# Dinosaur extinction **URL:** \ **Category:** Factual Questions\ **Created:** [July 17, 2010, 7:33pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053 "2010-07-17T19:33:52Z")\ **Posts on this page:** 12\ **Page:** 4
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [July 19, 2010, 7:01pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/61 "2010-07-19T19:01:52Z")
> [@Colibri](#): > > Molecular data suggest that quite a few [avian lineages](http://www.ncbi.nlm.nih.gov/pubmed/18226223) survived the KT event. That goes for [mammalian lineages](http://www.pnas.org/content/100/3/1056.full) as well. Maybe I’m misinterpreting the abstracts, but those papers seem to address when the currently extant lineages began, instead of how many of the lineages of that time survived the event. ---
**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 19, 2010, 7:29pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/62 "2010-07-19T19:29:06Z")
> [@engineer\_comp\_geek](#): > > I do see your point, but that’s not quite true. The K-T extinction event picked on certain types of species much more than others. Some families managed to survive almost completely intact. > > Everything big died. Period. Nothing over a few hundred pounds survived. This isn’t surprising, since when food gets scarce, the big guys that need the most food die first. Discovery Channel said everything over _twenty_ pounds died. Their supposition was that no large animals burrow, and only (in their supposition) burrowed species survived on land (the worldwide firestorms). They tested a representative plot of forest in blast furnace at 1500 degrees F, and ten inches below the surface the temperature was around 100 degrees or so, quite survivable. ---
**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 19, 2010, 7:33pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/63 "2010-07-19T19:33:06Z")
> [@Pleonast](#): > > Maybe I’m misinterpreting the abstracts, but those papers seem to address when the currently extant lineages began, instead of how many of the lineages of that time survived the event. It doesn’t give the percentage of survivors. My point was just that a variety of different lineages of both birds and mammals apparently survived the event, not just a few. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [July 19, 2010, 7:57pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/64 "2010-07-19T19:57:53Z")
> [@Colibri](#): > > It doesn’t give the percentage of survivors. My point was just that a variety of different lineages of both birds and mammals apparently survived the event, not just a few. I’m confident you’re right, because you know this field, but your cite doesn’t support “not just a few”, since it talks only about modern lineages and not at all about those that went extinct. For all I know (and consistent with that paper), there were thousands of bird lineages that went extinct at the KT event, and only a small fraction survived to modern times. Of course, I don’t know how many avian lineages there were and I assume you actually have a good idea (even if that cite doesn’t address it), so your statement is good enough for me. ---
**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 19, 2010, 9:04pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/65 "2010-07-19T21:04:51Z")
> [@Pleonast](#): > > I’m confident you’re right, because you know this field, but your cite doesn’t support “not just a few”, since it talks only about modern lineages and not at all about those that went extinct. For all I know (and consistent with that paper), there were thousands of bird lineages that went extinct at the KT event, and only a small fraction survived to modern times. By “not just a few” I mean more than two or three. Of course every species alive at the time represents a “lineage” in a sense. Since there probably were thousands of bird species extant at the time of the KT event, the ones that survived to the present do represent only a small fraction of the ones living at the time. [This article](http://www.sciencemag.org/cgi/content/abstract/275/5303/1109) indicates that there were at least 22. However, there could have been thousands of species of small non-avian dinosaurs also living at the time, and none of them made it (that we know of). So it’s a bit of a surprise why one group might have had a couple of dozen survivors, while the other had zero. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [July 20, 2010, 8:15am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/66 "2010-07-20T08:15:26Z")
Could the sparsity of dino fossils at or just before the K-T boundary be a result of the impact and its subsequent effects, rather than an indicator of a decrease in the number of dino species extant at that time? In other words, could the impact and all the attendant phenomenon (superhurricanes and whatnot) have destroyed many of the bones that otherwise would have fossilized? For example, it could have caused severe erosion in areas that had lots of buried bones, thus preventing them from fossilizing. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [July 20, 2010, 9:17am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/67 "2010-07-20T09:17:35Z")
Did any non-coastal, non-riverbank, megafauna survive the K-Pg extinction? ---
**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 20, 2010, 3:28pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/68 "2010-07-20T15:28:09Z")
> [@dtilque](#): > > Could the sparsity of dino fossils at or just before the K-T boundary be a result of the impact and its subsequent effects, rather than an indicator of a decrease in the number of dino species extant at that time? In other words, could the impact and all the attendant phenomenon (superhurricanes and whatnot) have destroyed many of the bones that otherwise would have fossilized? For example, it could have caused severe erosion in areas that had lots of buried bones, thus preventing them from fossilizing. That’s probably not the reason for it. Many places show an iridium-enriched layer at the KT presumably from the asteroid (and which is one of the primary lines of evidence for an impact) that would have been laid down immediately after the impact, indicating that there would not have been a great deal of erosion post-impact. > [@Quartz](#): > > Did any non-coastal, non-riverbank, megafauna survive the K-Pg extinction? No. Basically the only large air-breathing animals to survive the extinction were aquatic and semi-aquatic like forms like crocodilians and champosaurs. For millions of years after the event, the largest terrestrial animals were probably not much bigger than a small dog. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [July 20, 2010, 4:51pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/69 "2010-07-20T16:51:58Z")
About finding fossils: I don’t know that much, but this is what I have read: Yes, there’s a lot of land mass; but generally remains of animals decayed, were eaten, weathered, etc to dust. Fossils are a special case; in areas with severe sudden landslides, or rivers flowing with silt, shallow seas with silt deposits, any dead animals would be covered with mud and the bacteria would be deprived of oxygen, so decay would not set in very quickly. The result is that mud would harden to rock still containing the detectable remains. As a result, there are a few sites where the rock formations from early silt deposits still exist. For dinosaurs, this is in areas like up and down the west coast of the ancient inland sea that ran from Texas to the Arctic. There are a few other areas also famous for the deposits where dinosaur-era fossils can be found. Most discoveries are in these few areas, so the fossil record is limited to what died and got buried quickly in certain geological situations. IIRC, grass evolved later, so in those days erosion and silt build-up was much heavier. ---
**Author:** ![Grendel\_s\_Father](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grendel\_s\_Father](https://boards.straightdope.com/u/Grendel_s_Father)\ **Post date:** [July 20, 2010, 11:38pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/70 "2010-07-20T23:38:27Z")
> [@md2000](#): > > About finding fossils: I don’t know that much, but this is what I have read: > > Yes, there’s a lot of land mass; but generally remains of animals decayed, were eaten, weathered, etc to dust. Fossils are a special case; in areas with severe sudden landslides, or rivers flowing with silt, shallow seas with silt deposits, any dead animals would be covered with mud and the bacteria would be deprived of oxygen, so decay would not set in very quickly. The result is that mud would harden to rock still containing the detectable remains. > > As a result, there are a few sites where the rock formations from early silt deposits still exist. For dinosaurs, this is in areas like up and down the west coast of the ancient inland sea that ran from Texas to the Arctic. There are a few other areas also famous for the deposits where dinosaur-era fossils can be found. Most discoveries are in these few areas, so the fossil record is limited to what died and got buried quickly in certain geological situations. > > IIRC, grass evolved later, so in those days erosion and silt build-up was much heavier. All true, but in the late Campanian/early Maastrictian stages only a few million years before the K-Pg fauna, we have representative dinosaur faunas from all across the northern hemisphere and the explored parts of the southern-- North America, all across central and eastern Asia, South America, eastern Europe. Each had a diversity of species nearly double what we find in the few K-T age formations. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [July 21, 2010, 1:43am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/71 "2010-07-21T01:43:42Z")
Well, birds are dinosaurs by a cladistic definition. See when Richard Owen came up with that term, he included two very different reptile-like animals in what he called “Dinosaurs”. If you insist the two types are both dinosaurs, then birds are then also dinosaurs. (I don’t entirely agree, the fossil evidence is not solid enough to say _with certainty_ that birds did not evolve from archosaurs.) wiki ;_"Under phylogenetic taxonomy, dinosaurs are usually defined as the group consisting of “Triceratops, Neornithes [modern birds], their most recent common ancestor, and all descendants.”[11] It has also been suggested that Dinosauria be defined with respect to the most recent common ancestor of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria.[12] Both definitions result in the same set of animals being defined as dinosaurs, including theropods (mostly bipedal carnivores), sauropodomorphs (mostly large herbivorous quadrupeds with long necks and tails), ankylosaurians (armored herbivorous quadrupeds), stegosaurians (plated herbivorous quadrupeds), ceratopsians (herbivorous quadrupeds with horns and frills), and ornithopods (bipedal or quadrupedal herbivores including “duck-bills”). These definitions are written to correspond with scientific conceptions of dinosaurs that predate the modern use of phylogenetics. The continuity of meaning is intended to prevent confusion about what the term “dinosaur” means. There is a wide consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor must be included in a group for that group to be natural, birds would thus be dinosaurs and dinosaurs are, therefore, not extinct. Birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs.[13] From the point of view of cladistics, birds are dinosaurs, but in ordinary speech the word “dinosaur” does not include birds. Additionally, referring to dinosaurs that are not birds as “non-avian dinosaurs” is cumbersome. For clarity, this article will use “dinosaur” as a synonym for “non-avian dinosaur”. The term “non-avian dinosaur” will be used for emphasis as needed._" Some small bird-like dinosaurs seemed to have been feathered. Telling them apart from some of the “primitive” group of birds would quite possibly been very difficult. The line between “bird” and “dinosaur” is fine, if it exists at all, and in the early linage, it is very hard to tell who is who and what is what, there are few fossils. Certainly it is possible that some small feathered “dinosaur/proto-bird” such as Rahonavis could have survived the KT event, then to be pushed into extinction by later “true” birds who occupied that niche better. The fossil record simply isn’t good enough to say with certainly. > **[List of fossil bird genera](https://en.wikipedia.org/wiki/List_of_fossil_birds)** > > Birds evolved from certain feathered theropod dinosaurs, and there is no real dividing line between birds and non-avian dinosaurs except that some of the former survived the Cretaceous–Paleogene extinction event while the latter did not. For the purposes of this article, a 'bird' is considered to be any member of the clade Aves in the broadest sense. Some dinosaur groups which may or may not be true birds are listed below under Proto-birds. > This page contains a listing of prehistoric bird taxa... But all the “big dinos” died out. ---
**Author:** ![Grendel\_s\_Father](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grendel\_s\_Father](https://boards.straightdope.com/u/Grendel_s_Father)\ **Post date:** [July 21, 2010, 2:55am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/72 "2010-07-21T02:55:29Z")
> [@DrDeth](#): > > Well, birds are dinosaurs by a cladistic definition. See when Richard Owen came up with that term, he included two very different reptile-like animals in what he called “Dinosaurs”. If you insist the two types are both dinosaurs, then birds are then also dinosaurs. Not only that, birds are so solidly nested within a specific dinosaur lineage that keeping them out completely obliterates the whole group, not just splits it in two. You’d have to have dinosaurs (meaning only some plant eating dinosaurs), then a second group for the long-necked sauropods, dozens of groups for the off-shoots of the carnivorous theropod lineage leading towards birds, as long as you’re keen on keeping birds themselves out. If you want to define “dinosaur” in such a way as it excludes birds, then everything from T. rex to Velociraptor to Brachiosaurus can’t be considered dinosaurs either, because they’re all closer to birds than say, Triceratops or Iguanodon. > [@](#): > > (I don’t entirely agree, the fossil evidence is not solid enough to say _with certainty_ that birds did not evolve from archosaurs.) Really? All but maybe two fringe researchers in the field would not only strongly disagree with this position but have a good laugh. If [this kind of fossil evidence](http://en.wikipedia.org/wiki/Feathered_dinosaurs#Current_knowledge) isn’t strong enough, what would be? And what alternate hypothesis has stronger evidence? Anyway, dinosaurs are a type of archosaur. So birds did ultimately evolve from archosaurs, via the dinosaur lineage. [Previous page](https://boards.straightdope.com/t/dinosaur-extinction/547053.md?page=3)