A) There's a good chance you are misremembering. B) While the rules are set in place, it's very, very unlikely you'll get an examiner so cruel as to not give you marks just becuase you didn't write in the question number. In short, I wouldn't worry.
Posts by David Hone
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I recall an apparent average for mammals being posited at around 3-4 million years. This is based on bits of the fossil record where specimens are abundant and can be tracked accurately over extended periods of time. How well that value stacks up across all life is of course extremely uncertain, but I think that's essentially the best answer you'll be able to get hold of.
"Spinosaurus seems the type of bizarre creature that could only be dreamed up by Hollywood."
Not really. In my experience, the natural world is far more creative than human fiction - half the stuff in Avatar is rather obviously modified from extinct animals if you know which to look out for.
I have a couple questions regarding it's depiction in the media:
"1/ It's nasal sensors leed us to believe it was quite aquatic like a crocodile."
It's news to me that anyone has ever said anything about this. What leads us to think it was partially aquatic (note, partially, like an otter or croc, not fully like a dolphin or icthyosaur) is that is does have a very crocodile-shaped snout, and the position of the nostrils are like those of aquatic vertebrates, it's found in environments with lots of fish, and one of it's close relatives, Baryonyx, is preserved with parts of fish in the stomach.
"What evidence do we have that it spent significant time on land?"
Well the fact that it's a biped, and those tend to be primarily terrestrial (or at least more than capable of supporting their weight on land) and it's not built to swim well (no deep tail like a croc or beaver, no reduced limbs to cut drag, or greatly enlarged limbs and feet into paddles, so super dense bones to stop them floating etc.).
"Could its long fingers and toes have been webbed for a very acquatic existence? "
Well they aren't actually that long, but about normal for an animal of that size. They could have been webbed sure, but that wouldn't make them great in water, merely a bit better than other theropods.
"And could its long legs been used for Frog motion in water and Bird/Kangaroo hopping motion on land? (I don't think a full skeleton has been found so are it's limbs, hands and feet assumed from Baryonyx Walkeri?)"
There's no full skeleton no, but Suchomimus is nearly complete. To move the legs like a frog would take a complete rearragemnet of the legs and pelvis, so no. No 10 ton plus animal could hop either, so that's also out.
"2/ What evidence is there for it having a slim, lizard like physique with a skin covered sail along the spine"
Well that's how anuimals are built. They don't tend to have much mass outside the ribcage or packed over the backbone (camels are the exception not the rule).
" (are there any other animals other than Dimetrodon with such a spine?).:
Lots. Not jsut close relatives of Dimorphodon like Edaphrosaurus, but dinosaurs like Beckelespinax, Ouranosaurus and Dicraeosaurus.
" If it were a warm blood dinosaur, would it need a decent amount of insulation (fat/feather as per a penguin)"
It depends how active it was, waht the temperature was typically like, what water or shade was available etc. Hard to say, but based on the other large theropods, very probably not.
" if acquatic, whereas a cold blooded crocodile does not? Could Spinosaurus have been fat like a cetacean with skeleton bearing little resemblance to a larger physique?"
Nope, see above on ribs. And physiology / temperature is way, way more complex than just "hot" or "cold" blooded.
"The reconstructions of Spinosaurus seems to have started with a hypothesis of a crocodile;"
No, it's based on lots of good evidence: comparative anatomy, diet, isotope analysis and taphonomy among others.
" but could Spinosaurus have been more like a cross between a penguin, a frog and a manatee?"
Sorry but no, absolutely not in any way at all.
Well it's from a fish for sure looking at the bone texture and the way the teeth are anchored, and obviously a good sized one. After that though I'm afriad I'm out, but other colleagues on here can probably do better.
I think you're thinking that a species originates with just one or two new individuals, but that's really not how it works. If that were the case, then yes, inbreeding would be a huge problem. However, species don't jsut pop up like this, whole populations or lineages slowly becomes different enough to their relatives that we define them as separate species. But that may have occurred over thousands of generations and may involve a popualtion of thousands or even millions of individuals, so there's naturally a wealth of genetic variety there.
Shrews are not mice, but are, well, shrews. They are a a kind of insectivore and so more closely related to things like hedgehogs and moles than to rodents like rats and mice, though they do look simialr at first glance.
They are not poisonous (toxic if eaten) but venomous (that is, they have a toxic bite or injection system) well, some are at least. This is, I think, a salivary produce and runs down the teeth and into what they are biting.
Are you really sure it's the same one? They do kinda look alike. :)
I'm sure it's not normal, but not impossible. They are smart birds and food can be hard to come by. With the right winds a 100 mile journey is not necessarily a huge effort for them, so the trade off between the trip and what it might get out of it (more food from you) could be worth it.
Yeah, i think that's exactly what it is Richard. A dorsal rib fused onto one of the plates of the carapace. Not sure what species it's most likely from as I don't know the patterns of the plates well (though a quick bit of googling, suggests it's an Olive Ridley), but it's pretty big. It could be from a big terrapin or tortoise, though form a beach a marine is msot likely I agree.
There was an abstract from a conference some years ago on this describing ceratopsian skin referred to Triceratops with distinct nipple-like shapes on some sclaes, which implied something else came off from them. Coupled with the filaments seen on Psittacosaurus, this was presented as evidence for some bristles being on these animals. I'm not wholly convinced and much more importantly, to my knowldge, this has yet to be properly published / described. It's certainly plausible, but I was to see a formal, perr-reviewed description and comparison to other specimens and that has yet to appear.
Yes, I agree we have not yet hit carrying capacity (if only becuase we are still spreading etc., where most other species simly could not inhabit everything from the desert to ice caps). If we do though, then certainly things will kick in thought he complexity of humanity means this might well be more social evolution (pressure to have fewer kids) or technological (increasing plant yields) et.c rather than what we might consider more classical evolutionary pressures.
In the case of your large predaotr example, these patterns are quite consistent and we might indeed expect humanity to follow them - we could have fewer children (less resources used per generation), get smaller (less resources used), diversify (split into multiple species / lineages each focusing on different resources to reduce competition, pretty unlikely for us) or become more competitive (die back from lack of resources).
There's nothing specific for Pteranodon in the sense that there are no fossils of it directly preserved with fuzz (aka pycnofibers). However, this is only very rarely preserved, so our record o fit in pterosaurs is currently very limited. We do though see it in some of the most basal pterosaurs (anurognathids) and other basal forms as well as a couple of basal pterodactyloids. That's about it for now, but of course the more material we find, the more likely we are to turn up specimens.
I, and I think for other pterosaur researchers, would say that it's more likely than not that most if not all pterosaurs had pycnofibers. Pterosaurs were actively flying animals and regardless of their physiology, would be interested in retaining heat, and some kind of fiber covering would do that. Given how early this eveolves and that it's retained in a variety of forms for at least 100 mya, it would seem most odd if other pterosaurs didn't have it.
"Tyrannosaurus was almost certainly not an amphibian"
I think we can be a bit more certain even than that Peter. :)
I think you've been taking Jurassic park a bit too literally. It was a work of fiction - there's no evidence they were a fraction as intelligent as portrayed on the screen. Even if they were, yes there are a number of animals (some dolphins, New Caledonian crows, apes) that are extremely intelligent. As for the noises, well those were special effects, and based on living animals: there's traces of sealions and alliogators in there if you listen close.
I have a friedn who started a career in science in her late 50s. Did high-schools exams in evening classes and via remote learning, then went to university in her late 50s, got her degree and finsihed her PhD past pension age before getting a job as a lab technician. 45 is positively young by comparison.
I always liked Bill Hicks' response "You know it took more effort to tell me that than to leave me alone?". :)
Actually, quite a few animals are known to enagage in 'play' behaviours (here's a great review of soem of that: http://scienceblogs.com/tetrapodzoology t-to-play/ ) it's not just things like otters that get all the attention.
As for intelligence, crows (especially the New Caledonian crow) are exceptionally smart, potentially at the levels of some higher primates. They are capable of complex behaviours and problem solving.
I knew I'd seen soemthing on this. Here's an essay on the subject by occasional AAB contributor Dr Darren Naish: http://scienceblogs.com/tetrapodzoology pressions/
I really can't add any more than this, so hopefully it'll answer your questions.
I can't see them recognising themselves at any level. Recognition in a mirror is a recognition of self, but even if the clone, looked and smelled and acted identically to stimuli, it's still a different individual organism. Why would you recognise it as 'yourself' any more than you would an identical twin?
It's odd as male domestic rats have huge testes, so they are pretty hard to mix up with females. As David says though, the evidence is sadly rather compelling.
I have e-mailed Manabu and hoped he'd be around to tackle this, but as he's not, I'll have a go.
Spinosaurs have long jaws and in general this correalted with a low bite force (it's simple mechanics, it's hard to put pressure on something a long way away) and they don't have huge areas of muscle attachments at the back of the skull. Collectively then, they probably had (for their size) a pretty weak bite. I would not expect even a huge spinosaur to have a bite nearly as strong and a large tyrannosaur.
Yes it should be perfectly possible to focus on other groups, though as Peter notes, it may be impossible or difficult in some cases. If you are studying in a university with a series of researchers who focus on dog behaviour and evolution, naturally that will come up a lot and is potentially going to cause problems for you.
I would add that it's perfectly possible to study some groups without coming into physical contact with the animals. Most lion and shark researchers for example don't get too close to their subjects very often.
as someonme who did his PhD on pterosaur origins, you may have come to the right place.
The shprt version is that we really don't have a good idea of the origins of pterosaurs and their transition to flight. We have some ideas and there is work on this but not much, mostly becuase the fossils are very scarce. On average the smaller an animal is, the less likely it'll become a fossil, the older it is the less likely it'll become a fossil, the more fraile it is the less likely it'll be a fossil, the rareer it is the less likely it'll become a fossil, and the further from water (well you get the picture).
The first ptersoarus lived a long time ago, were small, probably few in number, fragile (hollow bones) and living in trees. It should be no suprise really that actually the fossil record of the earliest pterosaurs is pretty terrible. In fact I'd say it's better than we might think.
However, this is a typical creationist tactic and a pretty pointless one. If they want to show evoluton doesn't can't work, it's obviously unfair to pick on an example where we don't and can't know much. Surely if evolution were false and creationism correct, they would be able to simply disprove any proposed evolutionary transitions in the fossil record? Why did they not pick on the origins of birds where we have thousands of specimnes from dozens of species showing grliding and prachuting transition formas, the changes in feathers, wing shape, shoulder joints, tail anatomy, brain shape etc. etc.?
To pick a (possibly poor) analogy - it's like saying you can't say that car X was built from blueprints by picking a car for which you don't have the designs available. But then applying that same argument to all cars, even if you have all the blueprints and plans and design notes.
Sure, there's tons and tons of species where we don't have a good fossil record, or simply haven't researched on them much. But that's hardly a fair test. They can't attack the good examples that clearly demonstrate the principle with superb evidence, so attack those which we admit are lacking data and claim that also affect those that are better supported? Right.
As I say though, we do have some ideas. We have a good idea of pterosaur wing structure and that suggests early forms had a very broad wing which would link to a gliuding origin. It also looks like early forms were arboreal, again fitting this model, and so we can at least being to put together a plausible hypothesis about this.
I've just checked through Chris Brochu's huge description of Sue and he doesn't anywhere mention either value that I can find. Either way, whatever number floating around is likely to be wrong for two different reasons.
1. Sue isn't complete. Not all the tail is there, so the 'true' length of the skeleton isn't actually known and cannot be. All we can do is measure the length of the skull and all of the backbone (neck, body, pelvis and tail) and add it up to reach a total for what is preserved. Tails in dinosaurs varied a lot in length so we can't even necessarily guess very well quite waht is missing, certainly not to an accuract of 50 cm on something this size.
2. even if we did that, it's not very represenative of the true size in life. Vertebrae have discs of cartilage between them to give them some flexibility and protection when the animal moves. So even adding up all the bone lengths doesn't give us a 'true' value, there would have been spaces between them, increasing the length. How much we don't know, so again, any value we have is going to be a guess.
In short, we don't know and can't know. All we can do is get to a practical minimum and that still adds up to a huge animal.
You have to realise that we have only about 10 good Tyrannosaurus skeletons of a population that could have been in the tens of thousands and around for millions of years. The odds we have a good idea of the largest animal is pretty remote. God and pick 10 random lions today and the odds you have the largest lion ever (or even close to it) are basically nil.
So could Tyrannosaurus have reached 14 m or 15 m, very probably, 16 or 18, even 20? It's far from impossible. But of course picking out true giants can give you a poor impression of what these things were really like there might have been a single Tyrannosaurus that was bigger than every other theropod ever, but if 99% of them were smaller than an averaged sized Giganotosaurus say, it's not really right to say T. rex was bigger.
It's also worth noing that lenght can be pretty misleading. Add a huge tail to an animal and it wouldn't be much heavier bout could be twice as long - Diplodocus is about the same length as Brachiosaurus, but weighted probably less than half as much: would you really call them the same size?
Based on waht we know, there's half a dozen contendors for 'largest' theropod, Spinosaurus, Giganotosaurs, Mapusaurus, Tyrannosaurus and Carcharodontosaurus and probaly a few others like Tarbosaurus and Zhuchengtyrannus were in the same ballpark. Which was on avergae the longest / heaviest, we really don't know, most are know from far too little remains. But all were truly massive.
Hi Cody, I'm afriad I'm not quite sure what question you are asking. Are you talking in more general terms about division of pedators, or are you talking hypothetically about if mallamls still rose up etc.?
I ask becuase, well, if we looked at tyrannosaurs and dromaeosaurs now say (and don't forget the troodontids, they were around then), it's quite unlikely that they would be in the same shape. After all, there would have been 65 million years of evolution, and South America has joined the north in between, allowing abelisaurs, carcharodontosaurs and spinosaurs to move up. Things, in short, would have changed. Dinosaur ecosystems were structred rather differently to mammalian ones too (and not just in terms of size) so it's pretty hard to draw any parallels - a 10 ton bipedal predator is never going to really match up with a 150 kg cat.
In short, there's no real answer here as the two animals, and the two ecologies and just way too different.
I think a good few would do quite well. Things like whales have bounced back quite effectively as soon as hunting stopped so there;s no reason tot hink that if we aleviated various human pressuresd on them they wouldn't continue to improve. As David says, others might be byond the point of no return (not that they cannot be saved, but that it would requite human intervention to save them, so without us helping they might be doomed). Things like Sumatran rhinos are so rare and so scattered that a single disease or bad year with a few accidents might leave them with only a few animals so far apaprt they wouldn't be able to find each other and breed.
On balance I think an awful lot would do pretty well, but sadly not all.
We don't think of fossils species in this way with there being direct ancestor-descendent realtionships. We would say that Tyrannosaurus and Tarbosaurus share an ancestor but that population / species can't be identified (maybe one really did turn into the other, or both came from albertosaurus say, but as we can't know or prove it, we talk about close realtionships and shared ancestry).
As the to the migration question, again it's unknown. Therea re lots of tyrannosaurs in Asia and North America in the Late Cretaceous and there were probably multipl migrations to and from these continents, but an exact pattern has not been worked out.
There's also quite probably an age component. Evolution will select most strongly for things that affect reproduction and child rearing. While obviously there are cancers that affect children and young adults, once you hit middle age, you have grown up and generally had and raised your kids. A cancer hitting them doesn't affect reprodcution or passing on genes and while obviously horrible for the individual, doesn't really affect things in the long run. Hence there's no evolutionary pressure to evolve greater resistance.
Yes, I'd agree with Alistair. With both are felxible to a degree, in general Darwinism would imply simpl;y follwoing the Origin of Species as a maxim, and while this spells out the theory of evolution, that theory has grown and changed immensley since Darwin's day, and so invoking the ToE now implies something rather more advanced.
Eeek! Well there are a few things out there, people have welded together some big trees and while you cant use it as a single diagram (if that's what you want), I would try the Tree of Life website. You can click your way through that and it covers huge numbers of species living and dead.
It's the back part of a mammal skull, and I'd guess a rodent, possibly a rat.
In the lower picture we're looking at the skull from behind, that hole would hold the nerve cord coming from the brain to go to the rest of the body, the two bulges at the bottom look like auditory bullae (expansions to help them hear better, common and large in rodents) and the two spikes out the side are part of the zygomatic arches that link to the cheeks.
The top image shows the skull in ventral view (i.e you are looking up at the roof of the mouth) with the back of th skull at the top of the picture and the snout (if it was there) would rund down into the rock. If you look at this set of photos: http://www.bjorl.org/conteudo/acervo/im -fig01.jpg The one in the bottom left is a pretty good match for your top photo if you cut the front of it off.
Hope this helps.
It's certainly a crab I'd hate to try and say what species but the leg shape and position of the joints are right for a crab and wrong for a spider. Most obviously, it's got no visible abdomen which is pretty much essential for any spider and normal for any crab (in crabs they are present, but folded back under the body).
Whil I agree with the general sentiments here, I'd disagree with David's comment of "should easily get you into a PhD programme at any top university". IT will help certainly, but competition for PhD's are brutal and it's not uncommon for even people with a 1st and an MSc to struggle to find a programme, so I wouldn't say it would 'easily' get you into one.
Yeah, that's pretty much it. When they talk about relatedness at the local level (sibling, parents and offspring etc.) they are talking about only the bits on top of everything else that you do indeed share with a vast number of organisms. It's only a couple of % of your DNA that 'makes' you human so to speak, so yeah, it's that bit that you can be 50% realyed or 3/4 realated as we are indeed about 98% chimp and so on already.
Hi Christopher, as it happens I'm writing a paper at the moment on horned dinosaur sociality so that's rather handy. Your last line is the real issue 'presumed to', it is of course rather hard to work out, but if you keep regularly finding fossils of a dinosaur in groups, then its likely that they were spending a significant amliunt of time together, enough that whole groupd regulalry died together and we can fairly reasonably infer some kind of herding behaviour.
The obvious candidate for this is Pachyrhinosaurus which is known from a huge bonebed of dozens of individuals. Protoceratops is occasioanlly found in groups, but mostly as individuals (so did they come together for only part of the year, or some hered and some didn't etc?). I think Centrosaurus is also known in groups but I'll have to check.
That's interesting, and yeah, 7% is not really a lot by any measure, even if more go towards it later in life, that's a pretty small fraction.
I can't speak about other people's experience, but when I was doing biology in the UK back in the lat 1990s, most people were signing up to join banks or accountancy firms etc. A lot of major businesses like scienists - we are trained to handle number and stats, be organised, work in teams, test ideas and present data clearly. That's a core set of skill that can be applied widely and get get you any number of jobs, and it's not just about the animals and plants.
Surely 'most' can't become teachers or the world would be full of teachers who did a biology degree. If you look on a few departmnet websites, they often now advertise their employment rates or where graduates have gone. Tkae a look and see, or even ask the university what the stats are like.
The first one is a museum catalogue number, the second a nickname of a famous specimen and I assume the third is, but I've not heard of it.
Ah, falling prey to not checking our own index! :) Thanks.
I didn't know that etymology of that, cool stuff Dan.
Most of them are in more open environment it's true, but they do get into rainforests, so I don't think it inappropraite to talk about their potential to be king there. :)
You are right that to an extent 'jungle' overlaps with 'rainforest' to a degree, but I'd call the former a subset of the latter. I was taught that jungle is really just a term for especially thick plant growth at ground level. When a big tree comes down and lets the light in, or around the edge of water, you get huge tangles of short plants and this is jungle. So you get jungle in a rainforest.
As such, really the question could be more boiled down to, do you get lions in rainforests and yes you do, in both Africa and as you say, India.
And the two link together of course - there's a pretty simple mathematical equation that gives you a spiral, and the form of spiral we see in mullucs shells. So there's a real aesthetic in the shape of the shell, and also in the simplicity of the maths that produces it. Very different sides of the coin there I think.
Certainly. While we normally think of lions as living in a pride, it's quite normal for males to live on their own or just with a brother or two. Young males that have not yet taken over a pride or old ones that have been forced out generally live alone and are typically called 'nomads'.
Well the paper it's in says it would be a pterosaur of about 1 m in wingspan. That sounds resoanble, though I didn't see any maths or scaling in their paper (though I didn't read it fully).
My very strong suspicion is that this is a juvenile, and a very young one. Pretty much the smallest adult pterosaurs we know of are right around 1 m in wingspan, and post the Late Jurassic, I can't think of a pterodactyloid under about 2 m in wingspan, and the ornithocheiroids tend to be rather larger at adult (often 4 m and above), so a 1 m one would be rather exceptional.
Ok, I'm totally wrong, they really are very much immune to rattlesnakes and related forms. Wow. Cool!
No idea about the Asutralian lot though....
I think he means that if US possums are immune to rattlensnakes, then might not various Australian ones have evolved immunity to local snakes. I've never heard of possums being immune to snakes though, so while logically it's a reasonable question, I think the underlying assumption is likely incorrect. I'll have a dig a look for it through.
Yeah, it's not the kind of thing you can calculate odds for. I'd simply work under the assumption that if they're there, they'll turn up sooner or later. :)
Cool! I did wonder if such a thing was possible - I can imagine most things good at killing unicellular fungi would also take out other microbes.