(host) In 2011, a worker at an oil sands mine in Alberta, Canada, made one of the most exciting dinosaur discoveries of the 21st century. While digging up a cliffside, the worker's excavator struck an unusually hard object peppered with large tan splotches. He had just discovered the remains of a 110 million-year-old nodosaur. Nodosaurs were a group of armored plant-eating dinosaurs that lived during the late Jurassic and Cretaceous periods. And paleontologists have been studying these dinosaurs since the 1830s, but nobody had ever found a specimen like this one before. Researchers at the Royal Tyrrell Museum named it Borealopelta markmitchelli after the technician who spent over five years cleaning up the fossil. It represented a completely new species. And that was just the beginning. Although the dinosaur's tail and a few other parts were missing, everything that was left was amazingly detailed. There was a gorgeous skull, articulated neck vertebrae, several leg and foot bones, and portions of the torso and hip regions. But it was the rest of the fossil that made international headlines. From the hips forward, Borealopelta had an almost complete set of osteoderms. Osteoderms are bony plates that are embedded in the skin, just like what alligators have today. Nodosaurs and many of their relatives had backs that were covered in osteoderms-- possibly for defense. Better yet, Borealopelta contained super-rare remnants of softer body materials and even had traces of pigmentation, giving us important clues about the animal's color pattern. And the key to all this exceptional preservation was where Borealopelta ended up after it died and how it got there. Because the strange thing is, it was found lying on its back in a marine deposit. In other words, it was fossilized upside down underwater. And a lot of other nodosaur fossils have turned up in similar deposits-- ones left behind by ancient waters. So how did these dinosaurs end up getting buried at sea? The answer to this question is a gross but also kind of cool process of decomposition called-- wait for it-- bloat and float.

(Describer) Title: Eons.

Nodosaurs belong to a larger group of herbivorous dinosaurs called ankylosaurs. Scientists have found their remains on most of the world's continents-- including Antarctica-- and they generally divide ankylosaurs into two major groups: the ankylosaurids and the nodosaurids, or the nodosaurs. The ankylosaurids tended to have short, wide skulls, and many sported bony clubs on their tails that were probably used as weapons. But nodosaurs didn't have these clubs. Instead, many of them-- including Borealopelta-- had long spikes on their shoulders and narrower snouts. Two of the oldest nodosaurs on record are gargoyleosaurus and mymoorapelta. Both were around 3 meters long and lived in the western U.S. during the late Jurassic period. But nodosaurs persisted throughout the Cretaceous period, sticking around right until the age of dinosaurs ended 66 million years ago. And both nodosaurs and ankylosaurids often turn up in marine fossil deposits. Now, you might remember from our video When Sharks Swam the Great Plains that from about 95 million to 68 million years ago, a huge body of water called the Western Interior Seaway split North America in half. And earlier in the Cretaceous, much of west central Canada and the upper Great Plains were covered by the Mowry Sea, an extension of the Arctic Ocean. So there was a lot of available sea for the armored dinosaurs to end up in. For example, take the nodosaur known as Niobrarasaurus. It's known exclusively from the late Cretaceous marine deposits of western Kansas, and some of its fossils even bear the tooth marks of ancient sharks. And lots of other armored ankylosaurs-- including nodosaurs-- have been found in marine deposits from places like Queensland, Australia, and James Ross Island, Antarctica. One species was even found in California with fossilized oysters encrusting on its bones. And then we have Borealopelta, the spectacular nodosaur that those Albertan miners came across. Its remains were discovered in the early Cretaceous Clearwater Formation, where the fossils of marine reptiles like plesiosaurs and ichthyosaurs often turn up. But scientists had never found any dinosaur material out there until Borealopelta. So what happened? Well, after its death, Borealopelta's corpse hit the seafloor around 200 kilometers to 400 kilometers away from the closest shoreline. And it landed upside down, which turns out to have been a common fate for nodosaurs. Computer simulations suggest that these top-heavy animals would have flipped over pretty easily while floating in the water. So below the waves, Borealopelta came to rest in a layer of stagnant, oxygen-poor mud. Traces of burrowing sea creatures were found nearby, but paleontologists found no evidence that the dinosaur's body was scavenged. And when it was discovered, Borealopelta was encased in a tomb of hard rock called a concretion. As its body decayed, carbon dioxide and other substances were released, which changed the chemistry of the water inside the mud around the carcass. Soon enough, a tough layer of siderite-- a type of iron carbonate-- formed, protecting the dinosaur's remains. But how did it get so far away from the coastline? After all, Borealopelta was heavily armored and short-legged, so it was probably a terrible swimmer. And it lived on land anyway, so there's no reason to think that the nodosaur swam to its watery grave. It's more likely that the dinosaur's body was washed out to sea. Sometimes after an animal dies and bacteria start breaking it down, gases build up inside the corpse. And if the carcass ends up in a body of water while that's happening, it might start bobbing around at the surface. Scientists call this phenomenon "bloat and float." Eventually, those gases escape, the body stops floating, and it sinks to the bottom. And no matter where an animal dies, there's a good chance its remains will get scattered around after death. But the concretion around Borealopelta kept most of its skeleton together. Better yet, the rocky shell helped the dinosaur retain its three-dimensional shape even as layers of sediment piled up on the carcass over time. Between the bloat-and-float process and the sea floor environment where it landed, Borealopelta kind of hit the jackpot in terms of preservation. For example, along with those osteoderms, experts found that the fossil was also covered with tiny polygonal scales on much of its skin. And delicate skin structures were spread out across the skull, neck, back, hips, and even its legs. Plus, many of the dinosaur's osteoderms-- along with other parts of the body-- were coated in a dark gray material. This stuff has been identified as a kind of organic film. And it's loaded with the chemical traces and by-products of keratin. Keratin is a key ingredient in fingernails, hooves, feathers, and hair. and some modern reptiles like alligators have keratin sheaths over their osteoderms. Unfortunately, keratin often vanishes without a trace during the fossilization process. But the organic film on Borealopelta preserved the original three-dimensional structure of the keratin sheaths that covered and lengthened the bony osteoderms when the dinosaur was alive. The ones on Borealopelta's shoulder spikes are a centimeter thick in some places and make up about 25% of the total length of each spike. So this gives us a clearer picture of what the nodosaur actually looked like. But wait, there's more. The film of keratin wasn't even the most spectacular aspect of this fossil. This dinosaur had preserved evidence of coloration, and it came in an unexpected pattern. Some of Borealopelta's scales bear the chemical hallmarks of a pigment called pheomelanin. Judging by these traces, it appears that most of the dinosaur's back was a reddish-brown, while its underside was pale. This means that Borealopelta could have been countershaded, or darker on its upper side and lighter on its underside. Countershading can make animals much harder to see because of the way shadows help us perceive objects.

(Describer) ...like penguins.

When sunlight hits a three-dimensional body, it tends to look light on top and dark on bottom. So if these creatures are lit from above, they'll look almost uniform in color. Their dark backs will be illuminated, and their light underbellies will look darker. Because of that, predators might not even recognize countershaded animals as three-dimensional objects. Visually, they're harder to make out. This would have been really useful for Borealopelta because even though it was really big-- like, 1,300 kilograms-- back in the nodosaurs' heyday, massive carnivores stalked North America. And one of them was Acrocanthosaurus, a predator that measured 11 meters long and could have weighed a little over 7 metric tons. With enemies like that on the prowl, Borealopelta may have benefited from a little camouflage. Without the amazing preservational environment created by the concretion and the whole bloat-and-float thing in the first place, We wouldn't have any clue what color this huge dinosaur was or what it ate. And that brings us to a soccer ball-sized lump found in Borealopelta's abdominal cavity. In 2020, Royal Tyrrell paleontologist Caleb Brown and his colleagues recognize this lump as a cololite, which is a hunk of fossilized intestinal contents. Even though Borealopelta had ended up in a marine deposit, this cololite was loaded with bits and pieces of land plants. Fossil sites in other parts of Canada tell us that central Alberta was home to a wide variety of terrestrial plants in the early Cretaceous, with conifer forests dominating the landscape. But it doesn't look like Borealopelta was too keen on conifers. Leaf tissue makes up 88% of all the plant material that was identified inside the cololite, and the vast majority of those leaves came from ferns, which is interesting because scientists had always assumed that nodosaurs, with their long, narrow snouts, were picky eaters. Instead of chowing down on a mixed foliage indiscriminately, the dinosaurs would have carefully plucked their favorite plants. And Borealopelta's gut contents look like evidence of this, but they also point to something surprising about the environment that it lived in. Inside the cololite, the researchers discovered a few samples of charcoal that the dinosaur apparently swallowed. In fact, burned plant fragments represent 6% of the botanical material in the cololite. And perhaps that says something about Borealopelta's feeding behavior. Researchers think wildfires were quite common during the Cretaceous. When Borealopelta was alive, oxygen may have made up around 30% of Earth's atmosphere, compared to just 21% today. And when these natural disasters happen, ferns often bounce back faster than other plants do. For a brief period, ferns may actually dominate a postfire landscape as the environment recovers. So if Borealopelta was a picky eater with a taste for ferns, then maybe the dinosaur was attracted to wildfire-stricken areas where these plants were thriving. Between the remnants of keratin and its preserved dietary clues, Borealopelta might be the most significant nodosaur fossil ever found. And just think-- the dinosaur could have been lost to us forever if it hadn't bloated and floated across an inland sea. In death, this creature beat the odds, evading scavengers and the ravages of fossilization before it survived the mining process and caught an equipment operator's eye. By doing all this, it's given us a bounty of dinosaurian knowledge. So here's to Borealopelta markmitchelli, an improbable ambassador from the early Cretaceous. Accessibility provided by the U.S. Department of Education.

(Describer) Titles: In this episode, we refer to fossils from the homelands of the Cree, Métis, Denendeh, Cheyenne, Sioux, Arapaho, Eastern Shoshone, Ute, Osage, Pawnee, Kaw and Comanche peoples. Kallie Moore: Content Consultant, Host PBS. Accessibility provided by the US Department of Education.

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