In the long run, you're right. The problem is that global warming is happening ridiculously fast -- much, much faster than we can evolve to cope with it.

More importantly, it's happening much faster than particular cultures can cope with. Because of the importance of water, the great majority of people around the world live in river basins or by the sea coast. As the sea rises, we are seeing catastophic floods that kill thousands and displace millions.

As a species, we will survive global warming, sure. But how many of the seven billion individuals will die along the way?

If you're descended from your parents, how do they still exist?

Evolution, like more immediate descent, doesn't in itself do anything to the ancestral stock. Remember that evolution doesn't proceed in straight lines, but in branching patterns. Given a population of organisms that spreads into two different environments, the subpopulation in one environment will tend to select for different features from the other, which may still be perfectly well adapted to its environment.

In the case you mention, imagine a population of fish in a network of lakes. One lake is smaller and progressively dries up. The fish that survive in that lake are the ones that can cope on land, so that subpopulation will select for the ability to breathe air; but the subpopulation in a deeper lake that never dries up will carry on just fine.

I very much doubt that spiders have sufficienty sophisticated brains to be hypnotised in anything like the sense that we use the word of humans. But I can imagine them potentially being transfixed by a bright light, perhaps reflected from your aluminium brick. I suppose it's possible, too, that it saw its own reflection and reacted to it as it would to another of its species.

There are worms that can survive being cut in half, but it's not true of earthworms. Please don't try it! It's possible that one end will survive, but not both.

Most earthworms -- like many invertebrates -- reproduce hermaphroditically. That is, they have both male and female parts, and they engage both simultaneously with a mate. But there are some species that reproduce by themselves, yes. It's called parthenogenesis.

Is a human being a mammal, or is it a primate?

It's both. Humans are primates, and primates are mammals, and mammals are animals.

Similarly, great whites are sharks, and sharks are fish, and fish are animals.

Think of evolution as a great tree of life -- a very common and illuminating metaphor that goes back at least to Darwin. At each branch, two descendents issue from a common ancestor -- for example, dinosaurs and pterosaurs split about 230 million years ago. Most of the names we use for groups of living things represent whole branches of that three, including all the sub-branches.

So mammals include bats: by being a bat, a pipistrelle does not cease to be a mammal. In the same way, by being a bird, a wren does not cease to be a dinosaur. And by being a fish, a shark doesn't cease to be an animal.

(posted in Birds)

But surely it must be painful for the kiwi?

Ilana, I'm sorry but this is a whole long list of questions each of which would need an essay in response to do it justice. No-one here is going to have time to give your questions to answers they merit.

(Also, some of the questions bear a distinct whiff of homework -- and we don't answer homework questions.)

My advice would be that if any one of these questions -- not a homework one -- is of particular interest to you, post it as its own separate question.

Because it contains oxygenated haemoglobin. When the oxygen has been used up and the blood is returning to the heart, it is less strongly red.

Can you please post again with more photos from different angles? Also, can you tell us how big it is, and where in the world you found it?

(Great find, BTW. I am really jealous!)

You're right -- birds are dinosaurs since they're descended from dinosaurs, just as we are primates because we're descended from primates. And just as we inherited things from more primitive primates (big brains, forward-facing eyes, opposable thumbs), so birds inherited things from more primitive dinosaurs, including the structure of their feet.

The specific resemblance between the spiked inner toe of cassawaries and the curved inner toe of Velociraptor is not directly inhereted, though -- intermediates on the line leading to cassawaries lacked this, and it re-evolved (in a rather different form) independently.

Each cell in your body has 23 pairs of chromosomes. The only exceptions are sperm and egg cells. These and these alone have 23 chromosomes -- each one chosen at random from the corresponding pair. So each sperm contains a genetic code that is made by the equivalent of tossing 23 coins.

Does this mean they're all different? A typical ejaculation contains 250 million sperm cells. But the number of possible combinations of 23 chromosomes is 2^23 = 8.3 million. So your body is only capable of producing 8.3 milllion genetically different sperm cells, which means each ejaculation contains about 30 copies of each.

(I guess this means there's a small but non-zero chance that when there are two eggs, two genetically identical sperms will happen to win the race to fertilise them, and that fraternal twins can therefore ve genetically identical.)

Hi, Ian. It's always hard to be sure from a single photo, but I am pretty sure that this is the sternum (breast-bone) of a bird. The way you're holding it, it's upside down from how it would be in life: the bird is, if you like, lying on its back, with its head towards the right of the picture.

The next time you eat a chicken, once you've taken off all the breast meat, take a look at the oddly-shaped flat bone that it was attached to. That's the sternum.

Ah, Celia, this is not going to be easy for you. The world is full of poeple wanting to work in conservation, and most of those want to work with either big cats or primates. I'm not saying it can't be done -- I'm just saying you're going to up against a lot of competition, mostly from young, freshly trained people without the kind of life-commitments that you've probably built up by your stage of life. If this is going to happen, you need to find a way to make your physio experience a really significant positive, to offset the disadvantages you'll be dealing with.

I don't want to be discouraging; I just want to set your expectations at a realistic level.

I think the best thing you can do if find someone at your local university who works in conservation, and email them laying out your situation. See whether they can make time for you to pop in for a cup of coffee one day to discuss what the options might be. Perhaps try this with two or three different people at different universities to get a better feel for the options. Based on those chats, you should have better idea of what you might be able to do.

(And don't be nervous about contacting academics out of the blue. Most of us love any excuse to talk about our favourite subject. If the first couple of people you contact can't find the time, just move on any try someone else.)

How many colours are there in the spectrum? Six is one obvious answer (red, orange, yellow, green, blue, purple) but Isaac Newton thought seven was a more perfect number so he invented indigo so there could be seven colours. But you could equally argue for eight (turquoise is different from both green and blue), and so on. These are arbitrary distinctions; and so are those between biological kingdoms.

Well, David, I wonder how true that is? We all accept that IQ is a profoundly imperfect score -- just as BMI a flawed measure of obesity. But we would nevertheless not be slow to say that someone with a BMI of 35 is not going to make it as a tennis player; is it really so unreasonable to also say that someone with an IQ of 90 is unlikely to find a career in science?

So my message to Carrie is a bit different: you can justly be pleased about your IQ; but having now got from it a helpful indication, the best thing you can do going forward is to forget about it -- certainly don't invest time and effort into improving it. The place to put your effort is in developing effective study habits, learning relevent information, and forming good mental habits -- especially concentration and determination.

Hi, Evan, sorry for the slow response.

First, "nomen dubium" doesn't mean "possibly synonym", which is what's going on here. It means a name founded on holotype material so poor that it's effectively useless, so that it's impossible to say whether or not another, better specimen, belongs to the same taxon. That doesn't apply in this case, as there are very good specimens of both Tarbosaurus and Tyrannosaurus. Here, the question is whether they represent the same genus.

Note: genus, not species. In general, a genus contains several species. As far as I'm aware, no-one has suggested that the Asian and American giant tyrannosaurs are the same species, only that they are species in the same genus. If that idea is accepted, then Tarbosaurus bataar would become Tyrannosaurus bataar, another species of the genus Tyrannosaurus.

So, do both species belong to the same genus? You will be disappointed by this answer but it's essentially a matter of taste. Some taxonomists may say yes, others may say no. My sense is that most theropod workers are prepared to let the name Tarbosaurus stand, but ultimately it comes down to the question or whether they are sufficiently similar to be classified within the same genus; and there is no hard-and-fast way to assess what constitutes "sufficient similarity".

Hi, Chad, great to hear from you. Although my sense is that most of the contributors to AAB are agnostic or atheist, that is by no means true of all of them. I myself am a Christian, pretty active in my church. One of the things I very much enjoy doing when the opportunity arises is talking to church groups about precisely this issue: see my web-site Evolution For Christians (

In the simplest, soundbitey terms, my read is that science is a fantastic tool for telling us what happens, and how things happen; but has nothing to say about why they happen: for that you need philosophy, or theology. Equally, science tells you what is, but not how things should be.

Note that this is not in any sense a criticism of science: I'm just saying that's not what it'a for. It's more like noting that a hammer is not very useful for measuring distances. For that, you need a measuring tape. (And equally, a measuring tape is a terrible tool for driving nails into wood: in the same way, the Bible is unhelpful when used as a science textbook.)

So my understanding is that science and religion are answering two very different kinds of questions; and that to face all of reality, I need both.

Hope this is helpful; if you'd like to know more, you can easily reach me on the email address on the web-site.

Hi, Cody. It's been proposed that a few hadrosaurus may have survived for a short while after the end of the Cretaceous, but consensus seems to be that the fossil bones in question were "reworked": that is, that they were fossilised during the Cretaceous, then weathered out and subsequently reburied in new sediments after the boundary. So I'm afraid, no, it does look like the Cretaceous was the end for all the dinosaurs but the birds. (And like you, I can't help feeling they they don't really count! :-))

This is one of those situations where the Wikipedia article is perfect. … Revolution

As it happens I was one of the peer-reviewers for the paper that popularised the term: … /1650/2483
So at one point I was very familiar with it, though the passage of seven years has dulled my memory. As I recall, it was primarily a statistical paper, and its conclusions were admirably sober -- essentially the the KTR had little effect on dinosaur evolution.

Sorry, I haver to agree with David. I know you don't want to hear this, but I don't think you have important fossils here.

I'm not sure we really know. I share your love of pliosaurs (if I couldn't work on sauropods for some reason, it would be a toss-up whether I worked on them or azhdarchid pterosaurs), and it's always seemed wrong to me that they shouldn't have continued to dominate the seas right up to the present day.

But what we know is not just that they went extinct at the end of the Cretaceous (at the same time as the ichthyosaurus, pterosaurs, and all the dinosaurs except birds), but that they were already in decline before then, having apparently been largely replaced by mosasaurs.

To my way of thinking, mosasaurs are nothing but overgrown seagoing monitor lizards, and nowhere near as exciting or intimidating as pliosaurus. But we have to admit that evolution had other ideas, and mosasaurs may have outcompeted pliosaurs.

At any rate, the total upheaval in all global ecosystems at the end of the Cretaceous put an end to them. Sad, really.

Exactly right. The most usual phylogenetic definition of Dinosauria is something like "The most recent common ancester of Iguanodon and Megalosaurus plus all its descendants". That includes tryrannosaurus, sauropods, Triceratops, etc. and all modern birds, but omits pterosaurs, crocs, lizards, mammals, sharks, etc.

Hi, Ted, sorry for the slow response.

First of all, for most dinosaurs the situation is much worse than you suggest here -- we have complete preserved skeletons of only a tiny proportion of the known dinosaur species, I would guess maybe about 1/20 of them. So we often have to guess the size of the complete animal based only on a a few bones -- or even something as inadequate as half a dorsal vertebra, as in this case: … ig-was-it/

No, there is no general rule for extrapolating maximum body size from a single individual. Occasionally you may find fossils bones with an External Fundamental System (EFS) which indicates that that individual has finished growing -- but even then, there's no way to know whether it was a large or small individual of the species. Kate Moss and Hulk Hogan are both humans who have stopped growing, but they are very different sizes!

What we can say for sure is that most of the best-known big dinosaur specimens had not stopped growing at the time of death. For example, the big mounted brachiosaur in Berlin has separate scapulae and coracoids (shoulder bones), but mature brachiosaurs are known to have fused these bones into a scapulocoracoid. So that big boy would have kept right on growing if it hadn't died when it did. See … r-remount/

Right. In terms of scholarship and science, there is nothing to choose between Imperial and Bristol, so you just need to make a lifestyle choice -- something that we at Ask A Biologist can hardly help you with!

BTW., many congratulations on getting offers from two excellent universities.

And the reason for that, Eva, is that brachiosaurs share a more recent common ancestor with birds than with any aother living animal. In biology close relatedness is all about how recent the common ancestor is: so although crocs look kind of like lizards, they are actually more closely related to birds -- because crocs and birds have a more common ancestor, and you have to back further in time to find the more remote ancestor that gave rise to lizards as well.

(posted in Mammals)

Sorry, Jean, I can't make out an animal in youre picture -- unless it's the angular grey shape just to the left of the very middle of the picture. If it's that, then all I can say is that it looks like ... a dog?

Palaeontology as a career is incredibly competitive. You won't want to hear this, but the very first thing to do is study hard in all your subjects, get the best possible grades, so that you can get into a good university. That's the first step. Then you'll need a degree in a relevant subject (usually biology or geology) and then a Ph.D in palaeontology. From there, you have maybe a one in ten chance of landing one of the very few jobs. It's true in all the sciences that we produce far more Ph.Ds than there are academic jobs for then, but it's even truer in palaeo!

That said, some do manage it -- including several of the people who answer questions here on AAB. So if you're bright and prepared to work incredibly hard, then don't let me discourage you!

The other thing is to do palaeontology as a sideline, which is what I do. Palaeo is one of the sciences that has the fewest barriers for amateurs participating at a professional level. For much more, see … ntologist/
(I went from zero to publishing papers in five years, then it took me another four years to complete my Ph.D. If I can do it, you can.)

The first thing to say is: don't take Tarzan as a textbook!

The question of how and why civilisation arose only in humans in a no other animals is a big one, and very much the subject of ongoing research. As best I understand it, it's mostly thought to be an outgrowth of language. But then the question becomeswhy have we and no other animals developed language? (Yes, some animals have a repertoire of sounds and gestures that indicate danger, food and what have you: that is very different from an actual language with words that can be composed to form more complex concepts.)

No -- the experiences of the Italian wall lizard when transported from Pod Kopište to the Pod Mr?aru seem more like an example of allopatric speciation: see
That is, "speciation that occurs when biological populations of the same species become vicariant, or isolated from each other to an extent that prevents or interferes with genetic interchange."

The study that claimed Sinornithosaurus was venemous based this claim on two lines of evidence: longer-than-usual teeth, and grooves along those teeth by which venom could be delivered. A subsequent study showed that in fact, the teeth were not longer than usual, but had slipped part-way out of their sockets. It also showed that grooves are not unusual in theropod teeth. So there is really no evidence for venom-use in Sinornithosaurus.

It looks like the cold-blooded condition is what the earliest animals had: we can see that invertebrates, fish, amphibians and regular reptiles are all cold-blooder. The innovation of warm-bloodedness has happened only twice: once in mammals (or their ancestors the synapsids), and once in archosaurs (the group of reptiles that includes birds, dinosaurs and crocs). The most interesting thing here is that crocs seem to have lost their warm-bloodedness: probably as an adaptation to their sit-and-wait predator lifestyle, where it's more important to eke out each meal than to have a lot of stamina.

On the other hand, while evolution has no (or very limited) sense of direction, and doesn't "try" to reach a predetermined goal, it's still true that every organism that has ever lived is a direct linear descendant of the ur-organism. This is why I am perfectly happy with the old sequence-of-ape-to-man illustration that's so often used to illustrate evolution: https://evolutionisntscience.files.word … series.gif

It's a perfectly good line drawn through the branching evolutionary tree, and it happens to be one that we're particularly interested in, since we are on it.

I'm happy enough to admit that Brachiosaurus is a fish; it's just that the knowledge doesn't really cast any useful new information that helps us understand it. Whereas the knowledge that birds are dinosaurs really does cast them in a new light.

I think there's also the matter of nomenclature. The informal terms "dinosaur" and "mammal" are directly derived from the formal taxon names Dinosauria and Mammalia, so it makes sense to understand the informal terms as meaning the same as their cognates; whereas the informal term "fish" doesn't correspond to any formal taxon name. I imagine that biologists who struggle self-identify as fish would have no problem describing themselves as sacropterygians or gnathostomes (or indeed vertebrates!)

Well, that would be a typological definition of what a mammal is, but biology has moved away from such definitions ("a bird is a vertebrate with wings that can fly"). As we all know, Nothing in Biology Makes Sense Except in the Light of Evolution. … _Evolution

"Can life be sustained without the constant consuming of other lives?"

Yes, of course -- by photosynthesis, which is how plants do it.

Fascinatingly, the green sea slug seems to have acquired enough plant genes that it can manufacture its own chlorophyll to power the chloroplasts that it steals from algae:
So I think in theory, one of these animals could eat a single meal of algae, then survive for the rest of its life on sunlight.

You might also consider some parasites as sustaining their own life without consuming other lives -- they tale nutrients from their host, but without killing it, and perhaps in some cases without doing any harm at all.

"If they had then they wouldn't be mammals!"

Au contraire, sir! That would be like saying that naked mole rats are not mammals because they lack hair, or that whales are not mammals because they lack legs! Anything descended from a mammal is a mammal, just as everything descended from a dinosaur is a dinosaur (which is why birds are dinosaurs).

These days, the answer to every "Where can I get more information on ..." question is the same: Wikipedia. Its coverage of scientific matters is astonishingly complete and reliable. It's far, far better than any traditional encyclopaedia in such matters. So start at and follow the links -- especially the references.

(To keep this site easy to search and browse, we prefer to have one question at a time, so would you please re-ask your pycnofibre question separately?)

The biggest lizard we have evidence for was Megalania, an Australian monitor that lived 30,000 years ago would have resembled a Komodo dragon. Size estimates vary wildly, due to the poor material, but top out at 2000 kg. Something in the region of 500-1000 kg is probably more tenable.

So, yes, about the size of a cow. The biggest extant tortoises don't get much bigger than 250 kg. Extinct tortoises might have doubled this, or done a little better, but again no bigger than a cow.

A big part of the reason for this is simply that growing big takes a long, long time when your metabolism is slow. Aldabra giant tortoises take over a hundred years to reach their full size, and it's hard to survive long enough to get big at that rate. by contrast, cows are adult by two or three years. Endothermy lets you grow fast, which lets you get big before you die.

There is, or was, tantalising evidence of a sauropod -- i.e. a terrestrial dinosaur -- massing on the order of 200 tonnes. It was a single fossilised tibia 2 m long, from the Latest Cretaceous of India, named Bruhathkayosaurus. Unfortunately, the only description of it is woefully inadequate, and the published images are even worse. The bone itself has been destroyed in floods.

If this tibia is legitimate, then it suggests that animals that walked on land were able to rival in size the largest blue whales, which of course cheat outrageously by living in water and so not bothering to support their own weight.

Right. We can't generalise about evolutionary trajectories from a sample of size one.

(posted in Genes, Genetics and DNA)

THat is a very broad, general question. The best place to start is probably with the simple-English Wikipedia article on DNA:

It's really just a matter of tradition and inertia within subfields of zoology. Remember that taxonomic ranks like "order" and "genus" have no objective meaning -- only the meanings that we assign to them. Most dinosaur genera have only a single species, whereas the genus Quercus (oak trees) has something like 800 species. The only things these two taxa have in common is that we call them each a "genus", but that word is basically meaningless. "Order", even more so.

Zoology is a much bigger field that palaeontology, so your chances of finding a job and building a career are probably better there than in palaeo, which is extraordinarily competitive. But at your stage, you don't need to make a decision like this for a long time. I assume you picked all three sciences rather than the double award. For your A-levels, you'll want biology and probably another science, plus maths is always good, and geology is a useful complement if it's offered. Then you'll do a degree in biology, zoology or possibly geology -- degrees in palaeo exist, but they're rare. Only after you have your BSc. will you really need to decide on which way to specialise. Your Ph.D will be in a specific field, and that's when you'll need to make your decision.

So for now, just concentrate on getting s good, solid grounding in the relevant sciences and maths.

(posted in Evolution)

Right. But the heat-death of the universe is not a "harsh environment", as the original questioner has it; it's the absence of any environment at all, and indeed the absence of anything in an environment.

(posted in Evolution)

What you're talking about -- the heat-death of the universe -- will take place not over many generations but over many billions of years. And the final result will be that there is no structure to matter, so nothing for biological beings to be made of. No, nothing physical can survive that.

(posted in Evolution)

There are no doubt some fossils of individual mutants whose mutations were not beneficial. But think how rare such individuals are among extent species, and you'll see how rare their fossils are likely to be. Also don't forget that most maladapted organisms die very early in their lives (or before birth) so won't likely leave very recognisable remains. In particular, animals that die before birth have cartilaginous skeletons that have not yet turned to bone, and those fossilse only under exceptional circumstances.

Bodies evolved before brains: many organisms get by perfectly well without brains, including all single-celled creatures.

Consciousness is a very different matter. It's hard to study since it is essentially to do with how an organism perceives itself and the world, and it's impossible for most organisms to communicate with us. Arguable we can't even really communicate our own consciousness to our peers, so it's hardly surprising that cows, lizards, frogs, fish, sea-urchins, crabs etc. can't!

(posted in Fossils)

I don't know for sure, but I think this is more likely to be of human origin -- a decoration carved in stone -- than a fossil. I can't think of any organism that leaves a fossil of concentric rings like this. (If the rings were a spiral, this would look like an ammonite.)

"This is a biology site not science fiction."

True -- this is a biology question. Scientists (including me!) often lament the very poor science in sci-fi books and films, so I'm happy to encourage authors who do take the trouble to consult scientists. So: thanks, David, for answering.

Your GCSE choices are good: maxing out science is a must, geography is a good way into geology, and computing will help you to use the many very useful software packages that we use for things like 3d visualisation, phylogenetic analysis, principle component analysis, statistics and more.

To get a paid post in palaeo, you will need a Ph.D from a good university (and a huge slice of luck). To get the Ph.D, you'll need good degree -- probably 1st or upper 2nd in a relevant subject (most likely biology, geology or a subfield). So you need to get into a good university, which means you'll need excellent A-levels.

Bristol uni. would be a great choice -- it has a flourishing palaeo program in its Earth Sciences department (where I am an associate researcher), and a very good one-year Masters program in palaeo, which will help you prepare for your Ph.D. Other good universities for getting into palaeo include Oxford and Cambridge (obviously), UCL, Imperial and Manchester -- but really, any well-respected university can give you a way into a good Ph.D program, which is really the key.

Be warned that there are 20 or 30 newly minted palaeo Ph.Ds for every available research job: it's an incredibly competitive field, so you'd be well advised to have a backup plan. Your employment chances may be better in the USA, so one option would be to try to get onto a Ph.D course there, as a step towards residency and a job.

Finally, note that there's another path: you could aim towards a career in a less insanely competitive field, and do palaeo in your spare time. That's what I do (I'm a computer programmer in my day-job) and it's working out really well for me. For some information on this route, see this post on the blog that I co-run with Matt Wedel: … ntologist/
Also relevant: … eontology/

Some of these are probably possible. The difficulty with, for example, trilobites is that they're not merely unknown in present ecosystems, but unknown from fossils more recent than the end-Permian mass extinction 250 million years ago. So for trilobites to have survived, they'd need to have done so in a way that obscured a quarter of a billion years' worth of fossils. I won't say it's impossible -- perhaps they live only in very deep parts of the ocean which never come to the surface where the fossils can be seen. But it seems unlikely.

Why no one has funded a program for search of potential living fossils? Well, how would you do that? Where would you look? How could your search be focussed on living fossils only? I think that any natural history field expedition would be delighted to find specimens like these if they turned up, but that's just as likely to happen while they're working on something more tractable than if they're wandering at random in the hope of spotting relict taxa.