Monday, April 30, 2012

Fossil Fish Found Alive: Discovering the Coelacanth.

I read the book Fossil Fish Found Alive: Discovering the Coelacanth by Sally M. Walker, and it was very informative about Coelacanths. It didn't take long to read and it was great.

The book talks about how the earliest modern day Coelacanth to be found was caught in 1938 off the Camoros Islands, which are a French colony off the coast of Africa. This Coelacanth was named Latimeria chalumnae, after the person who discovered it, who had the last name Latimer. 

Latimer had no idea what the fish in her net was, so she took it to several places and asked what it was. They all said that they did not know. The last place she took it to said it looked like a Coelacanth, which at the time was thought to be extinct. The Coelacanth was believed to have gone extinct 65 million years ago, and at the time, the last Coelacanth fossils were 70 million years ago. No Cenozoic fossils of Coelacanths have ever been found, so to date the prehistory of Coelacanths stops in the Cretaceous. 

Prehistoric Coelacanths, from top to bottom: Allenypterus, Hoplophegis, Mawsonia, Axelrodicthys, and Miguashaia

Somebody named Smith came to see the Coelacanth and proved its identity. Smith wanted to find another Coelacanth. He caught an unusual fish in his net in the Camoros Islands. He thought it was a new species and named it Malania anjouanae. But then he realized his mistake. It was a Coelacanth. The dorsal fins and epicaudal fins were missing from this fish, so he thought it was a new species. The fins were probably just bitten off by another fish when the Coelacanth was young, or another such accident. It was not a different species. 

The modern day Coelacanth Latimeria

A new species of Coelacanth was described around 1998 and it was named Latimeria menadoensis. It was found in Indonesia, which is in Asia. That's unusual because so far Coelacanths had only been found in Africa and Madagascar, never in Asia. 

Scientists were desperate to find a live Coelacanth in its natural habitat. They started diving down in submersibles to habitats of Coelacanths. On October 29, 2000, they were finally successful and found live Coelacanths in South Africa. At first they found one, but then, on the next dive, they found many. They noticed that when the submersible got close, the Coelacanths did bizarre headstands. It was later found out that these were probably because the Coelacanths use the earth's electrical field to navigate, and in the disturbance of the electrical field they automatically did the headstands because of disorientation. 

It was found out that in the daytime Coelacanths rest in caves and only come out at night. When scientists started tagging Coelacanths, they found that they drifted around in the current, and when prey such as small fish got near, the Coelacanths sucked them in. This is another adaptation that conserves energy. 

Latimeria resting in a cave in the daytime

The largest Latimeria chalumnae ever found was 6-1/2 feet long. This population of Coelacanths was also the shallowest-living ever found, with depths of 344 feet. They were filmed by divers, but diving at that depth can be dangerous. Coelacanths usually live at about 700 feet down, so normally they would never be filmed by scuba divers. 

Coelacanths are one of the two groups of lobe-finned fish, or sarcopterygians, alive today. The other group are the famous lungfishes, which have the ability to breath air and can live under dried-up lakes for years. Unlike lungfish, Coelacanths, or at least modern day Coelacanths, live in salt water. There were a few prehistoric Coelacanths, like Undina from the Jurassic, that spent their lives in fresh water. The largest Coelacanth ever was Mawsonia gigas, from the Cretaceous from Egypt and Niger. Mawsonia was also found in South America, but this makes sense if you know that Africa and South America were joined together in the Cretaceous (which also explains the distribution of lungfishes in South America and Africa).

I learned that Coelacanths are full of oil, which helps them maintain balance just above the sea floor without having to actually move. The oil also makes the Coelacanth very disgusting to eat, which is why fisherman don't usually fish for Coelacanths as food. The reason why Coelacanths are fished is normally for maintaining specimens. 

Friday, April 20, 2012


Gonioceras was a benthic actinocerid orthocone of the Ordovician. Its distribution included the eastern half of North America, including Canada and the North Pole area next to Greenland. This would not have meant that it was a polar animal, it just means that the continents have shifted a lot, and that the climate has also changed quite a bit. In the Ordovician, the whole world was tropical, even the poles.

Gonioceras had a convex top of the shell and the bottom was flat. This was ideal for living on the sea floor, because that meant Gonioceras would not sink into the muck. This is the same principle as the spines of many trilobite, which helped the trilobites keep themselves from sinking into soft mud. Trace fossils show that tubular-shelled nautiloids did sometimes rest on the bottom, but they did not live their whole life there as Gonioceras did. Tubular-shelled nautiloids such as Cameroceras also probably sometimes dragged across the bottom to catch trilobites and other benthic prey.

Gonioceras chasing a trilobite

Gonioceras was a unique nautiloid because it was flat. Unlike other nautiloids, it had a triangular form. The name Gonioceras, meaning "angle horn," well suits this animal, because few other nautiloids, except for other actinocerids, were flat and triangular like this.

Gonioceras grew up to about one foot long. I hypothesize that it probably had little or no need for a complex balancing system because it almost always stayed touching the bottom, and it probably never ventured into midwater. For a creature this shape, hatched on the bottom of the ocean, it would take quite a long time for it to get its flat shape into the water. The shell could be compared to a one-foot-long flat rock, and it would have been very hard for such a small animal to lift such a heavy object up into the water. The shell would have been heavy in the first place, and considering the weights Gonioceras would have needed to keep the gas in its shell from slowing making it float up to the surface, it would have been very heavy. So it would have been hard for Gonioceras to lift itself up more than a few inches off the sea floor.

Top and side view of Goniceras

Gonioceras was actually smaller than its shell, because only a small part of the shell houses the live animal, which would have been a couple of inches long. Its bottom-dwelling habits must have meant that it preyed on bottom-dwelling animals like trilobites or worms. Rays and flounders may have a similar place in the food chain today as Gonioceras did in the Ordovician.

The only living relatives of Gonioceras are of the genera nautilus or allonautilus. Actinocerids like Gonioceras only lived in the Ordovician, but other orthocones lived to the Triassic, and orthocone-like ammonites such as Baculites lived in the Cretaceous.

Gonioceras was probably preyed on by eurypterids and larger nautiloids. Like all cephalopods, they had many tentacles surrounding a beak-like mouth, a syphon propelling them through the water, and a mantle behind their head. Nautiloids and aminoids are the only shelled cephalopods, besides the modern genus argonauta, a shelled octopus. Members of this genus can leave their shells at any time, and only the females have shells. The shells of Gonioceras were probably more delicate than those of other orthocones, because they were flatter and thinner. The whole shell is very rarely preserved in a fossil.

Gonioceras could probably partially bury itself in sand with backward shovel-like motions of its shell being propelled by the syphon,and its tentacles throwing sand on top of its body, similar to living rays and flounders, who do this with their fins. Some living cephalopods sometimes bury themselves by throwing sand on top of their body with their tentacles.

Gonioceras resting on the sea floor

Although nautiloids like Gonioceras and the modern nautilus do not have suckers on their tentacles, they have a very strong grip. Modern nautiloids can hardly ever be pulled off of their prey without ripping off their tentacles because the grip is so strong. Nautiloids also have more tentacles than other cephalopods.

Because of its flat shape, Gonioceras probably would have been very hydrodynamic on the sea floor, jetting itself quickly just above the bottom. Since the ventral side of its shell was flat, it would have been much easier for Gonioceras to rest on a flat surface such as sand or mud than on rocks, which meant it probably lived closer to sandy shores. Orthocones could not have lived in the deep sea because their shells would have cracked due to the pressure. Coiled nautiloids could have easily gone into deep water because their tightly-packed shells would have offered more protection.


Thursday, April 5, 2012


Lepidodendron was a giant lycopod tree that flourished in Carboniferous wetlands. It was up to 130 feet tall. 

For half of its life Lepidodendron lived as a telephone pole-like plant sticking out of the forest floor. Then it began branching. Finally, the branching growth stopped and spore cones formed at the end of the branches. Growth stopped. The tree was putting all its energy into making and releasing spores. 

In some species of Lepidodendron the tree died after it was finished releasing its spores, probably because they spent all their energy on doing just that, shedding and making spores. This is like salmon who die right after laying eggs because they use up all their energy swimming up rivers and jumping up waterfalls, and spend the last bit of energy laying eggs and transferring sperm to the female. 


Lepidodendron and other lycopod trees had the shallowest roots I've ever heard of. The roots barely went a couple feet into the ground for an enormous 100 foot tree. One of the reasons 
Lepidodendron didn't fall down was probably that, despite its enormous size, the trunk was probably pretty light. Inside the thick bark there was a cotton-like substance, which was the vascular system. Another reason Lepidodendron didn't fall down is probably that the roots were fat and also surprisingly long. But they barely went into the ground and were nearly unbranched. The bark of Lepidodendron was a couple of inches thick, which held the tree in an upright position. 


Lepidodendron had bark covered in scaly leaf scars. In the "telephone pole" stage, the leaves were gradually moving up the trunk. As the tree got larger, and older leaves fell off. Finally this process stopped as Lepidodendron started to grow its first branches. The first branches it grew were forked, and then off of those forks it grew branches that looked somewhat like those of conifers. 

Some people used to think that the bark was the remains of a giant snake or lizard, which turned out to be totally wrong. 



Prehistoric Life: The Definitive Visual History of Life on Earth, pg. 145