# Large Dinosaurs - Other Questions **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [March 11, 2019, 10:32pm UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972 "2019-03-11T22:32:15Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Robert\_Cook](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Robert\_Cook](https://boards.straightdope.com/u/Robert_Cook)\ **Post date:** [March 11, 2019, 10:32pm UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/1 "2019-03-11T22:32:15Z")
Unless large dinosaurs were less dense than modern animals, it would seem that their legs could not support their weight. Were they less dense? If the atmosphere were significantly thicker it would help support their weight. Is the earth losing its atmosphere, and if so, at what rate? If the rate is significant, how long can humankind survive? Is the atmosphere becoming thinner because of oxidation with components of the earth’s crust, which “turns over” and exposes the crust every 100-200 million years? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [March 11, 2019, 11:08pm UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/2 "2019-03-11T23:08:58Z")
> [@Robert\_Cook](#): > > Unless large dinosaurs were less dense than modern animals, it would seem that their legs could not support their weight. Except they did. > [@](#): > > Were they less dense? Some of them had hollow bones, but it wouldn’t have made a huge difference in their weight. > [@](#): > > If the atmosphere were significantly thicker it would help support their weight. It wasn’t. > [@](#): > > Is the earth losing its atmosphere, and if so, at what rate? Yes, and [very, very, very slowly](https://en.wikipedia.org/wiki/Atmospheric_escape#Dominant_atmospheric_escape_and_loss_processes_on_Earth). ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [March 11, 2019, 11:37pm UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/3 "2019-03-11T23:37:03Z")
> [@Robert\_Cook](#): > > Unless large dinosaurs were less dense than modern animals, it would seem that their legs could not support their weight. What calculations have you done to support your hypothesis? ---
**Author:** ![snowthx](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snowthx/32/10660_2.png) [@snowthx](https://boards.straightdope.com/u/snowthx)\ **Post date:** [March 11, 2019, 11:40pm UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/4 "2019-03-11T23:40:28Z")
[Linky to the relevant SD article](https://www.straightdope.com/columns/read/985/why-were-dinosaurs-so-big/) that precipitated the OP, I presume? ---
**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:** [March 12, 2019, 12:16am UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/5 "2019-03-12T00:16:14Z")
Practically speaking, the atmosphere can’t be dense enough to make a difference. Even if we assume that the air was ten times as thick in dinosaur times as it is now, that’d only support about 1% of an animal’s weight. They just had really thick legs, is all. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [March 12, 2019, 1:53am UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/6 "2019-03-12T01:53:33Z")
> [@Robert\_Cook](#): > > Unless large dinosaurs were less dense than modern animals,\*\* it would seem \*\*that their legs could not support their weight. Were they less dense? . . . ? As \*\*Telemark \*\*said, an intuitive feeling (seem) won’t cut it. > [@Darren\_Garrison](#): > > Except they did. . . . Some of them had hollow bones, but it wouldn’t have made a huge difference in their weight. . . . . Apologies, but I went a’googlin’. From [Laelaps](https://www.nationalgeographic.com/science/phenomena/2013/02/25/dinosaur-reproduction-not-ancient-gravity-made-sauropods-super-sized/): There were three things that contributed to sauropods being able to get really big. 1) The shape of sauropod neck bones suggests that, like birds, there were air sacs along the neck to lighten it. Body air sacs are also a possibility. 2) Sauropods, unlike mammals, have small heads, so the necks aren’t lifting something heavy. 3) Sauropods lay eggs that are small compared to their size. Unlike mammals, they aren’t carrying bigger babies the bigger they get. From Biology Stack Exchange: Theropods (think T Rex) balanced their upper body and tail directly over their legs while Sauropods developed a “wide gauge” stance to make it easier for their legs to support their tonnage. [From Biological Reviews of the Cambridge Philosophical Society](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3045712/) (long): > [@](#): > > Much of the axial skeleton, sometimes even including the ribs, was strongly pneumatized (Henderson, 2004; Wedel, 2005, 2007, 2009; Schwarz, Frey & Meyer, 2007a), with pneumatization moving gradually backwards along the skeleton during sauropod evolution. In the most derived sauropods, it even invaded the tail vertebrae and the ischia. A consensus has recently emerged that this pneumatization indicates the presence of an avian-style flow-through lung and large airsacs in the body cavity of sauropods (Perry & Reuter, 1999; Wedel, 2005, 2009; O’Connor, 2009; Perry, Breuer & Pajor, in press) In other words, their density was closer to that of birds than that of mammals. Quite a few of the articles said that older estimates of tonnage for different dinosaurs are probably off because the older estimates used the average density of crocodiles, rather than that of birds. Many articles mentioned that one of he reasons the head was light is because sauropods did not chew their food and therefore lacked heavy cheek muscles and the bone needed to anchor them. Many articles also mentioned that their legs were massive pillars. But we knew that part already. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [March 12, 2019, 6:54pm UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/7 "2019-03-12T18:54:35Z")
> [@Yllaria](#): > > In other words, their density was closer to that of birds than that of mammals. So, [about the same](https://www.sciencedaily.com/releases/2010/03/100322112103.htm). ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [March 13, 2019, 7:22pm UTC](https://boards.straightdope.com/t/large-dinosaurs-other-questions/830972/8 "2019-03-13T19:22:27Z")
> [@Darren\_Garrison](#): > > So, [about the same](https://www.sciencedaily.com/releases/2010/03/100322112103.htm). That’s just the bones. Birds have air sacs that aren’t in their bones.