# 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:** 20\ **Page:** 2
**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 18, 2010, 2:25am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/21 "2010-07-18T02:25:27Z")
One interesting group that survived the K-T event only to die off in the Tertiary (latest survivors in the Miocene) were the crocodile-like champosaurs, a group within the [Choristodera.](http://en.wikipedia.org/wiki/Choristodere) One member, [Lazarussuchus](http://en.wikipedia.org/wiki/Lazarussuchus), was so named because it represents a “ghost lineage,” a late appearance of a form (in the Oligocene and Miocene) of a group that had apparently been absent from the fossil record for many millions of years. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [July 18, 2010, 2:26am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/22 "2010-07-18T02:26:26Z")
> [@Colibri](#): > > Actually, since birds survived the K-T event it’s a little surprising that other small dinosaurs didn’t. They did; it’s just that they’d evolved intelligence and [escaped Earth in their spacecraft.](http://boards.straightdope.com/sdmb/showthread.php?t=571164) ---
**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 18, 2010, 2:33am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/23 "2010-07-18T02:33:31Z")
> [@Polycarp](#): > > and only one species of ground sloth survives (as an arboreal ‘tree sloth’). Excuse me for nitpicking this a little, but there are actually six species of tree sloths in two genera, the Two-toed Sloths _Choloepus_ and the Three-toed Sloths _Bradypus_. Oddly, the two kinds of tree sloths are not very closely related, being independently evolved from two different families of ground sloths. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 18, 2010, 2:52am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/24 "2010-07-18T02:52:27Z")
I know the 2-toed are Megalonychids (otherwise ground sloths) – but I thought the 3-toed were their own family, the Bradypodidae. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [July 18, 2010, 5:07am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/25 "2010-07-18T05:07:17Z")
I think the OP is less about dinosaurs and more about epistemology. He’s asking how closely we can come to certainty, with incomplete evidence. ---
**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 18, 2010, 5:16am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/26 "2010-07-18T05:16:44Z")
> [@Polycarp](#): > > I know the 2-toed are Megalonychids (otherwise ground sloths) – but I thought the 3-toed were their own family, the Bradypodidae. The ground sloths include five families, the Megalonychidae, Megatheriidae, Mylodontidae, Nothrotheriidae, and Orophodonitidae. As you say, the Two-toed sloths belong to the Megalonychidae. The Bradypodidae, including the extant Three-toed Sloths, seems to be more closely allied to the Megatheriidae - the really enormous ground sloths including Megatherium and Eremotherium - than they are to the Megalonychidae. ---
**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 18, 2010, 5:25am UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/27 "2010-07-18T05:25:46Z")
> [@Chronos](#): > > Apologies, **John Mace**. I somehow managed to completely overlook that post. Even, apparently, after it was pointed out to me. No worries. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 18, 2010, 6:35pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/28 "2010-07-18T18:35:39Z")
> [@Colibri](#): > > The ground sloths include five families, the Megalonychidae, Megatheriidae, Mylodontidae, Nothrotheriidae, and Orophodonitidae. As you say, the Two-toed sloths belong to the Megalonychidae. The Bradypodidae, including the extant Three-toed Sloths, seems to be more closely allied to the Megatheriidae - the really enormous ground sloths including Megatherium and Eremotherium - than they are to the Megalonychidae. Thanks. 🙂 That helps clarify things for me, at least. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 18, 2010, 7:03pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/29 "2010-07-18T19:03:37Z")
> [@panache45](#): > > I think the OP is less about dinosaurs and more about epistemology. He’s asking how closely we can come to certainty, with incomplete evidence. Agreed. What we know, we know from the fossil record, and it is necessarily incomplete. Soft-bodied forms in particular are very difficult to trace lineages of, since they only get preserved in a few _Lagerstatten_. For example, there is either a remarkable bit of convergence on a highly unusual body form, or there were soft-bodied forms throughout most of the Paleozoic with great appendages. _[Opabinia](http://en.wikipedia.org/wiki/Opabinia)_ and _[Tullimonstrum](http://en.wikipedia.org/wiki/Tullimonstrum)_ are clearly closely related – but save for a handful of _Lagerstatten_, mostly Cambrian except for the Mazon Creek formation from the Carboniferous (source of _Tullimonstrum_), those forms were not preserved. While dinosaurs had hard parts, they were land animals, and were preserved only where their corpses landed in sediments that were preserved. Animals that lived in forests or upland areas might not be well preserved. But all that said, the fact remains that dinosaurs were universally present prior to the K-T and completely absent from the fossil record (redeposition to one side) thereafter. That says something important, even if it doesn’t prove extinction to the satisfaction of a total linguistic pedant. ---
**Author:** ![The\_Other\_Waldo\_Pepper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_other_waldo_pepper/32/12370_2.png) [@The\_Other\_Waldo\_Pepper](https://boards.straightdope.com/u/The_Other_Waldo_Pepper)\ **Post date:** [July 18, 2010, 8:26pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/30 "2010-07-18T20:26:26Z")
> [@Colibri](#): > > Actually, since birds survived the K-T event it’s a little surprising that other small dinosaurs didn’t. All large terrestrial animals died off in the event; however, many other dinosaurs were as small as some birds, and you would think that a few of these might have made it through as well. But it seems that only the small avian dinosaurs, the ones that could fly, got through. What about the tuatara? ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 18, 2010, 8:37pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/31 "2010-07-18T20:37:51Z")
> [@The\_Other\_Waldo\_Pepper](#): > > What about the tuatara? Not even close. Birds **are** dinosaurs – the one group of small sauriscihians that evolved feathers and flight, and survived the K-T event. Crocodilians are archosaurs – depending on your classification scheme, they might be as closely related to tyrannosaurs as triceratops is. ---
**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 18, 2010, 8:53pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/32 "2010-07-18T20:53:06Z")
Tuatara are more closely related to lizards than to crocodiles Not dinosaurs, but not crocodilians, either. If that’s what you meant. ---
**Author:** ![Inner\_Stickler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inner_stickler/32/318_2.png) [@Inner\_Stickler](https://boards.straightdope.com/u/Inner_Stickler)\ **Post date:** [July 18, 2010, 8:53pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/33 "2010-07-18T20:53:09Z")
> [@Colibri](#): > > _Bradypus_ Slow Foot? I don’t know why but that amuses me greatly. ---
**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 18, 2010, 9:33pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/34 "2010-07-18T21:33:33Z")
> [@](#): > > Crocodilians are archosaurs – depending on your classification scheme, they might be as closely related to tyrannosaurs as triceratops is. Though it’s amusing to note that T. rex is more closely related to sparrows than it is to triceratops. This, incidentally, is the reason that birds are considered a subset of dinosaurs. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 18, 2010, 9:35pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/35 "2010-07-18T21:35:53Z")
> [@John\_Mace](#): > > Tuatara are more closely related to lizards than to crocodiles Not dinosaurs, but not crocodilians, either. If that’s what you meant. Sorry – you’re entirely correct, and I confused things by how I said what I said. Lizards, snakes, and tuataras are lepidosaurs, one large group of Eureptiles. Dinosaurs, including birds, pterosaurs, and crocodiles are archosaurs, andother large group. My statement was intended to be “tuataras are not even close to being the closest surviving relative of dinosaurs; crocodilians are the non-dinosaurian survivors that are closest” or something of that sort. ---
**Author:** ![EdwardLost](https://avatars.discourse-cdn.com/v4/letter/e/bbe5ce/32.png) [@EdwardLost](https://boards.straightdope.com/u/EdwardLost)\ **Post date:** [July 18, 2010, 9:54pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/36 "2010-07-18T21:54:37Z")
> [@Colibri](#): > > _Bradypus_ > > > [@Inner\_Stickler](#): > > > > Slow Foot? I don’t know why but that amuses me greatly. I think that means “Man-who-was-living-with-three-boys-of-his-own Foot” ---
**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 18, 2010, 9:57pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/37 "2010-07-18T21:57:15Z")
> [@Inner\_Stickler](#): > > Slow Foot? I don’t know why but that amuses me greatly. And _Choloepus_ means “lame foot.” ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [July 18, 2010, 10:04pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/38 "2010-07-18T22:04:34Z")
> [@Colibri](#): > > And _Choloepus_ means “lame foot.” And is probably the only living mammal which belongs to a family whose type specimen was described by a U.S. President. 🙂 ---
**Author:** ![The\_Other\_Waldo\_Pepper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/the_other_waldo_pepper/32/12370_2.png) [@The\_Other\_Waldo\_Pepper](https://boards.straightdope.com/u/The_Other_Waldo_Pepper)\ **Post date:** [July 18, 2010, 10:48pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/39 "2010-07-18T22:48:36Z")
> [@Polycarp](#): > > My statement was intended to be “tuataras are not even close to being the closest surviving relative of dinosaurs; crocodilians are the non-dinosaurian survivors that are closest” or something of that sort. So birds are dinosaurs, but assorted Jurassic-era saurian reptiles weren’t. Am I saying that right? ---
**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 18, 2010, 10:52pm UTC](https://boards.straightdope.com/t/dinosaur-extinction/547053/40 "2010-07-18T22:52:14Z")
> [@](#): > > And Choloepus means “lame foot.” I thought that was oedipus. [Previous page](https://boards.straightdope.com/t/dinosaur-extinction/547053.md?page=1) [Next page](https://boards.straightdope.com/t/dinosaur-extinction/547053.md?page=3)