# Most recent common ancestor of all living birds **URL:** \ **Category:** Factual Questions\ **Created:** [July 15, 2014, 11:10pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234 "2014-07-15T23:10:52Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [July 16, 2014, 4:02pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/21 "2014-07-16T16:02:51Z")
> [@iiandyiiii](#): > > Fine – they’re dinosaurs. They’re also birds, so I don’t think I’m confusing anyone when I say “birds evolved from dinosaurs”. Well… only if you’re also comfortable with people saying that the great white evolved from sharks. ---
**Author:** ![iiandyiiii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/iiandyiiii/32/7924_2.png) [@iiandyiiii](https://boards.straightdope.com/u/iiandyiiii)\ **Post date:** [July 16, 2014, 4:20pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/22 "2014-07-16T16:20:39Z")
> [@dracoi](#): > > Well… only if you’re also comfortable with people saying that the great white evolved from sharks. Sure… I don’t see how that would be a problem. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 16, 2014, 4:43pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/23 "2014-07-16T16:43:25Z")
> [@John\_Mace](#): > > When you consider the rareness of fossils, the odds are stacked against it being in the direct line of descent. But, of course, every paleontologist wants to be the guy (or gal) who discovers the so-called missing link, and not just some ancestor to a dead end branch on the evolutionary tree. You’ll almost never find a direct ancestor; the chances are too small to hit that one particular species of all that were in existence at the time. However, Archaeopteryx may not be particularly close to even the main line. [Here’s](http://link.springer.com/static-content/images/228/art%253A10.1007%252Fs12052-009-0133-4/MediaObjects/12052_2009_133_Fig4_HTML.gif)one concept of the phylogeny of early birds. Archaeopteryx branched off in the mid-Jurassic, while the common ancestor of modern birds dates to the Late Cretaceous. Archaeopteryx may in fact be closer to the Dromeosaurids than to the ancestors of modern, essentially a flying Velociraptor. (It had a “killing claw” like one.) Some have even proposed that _Velociraptor_ itself was descended from flying ancestors, and had secondarily lost the power of flight. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [July 16, 2014, 5:01pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/24 "2014-07-16T17:01:49Z")
> [@iiandyiiii](#): > > And, by the way, humans are more closely related to certain kinds of fish (like lobe-finned fish, if I understand it correctly), then those certain kinds of fish are to other kinds of fish (like sharks). So humans as a sub-category of fish, cladistically speaking, is just as accurate as birds as a sub-category of dinosaurs. Only because ‘fish’ is so broad and inclusive a collection as to be a useless term outside of the kitchen. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 16, 2014, 5:35pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/25 "2014-07-16T17:35:24Z")
> [@Shagnasty](#): > > No, it is not. Modern birds are firmly in the middle of the evolutionary pack when it comes to describing ‘dinosaurs’ that everyone tends to agree on in common nomenclature. They aren’t some modern offshoot of them. They are in fact dinosaurs and more closely related to species that anyone one would agree is a dinosaur than other ancient dinosaur species are to each other. Like other issues, such as whether apes are monkeys and humans are apes, what you call birds depends on whether you are using the words according to their common English meanings, or speaking cladistically. In common usage, “bird” means something different than “dinosaur,” just as “human” means something different than “monkey,” even if cladistically speaking they are part of the larger group. Scientifically speaking, a “bird” is any member of the clade Aves, which lies within the theropod dinosaurs. However, what forms are included in that clade is controversial. Some paleontologists include Archaeopteryx in the clade, while others do not. Besides the members of Aves, it seems that some other small feathered dinosaurs independently gained the power of flight, including the [bizarre four-winged _Microraptor_.](http://www.wildlifeartist.com.au/images/F046s.jpg) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 16, 2014, 6:02pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/26 "2014-07-16T18:02:36Z")
What gets called “birds” is pretty consistent between taxonomists and common folks. Yeah, there’s going to be some quibbling over Archaeopteryx and the like, but those are edge cases. Everyone agrees that sparrows, geese, and eagles are birds, while tyrannosaurs, triceratopses, and brontosauri are not. The term that varies in meaning is “dinosaur”, with taxonomists including birds, and most lay folks excluding them. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [July 17, 2014, 8:05am UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/27 "2014-07-17T08:05:24Z")
> [@Mangetout](#): > > Only because ‘fish’ is so broad and inclusive a collection as to be a useless term outside of the kitchen. Or in other words, if humans are fish, then so are dolphins and whales - there’s an order of magnitude difference between [humans being in the group ‘fish’], and [birds being in the group ‘dinosaurs’]. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [July 17, 2014, 9:48am UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/28 "2014-07-17T09:48:02Z")
Between species, I think it’s usually better to use the term “Last Common Ancestor” instead of “Most recent common ancestor.” It sounds to me like you are looking for the species from which all current birds are descended, along with modifications of a (sort of progenitor) gene set that was more or less entirely originally contained within that species. The MRCA is a commonly confused term, especially with respect to human ancestry, because people hear the term and think it means the individual(s) from which all our genes came. In fact, a (mathematically modeled theoretical\*) MRCA for humans may be the ancestor of almost none of the actual gene (variants) for a given living human. MRCA used that way just means all current individuals could trace grandparents back far enough to find their geneological MRCA somewhere in the past set of ancestors. Another post series, perhaps. Anyway, I think LCA is a better term to use here (or “concester,” to borrow a term I think Richard Dawkins credits Nicky Warren with creating). You might find Dawkins’ The Ancestor’s Tale interesting reading… [\*See mathematical modeling work by Douglas Rohde, for example.](http://www.nature.com/nature/journal/v431/n7008/full/nature02842.html) ---
**Author:** ![iiandyiiii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/iiandyiiii/32/7924_2.png) [@iiandyiiii](https://boards.straightdope.com/u/iiandyiiii)\ **Post date:** [July 17, 2014, 11:11am UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/29 "2014-07-17T11:11:20Z")
> [@Chief\_Pedant](#): > > Between species, I think it’s usually better to use the term “Last Common Ancestor” instead of “Most recent common ancestor.” It sounds to me like you are looking for the species from which all current birds are descended, along with modifications of a (sort of progenitor) gene set that was more or less entirely originally contained within that species. This sounds like exactly the same thing. How is LCA different than MRCA? The “most recent” is the “last”, and vice versa. I understand one is used, in general, for intra-species, and the other for inter-species, but they both call for the same creature. > [@](#): > > The MRCA is a commonly confused term, especially with respect to human ancestry, because people hear the term and think it means the individual(s) from which all our genes came. In fact, a (mathematically modeled theoretical\*) MRCA for humans may be the ancestor of almost none of the actual gene (variants) for a given living human. MRCA used that way just means all current individuals could trace grandparents back far enough to find their geneological MRCA somewhere in the past set of ancestors. Another post series, perhaps. This seems completely irrelevant to the thread. I’ve read the Ancestor’s Tale, by the way – one of my favorite books on evolution and science. ---
**Author:** ![Ken001](https://avatars.discourse-cdn.com/v4/letter/k/43a26b/32.png) [@Ken001](https://boards.straightdope.com/u/Ken001)\ **Post date:** [July 17, 2014, 11:53am UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/30 "2014-07-17T11:53:02Z")
> [@Chief\_Pedant](#): > > You might find Dawkins’ The Ancestor’s Tale interesting reading… That is a fascinating book which I have recommended to friends of a scientific bent and which I intend to re-read. But just for accuracy, there are birds which have teeth, its just that most of us are unaware of them. I give you the Greylag Goose (and friends) - > **[Brush Your Beak: 10 Amazing Birds With Teeth](https://webecoist.momtastic.com/2010/09/28/brush-your-beak-10-amazing-birds-with-teeth/)** > > Do birds have teeth? Ask any biologist and the answer will be "absolutely not!", but "absolute" is a relative term and when one stretches the definitions of what makes a bird or a tooth, birds with teeth aren't absolutely impossible anymore. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [July 17, 2014, 4:13pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/31 "2014-07-17T16:13:42Z")
None of those are true bird teeth. ---
**Author:** ![Koxinga](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@Koxinga](https://boards.straightdope.com/u/Koxinga)\ **Post date:** [July 17, 2014, 4:22pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/32 "2014-07-17T16:22:48Z")
> [@MrDibble](#): > > None of those are true bird teeth. Not even the ones sported by the Curtiss P-40 Warhawk? (I somehow suspect this wasn’t meant to be a strictly scientific article.) ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [July 17, 2014, 4:44pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/33 "2014-07-17T16:44:15Z")
> [@Ken001](#): > > That is a fascinating book which I have recommended to friends of a scientific bent and which I intend to re-read. > > But just for accuracy, there are birds which have teeth, its just that most of us are unaware of them. > > I give you the Greylag Goose (and friends) - > > [Brush Your Beak: 10 Amazing Birds With Teeth - WebEcoist](http://webecoist.momtastic.com/2010/09/28/brush-your-beak-10-amazing-birds-with-teeth/) > [@MrDibble](#): > > None of those are true bird teeth. Indeed. From the link (emphasis added): > [@](#): > > Tooth-like serrations called Tomia run along the outside edges of the Greylag’s beak… ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [July 17, 2014, 4:58pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/34 "2014-07-17T16:58:46Z")
Technically birds are a line of [maniraptoran theropod dinosaur](http://www.ucmp.berkeley.edu/diapsids/saurischia/maniraptora.html), generally from the line of critters that produced _Velociraptor._ Maniraptorans have unique wrist bones to enable a particular grasping motion with the forelimbs. It’s been theorized that this evolved into the “flight stroke” birds use for lift. I’ve seen several assertions that what survived the K-Pg extinction spike was not particularly related to such status as “birds” or “mammals” so much as it was “small.” No animal of any kind weighing more than about 20 pounds in mass is believed to have survived the meteor impact. The implication I’ve seen drawn from this is that _burrowing_ animals tend to be small. One experiment on one of those science channels showed that burrows only a few inches beneath the ground would be tolerable despite a 1,500-degree fire at ground level. Since the Chicxulub impactor probably set _the entire surface of the earth on fire_, only burrowing (i.e, small) land animals survived. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 17, 2014, 5:02pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/35 "2014-07-17T17:02:10Z")
> [@Ken001](#): > > But just for accuracy, there are birds which have teeth, its just that most of us are unaware of them. Just for accuracy, no modern birds have true teeth, in the sense of the dentine-and-enamel structures that other vertebrates have. The teeth depicted are modifications of the horny beak. The article, however, is interesting in showing how birds have successfully coped with the loss of true teeth by developing modifications of the bill. Early birds, like their theropod ancestors, had true teeth like those of other vertebrates. Modern birds have lost these. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [July 17, 2014, 6:03pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/36 "2014-07-17T18:03:47Z")
> [@Sailboat](#): > > Technically birds are a line of [maniraptoran theropod dinosaur](http://www.ucmp.berkeley.edu/diapsids/saurischia/maniraptora.html), generally from the line of critters that produced _Velociraptor._ > > Maniraptorans have unique wrist bones to enable a particular grasping motion with the forelimbs. It’s been theorized that this evolved into the “flight stroke” birds use for lift. > > I’ve seen several assertions that what survived the K-Pg extinction spike was not particularly related to such status as “birds” or “mammals” so much as it was “small.” No animal of any kind weighing more than about 20 pounds in mass is believed to have survived the meteor impact. The implication I’ve seen drawn from this is that _burrowing_ animals tend to be small. One experiment on one of those science channels showed that burrows only a few inches beneath the ground would be tolerable despite a 1,500-degree fire at ground level. > > Since the Chicxulub impactor probably set _the entire surface of the earth on fire_, only burrowing (i.e, small) land animals survived. I’ve seen estimates that also suggest nothing over about 5 pounds survived. Plus, there’s the steam/hot air blast, the flash that would have set much of organic matter on fire, etc. Then there’s the question of what to eat until the ecosystem re-established itself, and a series of deep winters brought on by smoke and soot, and cloud cover. it was a long-term challenge for anything to survive. By what DID survive - small, semi-aquatic or otherwise sheltered - we assume there are some tiny enclaves that survived long enough to become the prototypes to go forth, multiply, and replenish the earth; to expand to fill emerging ecological niches. These would be mouse-like creatures, chicken-sized or smaller feathered dinosaurs, some interesting hold-overs like crocodiles, turtles, etc. ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [July 17, 2014, 6:23pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/37 "2014-07-17T18:23:24Z")
> [@Shagnasty](#): > > Birds didn’t just _evolve_ from dinosaurs, they _are_ dinosaurs. That isn’t just a semantic quibble. Modern day birds like chickens are more closely related to T-Rex than T-Rex is related to crocodiles or even other dinosaurs like the Stegosaurus. Okay, but what’s the basis for calling them dinosaurs? I’m not disagreeing that they are dinosaurs, I’m just asking how we know that. That they’re more closely related to T-Rex than T-Rex is to other dinosaurs doesn’t tell me that birds are dinosaurs. I’ve always wondered this but never wondered hard enough to actually ask. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [July 17, 2014, 6:47pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/38 "2014-07-17T18:47:27Z")
The usual argument I see gives a simple tree and says see we call both of the things below this node dinosaurs and birds descend from just one of those types of things so you have to call birds dinosaurs, too. But the argument has to be more than that. I’m you can draw the same type of tree for reptiles and mammals. Mammals descend from one particular group of reptiles so if you want to say both types of reptiles are reptiles you have to include mammals. Now maybe evolutionary biologists do say that or something similar, but the only thing I see them beat us up over is “birds are dinosaurs” not “dogs are reptiles”. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [July 17, 2014, 6:52pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/39 "2014-07-17T18:52:51Z")
> [@Folacin](#): > > Seriously, though, teeth rot and/or fall-out, limiting the ability to eat. A beak seems a simpler solution. Although why more creatures don’t have beaks instead of teeth speaks against that idea. > [@Mangetout](#): > > No it doesn’t (the graped part) - evolution doesn’t work like that. Selection can only occur from things that are there to be selected. If other creatures never developed a mutation for a proto-beak, then it couldn’t be selected, and it doesn’t matter if it would have been better than what they had. **Folacin** ’s argument isn’t actually a bad one. It’s not a particularly strong argument, but it is valid to say “Given that there has been plenty of time for other lineages with vaguely similar diets to evolve beaks, and that we don’t know any reason why these lineages would have had any more difficulty transitioning to beaks than birds, the fact that other lineages haven’t evolved beaks is some evidence that beaks are probably not advantageous absent the particular situation of birds (most likely flight)”. Again, it’s only weak evidence: there’s so much we don’t know for sure, and there could be all kinds of reasons why a transitional partial beak was advantageous to early birds but wouldn’t be for mammals or reptiles. Since it relies on unknowns, it’s only a weak argument. But, absent any other knowledge or arguments for or against, it’s enough for me to tentatively conclude that, absent weight and balance issues of flying animals, teeth are generally superior to beaks. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 17, 2014, 7:18pm UTC](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234/40 "2014-07-17T19:18:14Z")
> [@Frylock](#): > > Okay, but what’s the basis for calling them dinosaurs? I’m not disagreeing that they are dinosaurs, I’m just asking how we know that. That they’re more closely related to T-Rex than T-Rex is to other dinosaurs doesn’t tell me that birds are dinosaurs. Under cladistic taxonomy, clades are defined on the basis of a most recent common ancestor. The clade Dinosauria is currently generally defined as that which includes the ancestors of both the Ornithischian (ceratopsians such as Triceratops, duckbills, stegosaurs, etc) and Saurischian (theropods, including birds, and sauropods). Since birds are theropods, they are therefore in the clade dinosaurs. From [Wiki:](http://en.wikipedia.org/wiki/Dinosauria) > [@](#): > > Under phylogenetic taxonomy, dinosaurs are usually defined as the group consisting of Triceratops, Neornithes [modern birds], their most recent common ancestor (MRCA), and all descendants".[12] It has also been suggested that Dinosauria be defined with respect to the MRCA of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria.[13] Both definitions result in the same set of animals being defined as dinosaurs: “Dinosauria = Ornithischia + Saurischia”, > [@OldGuy](#): > > But the argument has to be more than that. I’m you can draw the same type of tree for reptiles and mammals. Mammals descend from one particular group of reptiles so if you want to say both types of reptiles are reptiles you have to include mammals. Now maybe evolutionary biologists do say that or something similar, but the only thing I see them beat us up over is “birds are dinosaurs” not “dogs are reptiles”. Although the mammals evolved from animals similar to modern reptiles, the trend today is call these basal [amniotes](http://en.wikipedia.org/wiki/Amniote) instead of reptiles. Amniotes are animals with an amniote egg (or descended from them) suitable for reproduction on land. The ancestors of mammals branched off earlier than those of other surviving amniotes, and are recognized as the clade [Synapsida.](http://en.wikipedia.org/wiki/Synapsid) The other major branch of the amniotes is the [Sauropsida,](http://en.wikipedia.org/wiki/Sauropsida) which includes the living animals traditionally called reptiles plus birds. If a clade Reptilia is recognized, it includes the traditional members of the Class Reptilia (turtles, lizards, snakes, crocodilians, tuatara) + birds. This clade does not include mammals. Here’s a [diagram,](http://www.palaeos.org/images/thumb/6/62/Paraphyletic.png/334px-Paraphyletic.png) which indicates the traditional “reptiles” in purple. Recognizing mammals as Reptilia would be equivalent to just saying that Amniota is synonymous with Reptilia, which would be redundant. [Previous page](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234.md?page=1) [Next page](https://boards.straightdope.com/t/most-recent-common-ancestor-of-all-living-birds/693234.md?page=3)