Do Thunderbeasts Prove Giant Animals Are Inevitable?

e On's calendars are back for 2024 we've chosen to highlight paleo art from our episodes about human evolution including one new never-before-seen illustration of a famous early relative of ours you can click the link in the description or head on over to dftba.com eons to order one around 38 million years ago in a lush forest in westal South Dakota the ground shook with the Thundering footsteps of a herd of giants they were massive standing about 2 and 1/2 M tall nearly 5 m long and weighing close to 3 metric tons and while they were nearly elephant sized they were actually more closely related to horses Mega seraps col rensis was just one of many humongous members of the group called Bron AKA Thunder beasts that lived around this time but in the early e Epoch their ancestors were only about the size of a border colly yet somehow in the span of a mere 20 million years species weighing over 1 metric ton would become a common sight in fact Bron experienced one of the most extreme size increases ever seen among mammals and the journey the Thunder Beast took to reach such Mega proportions from such humble beginnings forces us to ask an important question when the paleontologists have been asking for more than a century from an evolutionary perspective is bigger always better everything big started out much smaller this may sound simple and obvious but the actual reason that size increases happen in animal lineages has been tricky for scientists to explain in the 19th century American p ologist Edward Drinker cop of bone Wars Fame wrote about the seemingly widespread Trend in the fossil record of species getting bigger over geologic time this idea became known as cop's rule it basically argues that there's a constant gradual push toward bigger and bigger sizes as lineages evolve over time with successive species generally increasing their body sizes compared to the ones that came before and the idea was that this trend is driven by a simple principle when it comes to survival and reproduction being bigger generally comes with a bunch of selective advantages over being smaller see scientists like cope assumed that being bigger meant better defense against predators or if the species itself is a predator then it could take down larger prey more easily many species also fight for mates and territory and you can generally bet on larger individuals winning those fights plus bigger bodies generally have bigger brains possibly opening up the door for greater intelligence to evolve which can offer survival advantages too so why don't we live in a world filled with giant animals today well for most of our species history that's exactly the world we did live in megap were everywhere from giant sloths in the Americas to Giant deer in Eurasia to Giant marsupials in Australia and their absence today is not entirely natural in many cases it's likely that we had a direct hand in their Extinction but on the flip side the largest animal ever known to have existed is actually around today the blue whale the most gigantic animal of all time is a modern one not a prehistoric one so does that mean that cop's rule is actually true and that it neatly explains why so many animal lineages including Bron reach such epic proportions well not exactly see the so-called rule has been criticized for pretty much as long as it's been around it can't be applied to all lineages in the fossil record not everything ends up getting much larger than its ancestors and these kinds of evolutionary Trends unfold over tens of millions of years and alongside many ecological variables so trying to identify such large scale patterns with any degree of confidence is really hard you need a lot of fossil data and ideally a lot of computing power to find Trends in all that data something that wasn't possible until relatively recently plus even for group that do seem to fit the trend on deeper investigation it RAR seems to be as simple as a constant linear push towards ever larger sizes take for instance parasaurs the biggest things that ever flew by the end of their reign the wingspan of some parasaurs exceeded 10 m but for their first 70 million years their wingspan stayed below 1.6 M the upward Trend in size only kicked in about halfway through their history at the end of the Jurassic period so it isn't as simple as bigger always equals better but then how do we explain the Thunder beasts rapidly increasing in in size by orders of magnitude pretty much as soon as ecosystems could support such large mammals after all if you line up the members of their group in chronological order they seem like a perfect example of cop's rule they started off as small dog-sized species like eot titanops that roam North America and Asia in the early esine by the midene more Hefty species had evolved like the calized Paleo cops and by the end of the esine less than 20 million years after they first appeared Bron had truly earned their nickname of Thunder beasts name inspired by Lakota cultural Legends of giant beings that caused violent storms that shook the Earth because those later roners were rhinoceros to elephant sized mammals that had no equals on land at the time and these Giants emerged in multiple places too Asia had the chunky Rhino Titan as well as emium whose name means battering ram Beast for example that's a pretty metal name and North America had among others perhaps the most famous of the massive bront megacerops which has also gone by a few other names in its history including titanum bront tops and brontotherium cope personally spent time studying fossils from across this timeline even naming a handful of Bronto species himself but did they actually obey his rule or not well to figure it out in 2023 a team of researchers published a new analysis of 276 fossils from 57 bronier species more than half of which grew to over a ton as the esine epoch unfolded they took into account several other ecological variables throughout that time period too like the presence of other herbivores that might have competed with them and carnivores that might have prayed on them and they analyzed all that data using computer models to try and test three evolutionary Pathways that Bron could have taken on their journey toward gigantism these Pathways included cop's rule that gradual sustained increase in size over time and they also included two others that argued that body sizes grew in successive phases or just Diversified without any overall direction and they found that it was actually the third scenario that best fit the data because Bron weren't simply getting bigger with time in a selective one-way push that was consistent with cop's rules instead they showed a completely different overall trend a trend in which Bron lineages continued to produce both larger and smaller new species as they Diversified with no particular preference in either direction the reason why there still seemed to be an overall net increase in body size over millions of years was due to a process called species sorting while smaller buer species were still evolving the ecological conditions of the E acted as a sort of filter that led to them generally doing much worse than the larger ones over the long term and the researchers think this was primarily because of competition see mammals that survived the extinction event at the end of the mesic that had dethroned the dinosaurs were all pretty small so competition in smaller niches was pretty intense as ecosystems recovered and mammals took Center Stage for the first time and while Bron were producing species with a range of sizes larger lineages generally found themselves occupying niches with less competition so there was a benefit to being one of the first mammal groups to produce big and bulky species this meant that smaller lineages and crowded niches were more prone to going extinct than larger ones resulting in in the overall pattern of body sizes increasing that we see in the fossil record instead of the Broner evolutionary tree growing only in one linear Direction it was more like the tree branched off in a range of directions with the ecosystem pruning off the smaller branches giving the illusion of a simple Trend toward becoming huge so for the Bron cop's rule turned out to be wrong and by the end of the esene around 34 million years ago Bron of all sizes were extinct probably as a result of environmental changes so it looks like bigger isn't always better like so many evolutionary traits that we're tempted to point to as signs of progress or Improvement whether they're good or not all depends on the ecological context and if deep time has taught us anything it's that change is the only [Music] constant so getting bigger and more complex may not be inevitable but what about getting smaller check out our episode how the smallest animal got so simple or as I like to call it Honey I Shrunk the life I don't call it that but Cali wants me to say that I call it that also we got to thank this month's biggest deontologists Jake Hart rafhael hassa Annie and Eric Higgins John Davidson ing Melanie lamb carnavale Addie Tony Dy and Juan M become an ianite at patreon.com and you can get fun perks like submitting a trivia question for us to read yep that's right we're transition from jokes to trivia I hope you're as happy about that as I am to get us started what famous dinosaur's genus name means Thunder lizard oh okay got it damn that took longer than it should have put your guesses in the comments and stick around after the blooper to see the answer and as always thanks for joining me in the Adam low Studio subscribe at youtube.com/ eons for more stoic Critters from an evolutionary perspective is bigger always [Music] better Blake no no no what did we just talk about this is dumb it's just this part I'm going to be fine as soon as the answer is brontosaurus I don't know why it took you so long to remember that it's like what I do for a living but Bronto the Thunder thing I don't know what the means but then the Bronto part I got what does the mean Beast Thunder Beast okay thunder thunder thing let us know if you got it right

Channel: PBS Eons

Views: 549,487

Keywords: Kallie Moore, Michelle Barboza-Ramirez, Blake de Pastino, eons, Hank Green, John Green, DFTBA, PBS, PBSDS, dinosaur, earth, natural history, paleontology, fossils, archaeology, geology, thunder beast, Megacerops, brontotheres, cenozoic, cope’s rule, megafauna, Eotitanops, Palaeosyops, Rhinotitan, Embolotherium, species sorting, evolution, biology

Id: uM51_Vui9tA

Length: 9min 55sec (595 seconds)

Published: Tue Oct 24 2023