Sacabambaspis.

Sacabambaspis is an Ordovician arandaspid, a kind of primitive armored jawless fish, that has been found in Bolivia in the Andes Mountains. It was about one foot long. Like all fish of its time, Sacabambaspis had no jaws, so its mouth was always open. It had no jaws and it didn't have any teeth either. If it did have teeth, it wouldn't have been able to use them, because it didn't have jaws. All Sacabambaspis ate must have been algae, plankton, and tiny pieces of carcass left behind by large predators such as Cameroceras, Endoceras, and Megalograptus. 


The only fin Sacabambaspis had on its body was the caudal fin, or tail fin. Its relative Astraspis didn't even have that. Scientists used to think that Sacabambaspis had a shark-like tail, but now they know that it had a tail similar to modern jawless fish, a sort of eel-like tail. 


The most striking feature about Sacabambaspis was the shell that covered its head. The armor that covered placoderm heads was more like a suit of armor. But Sacabambaspis had armor that was more like a clamshell. Placoderms had different plates of armor all over their head, which allowed different parts of their heads to move. Ostracoderms, armored agnathans, or jawless fish, had shell-like armor, which was usually two plates, one of the top of the head and one on the bottom. The shell on Drepanaspis, from the Devonian, gradually got smaller as Drepanaspis evolved, to form individual plates on the head, more like a placoderm, except it still had no jaws. 


Sacabambaspis had both of its eyes facing forward, which meant that it had 3D vision. Most other jawless fish did not have this feature. 

© lifebeforethedinosaurs.com
Sacabambaspis on a reef with a trilobite, an orthocone, a crinoid,
and rugose corals encrusted with bryozoans.

Sacabambaspis lived on reefs that were home to creatures such as trilobites, crinoids, orthocones, rugose coral, eurypterids, and bryozoans. At the time, any fish on a Bolivian reef almost had to be Sacabambaspis. There are no other known fish from the same place and time, in Bolivia 460 million years ago, when Sacabambaspis was found. 

© lifebeforethedinosaurs.com

Sacabambaspis, accompanied by rugose corals and bryozoan-encrusted rocks,
viewed from above.

The arandaspid family includes Astraspis, Arandaspis, and Sacabambaspis. They were all from the Ordovician. Astraspis was from North America, Arandaspis was from Australia, and Sacabambaspis was from South America. 

© lifebeforethedinosaurs.com

The arandaspid family: (from top) Astraspis, Arandaspis, Sacabambaspis

Arandaspis was more flattened on the sides than other arandaspids, and it was probably unstable and tilty. It had a rigid shell and was about four or five inches long. 


Astraspis was also about four or five inches long. It had no fins, not even a caudal fin, and a very bumpy shell. I hypothesize that with no caudal fin, it probably mostly slithered across the bottom, and from time to time it could have squirmed around and swam up into midwater to feed on plankton. It could then drift down again to feed on algae and scraps of leftover carcass, which is what it mostly ate. Astraspis is the oldest known North American vertebrate. 




References:


The tail of the Ordovician fish Sacabambaspis


Super Little Giant Book of Prehistoric Creatures


http://en.wikipedia.org/wiki/Sacabambaspis

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. 

© lifebeforethedinosaurs.com

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. 

© lifebeforethedinosaurs.com

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. 

© lifebeforethedinosaurs.com

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. 




References: 


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


http://en.wikipedia.org/wiki/Nautilus

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. 

Conodonta.

Conodonts were bizarre, fish-like probable chordates that may have resembled modern lampreys. They first evolved in the Cambrian, or possibly even the Precambrian, and died out in the Triassic-Jurassic extinction.

Conodonts were eel-shaped in form and most had large eyes, at least in comparison to the body. They had various toothy blades in the mouth to form what is known as "the conodont apparatus," which vaguely resembles the radula of a snail or slug.

Conodonts were probably capable of maintaining a cruising speed, but could not perform bursts of speed because their eel-like form would probably get them all tangled up. They would then be easy prey for any kind of predator trying to eat them. They probably swam in about the same style as an eel or loach. Although they had sharp teeth, they probably were not predators. Instead, they supposedly used "the conodont apparatus" as a sort of baleen to filter plankton from the water.

The largest conodont that has been found so far is Promissum, which reached lengths of 16 inches. Specimens of Promissum can be found in the Soom Shale of South Africa. Unlike most conodonts, Promissum had smaller eyes relative to body size. Promissum was about as long as an average house cat's body, without the head or tail.

The fist conodont specimens found were its individual toothy bars known as "conodont elements."

References:

http://www.ucl.ac.uk/GeolSci/micropal/conodont.html

http://en.wikipedia.org/wiki/Conodont

http://oceans1.csusb.edu/cdont_art.htm

Graptolithinia.

Graptolithinia is a class of shelled hemichordates that lived from the Cambrian to the Carboniferous. One of the first graptolites was called Chaunograptus, from the Burgess Shale. Chaunograptus made a living by hitching onto other animals like sponges and arthropods. Later graptolites, like Monograptus, had pelagic lifestyles and drifted with the ocean currents in the open sea. But one group of Graptolites, the dendroids, retained a benthic or a parasitic lifestyle.

The name graptolite means "writing on the rocks" in Greek, which refers to the fact that most graptolite fossils look like hieroglyphics. In life, some graptolites, like Monograptus, may have resembled hacksaw blades, where others, like Didymograptus, resembled pinking shears. There were hundreds, probably even thousands, of different forms of graptolites. The morphology of graptolites was very diverse.

The Ordovician graptolite Didymograptus.

Some graptolites were benthic, some were parasitic, some were pelagic, and there were many forms of graptolites living each of those lifestyles. Graptolites were hemichordates. They were not chordates, but they were very important in chordate evolution leading up to humans.

The Ordovician graptolite Phyllograptus. 

Graptolites are index fossils for the Ordovician and Silurian. Some graptolites are very common, like ammonites, which are also good index fossils. Most good index fossils are common, widely distributed, and from a limited time span. This helps scientists date rocks.

The Devonian graptolite Spirograptus. 

References:

http://www.ucmp.berkeley.edu/chordata/hemichordata.html

http://www.asoldasthehills.org/Graptolites.html

http://en.wikipedia.org/wiki/Graptolithinia

http://paleo.cortland.edu/tutorial/misc%20fossils/miscfossils.htm

Megalograptus.

Megalograptus was an Odrovician eurypterid that was about 4' long and had long, spiny "arms" that were probably for catching prey. Megalograptus could have preyed upon animals such as small orthocones, trilobites, early fish, conodonts, and possibly small echinoderms. It was probably prey for giant orthocones, such as Cameroceras and Endoceras. Megalograptus appeared in the Ordovician Period, and died out in the Ordovician mass extinction.

Megalograptus had an odd telson, or tail, with two semi-circular plates on the side and a spine in the middle. The spine probably did not carry venom, but I believe that it may have been used to make Megalograptus appear to be venomous, which would warn off predators. The two semi-circular plates on Megalograptus's telson may have been used together, as a paddle to help it swim. Megalograptus also had paddles on a pair of legs that came off of the head, which I believe helped it steer.

The first fossils of Megalograptus discovered were its appendages, so at first scientists thought the appendages were giant graptolite shells, which explains the name "Megalograptus," which means "great graptolite" or "big writing" (a lot of graptolite fossils resemble scribbles, lines, or writing). But Megalograptus was actually a eurypterid, or sea scorpion.

Megalograptus is thought to be rare. But since it is found around common fossils such as brachiopods, trilobites, echinoderms, crinoids, and other creatures, it may have been more common. Megalograptus might only seem rare because the exoskeleton of most Megalograptus did not fossilize.

References:

http://walkingwith.wikia.com/wiki/Sea_Scorpion

http://tanystropheus.wordpress.com/2009/08/06/wednesday-wonders-megalograptus/

http://en.wikipedia.org/wiki/Megalograptus

Agnostida.

Agnostid trilobites, or Agnostida, are bizarre trilobites that lived from the early Cambrian to the Ordovician mass extinction. In some Cambrian rocks, Agnostids are extremely common, and they are also spread all over the world in the fossil record. But in the Ordovician period, Agnostids become rare. But I believe they were probably still widespread.

A few Agnostid trilobite drawings of different species. [Artist unknown].

Most, but not all, Agnostids were blind, and they all were isopygous (meaning the pygidium, or tail, was the same size as cephalon, or head). Unlike other trilobites, Agnostids only had two or three thoracic segments, and like the order Nekaspida, which include Naraoia, some scientists do not believe that they are even trilobites. Instead they think that both these orders are more closely related to crustaceans than trilobites, but not stem group or crown group crustaceans.

Agnostid legs were unique among the appendages of trilobites, because most trilobites have legs similar to those of a pill bug. Agnostids have their own unique arrangement of legs and other appendages.

The ventral view of Agnostus, showing the legs and other appendages. 

Scientists disagree about whether Agnostids were benthic or pelagic. They seem to be benthic, because they are found with other benthic trilobites, and also have no eyes, which suggests that they would not be living at the surface where there is a lot of sunlight to help them see. But some scientists think they were pelagic because they are widespread, and usually pelagic animals can get to places more quickly and easily than benthic animals.

Some Agnostids could have been benthic predators that cannibalized and hunted in packs. Agnostids can commonly be found sheltered inside the remains of dead animals, including the abandoned tubes of the priapulid Selkirkia. Since the ones found in Selkirkia all have their head facing out of the tube, it indicates that they must have backed in for shelter and protection. Since the molted skins of Agnostids have not been found inside the tubes of Selkirkia, it means that they probably did not go into the tubes to molt.

References:

http://www.ucmp.berkeley.edu/arthropoda/trilobita/agnostida.html

http://www.trilobites.info/ordagnostida.htm

http://en.wikipedia.org/wiki/Agnostida

Halysites.

Halysites, commonly called "chain coral," is a coral that lived from the Ordovician to the Silurian Period. It looked like a bunch of straws or tubes linked together. From above, Halysites looks like a mass of chains or a brain.

From the side it looks like a fence.

Each individual corallite, or cell, is 2 to 6 mm in diameter. In each individual tube there was a tiny sea anemone-like animal called a polyp, similar to what you find in modern corals.

Corals today prefer warm, shallow, clear seas, so tabulate corals like Halysites and their relatives probably did too. So when sea levels rose in the Devonian, they became rare and then died out two periods later, in the Permian mass extinction.

Isotelus.

Isotelus is a trilobite that lived in the Ordovician Period. The biggest species of Isotelus is I. rex, which is one of the largest trilobites found yet. I. rex was about three feet long. Isotelus has been found in the United States, Canada, and Europe, and is the state fossil of Ohio.

Isotelus rex is on the far right.

Isotelus probably crawled along the sea floor and probably had to avoid predators like nautiloids. It was a kind of trilobite called an asaphid, which were trilobites that usually had between five and twelve segments in the thorax, and the pygidium and cephalon were similar in size.

The largest complete specimen of Isotelus rex was found in Manitoba, Canada in 1999. Isotelus maxiumus, another large species, has been found in Ohio.

Asaphus kowalewskii.

Asaphus kowalewskii was a peculiar genus of trilobite from the Ordovician period. It is sometimes classified as its own genus, Neoasaphus.

Asaphus kowalewskii had eyes on stalks, which probably helped it avoid turbid water (turbid water is murky water), which would cloud its vision. If it didn't evolve the eyes on stalks, it would have been devoured by predators because it would not be able to see right in the turbid water at the bottom.

A. kowalewskii probably crawled around beneath the mud and sand at the bottom of the ocean, with its two eyestalks poking out to watch for danger. A. kowalewskii had eyestalks that were sometimes as tall as one inch.

A. kowalewskii is a popular fossil because of its odd eyestalks. It has only been found in Russia. A. kowalewskii probably lived alongside animals such as Cothurnocystis.

Lituites.

Lituites is a peculiar genus of nautiloid cephalopod from the Ordovician Period. Its shell had a coiled tip. Juvenile Lituites did not have a conical part of the shell, they only had the coiled part of the shell. Then they later grew the conical part of the shell as they got older. Lituites was about seven inches long.

Lituites probably had to avoid predators such as Cameroceras and Anomalocaris. Lituites has been found in the United States (New York), China, Europe, and South America.

© lifebeforethedinosaurs.com

Some fossils of Lituites are similar to those of Orthoceras, because the fossils are the same color and preserved in the same way. But Orthoceras did not have the coil at the tip of the shell.

Eldonia.

Eldonia is an odd genus of animal that lived from the Cambrian to the Ordovician. When Charles Doolittle Walcott first found Eldonia in the Burgess Shale, he classified it as a holothurian (a sea cucumber), but other scientists didn't agree. They classified it as a medusoid (a jellyfish). Others classified it as a siphonophore. But no one knows for sure what it was.

There are three species of Eldonia: Eldonia ludwigii, Eldonia eumorpha, and Eldonia berbera. Although many people believe that Eldonia was a pelagic animal, some now believe that it was benthic and lived on the bottom of the ocean.

Some fossils of Eldonia show the lobopod Microdictyon feeding on them. Eldonia could grow up to 4 inches, but most specimens of Eldonia are smaller than this.

The part of the Burgess Shale where Walcott found so many Eldonia is called "The Great Eldonia Layer." Eldonia has also been found in China and in Morocco.

Cothurnocystis.

Cothurnocystis (coh-thur-no-SIST-is) was a strange genus of carpoid, which is an unsymmetrical animal that's either an echinoderm or a relative of an echinoderm. Cothurnocystis means "cothurnus bladder" (a cothurnus is a thick boot).

Cothurnocystis had a brain at the end of its tail. Some people believe that Cothurnocystis is a chordate, which is anything with a notochord, with or without a backbone. A notochord is like what is inside of a backbone. But Cothurnocystis did not have a backbone surrounding its notochord, so it was not a vertebrate.

At first people believed that Cothurnocystis's tail was a stalk, and that it attached itself to the sea floor or any other object with the stalk. Now people think this is unlikely. They now believe that Cothurnocystsis lay flat on the sea floor and used its tail to move about.

To feed, Cothurnocystis sucked water through a siphon, then filtered it out through gills on top. Bivalves feed the same way, but they don't have the same type of gills.

Cothurnocystis was four inches long, and probably had to avoid nautiloids such as Cameroceras. Cothurnocystis could have moved by slithering, like snakes do today. But that's only my hypothesis.

This well-preserved fossil of Cothurnocystis shows the delicate tail, which is not usually preserved.

Scenella.

Scenella (sen-ELL-uh) was an animal that lived from Cambrian to Ordovician. Although most people believe that Scenella was a monoplacophoran (which is a mollusk that looks like a clam with only one shell, and moves around on the sea floor with a squishy foot like a snail), some people now believe that Scenella could be related to today's Valella (also called the by-the-wind sailor) or the Portuguese Man o' War, floating on the top of the water.

Scenella was abundant. Individual fossils of Scenella have been found in groups, with some individuals overlapping each other.

Scenella had a flattened conical shell, where the cone appears to be partly squished flat. Scenella was probably good prey for predators such as Opabinia and Ottoia, because it was slow, defenseless, and easy to catch. Since Scenella was so tiny and there were so many predators around, Scenella was probably at the bottom of the food chain.

This fossil shows what a group of Scenella looked like. Huge predators like Anomalocaris, Amplectobelua, and Hurdia probably didn't bother to eat Scenella, because it was much too small for the big predators to eat. Scenella probably ate detritus and algae, like most other small snail-like animals from the Cambrian Period.

Cryptolithus.

Cryptolithus is a common genus of trilobite. Cryptolithus tessallatus is also called the Lace Collar Trilobite because of the indentations in the cephalon. Adult Cryptolithus had no eyes and felt their way about on the sea floor in search of edible detritus. Cryptolithus lived in the Ordovician period and probably had to avoid giant predators such Anomalocaris and Cameroceras. Complete skeletons of Cryptolithus are rare, but fragments of the cephalon are extremely common. The most distinct parts of Cryptolithus are the two posterior spines which were longer than the body.

Cryptolithus probably lived at the very bottom where it was too dark to see, because why would something that lives at the very bottom of the ocean evolve eyes? Trilobites like Cryptolithus were very successful until the Devonian mass extinction when only one family of trilobites survived (and then got wiped out in the Permian mass extinction).

The use for the indentations on the cephalon is unknown. First people thought that Cryptolithus shook its legs back and forth, dragging water into the cephalon so that the water would go out of the indentations. The edible particles of plankton and detritus would stay in the cephalon and then be devoured. But no one knows for sure, because there is no proof.

Orthoceras.

Orthoceras is a very abundant, worldwide orthocone, which is sometimes confused with Baculites. Many orthocone nautiloid fossils have been found in limestone from Sweden.

The tube running along the back of Orthoceras is called the siphuncle, and the round air chambers are called the septa. The septa helped Orthoceras ascend and descend, and the siphuncle was the tube that led to the siphon and pushed water out to move Orthoceras through the water.

Orthoceras probably ate trilobites like Walliserops and Calymene.

Orthoceras was about 6" long and probably had to avoid giant predators such as Eusthenodon, Eusthenopteron, and Dunkleosteus.

Orthoceras was Ordovician to Devonian, and resembles other orthocones like Cameroceras, Endoceras, and Dawsonoceras. But Orthoceras was much smaller than them, because Orthoceras was only 6" compared to huge nautiloids like Cameroceras, Endoceras, and Dawsonoceras.

When Orthoceras was first discovered, people believed that all orthocones belonged to the genus Orthocerus, but now the term Orthoceras is only used for the species Orthoceras regulare.

Orthoceras means "straight horn."

Cameroceras (Part 1).

Cameroceras was a huge orthocone which was one of the largest, or even the largest, animal in the Paleozoic Era. Cameroceras probably fed on everything it could get, such as eurypterids, anomalocarids, fish, trilobites, and even other nautiloids.

Cameroceras looked like a squid inside a thin ice cream cone. It could have probably torn up any prey with its tentacles and gotten to the soft parts inside, if the prey had armor. Cameroceras was a genus of giant orthocone. It was 17 feet, or possibly even larger. Its name means "chambered horn" because of the ring-shaped chambers it had along its shell, which probably helped it go up and down by holding air in to go up and letting it out to go down. 

Cameroceras may have even eaten other Cameroceras. Cameroceras probably lived in deep water because if it was in shallow water it would not have been able to move because it was so huge.