Episode 172: Temnospondyls

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This week let's go back back back in time to more than 300 million years ago, when amphibian-like animals lived in enormous swamps. Don't be fooled by the word amphibian: many Temnospondyls were really big! Further reading: Palaeos Temnospondyli Dvinosaurus, three feet long and full of teeth: And Sclerocephalus, five feet long and full of teeth. This one has a couple of larvae nearby: Fayella (art by Nix) Nigerpeton's astonishing NOSE TEETH: Mastodonsaurus had nose teeth too and it was way bigger than Nigerpeton, but somehow it just looks goofy instead of cool: Koolasuchus just looked weird: The largest Temnospondyl known, Prionosuchus: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re going back into the past, way before the dinosaurs, to look at an order of animals that resembled modern amphibians but weren’t precisely amphibians, or reptiles, or fish. Let’s look at the Temnospondyls. During the early Carboniferous period, which lasted from about 360 to 300 million years ago, the ocean levels were high, the climate across much of the world was humid and tropical, and the continents were in the process of smushing together to form a huge landmass called Pangea. Much of the land was flooded with warm, shallow water that created enormous swampy areas full of plants and newly evolved trees. These swampy areas, full of decomposing leaves, eventually became coal and peat beds. As the Carboniferous period continued, the climate turned milder and the sea levels dropped, but while the huge swamps remained, many life forms evolved to take advantage of the various habitats and ecological niches they provided. The armored fish of the Devonian went extinct, replaced by more modern-looking fish, including sharks and the first freshwater fish. The first conifer trees appeared, land snails, dragonflies and other insects, and the first animals that could survive on land for part of the time. This included the Temnospondyls, a numerous and successful order of animals whose fossils have been found worldwide and appear in the fossil record for more than 200 million years. But most people have never heard of them. Temnospondyls are grouped in the class Amphibia alongside Lissamphibia, which is the order all living amphibians and their ancestors belong to. But researchers aren’t sure if Temnospondyls gave rise to lissamphibians or if they all died out. The first Temnospondyl fossils were discovered in the early 19th century and early paleontologists immediately started debating what exactly these strange animals were. It was originally classified as a reptile, but as more fossils came to light, it became clear that these weren’t reptiles. Finally it was classified as a subclass of amphibian called Labyrinthodontia, where it remains today, at least for now. Temnospondyls do share many traits with modern amphibians. We know that at least some species had a larval form that was completely aquatic, with fossil evidence of gill arches. Some retained external gills into adulthood the way some salamanders do. But they still had a lot in common with their fish ancestors. Most Temnospondyls had large heads that were broad and flattened in shape, often with a skull that was roughly triangular. The earliest species had relatively small, weak legs and probably spent most of their time in the water, but it wasn’t long before species with stronger legs developed that probably lived mostly on land. When you think about amphibian relatives, you probably think these animals were small, maybe the size of a bullfrog. But while some Temnospondyls were small, many grew much larger. Some had smooth skin but many had scales, including some species with scales that grew into armor-like plates. Let’s look at some individual species of Temnospondyl and get an idea of how varied they were. Let’s start with a group of temnospondyls with one...

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