# Why were so many dinosaurs (especially predators) bipedal? **URL:** \ **Category:** Factual Questions\ **Created:** [June 21, 2011, 4:25pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302 "2011-06-21T16:25:37Z")\ **Posts on this page:** 17\ **Page:** 3
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [August 5, 2011, 12:46am UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/41 "2011-08-05T00:46:02Z")
To add just one thing to **Blake** ’s excellent analysis- energy conservation. If you’re a fast, active lifestyle endotherm, energy efficiency with regards to movement is vital. Because mammals evolved a vertically flexible spine, they can run with a bounding gait that in conjunction with the muscles and tendons of the spine alternately store and tap energy as movement against and with gravity. For a bipedal archosaur, the mechanism is different. With a vertically stiff, springy tail flexing horizontally, energy is tapped and released as the archosaur shifts its center of gravity alternately between hind legs. ETA: the difference between the mammalian spine and the reptilian spine shows up in another place. Cetaceans flex their tails vertically, while icthyosaurs flexed theirs horizontally like fish do. ---
**Author:** ![dropzone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dropzone/32/7515_2.png) [@dropzone](https://boards.straightdope.com/u/dropzone)\ **Post date:** [August 5, 2011, 2:14am UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/42 "2011-08-05T02:14:43Z")
> [@Sailboat](#): > > It may be what Stephen Jay Gould called “contingency” (basically, “luck”) – animals that were tending toward bipedalism may have been successful for _other_ reasons and just passed bipedalism on to their descendants. Ah, DUMB luck, attributing it to ANYTHING but a “creator.” I cannot explain Deep Time in human terms. We cannot understand it, and that’s not our fault. Nobody expected us to live longer than 100 years. ---
**Author:** ![Arrendajo](https://avatars.discourse-cdn.com/v4/letter/a/e0b2c6/32.png) [@Arrendajo](https://boards.straightdope.com/u/Arrendajo)\ **Post date:** [August 5, 2011, 4:59am UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/43 "2011-08-05T04:59:36Z")
> [@I\_Know\_Nothing](#): > > Do predatory birds qualify as bipedal? > > I might not have much of an imagination but, besides apes, I can’t think of many bipedal animals period. Well, all birds are bipedal when they’re not flying. Raptors hunt with their feet/talons, but there are plenty of predatory birds that don’t hunt with their feet. ---
**Author:** ![Hoyasaur](https://avatars.discourse-cdn.com/v4/letter/h/da6949/32.png) [@Hoyasaur](https://boards.straightdope.com/u/Hoyasaur)\ **Post date:** [June 14, 2012, 7:43pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/44 "2012-06-14T19:43:37Z")
Most, if not all, dinosaurs descended from bipedal ancestors. However, the origin of dinosaur bipedality remains a big mystery. To quote Gregory Paul from his 1988 book, _Predatory Dinosaurs of the World_, “The reason predatory dinosaurs became bipedal is not at all clear. […] The only thing that can be said in the end is that bipedalism was a serendipitously crucial adaptation…” I believe that bipedal hopping behavior in the very first dinosaurs in the Mid-to-Late Triassic (roughly Carnian time) led directly to obligatory bipedality, which characterized most primitive and many advanced dinosaurs, as I argued here. [Bipedal Hopping and the Origin of Dinosaurs](http://frontier-knowledge.com/earth/papers/1989.Bipedal_Hopping_and_the_Origin_of_Dinosaurs.pdf) Bipedal hopping would have enabled dinosaurs to move very quickly without being warm-blooded because hopping relies on elastic storage-and-release rather than metabolism, and it may help explain how the cold-blooded dinosaurs suppressed the increasingly warm-blooded mammal-like reptiles and mammals. Incidentally, footprints of hopping dinosaurs have been found - [Discovery of Trackways of Hopping Dinosaurs…](http://www.paleoglot.org/files/Bernier_84.pdf) Also, check this out – [Hopping dinosaur animation](http://www.youtube.com/watch?v=a39tVzLeqos) ---
**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:** [June 15, 2012, 1:10pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/45 "2012-06-15T13:10:47Z")
> [@Hoyasaur](#): > > Bipedal hopping would have enabled dinosaurs to move very quickly without being warm-blooded because hopping relies on elastic storage-and-release rather than metabolism, and it may help explain how the cold-blooded dinosaurs suppressed the increasingly warm-blooded mammal-like reptiles and mammals. Isn’t modern thinking that dinos were warm-blooded? Certainly at least [endothermic](http://en.wikipedia.org/wiki/Endotherm)? ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [June 15, 2012, 4:49pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/46 "2012-06-15T16:49:04Z")
When I was reading this, I was wondering if differing oxygen levels could contribute to differently favoring quadrupedalism or bipedalism. I recall hearing that Oxygen levels were higher in the past, although [Wikipedia says that’s still being debated](http://en.wikipedia.org/wiki/Dinosaur#Extinction_of_major_groups): > [@](#): > > The atmosphere’s composition during the Mesozoic is a matter for debate. While some academics argue that oxygen levels were much higher than today, others argue that biological adaptations seen in birds and dinosaurs indicate that respiratory systems evolved beyond what would be necessary if oxygen levels were high.[123] By the late Cretaceous, the environment was changing dramatically. Volcanic activity was decreasing, which led to a cooling trend as levels of atmospheric carbon dioxide dropped. Oxygen levels in the atmosphere also started to fluctuate and would ultimately fall considerably. Some scientists hypothesize that climate change, combined with lower oxygen levels, might have led directly to the demise of many species. If the dinosaurs had respiratory systems similar to those commonly found in modern birds, it may have been particularly difficult for them to cope with reduced respiratory efficiency, given the enormous oxygen demands of their very large bodies. Anyway, thought I’d throw the idea out there. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 15, 2012, 5:11pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/47 "2012-06-15T17:11:10Z")
> [@ZenBeam](#): > > When I was reading this, I was wondering if differing oxygen levels could contribute to differently favoring quadrupedalism or bipedalism. I recall hearing that Oxygen levels were higher in the past, although [Wikipedia says that’s still being debated](http://en.wikipedia.org/wiki/Dinosaur#Extinction_of_major_groups): > Anyway, thought I’d throw the idea out there. How would it contribute to bipedalism in particular? I can see oxygen level changes contributing to the extinction, but how would it have favored bipedalism in the first place? And in asking that question, I guess one answer might be that bipedalism was a more efficient way for dinosaurs to evolve that great size, though I’m not sure how. But the higher oxygen levels may have enabled the evolution of larger animals, and dinosaurs got there first somehow by being bipedal. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 15, 2012, 5:31pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/48 "2012-06-15T17:31:26Z")
> [@Sailboat](#): > > Isn’t modern thinking that dinos were warm-blooded? Certainly at least [endothermic](http://en.wikipedia.org/wiki/Endotherm)? Very generally, yes, although the jury is still out. I would also point out that the paper linked about hopping dinosaurs is far from mainstream. Do a Google search on the title, and you get exactly 2 hits, both on the same website. Plus, it was written in 1989, and there have been many further studies on locomotion in dinosaurs, none of which, to my knowledge, has confirmed a hopping origin for bipedality, or even hopping locomotion in later species. For example, from [this 2005 paper](http://www.rvc.ac.uk/aboutus/staff/jhutchinson/documents/JRH16.pdf): > [@](#): > > There is no evidence that any extinct dinosaurs hopped. Although some bipedal dinosaurs vaguely resembled kangaroos (long tails and legs), their anatomy is more similar to modern striding bipeds such as humans or birds, rather > than hoppers. Furthermore, there are no clear tracks of hopping dinosaurs; all known tracks from the Mesozoic are from striding bipeds. Many living birds do hop, but this is a specialized behaviour that has evolved a few times in > recent birds, not a legacy of extinct theropods. ---
**Author:** ![Shakester](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/shakester/32/437_2.png) [@Shakester](https://boards.straightdope.com/u/Shakester)\ **Post date:** [June 15, 2012, 5:47pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/49 "2012-06-15T17:47:25Z")
> [@Hoyasaur](#): > > Also, check this out – [Hopping dinosaur animation](http://www.youtube.com/watch?v=a39tVzLeqos) Looks pretty similar to [hopping kangaroos](http://www.youtube.com/watch?v=CiydVHrkQp0). ---
**Author:** ![Hoyasaur](https://avatars.discourse-cdn.com/v4/letter/h/da6949/32.png) [@Hoyasaur](https://boards.straightdope.com/u/Hoyasaur)\ **Post date:** [July 14, 2012, 6:16pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/50 "2012-07-14T18:16:12Z")
> [@Sailboat](#): > > Isn’t modern thinking that dinos were warm-blooded? Certainly at least [endothermic](http://en.wikipedia.org/wiki/Endotherm)? The issue is which dinosaurs were warm-blooded and also when did dinosaur endothermy evolve. It is certainly possible, maybe likely, that advanced dinosaurs in the Cretacous were warm-blooded, but that doesn’t mean that primitive dinosaurs in the Triassic were also warm-blooded, and it’s the primitive Triassic dinosaurs that are at issue here. Primitive dinosaurs and crocodiles were very closely related and possibly shared a common thecodont ancestor. Modern crocodiles are not warm-blooded, so it stands to reason that their Triassic ancestors, and by inference, primitive dinosaurs, weren’t either. Interestingly, Robert Bakker, in advancing his ideas about dinosaur endothermy back in the 1980s, suggested that endothermy actually evolved in thecodonts, which allowed them and their dinosaur descendants to suppress the warm-blooded mammal-like reptiles. (I don’t know if he still believes that.) But if thecodonts were warm-blooded, then why aren’t crocodiles? The idea that warm-blooded animals are inherently superior to cold-blooded animals, which was Bakker’s basic thesis, is bogus. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [July 14, 2012, 6:35pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/51 "2012-07-14T18:35:48Z")
Since this thread has been raised from the recently-dead, it’s as probably as good a time as any to mention this recent paper: [Associated evolution of bipedality and cursoriality among Triassic archosaurs: a phylogenetically controlled evaluation](http://www.bioone.org/doi/abs/10.1666/11015.1) > [@](#): > > This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals. ---
**Author:** ![Hoyasaur](https://avatars.discourse-cdn.com/v4/letter/h/da6949/32.png) [@Hoyasaur](https://boards.straightdope.com/u/Hoyasaur)\ **Post date:** [July 14, 2012, 6:38pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/52 "2012-07-14T18:38:51Z")
> [@Darwins\_Finch](#): > > Very generally, yes, although the jury is still out. > > I would also point out that the paper linked about hopping dinosaurs is far from mainstream. Do a Google search on the title, and you get exactly 2 hits, both on the same website. Plus, it was written in 1989, and there have been many further studies on locomotion in dinosaurs, none of which, to my knowledge, has confirmed a hopping origin for bipedality, or even hopping locomotion in later species. For example, from [this 2005 paper](http://www.rvc.ac.uk/aboutus/staff/jhutchinson/documents/JRH16.pdf): To quote Carl Sagan (and many others) “absence of evidence is not evidence of absence.” The weight of evidence can never prove any theory – it’s one of the fallacies of induction. But more to the point, footprints are made on a wet substrate, such as mud or sand in a floodplain or stream bank, which is a small (and unrepresentative) fraction of the total exposed landscape. In other words, the rarity of hopping footprints may simply be due to an unrepresentative sample – another fallacy of induction. It is entirely possible and not unreasonable to suppose that dinosaurs walked (alternating footfalls) on wet soil and shifted into high gear (hopping) only in the dryer uplands, where the footing was more secure but where footprints were not preserved. ---
**Author:** ![Hoyasaur](https://avatars.discourse-cdn.com/v4/letter/h/da6949/32.png) [@Hoyasaur](https://boards.straightdope.com/u/Hoyasaur)\ **Post date:** [July 14, 2012, 6:55pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/53 "2012-07-14T18:55:18Z")
> [@Darwins\_Finch](#): > > Since this thread has been raised from the recently-dead, it’s as probably as good a time as any to mention this recent paper: [Associated evolution of bipedality and cursoriality among Triassic archosaurs: a phylogenetically controlled evaluation](http://www.bioone.org/doi/abs/10.1666/11015.1) That begs the question: why did obligatory bipedality evolve? It is well known that many theocodonts were normally quadrupedal when standing still or walking but that they shifted to a bipedal gait at higher speeds – because bipedality was more efficient. (Modern crocodiles and some lizards do the same thing.) In other words, they were facultatively bipedal. But primitive dinosaurs were obligatory bipeds. Now, I’m sure someone will suggest that obligatory bipedality allowed the dinosaurs to free their forelimbs for other uses, and that is certainly true, but that still fails to explain how or why dinosaurs solved the “stability” problem, i.e. how they could maintain their balance on two legs when not moving at all. In [Bipedal Hopping and the Origin of Dinosaurs](http://www.frontier-knowledge.com/earth/papers/1989.Bipedal_Hopping_and_the_Origin_of_Dinosaurs.pdf), I argued that in perfecting the bipedal hopping gait, the dinosaurs serendipitously solved the “stability” problem, which enabled them to remain bipedal even when they were standing still. I am not aware of any other hypothesis that can explain that. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [July 14, 2012, 6:55pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/54 "2012-07-14T18:55:57Z")
> [@Hoyasaur](#): > > To quote Carl Sagan (and many others) “absence of evidence is not evidence of absence.” The weight of evidence can never prove any theory – it’s one of the fallacies of induction. But more to the point, footprints are made on a wet substrate, such as mud or sand in a floodplain or stream bank, which is a small (and unrepresentative) fraction of the total exposed landscape. In other words, the rarity of hopping footprints may simply be due to an unrepresentative sample – another fallacy of induction. It is entirely possible and not unreasonable to suppose that dinosaurs walked (alternating footfalls) on wet soil and shifted into high gear (hopping) only in the dryer uplands, where the footing was more secure but where footprints were not preserved. And, to quote Isaac Newton, “We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. Therefore, to the same natural effects we must, so far as possible, assign the same causes.” One could simply attribute the rarity of hopping ichnofossils to the absence of hopping in dinosaurs, especially given the lack of otherwise supporting evidence for that mode of locomotion. ---
**Author:** ![Hoyasaur](https://avatars.discourse-cdn.com/v4/letter/h/da6949/32.png) [@Hoyasaur](https://boards.straightdope.com/u/Hoyasaur)\ **Post date:** [July 14, 2012, 7:33pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/55 "2012-07-14T19:33:32Z")
> [@Darwins\_Finch](#): > > And, to quote Isaac Newton, “We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. Therefore, to the same natural effects we must, so far as possible, assign the same causes.” One could simply attribute the rarity of hopping ichnofossils to the absence of hopping in dinosaurs, especially given the lack of otherwise supporting evidence for that mode of locomotion. The Newton quote is off-point. Obviously, alternating footprints means alternating footfalls and therefore a symmetrical walking gait. No argument there. Newton also said _hypotheses non fingo_ when it came to the cause of gravity, and especially “action at a distance,” an absurd notion, which even Sir Isaac acknowledged, but upon which his theory of universal gravity is based. As far as the rarity (or even absence) of asymmetrical (hopping) footprints, then you are stating a hypothesis – dinosaurs did not hop – from which you deduce an empirical and testable prediction – therefore, hopping dinosaur footprints will never be found. That’s great! But, following Popper, if we find a single set of hopping footprints, i.e. counter-evidence, then your hypothesis will be falsified. Unfortunately, IMO, footprints can never be used to test my hypothesis that (primitive) dinosaurs hopped because the absence of asymmetrical footprints does not falsify it. Therefore, we must look to other sources of evidence, esp. fossilized bones and skeleton. My hypothesis predicts that in order to become efficient hoppers and for dinosaurs to maintain their stability when hopping (as opposed to running), dinosaurs needed to restrict leg motion to the parasagittal plane with no lateral deviations, and that’s exactly what their pelvis and upper leg elements reveal. Incidentally, there is also a paucity (or absence) of running trackways of large theropods. Here’s what mainstream paleontologist Gregory Paul said about that in his book on predatory dinosaurs: “It cannot be proven that large theropods were slow by their trackways because, as I’ve explained, this would be another case of unfair use of negative evidence. Someday the prints of a 5-tonne theropod running at high speed may be found and settle the issue once and for all. Until and unless that happens, we must turn to the design and stressing of the theropod skeleton for evidence of their speed.” Couldn’t have said it better myself. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [July 14, 2012, 8:29pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/56 "2012-07-14T20:29:14Z")
> [@Hoyasaur](#): > > As far as the rarity (or even absence) of asymmetrical (hopping) footprints, then you are stating a hypothesis – dinosaurs did not hop – from which you deduce an empirical and testable prediction – therefore, hopping dinosaur footprints will never be found. That’s great! False. What I am arguing against is when you said this, in post #44: > [@](#): > > Incidentally, footprints of hopping dinosaurs have been found - Discovery of Trackways of Hopping Dinosaurs… No. Footprints of hopping dinosaurs have not been found (aside perhaps from those of birds…). The footprints in the paper you linked to, from 1984, have since been interpreted as belonging to a turtle swimming in shallow water. _Some_ dinosaurs, notably small ones, may well have hopped. They certainly do so today. > [@](#): > > But, following Popper, if we find a single set of hopping footprints, i.e. counter-evidence, then your hypothesis will be falsified. Again, no. That is not my hypothesis. My _statement_ is that you are incorrect about footprints of hopping dinosaurs having been found, and that no accepted biomechanical studies have supported hopping locomotion in all but perhaps the smallest theropods. The video you linked to showing a hopping hadrosaur was part of a study performed by scientists at Manchester University; [here](http://palaeo-electronica.org/2009_3/180/180.pdf) is the associated paper (.pdf). The punchline of the paper is this: > [@](#): > > The simulator has clearly been able to find a large range of gaits that are both physiologically and anatomically possible given the constraints of the model. The fastest gait is the bipedal hop, followed by the quadrupedal gallop and finally the bipedal run. The question then becomes which of these gaits would the animal have chosen? Bipedal hopping would seem to be the obvious answer but this interpretation of the findings would be very bold. It is true that hopping has been described in dinosaurs based on trackway evidence, and an ichniospecies has even been proposed based on a putatively hopping gait: _Saltosauropus latus_ (Bernier et al. 1984). However the current interpretation of these ostensibly hopping tracks is that they are swimming traces probably > produced by a large turtle (Lockley 2007). The largest hopping mammals are probably the Pleistocene megafaunal species of macropodid _Procoptodon goliah_ with a mean estimated body mass of 232 kg (Helgen et al. 2006) so a 715 kg hopper is not an impossibility but identification of hopping based on morphological features is not straightforward. Whilst kangaroos are highly anatomically specialised, other hopping animals are less obvious: _Otolemur garnettii_ and _Galago crassicaudatus_ are morphologically very similar bushbabies and yet one is a habitual hopper when on the ground whereas the other employs a bounding gallop (Oxnard et al. 1990). **However, what is more likely is that the simulation is able to tell us that our reconstruction is incorrect: features of the model that are insufficiently constrained have allowed it to develop a highly effective hopping gait that would not be available for the animal itself.** (bolding mine) And the closing statements from that paper: > [@](#): > > This paper demonstrates what can be achieved with the current level of computer simulation technology. The simulations do demonstrate a wide range of possible locomotor modes and shows (a) that 10 independent repeats is probably > insufficient for a quadrupedal gait analysis and (b) that there are major gaps in our understanding of gait choice that are highlighted by this process. Whilst bipedality is currently the most likely option, a high-speed quadrupedal hadrosaur should not be ruled out as a serious locomotor possibility for this group of dinosaurs. Hopping may well have been possible in some groups, but the evidence thus far, from both ichnofossils and biomechanical analyses, does not point to such as common among bipedal dinosaurs, and thus cannot at this time sufficiently explain the evolution of bipedality. ---
**Author:** ![Hoyasaur](https://avatars.discourse-cdn.com/v4/letter/h/da6949/32.png) [@Hoyasaur](https://boards.straightdope.com/u/Hoyasaur)\ **Post date:** [July 14, 2012, 8:33pm UTC](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302/57 "2012-07-14T20:33:04Z")
> [@Darwins\_Finch](#): > > Hopping may well have been possible in some groups, but the evidence thus far, from both ichnofossils and biomechanical analyses, does not point to such as common among bipedal dinosaurs, and thus cannot at this time sufficiently explain the evolution of bipedality. That is your opinion; it is not mine. [Previous page](https://boards.straightdope.com/t/why-were-so-many-dinosaurs-especially-predators-bipedal/586302.md?page=2)