Tuesday, May 29, 2012


Dinocaridida is the group which contains anomalacarids such as Opabinia and Anomalocaris. There has been much debate over what kind of animal members of Dinocaridida actually were. They possess jumbled-up features of two groups of modern animals, the arthropods and the onychophorans. They lived on every continent except Antarctica. Only one species has been found in Africa so far, an unnamed Ordovician anomalocarid very similar to Peytoia (formerly Laggania). Very few have been found in Europe. Most are found in North America and Greenland, with notable specimens from Asia too. 

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From top to bottom: Jianshanopodia, Kerygmachela, Pambdelurion. Arrows represent method of capture.

The first Dinocaridids, from the early Cambrian, looked more like onychophorans than arthropods. Some had no eyes, like Kerygmachela and Pambdelurion. Kerygmachela had a tiny mouth, which would have meant it needed to chop up its prey before it ate it. It did that by means of its knife-like claws, which shredded prey. The inward-pointing hooks on the spines would have prevented escape. Although it sounds ferocious, Kerygmachela was only about the size of a human hand. Its relative Pambdelurion, which was the same size as Kerygmachela, was a peaceful filter feeder which captured millions of tiny plankton with its hairy claws, which it then "licked" off with its tiny mouth. On the other hand, Jianshanopodia had a unique method of capture. With a motion of its claws and the opening of the mouth, it sucked small creatures into its stomach. Jianshanopodia was also about the size of a human hand. 

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From top to bottom: Anomalmocaris, Opabinia, Petoyia

Typical anomalocarids from the middle Cambrian Burgess Shale were much more complex, looking like a cross between arthropods and onychophorans. Among these, Opabinia was unique. It had a long proboscis with a claw at the end. The mouth was not on the proboscis, but was actually under the head, as in all Dinocaridids. The proboscis was long and flexible, which helped it reach down worm burrows to grab hapless worms, which it ate. Opabinia was also a scavenger of dead arthropods and other animals, which it was very fit for, because of the flexibility of its proboscis, which enabled it to reach into cracks in the armor of a carcass and rip out chunks of internal organs and flesh from beneath the exoskeleton. It also had five huge eyes, which is not unusual in modern arthropods. Many insects have five eyes, except three of those eyes are tiny. In Opabinia they were all large. 

Anomalocaris was a top predator. It could grow to three, possibly even six feet long. It shattered exoskeletons of trilobites and other arthropods with its two seven-inch claws. Like all Dinocaridids (except Jianshanopodia), Anomalocaris had eleven lateral lobes, which it used for swimming. It would have been very stable, and also able to swim backwards. It could hover motionless in mid-water for a long time watching for prey. When it saw something promising, Anomalocaris would lunge forward with its claws flared out, and then grab the food item. It would then rip it to pieces and eat it. 

Peytoia was a filter feeder. I hypothesize that it rammed predators with its huge head, partially because the eyes and claws were set far back, which could have meant the head was doing something that its eyes and appendages should not be involved in, such as head-butting predators. I also think it could have been a mating display, where the males head-butted each other for the right to mate with the females. This could have been possible because only a few specimens showing the head have been found, and it's possible that all of them were males. I'm not really sure what that huge head was for, I just realize that Peytoia had a bigger head than any other Dinocaridid (except for Hurdia, which had strange headgear that made it look like an arrow). Peytoia also had no tail fin, and when wandering around it probably moved very slowly, although it could have been quite capable of bursts of speed. 

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From top to bottom: unnamed Ordovician anomalocarid from Morocco, Schinderhannes bartelsi, Caryosyntrips

Recently, Ordovician fossils of a Peytoia-like anomalocarid have been found in Morocco. My drawing of this unnamed animal above is based on the pictures of the fossils that I saw. 

Schinderhannes bartelsi is the most recent anomalocarid (in geological time). It had two huge flaps right behind its head which propelled it through the water. It had a stingless spine at the rear and no lateral lobes along its sides. The only fossil was found in Germany. It was only about four inches long and it preyed on animals such as small shrimp and worms. 

Caryosyntrips is a new discovery from the Burgess Shale of the middle Cambrian. The feature that stands out about Caryosyntrips is its claws. Instead of grabbing down, as in Anomalocaris, they pinched together like crab claws. They have been compared to nutcrackers. 


Arthropod origins: http://mzp.cz/ris/ekodisk-new.nsf/1a76d1df1a0e29f0c1256e2800520b9d/9a21746463a798e9c125708f002d7766/$FILE/str.%20323-334.pdf

A giant Ordovician anomalocarid: http://www.nature.com/nature/journal/v473/n7348/full/nature09920.html



Monday, May 14, 2012

I've been doing my blog for one whole year!

My very first post was on May 15, 2011, when my mom took pictures of my Lego jawless fish and asked me if I wanted to start a blog. And I did! I've been doing this for a whole year. To celebrate the anniversary, I picked five of my favorite creatures that I've written about in the last year, and here they are:

1. Anomalocaris (here and here). Anomalocaris was a giant Cambrian predator related to today's velvet worms. It crushed hard-shelled animals with its two seven-inch claws and its "pineapple ring" mouth. It had eleven lobes along the side of its body which helped it hover and swim in mid-water. It also had no legs. It was at least three feet long, but it was almost definitely no more than six feet. Most of the complete fossils are of juveniles. Coprolites containing bits of trilobites have been found in Australia. I hypothesized that Anomalocaris may have given live birth just like today's velvet worms. 

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2. Opabinia. A four-inch-long Cambrian predator, including its proboscis (three inches long without this appendage). Opabinia used its proboscis to poke around in worm holes and rip chunks of flesh off of carcass. Strangely, Opabinia had five mushroom-like eyes on top of its head, each one as large as the other. It was related to Anomalocaris and velvet worms, and I think it could have given live birth too. Opabinia also had eleven lobes along its sides and, like Anomalocaris, no legs. 

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3. Scyphocrinites. Scyphocrinites was a strange Silurian-to-Devonian crinoid that floated upside down at the surface of the water by means of a balloon-like organ called a lobolith in place of the gripping root-like organs that most crinoids possess. Unlike most crinoids, Scyphocrinites could not purposely move (bottom-dwelling crinoids can un-anchor themselves and drag their bodies across the sea floor with their arms to find a better attachment place). Scyphocritinies could only move with the current. Fortunately, this meant that it was always in the same place as its microscopic food, plankton, which was also being swept around by the current. Scyphocritinies was large, but I can't say how large, because I've never found a source that talks about its size other than that its large. The calyx (body) has never been found attached to the lobolith, but we know the calyx and the loboliths found belong to the same species. The same exact stem has been found attached to the lobolith, and that kind of stem has also been found attached to the calyx.  All the pieces of Scyphocrinites were found in Morocco.

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4. Helicoprion (here and here). Helicoprion was a bizarre shark from the Carboniferous to the Triassic. The only fossils that have ever been found of it are its mysterious "buzz saw" lower jaws, which helped it slice prey such as fish and squid. It is unlikely that Helicoprion ate hard-shelled animals such as ammonites, because if it ate mostly ammonites there would be a lot of broken teeth found in the tooth whorls. Broken teeth are nearly absent in the tooth whorls. And sharks tend to eat a lot. The biggest tooth whorls that have ever been found are about two feet across, which meant that Helicoprion would have been 30 to 50 feet long. A very long shark, which would have meant it needed a lot of food and would have had a monstrous appetite. It must have been a top predator. Helicoprion was related to other eugeneodontids such as Edestus and Ornithoprion. It is not known where exactly in the lower jaw the tooth whorl went, but the most modern idea is that it was embedded in cartilage to make a circular extension of teeth on the lower jaw. This idea also includes that the lower jaw was as long as the upper jaw, and that they were both quite long. Most reconstructions of Helicoprion show that it had little or no teeth in the upper jaw. 

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5. Siphusauctum. Siphusauctum is a weird, newly-discovered Cambrian stalked animal. It looked reminiscent of a ctenophore on a stalk and was a filter feeder that fed on plankton. The body was roughly four inches tall. There is a very small amount of information on this animal because it is so newly discovered. It was found many years ago in the Burgess Shale, but was discovered in the collection at the Royal Ontario Museum in 2012. It was described by Jean-Bernard Caron and Lorna J. O'Brien. 

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