# Why are there no dinosaur-size land animals today? **URL:** \ **Category:** Factual Questions\ **Created:** [August 10, 2017, 5:18am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226 "2017-08-10T05:18:16Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 12, 2017, 11:53pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/81 "2017-08-12T23:53:40Z")
> [@Chronos](#): > > The theropods might never have reached the size of the largest sauropods, but they did get significantly larger than the largest current land animals, somewhat larger than the largest land mammals ever, and significantly larger than any non-theropod land carnivore ever. … Let’s fact check that. [_T. Rex_](https://www.livescience.com/23868-tyrannosaurus-rex-facts.html), one of the largest, clocked in at about 9 tons. Not much less than the _[Giganotosaurus](https://en.wikipedia.org/wiki/Giganotosaurus)_ and the record holding for weight carnivorous dinosaur, the [_Spinosaurus_](https://www.livescience.com/24120-spinosaurus.html). Other theropods not so huge. Those biggest were a bit bigger than the the current largest land animal, the African elephant (about 6 tons with the record known to be 11 tons) but “significantly” is a stretch. Cites given earlier in this thread though are of mammals that hit over 15 tons and maybe even one over 20 tons historically. So “somewhat larger than the largest land mammals ever” seems to be a clear false statement. That level of gigantism land mammals are documented to have done as well and is in the rough range of the largest extant ones. Why so many more large dinosaur predators? Could their size have been driven by the size of the prey? Even adolescent sauropods were big. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2017, 12:49am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/82 "2017-08-13T00:49:10Z")
> [@watchwolf49](#): > > Just an amazing coincidence that all the megafauna dies off as soon as humans arrive … Not even close; the biggest, the Paraceratherium aka Baluchitherium, Indricotherium, and Dzungariotherium went extinct 23 million years ago. And of course, we dont know exactly when ancient species go extinct, we just know when they stopped leaving fossils. Some North American Megafauna went extinct around 8000 years ago, and of course humans arrived before that, maybe 24,000 BP. Maybe befroe. But before 13500 BP for sure. [http://nouvelles.umontreal.ca/en/article/2017/01/13/the-first-humans-arrived-in-north-america-much-earlier-than-thought/](http://nouvelles.umontreal.ca/en/article/2017/01/13/the-first-humans-arrived-in-north-america-much-earlier-than-thought/) > **[When Did Humans Come to the Americas?](https://www.smithsonianmag.com/science-nature/when-did-humans-come-to-the-americas-4209273/)** > > Recent scientific findings date their arrival earlier than ever thought, sparking hot debate among archaeologists [https://www.seeker.com/culture/archaeology/earliest-evidence-of-humans-in-the-americas-could-change-everything-if-trueNot](https://www.seeker.com/culture/archaeology/earliest-evidence-of-humans-in-the-americas-could-change-everything-if-trueNot) to mention Bison, Elk, moose, grizzly are all extant megafauna. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2017, 12:50am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/83 "2017-08-13T00:50:13Z")
> [@Darren\_Garrison](#): > > [This](http://phenomena.nationalgeographic.com/2015/07/14/the-largest-beasts-to-walk-the-earth/) site makes the good point that the fact that the biggest known elephant relative and the biggest known rhino relative are more or less tied for size (as best as we can determine) may indicate that this is the size limit for land mammals. (That article also links to [this](http://phenomena.nationalgeographic.com/2011/01/26/jumbo-shrimps-why-mega-mammals-still-looked-puny-next-to-the-biggest-dinosaurs/) relevant one.) That’s a good site. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2017, 12:54am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/84 "2017-08-13T00:54:07Z")
> [@qazwart](#): > > Okay, not really true, but at one time, something called _megafauna_ mammals ruled the land all around the world and just happened to disappear about the same time humans started colonizing those areas. > > Elephant type species use to be found all over the world, but quickly disappeared in Europe, most of Asia, and the Americas about the same time humans populated those areas. Other extremely large mammals like the giant sloths also disappeared at the same time. > > Coincidence? . Not so much since there is no longer any such coincidence in dates. Of course, that doesnt mean humans didnt eat their share. Not impossible at all that hunting drove a species or two to extinction- altho it hardly every happens. Otoh humans did bring along other species and diseases and also started modifying the environment with fire. So, sure, humans are no doubt a culprit. ---
**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:** [August 13, 2017, 1:27am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/85 "2017-08-13T01:27:12Z")
> [@DrDeth](#): > > And of course, we dont know exactly when ancient species go extinct, we just know when they stopped leaving fossils. Darn that [Señor Lips](https://en.wikipedia.org/wiki/Signor%E2%80%93Lipps_effect)! ---
**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:** [August 13, 2017, 2:03am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/86 "2017-08-13T02:03:41Z")
There’s nothing that says that the extinction of any species had to have a single cause. Maybe the mammoths could have survived climate change, and maybe they could have survived humans, but they couldn’t survive both happening nearly at once. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2017, 2:30am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/87 "2017-08-13T02:30:22Z")
> [@Chronos](#): > > There’s nothing that says that the extinction of any species had to have a single cause. Maybe the mammoths could have survived climate change, and maybe they could have survived humans, but they couldn’t survive both happening nearly at once. Indeed. Especially human caused environment change. This article posits a extraterrestrial cause: [http://www.pnas.org/content/104/41/16016.short](http://www.pnas.org/content/104/41/16016.short) _A carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ≅12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America._ This article posits environmental change:[Megafaunal isotopes reveal role of increased moisture on rangeland during late Pleistocene extinctions | Nature Ecology & Evolution](https://www.nature.com/articles/s41559-017-0125.epdf?referrer_access_token=uDrrXWo5-5l9fHm9IY_W-dRgN0jAjWel9jnR3ZoTv0PaK4aqrQ-d59og4YuZKC2XUx-tc4CXT202sPg5epBHhJ50LEHpAqMTBj4_1Y6TwQNqP91AqMbaKdM4xssEu5NUb2TLfVq_6xM4nJJtsgFJ3L84HeOkTJgpxS3k7aCWoJqGzsthhboicHcBbsJ5CEoa1gapqq0-gOHZPyRy5l08w9KK-a5w3WeIQ-fL7wvZeMXJDC04OIvTq_zOMvyaqd_VPDejAYR7SP1pBHKHKLeqtA%3D%3D&tracking_referrer=www.newsweek.com) [https://www.nature.com/articles/s41559-017-0125.epdf?referrer\_access\_token=uDrrXWo5-5l9fHm9IY\_W-dRgN0jAjWel9jnR3ZoTv0PaK4aqrQ-d59og4YuZKC2XUx-tc4CXT202sPg5epBHhJ50LEHpAqMTBj4\_1Y6TwQNqP91AqMbaKdM4xssEu5NUb2TLfVq\_6xM4nJJtsgFJ3L84HeOkTJgpxS3k7aCWoJqGzsthhboicHcBbsJ5CEoa1gapqq0-gOHZPyRy5l08w9KK-a5w3WeIQ-fL7wvZeMXJDC04OIvTq\_zOMvyaqd\_VPDejAYR7SP1pBHKHKLeqtA%3D%3D&tracking\_referrer=www.newsweek.com](https://www.nature.com/articles/s41559-017-0125.epdf?referrer_access_token=uDrrXWo5-5l9fHm9IY_W-dRgN0jAjWel9jnR3ZoTv0PaK4aqrQ-d59og4YuZKC2XUx-tc4CXT202sPg5epBHhJ50LEHpAqMTBj4_1Y6TwQNqP91AqMbaKdM4xssEu5NUb2TLfVq_6xM4nJJtsgFJ3L84HeOkTJgpxS3k7aCWoJqGzsthhboicHcBbsJ5CEoa1gapqq0-gOHZPyRy5l08w9KK-a5w3WeIQ-fL7wvZeMXJDC04OIvTq_zOMvyaqd_VPDejAYR7SP1pBHKHKLeqtA%3D%3D&tracking_referrer=www.newsweek.com) \*Boulanger and Lyman compiled databases of radiocarbon dates from both megafaunal finds and Paleoindian sites for the northeast, throwing out any dates whose reliability had been or could be questioned. This gave a final sample of 57 megafauna dates from 47 different sites and 25 Paleoindian dates from 22 sites. When the two databases were compared, it became clear that most of the megafauna had already disappeared before humans came on the scene—suggesting that the humans had little to do with their demise. The radiocarbon dates also suggest that northeastern megafauna underwent two major declines before finally going extinct. The first was 14,100 years ago, before any humans were in the region, but the number of animals then recovered after about 500 years; the second and final population crash began 12,700 years ago, when Paleoindians had just arrived in the region, according to the archaeological record. Moreover, the team reports in the 1 February issue of Quaternary Science Reviews, even though humans and megafauna continued to coexist for about 1000 years before the animals finally went extinct, the animals were already on their way out: Between 75% and 90% of the northeastern megafauna were gone before humans ever came on the scene. Yet even during the millennium of human and animal overlap, the team argues, there is no evidence for hunting: Neither megafaunal nor Paleoindian sites in the northeast contained animal bones that were butchered or otherwise modified.\* ---
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [August 13, 2017, 6:13pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/88 "2017-08-13T18:13:47Z")
> [@TSBG](#): > > 1. Why was oxygen content of the atmosphere higher in the dinosaur era and why is is it lower now? I’m not sure it is a question gross content, more that it is a question of ratios. You’d need one of the more scientific guys to give you any factual specific answers But one reason the percentage of oxygen fluctuates is that the earth sequesters and releases various other gases on an ever changing basis. Carbon is a real common one that most people understand. Trees and plants take in carbon over their life times, they die. If they become buried away so they dont normally just decompose, their carbon content is locked away in the ground and not returned to the atmosphere. Have lightning make a huge forest fire, all those trees burning are releasing their carbon, it is no longer sequestered Oceans are also big carbon sinks, and various things can induce the ocean to give up its carbon to the atmosphere. Release a large amount of carbon, and the oxygen content per volume goes down. The raw amount of oxygen did not go away, there is just now more of other things. Like if you take a cup of bleach, you cant drink that, poison… Now if you pour 100 gallons of water in with it, you can drink it. Yet its still the same exact 1 cup of bleach, except to get that 1 cup in your tummy you have to drink the 100 gallons of water it is diluted into. > [@](#): > > 1. Why don’t massive forests of the plants you mention exist any more? [/quote] There is no one reason, many different things and different things in different places. Some places that were hospitable are now frozen and buried under ice, some are now desert, many are no longer tropical nor sub tropical. Some could have possibly been wiped out by the results of a large impact, volcanic event, tectonic movements etc. Environment and climate is a big deal for plants, they can not simply migrate or make rapid adaptations. Once antarctica and alaska were more like florida is today, imagine what would happen to plants native to florida if it became like alaska? How about if it became like antarctica? Some were simply beaten out by emerging modern plant forms. Pretty sure we have some people here that can give you a better more specific answer. ---
**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:** [August 13, 2017, 9:18pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/89 "2017-08-13T21:18:30Z")
Quote function not working for me for the post from DrDeth a couple of posts above, but the Firestone/West hypothesis has been an insane bag of ignorant crazypants from the very beginning, and I _have_ followed it from the very beginning, including reading their moronic book. I could go into it at length when I’m not tapping it out on a phone–for now, I’ll leave just [this](https://psmag.com/environment/comet-claim-comes-crashing-to-earth-31180) tidbit. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2017, 10:03pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/90 "2017-08-13T22:03:58Z")
> [@Darren\_Garrison](#): > > Quote function not working for me for the post from DrDeth a couple of posts above, but the Firestone/West hypothesis has been an insane bag of ignorant crazypants from the very beginning, and I _have_ followed it from the very beginning, including reading their moronic book. I could go into it at length when I’m not tapping it out on a phone–for now, I’ll leave just [this](https://psmag.com/environment/comet-claim-comes-crashing-to-earth-31180) tidbit. Whether is it right or wrong it was published in a peer reviewed scientific journal, so calling them _“insane bag of ignorant crazypants”_ is pretty much the opposite of how science works. ---
**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:** [August 13, 2017, 11:07pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/91 "2017-08-13T23:07:34Z")
Okay, more of Firestone and West. They published their “theory” in the form of a mass-market book with the title The Cycle of Cosmic Catastrophes. Here is just a small sampling of their ideas, quoting from the book. (Spoilered for length.) 41,000 years ago, the initial burst from a nearby supernova reached Earth.: > [@](#): > > It was warm that night in Southeast Asia, too warm for a fire, but the tribe built one to roast the two deer they had killed that afternoon. At the edge of the rock shelter in the foothills of the mountains, some of the tribe members stretched out against rocks and others dozed while the meal cooked. They were tired; they had trotted for dozens of miles after trapping the deer. > > Suddenly, high in the sky, a star exploded soundlessly. The colossal flash filled the night sky, shining brighter than the full moon. Instantly alert, some of the startled hunters grabbed their spears and jumped to their feet. As the shocked tribe looked up, the brilliant light in the sky wavered and shimmered. Larger now than the moon, it radiated glittering spikes of multicolored light in all directions. Around the frightened tribe, the nighttime landscape lit up under the eerie flickering glow, causing shadows to shift, flow, and merge as if demons crawled among the bushes. Fearful, the hunters edged backward toward the shelter. > > The stellar rays damaged oxygen in the atmosphere to create ozone. Like the smell after a strong thunderstorm, ozone filled the air with its unmistakable and pungent odor. > > Colliding with atoms of the atmosphere at nearly the speed of light, the deadly radiation launched cascades of particles that lit up the atmosphere with weird electrical effects. Multihued auroras shimmered across the Southeast Asian skies in unprecedented displays, and nearly nonstop lightning flickered from cloud to cloud or leaped earthward. Thunder rumbled nearly continuously as the tribe watched the strange lightning flash across the horizon. > > Skilled as warriors, the men scanned the electrified sky looking for danger, but they confronted no earthly enemy—the true menace was beyond their senses. And it was unstoppable. For ten seconds, the intense radiation shot through their bodies and brains, and it was too much for some. A few dropped to the ground moaning; others quickly pulled the fallen ones into the shelter, but none of them would recover. The rest who were outside the cave moved quickly under the overhang, but most of them would not survive either. Because of the high altitude, the only ones that made it through were those in the cave who were shielded from the direct glare of the exploding star. The explosion happened while above the horizon in Southeast Asia and Australia, so it caused a megafaunal die-out there, but Europe and the Americas were fine. Then 34,000 years ago, the shock wave from the supernova hit the Earth: > [@](#): > > Across the Northern Hemisphere, inhabitants may have noticed more “fireflies” in the sky. The profusion of shooting stars striking the upper atmosphere was the result of the rain of cosmic ions and grains, rich in iron and titanium along with radioactive thorium, potassium, and uranium. The native people interpreted the shooting stars as a bad omen, and they were right. The flux of particles damaged the ozone layer, and although no one noticed, levels of harmful radiation began to creep higher. Over time, ultraviolet light and increasing levels of silent cosmic rays began to injure plants and animals, especially the weaker ones. > > Occasionally, the hypervelocity cloud kicked loose new waves of comets and asteroids, which, along with the dust and debris in the fast-moving cloud, produced impacts on Earth or aerial bursts in the sky. Most of the incoming debris was small and did little damage, but sometimes the objects were large enough to penetrate the atmosphere. Slamming into the ground, the oceans, or the ice caps, they exploded violently, sending out high-velocity microscopic shrapnel that was lethal to animals, plants, and people. Sometimes waves of debris collided with the Earth, producing multiple explosions, which devastated the herds of mammoths, bison, and horses beneath. Big Ed, the mammoth, was in one of those herds. The incoming grains were high in toxic metals and radioactive elements, so that some animal species began to suffer from radiation sickness and heavy-metal poisoning. The second round of extinctions was under way. Then there was the third wave of extinctions. I won’t quote the more lengthy descriptions of this, but at the moment of the supernova, giant chunks of silicates formed in its atmosphere and were tossed out in all directions. The chunks were miles across but less dense than a snowflake. Many of those chunks reached the Earth between 16,000 and 13,000 years ago. One of them, 300 miles across but less dense than styrofoam, exploded over the Canadian ice sheet at 70,000 miles an hour. That explosion is what wiped out the Clovis people and the lost megafauna in the Americas. It left no crater in Canada, but debris from it carved out all of the Carolina Bays and similar structures with different names. Also, all the meteorites recovered in the American Midwest through the efforts of H.H. Nininger (of various dense silicate, iron, and other types) are debris from this 300 mile wide snowflake. Also, all the gold and precious stone deposits in the middle of the US were debris thrown up from Canada by the atmospheric exploding snowflake, and the sky rained diamonds for months after the impact. (I’ve just barely skimmed over my ebook of this for these sample passages—some of those claims may not have appeared in the book but instead in reports in the credulous popular media, which published “news” articles on these ideas.) Oh, heck—I said I wouldn’t quote from this, but I’m quoting from this: > [@](#): > > Yelling in alarm, one of the men pointed a trembling finger at the crescent moon. As the group stopped and stared at the sky, a huge, silent fireball engulfed the moon’s dark upper-left limb. The explosion was brief but violent. Convinced that the gods were angry, the men and women ran hastily toward shelter in a series of small caves cut into a rock overhang. It was a critical choice that shielded them from the worst of the trouble that was racing toward them. At that moment, the densest part of the debris cloud of dustball comets began to collide with the solar system. Angling in from the northern sky, the lumpy cloud of cosmic debris slammed sideways into the plane of the planets. The tribe could not see it, but enormous silent explosions were ripping across Mars, Venus, and the other planets and their moons; the worst of the system-wide onslaught continued for many hours. > > At the same time, although invisible to those hunters, giant cosmic dustballs were plunging soundlessly into the flaming body of the sun. Instantly, writhing plumes of sun-stuff exploded as massive flares, some of them heading directly toward the Earth. Within minutes, high-energy solar particles were buffeting the upper atmosphere, sending colorful auroras twisting and arcing across the daytime sky. > > The shaman had never seen these sky-signs before, but, trying to hold down his rising fear, he knew they were bad. As the tribe nervously huddled in the rock shelter, he hurriedly recited incantations and tried to intercede with the gods, but it was too late. > > Scrambling backward like a crab, one of the tribesmen near the outside shouted in terror as he tried to squeeze farther under the overhang. Wedging his way inside, he repeatedly stabbed a finger at the sky, where an array of glowing blue-white comets now stretched from horizon to horizon. Growing larger every second, they streaked into the atmosphere, each one lighting up brighter than the sun. One dustball comet was more than 300 miles wide; others were nearly as big. Shimmering fiercely, the largest fireball was too brilliant to watch. It cast shadows that shifted rapidly across the back of the cave as the comet moved, forming silhouettes of the tribe that twisted over the rock wall like drunken dancers. > > Heated to immense temperatures by its passage through the atmosphere, the lethal swarm exploded into thousands of mountain-sized chunks and clouds of streaming icy dust. The smaller pieces blew up high in the atmosphere, creating multiple detonations that turned the sky orange and red across the horizon. Beyond sight of the tribe, the largest comet crashed into the ice sheet, instantly blasting a gigantic hole through the ice into Hudson Bay. Within moments, other comets exploded over Lake Michigan, northern Canada, Siberia, and Europe, as every northern continent took direct hits. > > The dazzling flash of the nearest explosion temporarily blinded some of the tribe. Others closed their eyes tight, but even then, the fierce light stung their eyes. Some held their hands up as shields, but the intense light illuminated their flesh with an orange glow, eerily outlining the bones in their hands. Most of them curled up and buried their heads to shut out the painful brilliance, but their skin began to blister from the intense glare and heat. Hastily, they pulled cloaks and blankets over their heads, mumbling frantic prayers to the angry gods. So, that’s your scientific credibility of Firestone and West right there. These people were crackpots spewing insane horseshit. If you really want to side yourself with them, that’s your choice, but that isn’t glory that you are covering yourself with. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [August 13, 2017, 11:10pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/92 "2017-08-13T23:10:44Z")
> [@Chronos](#): > > Nowadays, an elephant is already big enough that nothing can prey on it. Why go bigger? Because going bigger will let a predator eat elephants? I’m not sure if it’s true that elephants have no predators. [Crocodiles will attack elephants](https://www.youtube.com/watch?v=ZVAMnirC72c)in the water or at the water’s edge. My Google-fu has failed to detect if they are ever successful. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [August 13, 2017, 11:42pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/93 "2017-08-13T23:42:11Z")
> [@Darren\_Garrison](#): > > So, that’s your scientific credibility of Firestone and West right there. These people were crackpots spewing insane horseshit. If you really want to side yourself with them, that’s your choice, but that isn’t glory that you are covering yourself with. I didnt quote their book. I quoted their _article in a peer reviewed scientific journal._ Nor was I siding with them. Their article was interesting, and relevant. The peer reviewed scientific journal is hardly a refuge for _crackpots spewing insane horseshit._ Has a article in a _peer reviewed scientific journal_ been posted that refutes them? I would like to read it. That’s how _science_ works , you know. Not by name calling. ---
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [August 14, 2017, 1:00am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/94 "2017-08-14T01:00:24Z")
> [@Peter\_Morris](#): > > Because going bigger will let a predator eat elephants? Balance Predator has to remain in balance with his environment at large, or he will cease to be a predator and become a fossil. Elephant is not the most highly stocked shelf in the meat market and all the other meats come in smaller packages. And getting those meats is expensive. So you sit in the median range with the largest possibility of food. Even the dinosaurs were like this, the largest predators were not the biggest boys on the block, can’t over grow the available groceries. > [@](#): > > I’m not sure if it’s true that elephants have no predators. [Crocodiles will attack elephants](https://www.youtube.com/watch?v=ZVAMnirC72c)in the water or at the water’s edge. My Google-fu has failed to detect if they are ever successful. They are on the calves, not sure on a healthy adult, risky dinner to say the least ---
**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:** [August 14, 2017, 1:42am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/95 "2017-08-14T01:42:11Z")
Especially since, in the rare event that a lioness manages to take down an elephant calf, the elephants will band together to seek out and kill the lioness and all of her cubs. I imagine that they do the same to crocodiles, too. ---
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [August 14, 2017, 2:35am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/96 "2017-08-14T02:35:45Z")
> [@Chronos](#): > > Especially since, in the rare event that a lioness manages to take down an elephant calf, the elephants will band together to seek out and kill the lioness and all of her cubs. I imagine that they do the same to crocodiles, too. Somehow i imagine that takes place about 12 nano seconds after the “Fwew, finally got this tike down” STOMP STOMP STOMP SLAM SLAM SLAM ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 14, 2017, 3:21am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/97 "2017-08-14T03:21:54Z")
> [@Chronos](#): > > Especially since, in the rare event that a lioness manages to take down an elephant calf, the elephants will band together to seek out and kill the lioness and all of her cubs. I imagine that they do the same to crocodiles, too. I would be very interested in seeing some reputable source for that behavior, a group of elephants hunting down a specific lioness to wreak revenge on both her and her cubs. What is your source for that claim? ---
**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:** [August 14, 2017, 10:01am UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/98 "2017-08-14T10:01:03Z")
> [@DrDeth](#): > > Has a article in a _peer reviewed scientific journal_ been posted that refutes them? I would like to read it. Is [_Science_ good enough](http://science.sciencemag.org/content/329/5996/1140)? How about [this](https://www.researchgate.net/publication/251557038_The_Younger_Dryas_impact_hypothesis_A_requiem) one? Or [this](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4938604/) one? Or [this](https://blogs.scientificamerican.com/history-of-geology/httpblogsscientificamericancomhistory-of-geology20110727the-younger-dryas-impact-hypothesis/)? Or pick your own from the citations in [the Wikipedia article](https://en.wikipedia.org/wiki/Younger_Dryas_impact_hypothesis#Criticism). The story was horseshit by crackpots more than 10 years ago when I first started reading about it, and is horseshit from crackpots today. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [August 14, 2017, 1:57pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/99 "2017-08-14T13:57:40Z")
**Darren Garrison** , it certainly seems that the Younger Dryas impact hypothesis has been very throughly investigated and pretty much completely debunked. Two questions for you. 1. Given the lack of any impact experts as part of the original group and the Pinter et al characterization of impact hypotheses as “novel, self-contradictory, rapidly changing, and sometimes defying the laws of physics”, how did they get published in PNAS in the first place? That’s not some vanity journal, it’s real peer review. You’d think the impact experts who reviewed it would have seen the problems. Were these people “big enough” for other reasons that giving their pet crackpot ideas a full airing was somehow required? 2. Your response to seeing the hypothesis brought up was quite strong - not just educating we TMs that the hypothesis has already been throughly investigated and has been tossed aside by now - do you have some additional personal connection to this story or is there some other reason that this “cautionary tale for researchers, the scientific community, the press, and the broader public” has particular meaning for you? Is it just frustration with pop media running with marginal speculative hypotheses as if they are serious science while relatively ignoring the major scientists in a field? Or more personal? ---
**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:** [August 14, 2017, 2:40pm UTC](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226/100 "2017-08-14T14:40:00Z")
> [@DSeid](#): > > 1. Given the lack of any impact experts as part of the original group and the Pinter et al characterization of impact hypotheses as “novel, self-contradictory, rapidly changing, and sometimes defying the laws of physics”, how did they get published in PNAS in the first place? That’s not some vanity journal, it’s real peer review. You’d think the impact experts who reviewed it would have seen the problems. Were these people “big enough” for other reasons that giving their pet crackpot ideas a full airing was somehow required? Firestone is a real scientist in the area of studying isotopes–he [wrote a book on the subject](https://www.amazon.com/Table-Isotopes-Richard-B-Firestone/dp/0471077305) that is apparently well regarded. But his understanding of science outside of atomic isotopes is insanely wrong, and when he got some clue about how wrong something was, he would adjust it to be equally wrong in the opposite direction. For instance, his original claims were that his supernova comets were traveling at around 10,000 miles per second when they hit Earth–when it was pointed out how wrong that was, he adjusted it to 1,000 miles per hour, which is impossibly low. And in the book, the comets (that formed inside a supernova explosion) were hundreds of miles across but with a density of 0.02 grams per cc. An utter impossibility-- those comets would collapse into a denser state even under their small gravity (of course, comets wouldn’t be forming in an exploding supernova in the first place.) I have no idea how he got his article published in a peer-reviewed journal other than the fact that reviewers can’t be well versed in _all_ areas of science. But for someone who is even just a hobbyist in meteoritics and impacts such as myself, there were many glaringly obvious errors from the very beginning, and as he constantly adjusted his story, he constantly generated new errors. West, on the other hand (as mentioned in the fist article I linked) was simply a con-man with a degree from a bible college (if any degree at all) who was hiding behind a pseudonym to cover his criminal history. [Previous page](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226.md?page=4) [Next page](https://boards.straightdope.com/t/why-are-there-no-dinosaur-size-land-animals-today/793226.md?page=6)