Wikipedia:Reference desk/Archives/Science/2016 May 10

= May 10 =

"glider"? "holed shere"?
49.135.2.215 (talk) 00:38, 10 May 2016 (UTC)Like sushi


 * Do you have a question? --69.159.61.172 (talk) 04:04, 10 May 2016 (UTC)


 * A punctured sphere, in which the boundary is included with the sphere is homeomorphic to a disk, and if only a single point is punctured ( or boundary is not included) it is homeomorphic to a plane. Graeme Bartlett (talk) 12:19, 10 May 2016 (UTC)


 * Glider_(Conway's_Life) might be what you're looking for. SemanticMantis (talk) 14:55, 10 May 2016 (UTC)

Light based lifeforms
After seeing this http://phys.org/news/2013-09-scientists-never-before-seen.html, I have wondered whether anyone has proposed the possibility of life forms that are photon-based. Has anyone hypothesized about it? — Preceding unsigned comment added by 24.207.71.235 (talk) 00:41, 10 May 2016 (UTC)
 * If there's somewhere where something crazy "sci fi" might be speculated, a good bet is to start with Star Trek and indeed, they've played with the idea of Photonic lifeforms .But as far as I know, it hasn't gone much further than pure speculation. Vespine (talk) 00:53, 10 May 2016 (UTC)
 * Don't photons usually move? How would you keep it from flying apart at many miles per millisecond? Sagittarian Milky Way (talk) 01:22, 10 May 2016 (UTC)
 * This article is kind of a special situation - something called a Rydberg blockade (despite the bluelink, we don't really explain that, alas). But there is a more general category of two-photon physics.  There are media that slow light substantially.  There are also environments like the photon sphere of a neutron star that bring it around in circles.  I cannot tell you whether and certainly not how you get from such interactions to "life", however it might be defined (which is another can of worms).  But I wouldn't rule it out. Wnt (talk) 02:07, 10 May 2016 (UTC)


 * The light is in an unusual medium that probably wouldn't occur naturally, and that in any case is made of atoms. In vacuum, there is a weak interaction between photons (mediated by virtual charged particles), so it's not necessarily impossible to build an information-processing device out of nothing but photons. It would have to be pretty large, and would probably be ruled out by the positive cosmological constant if nothing else (the cosmological constant limits the size of any object to a few tens of billions of light years across). I think people have written about this sort of thing, but a web search isn't turning up anything. It's hard to come up with good search terms. -- BenRG (talk) 06:29, 10 May 2016 (UTC)


 * See Hooloovoo, a life form referenced by both Douglas Adams and Doctor Who. -- Jayron 32 11:17, 10 May 2016 (UTC)


 * Another place to look (though it's not strictly all-photonic) is self-focusing. It is believed that light beams through interstellar medium can self-focus (there's something about it here, though I remember seeing a better source).  Normally this is seen as inert, i.e. a "railroad" in that source.  However, if you have pulsars and such spinning away broadcasting bright beams that have self-focusing effects, who knows what manner of selective pressures and interactions occur over billions of years of travel?  I doubt it would be anything too spectacular, but I suspect the interaction of the light beams and refractive indexes, with different spots pulling in light from one another and so forth, conceivably might rise to within some technical definitions of life. Wnt (talk) 12:11, 10 May 2016 (UTC)

reverse triangle measurement?
(I would not be commenting, probably)

49.135.2.215 (talk) 00:43, 10 May 2016 (UTC)Like sushi
 * See Trigonometry. --Kharon (talk) 01:38, 10 May 2016 (UTC)

Scalp vs. Beard Follicles
So, this is a question that came up recently, and I don't know if much work has been done on it, since it's kind of a... (I don't want to say useless) but less-important question. Have the changes in cell lines that make up the differences between scalp and beard follicles been identified? I assume it's a series of steps in differentiation that lead to very slightly changed expression of proteins, but I haven't found (so far) any studies that definitively show this.

I did find some interesting papers at this old study and this still pretty old study(the latter of which I haven't fully read since I'm not on campus) that suggest there is a difference that's probably tied to various factors. So I'm curious if this has gone any further.

Thanks, PiousCorn (talk) 04:21, 10 May 2016 (UTC)

ambiguous state diagram
this diagram is from a datasheet on a certain chip by a renowned vendor. I couldn't help but notice that the states 5 and 7 have three outgoing arrows, two of which are associated with the same inputs. so, for example, if we're in state 5 in the middle of the diagram and see {1,0}, we don't know whether to go left or right. I compared the diagram with one from a datasheet by a different vendor which was in a slightly different format, for which purpose I first had to deduct deduce guess which states are which because their numbering scheme was different than my ad-hoc one. In it, only one arrow is associated with the input {0,1}. is this a printing error (in the first diagram) or is there a deeper meaning? If it's a mistake, are such things common in technical documentation? Asmrulz (talk) 11:32, 10 May 2016 (UTC)
 * Please check your link to a diagram which did not open in IE 9. AllBestFaith (talk) 11:57, 10 May 2016 (UTC)
 * It works on Firefox. Are you sure about which input is selecting the line? Perhaps the next state to go to is selected by the numbers in the table below, and the numbers in the circles are the outputs. Graeme Bartlett (talk) 12:06, 10 May 2016 (UTC)
 * I find the diagram opens in Google Chrome. May we know the device because it looks like part of a CMOS 4046 PLL chip? AllBestFaith (talk) 12:28, 10 May 2016 (UTC)
 * The OP seems to have selected part of Figure 1 from this Motorola(?) data sheet where the state change directions for "Phase Comparator 2" are inconsistent with my own Motorola catalog from 1976. (Hint: there's no escape from the extreme left or extreme right states.) I put a question mark after Motorola because their old catalog drawing shows better care with draughtmanship than the obviously hand-sketched lines in the example belie. The same Figure in a different manufacturer's 4046 data sheet is correctly drawn and free of ambiguity. As to the question whether such mistakes are common, there is always a finite probability of error every time technical data is copied manually, that probability increases when the copy is not immediately verified and I once encountered an uncommon form of dyslexia affecting arrow directions. This was a handbook writer who persistently drew diodes the wrong way round when copying from a circuit diagram but couldn't recognize the error when it was repeatedly pointed out. AllBestFaith (talk) 14:02, 10 May 2016 (UTC)
 * you are entirely correct! It's from Motorola's 4046 datasheet I found here. I didn't want to "point the finger" in case it's me who doesn't get something (as a hobbyist) or there exists somewhere a newer, fixed revision (perhaps for people with institutional access to these things). There's something else I don't get. Most of the diagram is edge detection. What if I get hardware interrupts on rising edges anyway (on an ATTiny)? If I have a state table and a step function which takes the inputs, sets the outputs and advances in the table accordingly, where do I plug it (the function, I mean)? Asmrulz (talk) 16:00, 10 May 2016 (UTC)
 * The only likely use for an edge-counting phase comparator is in a PLL where it keeps two equal-frequency i.e. synchronous signals locked together in phase. As long as the rising edges of the two signals arrive simultaneously, the Type 2 comparator output is high impedance which lets the controlled oscillator continue its present frequency neither increased nor decreased. (The 4046 also has a Type 1 comparator which is an XOR gate that can be used in a PLL to lock two equal-frequency Square waves in quadrature.) However you are interested in a CPU handling hardware interrupts that are necessarily asynchronous events that are not timed by or predicted by the main program flow. Historically the Zilog Z80 8-bit microprocessor offered a key feature of a duplicate set of registers which allow the processor to handle the demand of an interrupt while keeping the main program on hold. Modern computer software handles interrupts from multiple sources by using an Interrupt vector table to direct the main CPU temporarily away from the main program to a relevant Interrupt handler code. Wikipedia has articles about interrupt handling in PCs where the main hardware element is the 8259 Programmable Interrupt Controller, and in the 65xx processors. The interrupt handling capability of a particular processor has to be found from its datasheet and usually involves a state machine that is implemented in standard components for that processor. The ATtiny can handle 6 external interrupts and here is its Summary Data Sheet. Its external interrupt handling is described here on page 49. AllBestFaith (talk) 17:18, 10 May 2016 (UTC)
 * sorry, now I'm being ambiguous:) A PLL is what I'm trying to do. Only the first signal is asynchronous. The second signal will be from an oscillator (ideally a software NCO running on the same ATTiny.) I want to output a frequency and an integer multiple of that frequency having a (more or less periodic) pulse train of short pulses as input (from a reed switch.) I read somewhere that the type II comparator is better due to its being immune to duty cycle variations. Asmrulz (talk) 21:32, 10 May 2016 (UTC)
 * You are correct that the edge-counting comparator is unaffected by duty cycle variations in its inputs. But the 4046 comparators are intended to control an analog VCO (there's one inside the 4046) via a low-pass filter that ensures the loop is stable. The filter design is critical if signal purity and speed of acquiring phase lock are important. Alternatively, for a digitally controlled oscillator the article Numerically controlled oscillator may help. That would be a demanding task for a general-purpose 8-bit CPU. AllBestFaith (talk) 00:09, 11 May 2016 (UTC)
 * maybe I should just take the 4046 and use the MCU only as the divider in the feedback path... anyway, thanks a lot! Asmrulz (talk) 08:34, 11 May 2016 (UTC)
 * Thank you everyone for your answers Asmrulz (talk) 08:34, 11 May 2016 (UTC)


 * Asmrulz, since you're building a PLL, you may find Clock and Data Recovery useful. Like everything produced by humans, it probably has some mistakes in it. Like every wiki, we invite you to fix any mistakes you see. --DavidCary (talk) 13:13, 13 May 2016 (UTC)
 * thank you, ! Clock recovery seems relevant. However, "building" is a bit of a grandiose term for what I'm doing :) Asmrulz (talk) 20:39, 13 May 2016 (UTC)
 * I've had moderate success with a 100Hz input signal, a 24-bit NCO which is updated at 8kHz and the state machine phase comparator from the datasheet. I'm simply adding the value (-1,0,1) to the NCO's control word which mathematically is the same as integration. It takes some time to "converge" and there is some jitter. I've had no success with a (naive) software LPF, nor with a running average filter. It oscillates wildly. I think what I'll try next is to output the phase error (moreso as the MCU's pins are tristateable), filter the signal with a real RC network and feed it back to the ADC which will set the control word... Asmrulz (talk) 21:12, 13 May 2016 (UTC)

bullets
If a projectile flies at supersonic speed how it is then with the electrons in the electron orbit of the atomic nucleus? Do they get somehow badly disturbed or pushed out of their orbit? --Ip80.123 (talk) 15:24, 10 May 2016 (UTC)
 * They don't - supersonic speeds are really slow compared to the dimensions relating to the electronic binding forces. --Askedonty (talk) 15:31, 10 May 2016 (UTC)
 * Hypersonic speeds, however, can produce ionization. See particularly Atmospheric entry. Tevildo (talk) 16:28, 10 May 2016 (UTC)
 * It's the gases near the projectile or device in case of reentry which are subject to ionization, but you're right particularly that temperature is to be taken into account. --Askedonty (talk) 17:21, 10 May 2016 (UTC)
 * Calculations show that electrons travel at about 2,200 kilometers per second. That's less than 1% of the speed of light, but it's fast enough to get an electron around the Earth in just over 18 seconds. A very fast bullet is doing about 1200 meters per second - much slower. At that speed a bullet would take over 9 hours to go round the planet. 81.132.106.10 (talk) 16:49, 10 May 2016 (UTC)
 * If electrons "travel". There's problems with that.  See, for example, Larmor formula.  Treating electrons like bullets creates major problems under classical mechanics.  Treating electrons like standing waves instead is much nicer, c.f. Schrödinger equation, quantum mechanics, etc.  -- Jayron 32 16:59, 10 May 2016 (UTC)


 * If the original question regards a supersonic speed of a projectile in air - then indeed that speed (and, more importantly, the acceleration that the projectile undergoes to attain that speed) is too low to substantially perturb the bound electrons, or even the conductance band electrons that are not bound to any particular atom in metal parts of the projectile. Indeed, Fermi energies in typical metals are in the ballpark of 10 eV, which corresponds to electron "velocities" of over 106 m/s, compared to 103 m/s for the projectile itself; and whatever small currents and polarization are induced (by projectile acceleration and charge carriers inertia) should, I think, be quickly dissipated under normal conditions (although I never saw this discussed in literature; I can do the math, but Wiki is not really a place for original research) . By contrast, if you are talking about supersonic speed of propagation in the projectile material itself, then the situation may be different. Supersonic compression wave is called a shock wave. Depending on the strength of the shock and the properties of the material being shocked, the heating in the front of the shock wave may be sufficient to excite or ionize at least some atoms of the material. This does not happen when a bullet is fired from a conventional firearm, but when a sufficiently fast projectile (e.g. from a railgun) impacts a target then these effects may be significant. For further reading see Rankine–Hugoniot conditions. --Dr Dima (talk) 18:03, 10 May 2016 (UTC)


 * Electrons in an atom aren't like little planets orbiting a star. In a sense they're both everywhere and nowhere at the same time, although they have a higher probability of being found in certain places (atomic orbitals). Things are weird at the quantum level, at least to our ape brains that are designed for keeping us alive on the African savanna. Unfortunately this "planetary" or Rutherford-Bohr model still gets displayed all the time as a depiction of "what atoms look like", often without any discussion of what's wrong with it, which puts misleading ideas in people's heads. --71.110.8.102 (talk) 04:47, 11 May 2016 (UTC)


 * The electrons do move at incredible speed - the speed of light times the fine structure constant, or about 1/137 c, in the bottom hydrogen orbital, and faster in proportion to nuclear charge in larger atoms. One result is that around element 137, or 173, the periodic table runs into some weirdness (see extended periodic table - the speed of the electron seems to have to be near c, and if fully ionized, nuclei create electrons and positrons from nothing, and supposedly, this means that neutral atoms of higher numbered elements can't exist.  I do not understand these deductions (note the outermost electrons move far more slowly), but you can see relativistic Dirac equation.
 * That huge thread I have about the magnetic quantum number gives me a way to describe this. The possible position of an electron can be viewed as a standing wave, which is made up of components orbiting in opposite directions.  An electron in an s orbital is just sitting in place in a smooth sphere of probability, but in a p orbital or higher they have angular momentum, so they are orbiting round and round.  Or you may know they are vibrating back and forth along one axis but not know which way they are orbiting round and round, and in quantum terms, that just means you add the orbitals up into a dumbbell.
 * But why don't the electrons fly out? Because electron charge, nuclear charge, is an unimaginably powerful force!  We see lightning spark across the sky from tiny inhomogeneities in the number of protons and electrons.  But in an atom, the charge difference is absolute, and they are absurdly close together.  It's an inverse square law, so in outer orbitals they are less close together - the difference between knocking electrons out with a photon of ultraviolet light versus one of infrared.  And so they move more slowly there. Wnt (talk) 10:38, 11 May 2016 (UTC)

In multiple births, can you get different combinations of fraternal and identical babies?
Let's say that a woman has multiple births: triplets or more. Is it possible that some of those siblings are identical "twins", but some are fraternal "twins"? Or does it have to be all "one or the other"? Thanks. Joseph A. Spadaro (talk) 16:57, 10 May 2016 (UTC)


 * Read the Wikipedia article titled Multiple births, specifically the section Multiple birth and see if that doesn't answer your question. -- Jayron 32 17:00, 10 May 2016 (UTC)


 * Let me check that out. Thanks. Joseph A. Spadaro (talk) 17:04, 10 May 2016 (UTC)


 * No, actually that didn't answer my question. (But -- on a side note -- I never knew that Elisabeth Kübler-Ross was a triplet.)  Let me clarify my question.  Say a woman has 8 babies.  Can Baby 1 and 2 be identical twins (identical only to each other)?  And Baby 3 and 4 and 5 are fraternal triplets?  And Baby 6 and 7 are identical twins to each other (but not identical to Baby 1 and 2)?  Different permutations like that?  Or are all 8 going to be completely identical or completely fraternal?  Thanks. Joseph A. Spadaro (talk) 17:08, 10 May 2016 (UTC)
 * From the first sentence of the section I directed you to: "Identical triplets come from a monozygotic pregnancy, three fetuses from one egg. The commonest set, strictly fraternal triplets, comes from a polyzygotic pregnancy of three eggs. Between these types, triplets that include an identical (monozygotic) pair of siblings plus a fraternal sibling are the result of a dizygotic pregnancy, where one zygote divides into two fetuses and the other doesn't. The Kübler triplets (see Elisabeth Kübler-Ross) were of this type." That is, the answer is "all possible variations can exist".  -- Jayron 32 18:05, 10 May 2016 (UTC)
 * Here's a study on triplets that says "65.8% of the sets were thought to contain both identical and fraternal siblings." The authors then say detailed genetics will be presented in a future study, and I don't time to look that up right now. But at 65.8 percent, even with a lot of error, it sounds like the answer to your question in is "yes" - in triple and higher multiple births in humans, some groups can be monozygotic while other groups came from a different zygote, all in the same litter. SemanticMantis (talk) 17:26, 10 May 2016 (UTC)


 * Yes. It's statistically unlikely just because identical twins aren't that likely and neither are triplets or higher - but there is nothing to prevent it from happening. SteveBaker (talk) 17:28, 10 May 2016 (UTC)


 * I see now that this is actually made clear for n=3 at Multiple_birth. It is not the case that all n babies would have to be either all fraternal or all identical - they can be mixed and matched. For n>3, the section on quadruplets also makes it clear that all-identical quadruplets are much rarer than general quadruplets, and clearly states (though without explicit reference) that other combinations (4F, 2F-2I, 1F-3I, 2I-2I) are all possible. SemanticMantis (talk) 17:33, 10 May 2016 (UTC)


 * If you want to get freaky, take a look at superfecundation. 91.155.193.199 (talk) 18:13, 10 May 2016 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 16:21, 14 May 2016 (UTC)

The percentage of surfactants in my washing up detergent
The ingredients on many cleaning products give a range of surfactants instead of a fixed percentage. Are they doing this because they want to give us 15% and tell us we're getting 15-30% or is the manufacturing process just so hit and miss than they're not sure how much anionic surfactants we're getting? — Preceding unsigned comment added by 78.148.108.58 (talk) 21:45, 10 May 2016 (UTC)
 * More probably because a group of chemistry students, testing the product using different methods will get a range as the result, not a stable quantity. See Surface tension, Gibbs isotherm (definition of surface excess), Hydrophilic-lipophilic balance. -Askedonty (talk) 22:32, 10 May 2016 (UTC)
 * Why should students' results matter? Surely a business producing cleaning products knows what they're putting in and can employ a graduate if necessary?? --78.148.108.58 (talk) 23:51, 10 May 2016 (UTC)
 * You can guess that the head of laboratory agrees with your analysis and they already applied the strategy. The point is that they want to give numbers regarding efficiency and so it's not only about measuring grains, because the substance will behave differently according to conditions (see Gibbs isotherm, aso ). So far as I remember they are doing so also as a way of strongly marking the boundary between their field and all the various food industries, this was considered an important point in the past 60's-70's, so the reference to students, as safety conducts in the industry and this more than in one way do start with them. --Askedonty (talk) 07:38, 11 May 2016 (UTC)


 * Under European rules, the ingredients of a washing up liquid need to be listed, but for trade secrets reasons, they don't have to give the exact formula. Instead, they can simply label them in bins of "less than 5%", "5% to 15%", "15% to 30%" and "more than 30%". See Guidelines on the implementation of the Detergents Regulation, page 11. Smurrayinchester 08:10, 11 May 2016 (UTC)
 * What I don't get is why this subterfuge is useful. I would think by now that some intro chemistry classes around the world (if no one more commercially interested) would make a point of analyzing brands and publishing best guesses about the ingredients.  It seems like a public-interest thing, and a potential geek hobby. Wnt (talk) 12:45, 11 May 2016 (UTC)
 * And anyone with the right screwdriver and a pair of pliers can take apart an iPhone, but Apple still keeps its plans super-secret. No reason to make the task of reverse engineering any easier than it has to be. Smurrayinchester 13:22, 11 May 2016 (UTC)

2 Dinosaur questions
1. What was the difference between a pterodactyl and a pteranodon? 2. are birds living dinosaurs? 50.68.120.49 (talk) 22:00, 10 May 2016 (UTC)
 * Is this a homework question? The 1st question was very easy to answer just by reading a little of the articles. The second question is also very easy to answer with a simple google search. Is there something specific you are having trouble understanding? Vespine (talk) 22:28, 10 May 2016 (UTC)
 * I somehow doubt this is a homework question as it wouldn't ask about 1 in a dinosaur assignment. This isn't any easier to find in our articles than half the other questions around here...
 * 1) Neither are dinosaurs, so this is not a dinosaur question. They are two different genera of pterosaur. It is sort of like the difference between humans and chimpanzees. We are both in the hominid family, but we are different genera and species. I think they may also have been in different families, putting them further apart. Are you looking for more phylogeny differences?
 * 2) That does seem to be the scientific consensus, yes. See evolution of birds. --OuroborosCobra (talk) 22:34, 10 May 2016 (UTC)
 * Birds are dinosaurs, but pterosaurs are not, despite the name! The article on Pteranodon places it in Pterodactyloidea, i.e. it is a pterodactyl; the term is used more broadly but inaccurately to refer to other pterosaurs, but not birds/dinosaurs.  It is widely believed flight evolved independently in birds and pterosaurs. Wnt (talk) 10:53, 11 May 2016 (UTC)
 * Pterodactyl and Pterodactyloidea are not synonymous; one is a specific genus within a family and order, the other is a given order (or suborder). A pteranodon is not a oterodactyl, but it is a pterodactyloidea. --OuroborosCobra (talk) 11:51, 11 May 2016 (UTC)
 * I see pterodactyl redirects to Pterodactylus. Nonetheless, as explained at Pterodactyloidea, the term is used more broadly to include that group.  "Pterodactyl" is, after all, a near common name generally used for a broad group of animals, and an interpretation that limits it to just one species seems contrary to this. Wnt (talk) 12:41, 11 May 2016 (UTC)
 * It may help to step back a bit and consider how organisms are classified:
 * 1) The traditional way was to group similar species in to genra, genera into families, and so forth. The main ranks were species, genus, family, order, class, phylum, and kingdom.  To answer your first question: pterodactyl and pteranodon were separate genera, in separate families, within the order Pterosauria.  This means they were not dinosaurs, because "dinosaurs" was a super-order made of two other orders.  Dinosaurs and pterosaurs are closely related, but are different enough to be considered different.
 * (But if you just want a basic descriptive answer: Pterodactyl was about the size of a parrot, Pteranodon was about the size of a hang glider (and had a bony crest on the back of its head)).
 * 2) Under the old Linnaean scheme, birds are not dinosaurs. Birds are a class, which is a higher rank than dinosaurs.  This is despite them being directly descended from them (and more specifically, from a specific group of them).  And this is where the Linnaean system starts to break down and give some silly results.  Also, I mentioned that dinosaurs are a super order.  People like neat classifications, but Nature doesn't.  There are all sorts of animals and groups of animals that are too different to fit into one of the classic ranks, but too similar to be spilt between higher ranks.  So you end up with a whole mess of sub/super/infra groups.
 * For this reason, a lot of scientists now prefer to ignore the old ranks completely, and group things into unranked Clades, defined by ancestry. Under this scheme, birds are a type of dinosaur, because anything descended from a dinosaur is by definition also a dinosaur.  This can take a bit of getting used to, but when you consider that there is no clear point when "obvious" dinosaurs turn into "obvious" birds, but rather a gradual transition with a lot of dinosaurs that look rather bird-like (including ones that were not ancestors of birds), and a lot of early birds that still had many "traditional" dinosaur features, it starts to make sense.  (Consider for example: most of the relatives and ancestors of T. rex had feathers. See also Deinonychus and Velociraptor.  Or more generally, Feathered_dinosaur.  Iapetus (talk) 12:24, 11 May 2016 (UTC)


 * To add a perspective to Iapetus's excellent answer, imagine that you're standing in a forest 68 million years ago. Many of the creatures you can see around you are dinosaurs. Some of the species you see are big reptilian looking things, some are similar but with feathers (T. Rex itself may have had feathers when juvenile), some are smaller with feathers but are not birds, some other very similar and related ones are birds looking quite similar to modern birds, and it's obvious (both from casual inspection and from any anatomical and genetic analyses you care to do) that there are no major differences between the "non-birds" and the "birds": the "birds" are just some of the varieties of these smaller feathered dinosaurs. (Then a T. rex eats you.) This is not so obvious today because in the present time we only see the birds around us, not any of the very similar small feathered dinosaurs, or any of the less bird-like dinosaurs: if we could see the latter also we'd realise more easily that the birds were and are just a particular subset of dinosaurs. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 13:54, 11 May 2016 (UTC)
 * All of that and no one has actually mentioned the MAIN difference between Pterodactylus and Pteranodon. A pterodactyl grew to have a wingspan of about 1m, while a Pteranodon grew to an average wingspan of almost 6m! Vespine (talk) 22:44, 11 May 2016 (UTC)


 * Birds in general are not always living dinosaurs a clear counter example can be seen here: https://www.youtube.com/watch?v=npjOSLCR2hEGr8xoz (talk) 22:48, 11 May 2016 (UTC)


 * When I visited Glen Rose, Texas - where one may visit Dinosaur Valley State Park and to put your hand into a for-real dinosaur footprint (PICTURE) on the same day watch Emu's feet (PICTURE) at the nearby Fossil Rim Wildlife Center - it's hard not to believe that the animals are related. SteveBaker (talk) 01:57, 12 May 2016 (UTC)