Professor Nick Cutter (![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
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fandomhigh2024-12-11 09:17 pm
itsananomaly) wrote in fandomhigh2024-12-11 09:17 pm
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Introduction to Fossils - Wednesday Period 1
“Good morning,” Cutter began that week’s class, Connor was still busy helping Prospero so he still by himself, “this week we’re going to be covering shark fossils,” he explained, “Sharks first appeared in the geologic record 450 million years ago during the Silurian Period. Due to this lengthy fossil record, sharks are often referred to as "living fossils." Occasionally a fossilized vertebra (bones comprising the spinal column) will be discovered, but usually the teeth are the only elements of a shark that will undergo fossilization.”
“Sharks belong to a group of creatures known as cartilaginous fishes, because most of their skeleton is made from cartilage rather than bone, The only part of their skeleton not made from this soft, flexible tissue is their teeth.”
“The earliest shark-like teeth we have come from an Early Devonian (410-million-year-old) fossil belonging to an ancient fish called Doliodus problematicus. Described as the 'least shark-like shark', it is thought to have risen from within a group of fish known as acanthodians or spiny sharks. By the middle of the Devonian (380 million years ago), the genus Antarctilamna had appeared, looking more like eels than sharks. It is about this time that Cladoselache also evolved. This is the first group that we would recognise as sharks today, but it may well have been part of the chimaera branch, and so technically not a shark. As active predators they had torpedo-shaped bodies, forked tails and dorsal fins. “
The Carboniferous Period (which began 359 million years ago) is known as the 'golden age of sharks'. An extinction event at the end of the Devonian killed off at least 75% of all species on Earth, including many lineages of fish that once swam the oceans. This allowed sharks to dominate, giving rise to a whole variety of shapes and forms.
"Some of the most bizarre prehistoric 'sharks' to appear during this time actually evolved out of the chimaera lineage. These include Stethacanthus, which had a truly peculiar anvil-shaped fin on its back, Helicoprion with a spiral buzz saw-like bottom jaw, and Falcatus, in which the males had a long spine jutting out of the back and over the top of the head.
Modern-day chimaeras are much less diverse and typically live in the deep ocean. Growing up to 1.5 metres long, they are not actually sharks. Their upper jaw is fused with the skull, and most chimaera also have venomous spines. “
“The end of the Permian Period (252 million years ago) saw yet another mass extinction event with wiping out around 96% of all marine life. But a handful of shark lineages persisted. During the Jurassic Period (195 million years ago) the oldest-known group of modern sharks, the Hexanchiformes or sixgill sharks, had evolved. They were followed during the rest of the Jurassic by most modern shark groups. It was at this point that they evolved flexible, protruding jaws, allowing the animals to eat prey bigger than themselves, while also evolving the ability to swim faster.”
“During the Cretaceous (145 million to 66 million years ago) sharks were once again widely common and varied in the ancient seas, before experiencing their fifth mass extinction event. While much of life became extinct during the End-Cretaceous extinction event, including all non-avian dinosaurs, sharks once again persisted. But they were still affected. Fossil teeth show that the asteroid strike at the end of the cretaceous killed off many of the largest species of shark. Only the smallest and deep-water species that fed primarily on fish survived.”
“Sharks soon began to increase in size once again, and continued to evolve larger forms throughout the Palaeogene (66 to 23 million years ago). It was during this time that Otodus obliquus, the ancestor to megalodon (Otodus megalodon), appeared. O. megalodon is one of the biggest sharks to have ever lived. At between 15 to 18 metres in length, is was around the same length as today's whale sharks. Scientists consider megalodon one of the most powerful predators to have evolved.”
“The megalodon is not related to the great white shark and it is believed that they may have been in direct competition with the great white shark’s ancestors which evolved during the Middle Eocene (45 million years ago) from broad-toothed mako sharks.,” Cutter finished the lecture.
“For today’s class I have brought in a couple of examples of fossil teeth for you to have a look at and as always if there’s any questions I’ll be happy to help answer them,”
“Sharks belong to a group of creatures known as cartilaginous fishes, because most of their skeleton is made from cartilage rather than bone, The only part of their skeleton not made from this soft, flexible tissue is their teeth.”
“The earliest shark-like teeth we have come from an Early Devonian (410-million-year-old) fossil belonging to an ancient fish called Doliodus problematicus. Described as the 'least shark-like shark', it is thought to have risen from within a group of fish known as acanthodians or spiny sharks. By the middle of the Devonian (380 million years ago), the genus Antarctilamna had appeared, looking more like eels than sharks. It is about this time that Cladoselache also evolved. This is the first group that we would recognise as sharks today, but it may well have been part of the chimaera branch, and so technically not a shark. As active predators they had torpedo-shaped bodies, forked tails and dorsal fins. “
The Carboniferous Period (which began 359 million years ago) is known as the 'golden age of sharks'. An extinction event at the end of the Devonian killed off at least 75% of all species on Earth, including many lineages of fish that once swam the oceans. This allowed sharks to dominate, giving rise to a whole variety of shapes and forms.
"Some of the most bizarre prehistoric 'sharks' to appear during this time actually evolved out of the chimaera lineage. These include Stethacanthus, which had a truly peculiar anvil-shaped fin on its back, Helicoprion with a spiral buzz saw-like bottom jaw, and Falcatus, in which the males had a long spine jutting out of the back and over the top of the head.
Modern-day chimaeras are much less diverse and typically live in the deep ocean. Growing up to 1.5 metres long, they are not actually sharks. Their upper jaw is fused with the skull, and most chimaera also have venomous spines. “
“The end of the Permian Period (252 million years ago) saw yet another mass extinction event with wiping out around 96% of all marine life. But a handful of shark lineages persisted. During the Jurassic Period (195 million years ago) the oldest-known group of modern sharks, the Hexanchiformes or sixgill sharks, had evolved. They were followed during the rest of the Jurassic by most modern shark groups. It was at this point that they evolved flexible, protruding jaws, allowing the animals to eat prey bigger than themselves, while also evolving the ability to swim faster.”
“During the Cretaceous (145 million to 66 million years ago) sharks were once again widely common and varied in the ancient seas, before experiencing their fifth mass extinction event. While much of life became extinct during the End-Cretaceous extinction event, including all non-avian dinosaurs, sharks once again persisted. But they were still affected. Fossil teeth show that the asteroid strike at the end of the cretaceous killed off many of the largest species of shark. Only the smallest and deep-water species that fed primarily on fish survived.”
“Sharks soon began to increase in size once again, and continued to evolve larger forms throughout the Palaeogene (66 to 23 million years ago). It was during this time that Otodus obliquus, the ancestor to megalodon (Otodus megalodon), appeared. O. megalodon is one of the biggest sharks to have ever lived. At between 15 to 18 metres in length, is was around the same length as today's whale sharks. Scientists consider megalodon one of the most powerful predators to have evolved.”
“The megalodon is not related to the great white shark and it is believed that they may have been in direct competition with the great white shark’s ancestors which evolved during the Middle Eocene (45 million years ago) from broad-toothed mako sharks.,” Cutter finished the lecture.
“For today’s class I have brought in a couple of examples of fossil teeth for you to have a look at and as always if there’s any questions I’ll be happy to help answer them,”
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