Life Before The Dinosaurs

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I am seven years old. I really like the life before the dinosaurs. And I really think arthropods are cool.

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Nectocaris was a weird creature which might have been a cephalopod. The image on the left shows an earlier idea of Nectocaris, but now they believe that the image on the right would be what Nectocaris really looked like.
When Walcott first discovered Nectocaris in the Burgess Shale, he never had time to study it. Then, later, someone described it to be an arthropod. Last year, in 2010, someone described it to be an early cephalopod.
Fossil evidence shows that mud must have gotten into the gills, so Nectocaris was probably a nektobenthic creature, meaning that it lived at the bottom, but swam above the sediment.
Nectocaris was probably either a predator or a scavenger, grabbing food with its two tentacles. Scientists aren't exactly sure if cephalopods started out with two tentacles then they evolved more over time, or if Nectocaris's two tentacles were just made up of its other tentacles.
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Lanarkia was an odd member of the thelodont group. Very close to the front, it had one thin pectoral fin on each side. On the caudal fin, it was basically just skin and bones. It had a very skinny v-shaped caudal fin.
Here are Lanarkia and some other thelodonts together. All thelodonts were jawless, so they had to suck in very tiny things into their mouths. 
There are two species of the genus Lanarkia. They are Lanarkia spinosa and Lanarkia horrida. 
Lanarkia lived in the Silurian Period and was a pretty small fish, so it had to avoid giant eurypterids, such as Pterygotus. 
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Parexus was a bizarre acanthodian with a large spine in front of its dorsal fin. Like all acanthodians, like Climatius, Howittacanthus, and Gyracanthus, it had a spine in front of each fin. A very good adaptation if something is going to be near the bottom of the food chain. Acanthodians were small compared to the sharks and placoderms that they were living with.
Acanthodians, also known as "spiny sharks," appeared in the Ordovician and died out somewhere in the Permian, but definitely not at the end or near the beginning. Parexus was 6" long. A variety of acanthodians were 6" long, like Climatius. Parexus was from Britain, like Climatius. 
Acanthodians, like true sharks, lost old or damaged teeth and then new teeth grew in the spaces where those old teeth were. 
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At first, people had only found disembodied plates of this weird fish, then they uncovered a complete skeleton preserved in very good detail. 
Phyllolepis was a freshwater fish of Europe and North America. 
Even though it was jawless, it was a predator, so it had to suck in its prey. It started the chase by a quick movement of its long, tapering tail, which would make it a very fast hunter. Another thing that it could use to be a very good predator would be ambush. It sat at the bottom of the body of water, then when prey passed, it swam up and sucked its prey in. 
One of the strange things is that it either was blind, or had the poorest eyesight of any fish, such as all other phyllolepids. Its name means "leaf scale." Exactly how it sensed its prey is known. It had grooves that could sense any movement in the water, just like Cephalaspis did. 
There was another phyllolepid that looks remarkably like it. It is called Austrophyllolepis. It's from Australia, and its name means "Australia leaf scale."
Phyllolepis, like all phyllolepids, was flat. Being flat is perfect for sitting on the bottom of a body of water without being seen by its prey. 
In the Devonian Period, placoderms had the widest variety than any other time. That's probably why giant placoderms such as Dunkleosteus and Titanichthys ever evolved. Suddenly, at the end of the Devonian, there was a mass extinction that wiped out all the placoderms, because at that time the placoderms were the top predators and the top organisms of anywhere in the seas. The seas were really the only place on earth where life was really going on very well. 
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Pteraspis was a Devonian heterostracan with a beak-like rostrum in front of its head and wing-like things sticking out of the two back sides of its head armor. Pteraspis means "wing shield." 
It had a protective spine pointing backwards that would probably harm a predator that would try to eat it. Pteraspis was only about 8" and there were monster predators around like Eusthenopteron and Dunkleosteous. Pteraspis was jawless, so it had to suck in plankton through its mouth. 
Pteraspis was one of the last heterostracans and one of the last placoderms because placoderms went extinct at the end of the Devonian and so did the heterostracans (because heterostracans were placoderms).
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Doryaspis was a weird jawless placoderm with a mouth on top of its saw, and two fin-like appendages that could have worked as pectoral fins. But they were not fins, they were part of the head armor. 
Like all placoderms, except for the giant placoderms like Dunkleosteus and Titanichthys, it had to stay near the bottom because of its heavy head armor.
This image shows a different Doryaspis. But all the species of Doryaspsis are pretty much the same. All the species of Doryaspis have two pectoral spines and one spine right under the mouth in front of their head. Which is why Doryaspsis's mouth probably had to point up. 
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