well separated, but they are also related. Compared to say, Dilophosaurus, they are quite close, compared to a crocodile, very close, compared to Troodon, not close. That statement is as true as it is false.

But is it really so hard to use a qualifier or two? Something like ‘Linheraptor is not a particularly close relative of Velociraptor’ is potentially confusing and in a sense no more accurate than ‘Linheraptor is a particularly close relative of Velociraptor’ – just how ‘not close’ or ‘close’ is it? But add just a few extra words and the distinction is obvious, accurate, succinct and informative: ‘Linheraptor belongs to a small group of dinosaurs called dromaeosaurs that includes Velociraptor, but within the group the two are not especially close relatives”. There’s really quite a lot of information in that 20-odd word sentence. It puts the two in context with each other, and the wider group of dinosaurs or theropods as a whole (since this sentence should obviously not stand in isolation in an article). So stick in a few qualifiers and make things more clear, it really will help and it might stop a few discussions were both people are right but arguing pointlessly from different perspectives.

Some specimens are more equal than others

I got into a discussion with my colleagues the other day about the merits of collecting multiple specimens of taxa versus collecting something new. The reality of course is that there is rarely a choice to be made – you bring back everything you find in the field that you can. However, as a hypothetical discussion it is interesting since of course you can do very different science with 10 specimens representing 10 different species and 10 specimens of a single species.

This debate aside (one for another time) it led me to get around to writing this post which I have long intended to complete on the differing importance of different specimens. It is understandable that some people might think “so you have 25 Triceratops, so what? Surely once you have one good, complete one, there’s not much more to learn?” but of course this is far from the truth.

As I have covered before on my series of posts on taxonomy, multiple specimens can give you a huge insight into the variation of fossil animals as living organisms – be it intraspecific or sexual. If animals are of different ages then you can learn about ontogeny and growth and of course there is always the change that a new specimen shows off some odd characteristic like a pathology, bite marks from a predator or something like this.

Some specimens (and the fighting dinosaurs are a great example) cannot easily be prepared for research, no matter how good they are (or in this case, not without losing a lot of other important information). Another specimen where all the bones can be separated out and viewed and analysed in 3D is great therefore allowing all kinds of extra information to be accessed and things like range of motion in joints to be examined firsthand. Similarly, having a ‘sacrificial’ specimen is great – no one wants to chop up a brilliant holotype to look at the bone histology or look at replacement teeth or the braincase, but a second specimen allows you to be a bit free-er with your methods and destructive sampling becomes a serious option – even a very fragmentary partial bone can be enough for this.

OK, maybe we don't need to collect this.

So while obviously for most palaeontologists a single complete skeleton is a great find, every little specimen is valuable. However, it would be a mistake to consider each of equal value – a single broken femur is good for destructive sampling, but an articulated leg is more useful and obviously several complete animals are better still. Even this varies from researcher to researcher – histologists are likely overjoyed by a bunch of otherwise largely unimportant partial specimens that they can sample while behaviourists won’t get too worked up until they hit a whole herd preserved together.

I imagine most of this is largely very obvious, but still there is typically always one more angle to think about and I hope I may have highlighted one or two here. It’s easy to get stuck in the mindset of ‘what would I do with that fossil’ which might be very useful for you, but not always that of your colleagues.

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Tyrannosaurus is a tyrannosaur, but not all tyrannosaurs are Tyrannosaurus

The title of this post is perhaps blindingly obvious to the vast majority of the readers here – we all know that bongo are antelope, but not all antelope are bongo, mackerel are fish, but not all fish are mackerel and well, ad infinitum for the whole of biology really. Now, I do appreciate that with palaeontological names (and those in general without ‘common’, non-Latinised names) this can get trickier (so zebras are indeed within the genus Equus and are equids, though of course, not all equids / equines / equoids are in Equus!) and those little endings (-inae, -ines, -ids and more) complicate things but still, there does seem to be an annoying and unending confusion that somehow family etc. names are basically synonymous with species and generic names. This is no more obvious than with that most ubiquitous of dinosaurs in the media, Tyrannosaurus.

I really could not even begin to try and count how many times I see reports that refer to Tyrannosaurus, when they mean tyrannosaur. It is annoying as it can confuse things (tyrannosaurs have a good distribution in time and space, Tyrannosaurus does not, so saying you have an Asian Jurassic Tyrannosaurus is out). This for me (in terms of writing this piece) has come to a head with the reporting on Raptorex which for those who missed it is a new, small Asian tyrannosaur. In addition to the age old and very annoying ‘ancestor issue’ an unending stream of media reports called this animal “a new Tyrannosaurus” (italics and ‘rex’ are optional, see various reports for examples).

To go back to my well worn ‘rant hat’ and lay into the media once more, I really do understand that even many science journalists are not, and cannot, be experts in every field of science. However, this is absolutely basic biology and thus I think reasonable to expect them to get it right. I did the basic KPCOFGS stuff at school aged about 10, and while obviously taxonomy is more complex than that, journalists should be able to distinguish between a Latin binomial and an anglicised family name. They should be able to of course, but clearly almost none of them can. This is not hard and in the UK at least is taught as basic science to kids who are not yet teenagers. Getting it wrong therefore is pretty near inexcusable – if you can’t tell the difference between a species and a family, I’m not going to be brimming with confidence that you can tell an electron from an atom or a county from a country, let alone absorb, digest and accurately regurgitate the latest papers on quantum theory or cancer research.

Whether you are nodding in agreement at this point or shaking your head matters not as you can head here and listen to both sides in a debate on science journalism and its effects between Ben Goldacre of Bad Science and the UK minister of science, Lord Drayson. And in a similar vein, check out this handy little guide to reading and understanding media stories on health.

Sexual dimorphism and taxonomy

The final of my posts on characters that vary in populations that can cause problems for taxonomists. I’ve already covered ontogeny (growth) and intraspecific variation and now for perhaps the most tricky aspect of them all, sexual dimorphism. For those who have not come across the term before this basically refers to differences between genders as exhibited (typically) by adult organisms. It should be easy to see how this complicates things by taking humans as an example. In general men are taller than women, with proportionally broader shoulders and a narrower pelvis but of course the range of intraspecific variation covers most if not all of this, and ontogeny can cloud the issue further (young teenage girls are often taller than their male counterparts as they hit their growth spurt earlier). If you only have part of a skeleton (like an arm) to work from it could be very hard to say if you have a tall woman or short man before you.

Even if we go outside of mankind to animals with more obvious sexual dimorphism like a peacock, it’s not entirely clear how much of the obvious male and female differences would remain if you stripped off the feathers. Some for sure (like the males’ fighting spurs) but it would not be as clear. Even with obvious bony differences (such as the antlers and horns of deer and antelope) these can be shed regularly or lost in some individuals. In some species male and females both have horns and even very similar horns to each others and in some (like reindeer) females retain their antlers at times when males lose theirs. Even if as a palaeontologist you had a fairly complete skeleton of a male and female antelope, it might be clear that they are similar enough to be the same species and different enough to be sexual morphs, but it may not be clear which was which.

As such palaeontologists (or at least the ones working on archosaurs) do not often deal with sexual dimorphism. Some archosaurs (like crocs for example) really don’t have much difference to detect. Others might be present, but to sort it out first one needs a good sample size of individuals to work with (even if you have ten specimens, they might all be males, or a variety of ages, or if the pieces are non-overlapping it will be hard to spot patterns of differences). Even then a pattern can be hard to interpret – you might find that specimens fall into two fairly distinct and separate size categories but is this male and female, or two different species (one big and one small)? If it *is* male and female, which is which? It is true that in general male animals are ornamented so one measured group may have horns and another lack them or have smaller horns but again this may be a species split (look at just how similar many antelope and gazelle are in the African savannah that live side by side).

In some cases there are clues available to the lucky few such as the structure of the bones, (recently used to diagnose a Tyrannosaurus specimen as female), eggs or embryos being found inside a female, an enlarged pelvis for egg-laying and so on that can be more fixed but one still has to be careful when identifying putative males. There are few dinosaurs or pterosaurs with enough of a group of specimens to be able to work on effectively, but a number have been suggested as being males and females.

The problem here for a taxonomist is of course that it is so hard to tell these things apart with the limited information we have. It is easy to think that two animals are rather different in size and form and name them as different species when in fact they are two different genders (especially if one has a crest and the other does not for example). Without the large numbers of specimens required to even being to piece together possible differences, it can be futile to try to separate them out. There are probably therefore at least a few males and females languishing as separate species in the records of taxonomists – of the few putative male and female dimorphs that have been suggested, most are hotly contested. Of course in many cases this is largely irrelevant – if you have only a few bones for your specimen, its gender is not much of an issue, but when you have things like the ceratopsians where much of the taxonomic difference lie in the frills and horns that you might also think could well denote male and female differences (as with many modern ungulates) then you can see how things rapidly get much trickier. This can get still more complex as these kinds of characters often only show up in adults and thus juveniles which lack ornaments or have smaller ones can also be thrown into the mix to mess up the efforts of taxonomists.

As a vague conclusion to the three pieces here, taxonomy is about more than just looking for similarities and differences and erecting new species based on differences, or synonymising others based on similarities. One must assess these characteristics themselves to ensure that what you are naming is a genuinely different organism and not just a large and robust adult, a juvenile or a female. There is an awful lot of variation out there in biology and when working with only half a 200 million year old skeleton it can be tricky to keep on top of things. However these aspects (variation, ontogeny and dimorphism) are important and should not be ignored or underestimated.

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