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Early Mammal Fossils
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0:00
when a researcher stumbled upon the fossil of a small mammal called the multituberculate in the late 1960s in the foothills of Southwestern Montana it came as a shock you see at that point fossil collecting around the Rocky Mountains had been going on for just over a century so paleontologist had a pretty good idea of what animals they should expect wear and multituberculates a group that first appeared in the fossil record about 165 million years ago were extremely common until about 56
0:29
million years ago after modern groups of mammals evolved and started to out compete them but these Montana rocks dated to 17 million years after most of them went extinct and these fossils came from the Foothills instead of the low-lying basins where paleontologist typically find multi- tubercular fossils this discovery pointed paleontologists toward the mountains which would eventually reveal something even stranger about a group of mammals even closer to home primates because it turns
0:57
out mountains have a unique effect on diversity messing with their understanding of animals through time and pretty much just making Evolution weird at the beginning of the esin epoch 56 million years ago the area that's now Wyoming was as warm and wet as the modern Tropics here trees related to swamp dwelling bald cypress and fruiting and flowering Elms supported a novel group our own relatives the primates and these primates were thriving diversifying into a range of species
1:29
they grasping hands and feet allow them to navigate the canopy more easily than any mammals before them and after many decades of collecting fossils in the American West scientists had a pretty good sense of their evolutionary story or so we thought they seem to fall into two groups the larger lemur likee adapoids and the small tarer likee omomyids the adapoids which were fruit and leaf eaters were represented by only a few species at any one time while in contrast the omomyids were extremely
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diverse evolving multiple species that were highly specialized for eating insects or small vertebrates as well as fruits and seeds in North America alone there were almost 40 Genera of omomyids between 55 and 36 million years ago which themselves fell into two groups the first was the anapt morphine omomyoids which appeared about 55 million years ago and dominated North America these were extremely small Critters one of the smallest trogo liur weighed only about 50 g about as much as
2:30
a lemon and these little inapam morphins could be identified by the sharp cusps on their teeth and they're especially prominent fourth premolar but within the next 5 million years in the middle eosine they began to decline leaving the other group The omamay omomyoids more prevalent on the landscape these omin were slightly bigger up to 3 Kg in one genus macarius they had shorter cusps on their teeth and didn't have the prominent fourth premolar seen in an apomorphine now because there are eosine
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H deposits all over North America from Mexico to Mississippi to Canada we could see that the OM mayin were out competing the inapam Morphin all over or so paleontologist thought because here's the thing these fossils had all been collected in relatively low elevation sites where sediments accumulate in basins that began to change in the 1970s when a group of scientists inspired by the discovery of those multi turculet in Montana started looking for primate fossils in the foothills of Central
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Wyoming and despite being from the Middle eosine the Foothills sitting about 1,980 m in elevation revealed an apomorphine primates that were not only surviving but diversifying and evolving into new species seeking answers researchers moved further up in elevation and at a pass to the South around 2,200 M High researchers working in the 1990s collected a huge amount of fossils including more than a dozen species of primates they were tiny and tarer like in their Anatomy with subtle
4:00
differences in their teeth marking all these species as distinct from one another from artonius with its massive fourth lower premolar to that lemon siiz trogo lemur with its small fourth prolar and diminished cusps so this new site had substantially more species than any of the lower elevation sites dating to this time despite those having been explored for nearly a century with many specimens collected and these new finds included multiple gener that are usually
4:26
extremely rare during this period like artonius which is was among the most abundant primates here the relative abundance we come to expect was basically flipped on its head even omam cartery in omay that is often one of the most abundant species of that time period was barely present and data from the 2010s from an even higher elevation site near Yellowstone National Park at just over 3,100 m in elevation showed that same pattern with omam Carter ey it was clear that these mountainous regions
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were different but why what could be going on to creat such a different evolutionary pattern from the basins there almost seemed to be a mismatch between the ages of the rocks and the animals found in them which sometimes happens with a process called time averaging where instead of representing one discrete chunk of time sediments of different ages are mixed together this can happen when different layers of rock or sediment are exposed along a hill and Rain erodes out the layers which then
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accumulate at the bottom and that accumulation turns into a new fossil deposit that actually represents all of the time periods exposed along the hill not just one so you end up with a jumble of things that don't seem like they belong together because they actually don't belong together but at these sites there were welld layers above and below the sediments so that couldn't really explain the pattern so the scientists started to wonder what if it was the mountains themselves in the environments
5:51
they created that were causing these patterns elevation can play an important role in supporting diversity in part because mountains often have greater environmental variation than low-lying areas there are a few reasons for this the changes in atmospheric conditions As you move up and down the mountains create variation from temperature shifts to air density to UV radiation and in mountains there's greater topographic complexity not just in the sense that
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mountains are tall but also because they get more rain leading to more active erosion dividing the mountain into many different small river systems each carving up the landscape in different ways which means that within a single sare mile there are more topographic changes in mountains than in low elevation areas not to mention the cliffs crests and further divisions to the environment that can happen during the tectonic processes that form mountain ranges like the Rockies these
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varied environments mean more environmental niches supporting more species and more habitat variation means it's increasingly likely that a trait might offer an animal some advantage and be selected for which means there is a better chance that new species will evolve so when we see higher diversity we may be seeing the preserved evidence of the speciation caused by habitat variation this is probably why we get the higher primate diversity at that Medium elevation site additionally more
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niches mean less competition for the same Niche so animals that may be out competed in low-lying areas might be able to persist longer in mountainous regions these are called refugia where a species survives in a small region that forms a subset of a once much larger range so those an apomorphine persisting longer in in the Foothills without getting out competed by the omamay are evidence of refugia this combination of speciation potential and refugia may lead mountains to act almost like
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Islands supporting isolated pockets of diversity in a similar way and this islandlike pattern might explain why there are primate species seen only at these high elevation sites also some animals just prefer to live in mountains so when we see things like artonius which is typically rare in lowlands maybe we're not seeing an uncommon animal like scientists once thought we're just seeing habitat preference but there's one final piece to consider about the world in which these eing
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creatures live the mountain building events themselves in fits and bursts ranges like the Rocky Mountains appeared on the landscape through faulting and folding that lifted and shaped the Earth's crust and these events were often accompanied by episodes of volcanic activity that deposited thick layers of ignest rock while there's debate about the exact timing much of the Rockies were the product of a mountain building episode that unfolded between 880 to 40 million years ago so
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during the time the inapam Morphin and omin were evolving and competing for resources mountains were actively forming and dividing the landscape and part of this activity included nearly 15 million years of periodic eruptions in Wyoming itself that cast Ash and Volcanic material for hundreds of miles in all directions this single volcanic group alone is responsible for depositing about 1.5 km of sediments in parts of Wyoming only in increasing the effects of the mountains on the animals
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living in them so as this complex landscape comes into focus it becomes clear that there's still a lot to be learned and this is tricky in mountains which have steeper gradients big erosion potential and overall poor preservation but what we have learned from the fossil record of these unique environments from multituberculates to eosine primates is that Extinction isn't always uniform it isn't always an onoff switch it wasn't until scientists found the an aptom
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morphine surviving and speciating in the mountains of the middle eosine that we realized they hadn't gone extinct they just adapted so while the original story of anapt Morphin being replaced by omam Mayans was far more complex than it had seemed it was also more interesting and expanding the fossil record upward can allow us to learn new lessons from the mountains [Music] now as we've learned early primates not only lived in North America they thrived so what happened to those ancient
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relatives of ours find out in our episode what happened to primates in North America and mountains of thanks to this month's e onist Addie Annie and Eric Higgins Carl wolle Jake har John davidon in Juan M Melanie lamb carnavale Nico Robin Raphael H by becoming an eonite at
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access to behind the scenes content including clips from Eon shoots and as always thanks for joining me in the Ken bar studio subscribe to youtube.com/ eons for more evolutionary [Music]
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escapades it that was it man scientists choose easier words just kidding
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[Music]
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