How Plankton Created A Bizarre Giant of the Seas

Video Statistics and Information

Video
Captions Word Cloud
Reddit Comments

Interesting, great share!

👍︎︎ 3 👤︎︎ u/juan_prada 📅︎︎ Nov 10 2020 đź—«︎ replies
Captions
In 2014, at a site in Morocco that now borders the Sahara Desert, a local fossil collector came across the remains of a big...something.  It was dated to 480 million years old, near the start of the Ordovician Period.  The paleontologists who described the new fossil named it Aegirocassis And they recognized that it was a member of the group of strange creatures known as radiodonts.  Radiodonts are long-extinct animals that looked kinda like lobsters.  They had partly segmented bodies and eyes on stalks, like lobsters do, but they also had flaps hanging off of each body segment that might’ve been used for swimming, and a pair of long head appendages that were used for feeding. And their name comes from their distinctive circular mouths, that were surrounded by overlapping tooth-plates, like a camera lens aperture.  While fossils of these bizarre creatures were first found in the late 1800s, it wouldn’t be until 1994 that paleontologists figured out that radiodonts were early arthropods.  Although they looked different from today’s marine arthropods - like lobsters, crabs, and shrimps - radiodonts had some telltale arthropod features, like a tough exoskeleton, a segmented body, gills, and appendages with joints.  But what was even weirder about this radiodont from Morocco was its massive size.  At more than 2 meters long, it was not only the biggest radiodont ever, but it also may have been the biggest animal in the Early Ordovician.  And the reason it could get to be that huge is pretty surprising. This bizarre marine giant may have only been possible, thanks to a major revolution among some of the tiniest organisms in the world.  The first radiodonts show up in the fossil record in the early Cambrian period, about 40 million years before that big one from Morocco.  And some of these radiodonts were tiny.  For example, one early radiodont from China was about the size of a stick of gum. But it looks like it was a pint-sized predator.  It had two appendages on its head that were curved and had sharp spines, which it probably used for grabbing equally tiny prey. And the top predators of the Cambrian were also radiodonts, with the biggest and best-known ones in the genus Anomalocaris. Anomalocaris canadensis was found in the famous Burgess Shale of British Columbia and dated to 505 million years ago.  Fossils of this species show that it grew up to half a meter long.  While it would’ve been small compared to Aegirocassis, Anomalocaris was the largest predator in the Cambrian seas. It caught prey with its frontal appendages, each equipped with trident-like spines. The jury's still out on whether its prey were hard-bodied, like trilobites, or soft-bodied, like worms and jellyfish, but either way it was still a formidable predator And with around 25 million years of evolution between those two radiodonts, why wouldn’t the members of this group have just gotten bigger and badder over time? But, weirdly enough, when paleontologists examined the feeding apparatus of Aegirocassis, they were surprised to discover that it was clearly not an active predator that went after large prey.  Instead of grasping spines on its head appendages, they found an intricate structure made up of fine, hair-like, parallel spines - like the teeth of a comb. It looked like the kind of structure you’d find on a plankton eater, like a modern baleen whale.  So, instead of a fierce predator, paleontologists concluded that this giant of the Ordovician seas was a suspension feeder - an animal that feeds by straining plankton from the water rather than chasing larger prey. And it might be this feeding strategy that allowed it to get so big. If you look back into the fossil record at earlier radiodonts, there are a few other suspension feeders, but they started out a lot smaller. For example, Tamisiocaris was about the size of a shoebox and lived in the early Cambrian. Its appendages had evenly spaced, super-fine spines on them that could filter out some of the smallest parts of marine food webs - plankton. Now, plankton come in two basic groups. Phytoplankton make their own energy through photosynthesis and Zooplankton that eat phytoplankton and algae.  Phytoplankton are microscopic, while some zooplankton are a bit bigger. And the delicate combs of Tamisiocaris would have allowed it to filter out prey as small as half a millimeter, like copepods, which are teeny-tiny crustaceans that are still around today. An even smaller suspension-feeding radiodont showed up later in the fossil record, in the Middle Cambrian of Utah, about 502 million years ago. Named Pahvantia, it was just under 24 cm long.  Its head appendages had sharp spines in rows that were so close together that it could have filtered not only zooplankton, but also the smaller phytoplankton. So, being a suspension feeder doesn’t necessarily make for large body size - and you don’t always need to be huge to subsist on plankton. That means that something else must have been going on in the Late Cambrian to explain the rise of the biggest radiodont ever at the start of the Ordovician. And that something else was the tiniest revolution at the base of marine food webs - one that would have extra-large consequences. In modern ocean systems, phytoplankton live in sunlit zones, where they photosynthesize and then supply energy to the darker, deeper zones as they get eaten by zooplankton whose poop or decaying bodies sink to the ocean floor. This is part of the process known as the biological pump, which transfers biomass and energy from the surface of the ocean to the sea floor. And paleontologists thought that, during the Cambrian, the surface was less connected to the dark ocean bottom, because the water column in between was not full of plankton like it is now. The only fossil evidence of Early Cambrian phytoplankton are microfossils called cysts. Many marine plankton today make cysts, which are little hard casings that may provide defense from toxins in their environment, or to allow them to go dormant for a while. The fossil record for zooplankton is a little better.  There are preserved mouth-parts from tiny crustaceans and mineralized skeletons of radiolarians - single celled animals that are usually considered to feed on phytoplankton. Both are similar to what you'd find today. Now, while plankton did become more complex throughout the Cambrian, overall they seem to have been less diverse and abundant until the end of the period. And as the Cambrian came to a close, a large radiation event got started. This is known as the Paleozoic Plankton Revolution. And it continued into the earliest Ordovician, with the whole event lasting less than 15 million years. While researchers are still debating exactly what caused the Plankton Revolution, it looks to have been linked to a major change in climate. 500 million years ago, there were upheavals in the Earth’s crust from tectonic activity. More rock was exposed to weathering, which drew carbon dioxide out of the atmosphere.  This caused what scientists call a reverse greenhouse effect. The Earth cooled rapidly, in geologic terms, as carbon dioxide levels plummeted over the span of 2 million years. The cooling created more suitable ocean temperatures for plankton, which began to flourish.  Photosynthesizing phytoplankton took in --more carbon dioxide and released oxygen into the atmosphere, which made the temperature changes happen even faster. As plankton grew denser and more diverse, they may have ramped up the biological pump going from the sunlit ocean surface to the deep sea floor - transforming oceans into more nutrient-rich, productive ecosystems, like what we see today. And that is when the BIG radiodont Aegirocassis showed up. More abundant plankton meant suspension feeders could get much larger, because there was just more food available. Paleontologists count Aegirocassis as the first of the giant  suspension feeders. These would eventually come to include members of the agnathan fishes, nautiloids, placoderms, sharks, bony fishes, reptiles, ammonites, and mammals. And, in fact, recent research links suspension-feeding to large body size in whales. The biggest animal on Earth now...or ever... is not an active predator, but a plankton eater: the Blue Whale. While the radiodonts didn’t make it beyond the Devonian Period, the evolution of Aegirocassis was a preview of what was to happen, independently, in many other groups of animals. It took a tiny explosion at the base of marine food webs almost 500 million years ago to set the stage first for the largest radiodont ever and, ultimately, for our modern oceans. Hey! It's Blake popping in. I just wanted to say thanks for watching Eons, which is produced by Complexly. If you want to keep imagining the world complexly with us, check out Bizarre Beasts.  Once a month, hosts Hank Green and Sarah Suta introduce you to a new bizarre beast and explore what makes these animals so weird to us. From birds whose babies have claws on their wings, to lizards with glowing bones somehow, the show examines the how and why of some of the world's most amazingly strange critters.  The link for the channel is in the description below! Gentle giant high fives to this month’s Eontologists: Lucan Curtis-Mahoney, Sean Dennis, Jake Hart, Annie & Eric Higgins, Jon Davison Ng, and Patrick Seifert! To become an Eonite, pledge your support at patreon.com/eons. One benefit of being an Eonite is getting to submit a joke for us to read! Like this one is from Meghan. Why are volcanoes so jolly? Whenever they hear a joke, they erupt with laughter These are so good! Keep sending us your jokes and we’ll keep reading them on the end of our episodes And as always thank you for joining me in the Konstantin Haase studio. Subscribe at youtube.com/eons for more creature features!
Info
Channel: PBS Eons
Views: 806,854
Rating: 4.9432626 out of 5
Keywords: dinosaurs, dinos, paleo, paleontology, scishow, eons, pbs, pbs digital studios, hank green, john green, complexly, fossils, natural history, anomalocarid, suspension feeding, Cambrian, Ordovician, plankton, body size, biological pump, climate change, productivity
Id: G0oKBPZODhM
Channel Id: undefined
Length: 10min 5sec (605 seconds)
Published: Tue Nov 10 2020
Related Videos
Note
Please note that this website is currently a work in progress! Lots of interesting data and statistics to come.