Friday, March 23, 2012

Cameroceras (Part 2).

I've written about Cameroceras before, but there is more about this relative of the modern nautilus that I would like to explain. 

Cameroceras is a species of Ordovician nautiloid that had a straight shell right behind its head. It belongs to a group of nautiloids called orthocones, along with Orthoceras, Endoceras, and Gonioceras. 


Although the widely accepted size estimate of Cameroceras's length is 20 feet, there is some debate. Paleontologists often find partial shells of Cameroceras, very rarely the whole thing. When they do find a complete specimen of the shell, it is usually of a small individual. Unless we have the living chamber or the tip of the shell in the specimen, we cannot accurately determine the length of the animal. Based on partial specimens of large individuals, we can only know that it could have grown very big, but not the exact length. In the future we may find a way to determine which part of the shell the fossil belonged to. 

In the image below, I drew Cameroceras hunting near the seabed. This individual has successfully caught the eurypterid Megalograptus. Another Megalograptus is swimming away, and Isotelus is crawling on the sea floor directly below the Megalograptus. On the left side, near the head of Cameroceras, there are two rugose corals and one crinoid. 


Like the modern nautilus, Cameroceras probably had an extremely strong grip with its tentacles. Once something was caught, it would be very hard for the prey to escape. The tentacles were probably stronger than those of the nautilus, because Cameroceras was much bigger (the modern nautilus only has a shell diameter of 8 inches). 

Cameroceras had an amazing way of keeping its head from facing towards the bottom of the ocean and the tip of its shell from facing towards the surface. Cameroceras had a long siphuncle, a kind of tube, running down from its siphon. The siphuncle had traffic cone-shaped blocks of calcium in it, which counter-weighted the body and kept it horizontal. Like all nautiloids, it had upward-facing rings called septa. They were filled with gas and kept Cameroceras afloat. It was a very efficient strategy of locomotion. 


The siphon, which was connected to the siphuncle, sucked in water and then shot it out again to propel Cameroceras in the opposite direction of whatever way the extremely flexible siphon was pointing. Modern cephalopods can swim backwards and forwards and also steer very well, because of the flexibility of their siphon. Cameroceras probably had a very flexible siphon too, and this extreme maneuverability would have made it an efficient hunter. 


A Sea Without Fish by David L. Meyer and Richard Arnold Davis, pg. 132-134.

Thanks to Paul Mayer at the Field Museum for discussing how paleontologists find out the size of orthocones when they don't have the complete shell. 

Tuesday, March 6, 2012

New research on Pikaia from Simon Conway Morris and Jean-Bernard Caron.

In Pikaia gracilens Walcott, a stem-group chordate from the Middle Cambrian of British Columbia, published online March 4, 2012, Simon Conway Morris and Jean-Bernard Caron confirmed that Pikaia was a chordate after all. They looked at the anatomy of 114 specimens of Pikaia (I thought there were only 16 known Pikaias!)and found myomeres, v-shaped blocks of skeletal tissue that are only found in chordates. The scientists also found evidence of a vascular system, and found that at least part of the alimentary canal was preserved in almost every specimen. 

Externally, Pikaia was mostly just a flattened, tie-shaped body tapering from a tiny head. It had tentacles on its head, two antennae, and a thin dorsal fin. 

What was first thought to be the notochord in Pikaia is now interpreted as a "dorsal organ," which was possibly hollow. This doesn't mean there's no notochord. Under this dorsal organ there is a thread of tissue that is now interpreted as the notochord and nerve chord. 

I've only read the abstract, but when I read the actual article I'll learn more information. 

Friday, March 2, 2012

Chicago After The Field Museum (Part 4 of 4): Shedd Aquarium.

I went to Shedd Aquarium and it was so cool. They had an exhibit on jellyfish, which I was excited about. They had really weird jellyfish. 

They had a really big tank full of moon jellies and it was packed. There were jellyfish in a huge swarm and each had a bell that was about one foot across. I could even see the orange food that they had eaten because they were so transparent. It was all up inside their stomach, which is in the center of the jellyfish.

The moon jellies were so cool that we took a video of them:

Jellyfish have been around since the Cambrian Period, and I have a couple of fossilized jellyfish from the Carboniferous Mazon Creek.

These are sea nettle jellyfish. Their pulses looked very strong, and that probably helps them drawn water into their bell with plankton, and then push out all the plankton onto their tentacles, where it is then stung and killed, and then fed to the mouth.

These are upside-down jellyfish, a very bizarre kind of jellyfish that spends almost its whole life stuck upside-down to the bottom of the ocean (hence the name upside-down jellyfish). Although this is for a reason. They have algae living inside their bodies which gives them food. In turn, the jellyfish stick upside-down to the bottom and face the light, which helps the algae grow. They have a symbiotic relationship with the algae.

These are called hairy jellyfish, which is obvious when you look at their tentacles, which are very thin and hair-like. They also were very slow, and there was a lot of time between each pulse. They look a lot like some deep sea jellyfish, and they also look like box jellyfish a little bit. 

This is a video of Pacific sea nettle jellyfish, a larger species of sea nettle than the ones in the photograph  I previously mentioned. It's a really cool video. The jellyfish seem even stronger than the other sea nettles, and they are certainly formidable predators of copepods and other plankton. 

This photograph is of two arapaimas, a type of fish from the Amazon River that grows to ten feet long, and is also a living fossil that has its origins in the Cretaceous. The related arowana is also a living fossil. They had those at Shedd Aquarium, but I didn't get a picture. They were about one or two feet long.

This is a picture of me posing next to a freshwater stingray from the Amazon River. It is stuck to the glass, and its mouth and gills are clearly visible. I thought the freshwater stingrays were really amazing.

This was a huge life-sized model of an arapaima, which shows just how big they can get. The scales were huge.

This is an image of a huge school of cardinal tetras, a fish from the Amazon River which is commonly found at pet stores, probably because of how beautiful the shimmering swarms of them can be. I could see them from a long way away. They were so bright. It's almost like they were glowing.

This image shows a moray eel, a beautiful marine eel that grows to ten feet long.

We also saw some electric eels, a type of knifefish that can grow to eight feet long, which makes it the largest knifefish species. They are also deadly because they can shock up to 650 volts.

They had a giant spider crab, the biggest species of crab in the world. In the wild they are often found in the deep sea where they have an opportunistic lifestyle, picking up and eating any scrap of edible debris they can find.

The next day it was time to leave Chicago, and I really didn't want to go. It was so sad to leave.

We went to the airport and the Kronosaurus had to go through the X-ray two times for some reason.

I couldn't stop reading my new book.

Art had a ton of new experiences and a fantastic time in Chicago. A million thanks to: Paul Mayer, Jane Hanna, University of Chicago Secular Student Alliance, Stephen & Kayla & Greta, Casey, Mike, Dave Monroe, PZ Myers, and the 72 incredible people who pitched in to help fund our trip to the Field Museum.