Saturday, January 15, 2011

Monsters Part 4: Big Bugs

For our final foray into the world of prehistoric monsters, we will go back to a time of forests and fires and have a look at four beasties. If you don’t like bugs, I suggest you skip this post.

Around 360-300 million years ago the world was a different place entirely. A lot of the planet’s surface was covered in dense forest and the geologic period is named after the large amount of coal present in the rock of this age. The atmosphere was also considerably different. Whilst we have an atmosphere which is about 20% oxygen, this time’s atmosphere was 35% oxygen. This had a specific effect on some of the creatures which live during this time.

One of the limits on the size of bugs in our time is the way they breathe. They have these tiny little organs, called spiracles and tracheoles, which allow oxygen to diffuse into their body, and the ability for the oxygen to diffuse limits the size of the bug. One way to make oxygen diffuse better is to increase the concentration of oxygen in the atmosphere. So, with oxygen contents which are about 175% those of today, you can get some seriously large insects and arachnids.

The first beast we’ll have a look at is possibly the least dangerous. Arthropheura was a 2.6m long relative of the centipedes and millipedes. It has the title of the largest known and invertebrate to have walked the land. These things lived in North America and Scotland and it is not quite known what they ate. One theory gives them powerful jaws and the possibility of being carnivores, whilst another theory suggests that they were herbivores. I prefer to think of them as herbivores, because a 2.6m long millipede which can outrun me and eat me is just scary. They could move quickly, likely by elongating their body, and could dodge obstacles easily. If it was chasing you, getting across a river wouldn’t help, because it was probably able to travel under water. Scary, huh?
Now, this would be scary to find at the bottom of the garden

I bet you’ve seen some pretty big dragonflies on a hot, humid day. Well, they have nothing on this next beast. Meganeura was a dragonfly with a wingspan on 75cm, and was the largest known flying insect in the fossil record. These things would have definitely make a decent noise as they flew around, so at least you would get a bit of warning before they came at you. They were probably carnivorous, so they would have tried to eat you. They had really strong wings, and probably fed on both insects and amphibians. Here’s what they looked like.
Not your average dragonfly

Next in our journey of monstrous bugs is the Pulmonoscorpius. These were really big, metre long scorpions. They would have been daytime hunters, as they had large compound eyes. They also had really large stingers with big venom glands, which they would have used to subdue their prey. They had comparatively small pincers, but their venom would have probably begun the digestion process, much like spider venom. It probably hunted and ate tetrapods, amphibians and reptiles which would have live around this time.
Metre long scorpions are not everyones cup of tea

Lastly, we will encounter the largest arthropod known to have existed. With an average size of 2.5m, the Jaekelopterus was a true under water monster. Part of the Eurypterids, these beasts are known to have had claws which were up to 50cm in length. These things were pretty much the kingpins of predators in the Carboniferous lakes, rivers and coastal environments. Whilst most were less than 20cm in length, the big beasts had large, powerful claws and tails with spikes which may have injected venom. Some were amphibious, having walking legs along with paddles, and two pairs of eyes, one pair being compound. They likely hunted fish and the like, but are also likely to have hunted amphibious tetrapods and other shelled creatures which lived at least partially in the water. So, they were mean, and sort of like the crocodiles of the Carboniferous.
A collection of sea scorpions
Hard shells are good for fossilisation

Luckily, due to the drop in oxygen levels in our atmosphere, we don't need to worry about these things coming back. They simply couldn't breath in out atmosphere. The largest arthropods we can expect to see are like the Goliath Bird-Eating Spider of South America, or the Giant Huntsman of Laos, with a leg span on a measly 30cm.

Just as a final point, if you didn't think the Carboniferous period was dangerous enough with all the big bugs, there was also a much higher frequency of forest fires. These were basically due to the amount of oxygen in the air. One of the things wood needs to burn is oxygen, and having more of it around makes things burn easier. So, if you didn’t get eaten, it’s likely you would have been cooked. On the plus side, at least your dinner would be cooked too.

Question comments or ideas? Please tell me!

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