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Post by dinosauria101 on May 23, 2019 3:51:04 GMT 5
Whoops, looks like I got that the wrong way around
Judging by a quick search, no other mammal seems to have hollow bones/pleurocoels
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Post by Infinity Blade on May 23, 2019 4:03:07 GMT 5
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Post by Exalt on Aug 19, 2023 4:38:41 GMT 5
I'm not sure if this is the right place to ask, but I have a question regarding Sauropods.
I learned not too long ago that warm-blooded animals need to eat more than cold-blooded animals, because of metabolism. I have also heard, thanks to prehistoric planet and other recent stuff that I've looked into, that many dinosaurs, including sauropods, are thought to be warm-blooded.
Additionally, I am told that elephants and other large herbivores spend a very large portion of the day eating. However, sauropods can far outclass even the elephant in size. How could sauropods possibly get enough to sustain themselves, given these premises?
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Post by Infinity Blade on Aug 19, 2023 5:40:19 GMT 5
I'm not sure if this is the right place to ask, but I have a question regarding Sauropods. I learned not too long ago that warm-blooded animals need to eat more than cold-blooded animals, because of metabolism. I have also heard, thanks to prehistoric planet and other recent stuff that I've looked into, that many dinosaurs, including sauropods, are thought to be warm-blooded. Additionally, I am told that elephants and other large herbivores spend a very large portion of the day eating. However, sauropods can far outclass even the elephant in size. How could sauropods possibly get enough to sustain themselves, given these premises? All else being equal, a larger animal will always have a slower metabolism than a smaller one. This is true even when the larger and smaller animal are just as endothermic as each other. What this means is that while the larger animal has to eat more food in absolute terms, it doesn't need as much food relative to its body mass. For example, a 5,000 kg elephant needs to eat 60 kg (dry weight) of food per day, while a 2.4 g Etruscan shrew would only need to eat around 4.8 g of food per day. While in raw numbers the elephant needs to eat way more food, it only needs to eat 1.2% of its body mass in food per day. The shrew needs to eat 1.5-2 times its body mass in food per day (and can't go more than a few hours without eating). The same would hold true for a sauropod. While it's true that sauropods were endothermic, and they would need to eat a greater absolute amount of food than an elephant would, it would be a smaller proportion of their body mass, and this fact would help greatly. |
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Post by theropod on Aug 19, 2023 13:54:24 GMT 5
I'm not sure if this is the right place to ask, but I have a question regarding Sauropods. I learned not too long ago that warm-blooded animals need to eat more than cold-blooded animals, because of metabolism. I have also heard, thanks to prehistoric planet and other recent stuff that I've looked into, that many dinosaurs, including sauropods, are thought to be warm-blooded. Additionally, I am told that elephants and other large herbivores spend a very large portion of the day eating. However, sauropods can far outclass even the elephant in size. How could sauropods possibly get enough to sustain themselves, given these premises? All else being equal, a larger animal will always have a slower metabolism than a smaller one. This is true even when the larger and smaller animal are just as endothermic as each other. What this means is that while the larger animal has to eat more food in absolute terms, it doesn't need as much food relative to its body mass. For example, a 5,000 kg elephant needs to eat 60 kg (dry weight) of food per day, while a 2.4 g Etruscan shrew would only need to eat around 4.8 g of food per day. While in raw numbers the elephant needs to eat way more food, it only needs to eat 1.2% of its body mass in food per day. The shrew needs to eat 1.5-2 times its body mass in food per day (and can't go more than a few hours without eating). The same would hold true for a sauropod. While it's true that sauropods were endothermic, and they would need to eat a greater absolute amount of food than an elephant would, it would be a smaller proportion of their body mass, and this fact would help greatly. That being said, if sauropods were just upscaled elephants, they likely would be impossible indeed. The key difference here is that an elephant spends 8 hours eating each day because it needs to chew its food, while sauropods did not chew their food and where therefore vastly more efficient "eating machines" that merely had to rip of and swallow the plant matter, with all subsequent processing happening in the gut, mainly through bacterial fermentation. An important factor is also what plants sauropods (likely) ate. The following graph shows gas production (as a proxy of the nutritional energy made available) during the bacterial fermentation process of different plants over time. As you can see, important mesozoic plants like Araucaria and Horsetails contain as much or more energy than extant equivalents (like grasses and dicot browse), but require relatively long fermentation times. That likely makes the "no chewing, long fermentation in the gut" strategy of sauropods particularly viable in mesozoic ecosystems, as is it the optimum way of extracting nutrients from these plants, and at the same time makes giant body size both possible (because it solves the problem of not having sufficient time to chew) and particularly advantageous, because it allows for longer gut retention, and thus fermentation time (that is because the volume of the animal and its gut increases more quickly than its metabolic rate, as Infinity Blade pointed out). |
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Post by Exalt on Aug 20, 2023 9:54:07 GMT 5
Why did the mesozoic plants contain more energy?
Additionally, why did Sauropods grow the long necks, to begin with?
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Post by theropod on Aug 20, 2023 13:40:31 GMT 5
Why did the mesozoic plants contain more energy? Well they contained fairly similar amounts of energy, maybe slightly higher, but not a dramatic difference. The interesting observation here is that they required longer fermentation times to make all of that energy metabolically available, which favours the evolution of large body size, to enable very long gut retention times that could more efficiently extract the nutrients from these plants. As far as overall energy content is concerned, I am neither a botanist (though I have dabbled in paleobotany a bit for job-related reasons) nor an agricultural nutritionalist, but I thinkg that usually breaks down to how much carbohydrate content (usually in the form of cellulose) there is in a plant. As for the longer gut retention times needed to release the energy in horsetails or Araucaria, I think that intuitively makes sense, as compared to modern plants there are very tough plants with thick waxy cuticles and or extremely high silica content, which likely just take longer to break down than extant equivalents (grasses or leaves).
Many reasons. Mainly, they are a way to enlarge the "feeding envelope", i.e. the volume of space a sauropod can forage in without needing to physically move somewhere using its legs. The larger this space is, the less energy an animal needs to waste for moving a multi-ton body around all the time, and the efficiently the animal can use its energy. They are also, of course, a way to reach plants that are out of reach for all other large herbivores. Neither of which is a sauropod-specific thing, it’s just that they developed it to an extreme never seen before. Giraffes and elephants today also use their long necks or their trunks to reach plants beyond the reach of other herbivores, and to increase their feeding envelopes.
Then of course there are various other accessory purposes that have been proposed for those necks, from sexual display to fighting, and all probably hold some degree of water at least for some taxa, but the advantages for feeding are likely the main reason the necks evolved to be the length that they were.
Another important reason is also simply: that they could (unlike mammals, probably). Such a long neck might also have evolved in mammals, if we didn’t have several evolutionary constraints that make this more difficult for us. First of all, mammals are almost universally unable to evolve more than 7 neck vertebrae (apparently for developmental reasons that I don’t fully understand), while reptiles have no such constraints. Based on sauropod necks, it would appear that the mechanically optimal number of neck vertebrae for such an extremely long neck is quite a bit higher than 7, more like twice as many. Then secondly, saurischian dinosaurs have hollow bones invaded by airsacks, which imparts a two-fold advantage: It enables the neck vertebrae to be lighter while retaining their strength and flexural stiffness (by reducing mass for a given diameter or volume), and it increases the respiratory volume and therefore mitigated the "deadspace problem" that you can get with breathing through a very long tube (such as a very long trachea). For example humans cannot breathe through a 10 m long snorkle, simply because the volume of air in that snorkle is bigger than the volume we can move with our lungs, so if we tried to breathe through it we would just push the same used air out and then suck it back in. But sauropods had massive air sacks for respiration, containing a much greater volume than a mammal of similar size, so this problem would be greatly reduced in them.
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Post by Exalt on Aug 20, 2023 21:35:57 GMT 5
Giraffes, oddly enough, are part of why I asked. I watched a video that discussed the idea that the evolution of their necks isn't as cut and dry as we're taught as kids.
I've heard a bit about the air sacs, but do those also play a role in why large Theropods were the largest known terrestrial carnivores? Since that's the other side of Saurischia.
(Speaking of Saurischia, the one thing that grinds my gears about birds being dinosaurs is that they are not "bird-hipped dinosaurs" despite being both birds and dinosaurs.)
Actually, since birds are dinosaurs, can I technically get away with asking about the upper size limit for birds?
Regardless, thank you all for answering.
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Post by Infinity Blade on Aug 20, 2023 22:36:23 GMT 5
Yes. As with sauropods, they would’ve helped them get bigger (although for other reasons they didn’t get anywhere near as massive as the largest sauropods).
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Post by theropod on Aug 21, 2023 0:20:47 GMT 5
Giraffes, oddly enough, are part of why I asked. I watched a video that discussed the idea that the evolution of their necks isn't as cut and dry as we're taught as kids. Well for giraffes, as for sauropods, the necks impart many separate advantages. I am not an expert on Giraffe evolution, but I’ll wager that most likely the benefits for feeding are the most important ones, but of course Giraffes also use their necks for intraspecific aggression, which would suggest that they could also be a component of sexual selection affecting their length. Most likely yes. They definitely didn’t hurt their ability to grow large as active terrestrial carnivores. Their body plan would most likely have been more difficult to achieve had they not had air sacs. Indeed, a common thing that confuses people. Think of it less as "bird hipped" (that name really hasn’t helped matters), and more as "herbivore hipped". The retroverted pubis that’s characteristic of the bird and ornithischian pelvis evolved repeatedly (and really, an extant bird hip looks very different from that of a hadrosaur or stegosaur, except for this feature), mainly in herbivorous taxa in order to provide more space for the abdominal cavity. The thing with proposed "size limits" is that you should rarely trust them, or at least that you should rarely think of them as a hard limit, more as a size that might be a limit based on the currently known adaptations. People thought Pteranodon was the largest any flying animal could ever get. A few decades later Quetzalcoatlus was discovered. People used to think Apatosaurus or Brachiosaurus were the largest any terrestrial animal could ever get. A few decades later Antarctosaurus, Argentinosaurus and so forth were discovered. In the case of birds, the largest we currently know of is Aepyornis maximus. A recent study→ estimated that some individuals might have reached about a ton, although that estimate appears to be only based on eggshell fragments and is likely not that trustworthy. Previous studies estimated the largest individuals as between 500-800 kg, if memory serves. Somewhere around that size might be the "limit" to how large a bird can get while maintaining certain constraints that birds tend to have, such as incubating their eggs (which requires the eggs to be able to withstand the weight of the brooding female) and laying proportionately large eggs (which cannot get too large, otherwise the chick couldn’t hatch any more). But of course that is not to say that at some point, there couldn’t be or have been a bird that had somehow escaped those constraints, enabling it to grow larger. All known birds are bipedal, and it would appear that that’s a constraint that’s quite hard to escape for them due to the degree of modification of their forelimbs, but as a bipedal animal they could still realistically attain sizes similar to the largest known theropods, at least. |
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