Pachytheca.

Pachytheca was a very primitive sphere-shaped plant that lived from the late Silurian to the early Devonian. Pachytheca is related to Prototaxites, so my hypothesis is that it is a fungus. It was up to 6mm long. 


This organism had a prominent outer layer. It's possible that in juvenile specimens this layer was thicker, and on the adults it was thinner. The structure of Pachytheca was made up of tubes. Thicker, stronger tubes on the outer layer, and thinner, more brittle ones on the inner layer. 

Some of the fossils look like marbles, while others look like tiny geodes. At first the organism was thought to have been a piece of a bigger plant or the tooth of a fish. Then it was incorrectly classified as an alga. 

Pachytheca and Prototaxites are now classified as Nematophytes, enigmatic organisms that were either plants or fungi. Pachytheca has been found mostly in western Europe, but they also lived in places such as Canada and Australia. 

References:

http://steurh.home.xs4all.nl/engpach/epachy.html

http://www.chertnews.de/Pachytheca.html

http://de.wikipedia.org/wiki/Pachytheca

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

Mid-Devonian Tetrapod Tracks.

Tetrapods are four-legged vertebrates that were first thought to have appeared in the late Devonian Period, and they were thought to be descendants of elpistostegid fishes like Tiktaalik and Panderichthys. But in 2010, in Poland, scientists found tetrapod tracks from the middle of the Devonian Period, meaning tetrapods appeared earlier than previously thought.

Illustration by Robert Back

Since these tetrapod tracks are older than the earliest
elpistostegid, this means that the elpistostegids, like the famous Tiktaalik, were not ancestors of tetrapods. Instead, the direct fish ancestors of tetrapods are not currently known.

Some of the trackways that have been found indicate that these early tetrapods grew up to at least two meters long. They probably looked a lot like other Devonian tetrapods, such as Ichthyostega.

Scientists used to think that tetrapods had their origins in freshwater environments, such as swamps and lakes. But the tetrapod tracks found in the Zachelmie Quarry were found in what had been a marine environment, like a lagoon. This means that tetrapods may have had their origins in saltwater environments.

The trackways indicate that these tetrapods walked in a sprawling gait, like lizards. The trackways also show that the tetrapods that made them were not walking on land. They were actually partially submerged in shallow water. If they were sprawling on land, their stomachs would have left a drag mark. But there are no stomach drag marks in the trackways in the Zachelmie Quarry, which means the tetrapods that made the tracks were floating, and their feet were pushing them along the bottom of the lagoon.

Many thanks to Robert for showing me these tetrapod tracks from the Zachelmie Quarry, and for letting me use his really cool illustration of what the tetrapod that left those tracks is believed to have looked like. 


References:

http://news.bbc.co.uk/2/hi/8443879.stm

http://scienceblogs.com/notrocketscience/2010/01/fossil_tracks_push_back_the_invasion_of_land_by_18_million_y.php

http://www.nature.com/nature/journal/v463/n7277/edsumm/e100107-01.html

http://www.earthmagazine.org/earth/article/2e6-7da-1-7

http://www.multi.fi/~rback/

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

Scyphocrinites.

Scyphocrinites (sky-foe-cry-NITE-ees) is a genus of crinoid that lived from the late Silurian to the early Devonian. Its fossils have been found in Asia, North America, Europe, and Africa.

Instead of being rooted to the ground like most crinoids, Scyphocrinites had a lobolith, which is a floating sphere that keeps an animal afloat in water. Unlike other crinoids, Scyphocrinites hung upside down at the surface.

This is a fossil of a lobolith from Scyphocrinites. The lobolith would have allowed Scyphocrinites to move with the current, which benthic crinoids could not do. Scyphocrinites was probably the only crinoid with a lobolith, but there may have been others.

This fossil shows the calyx of Scyphocrinites. In zoology, a calyx is a cup-shaped structure. In botany, it's the sepals that protect a flower. The arms coming off of the calyx would have allowed it to snare tiny plankton to eat. We know that because living crinoids use their arms for the same purpose. Fossils of Scyphocrinites are sometimes found in huge clusters, similar to how the Cretaceous crinoid Unitacrinus is found.

References:

http://www.fossilmuseum.net/Fossil_Galleries/Crinoids/Scyphocrinites/Scyphocrinites.htm

http://www.mineraltown.com/Reports/crinoid_fossils/crinoids.php?idioma=2

http://www.mprinstitute.org/vaclav/Scyphocrinites.htm

http://dictionary.reference.com/browse/calyx

Phacops.

Phacops is a trilobite that lived from the Silurian to the Devonian Period. It had a large and bumpy glabella, or middle cheek.

Even though many other trilobites could roll up like pill bugs, Phacops could do it more efficiently than other trilobites. But sometimes when they were rolled up they could get buried in sediment. Many fossils of Phacops are found rolled up into balls.

Phacops was up to six inches long. Some people recognize it by its eyes, which resembled frog eyes.

Phacops has been found in the northeast United States and Morocco, and is the state fossil of Pennsylvania.

Phacops had a 360 degree view because it could turn its eyes to different angles. Phacops is one of the most common Devonian trilobites.

Coccosteus.

Coccosteus is a Devonian arthrodire placoderm that resembles the larger Dunkleosteus. Coccosteus mainly lived in fresh water, but could have possibly also lived in the sea, like a bull shark in reverse. Fossils of Coccosteus have been found in Europe and North America.

Coccosteus was usually about 8 to 10 inches, but the largest specimen is 16 inches long. Its name means "seed bone."

Like all other arthrodires, Coccosteus had a joint in its neck that would have allowed it to open its mouth wider than most fish and swallow larger prey. Coccosteus had a sharp beak which would have helped it slice open prey. It had bony plates covering its head which could have protected it from predators.

Coccosteus lived from the middle to late Devonian Period.

Greenops.

Greenops is a Devonian trilobite with odd spines growing out of the pygidium (the last body section). Finding a complete specimen is very rare, but scattered bits and pieces are common in New York State and Ontario, Canada.

Greenops was about 1 to 1.5 inches long and probably had to avoid being eaten by predators like placoderms, ammonoids, orthocones, and sharks. It lived in deep warm water, but usually not very deep. Fossils of Greenops are often found in Devonian limestone deposits.

Greenops had a schizochroal eye, which are compound eyes that had few large lenses separated by thick walls. This type of eye in found only in some phacopid trilobites.

Dicranurus.

Dicranurus is a bizarre genus of Devonian trilobite. Its name means "twin head-tail," referring to the curled tail-like horns on the head. The long spines probably protected Dicranurus from predators such as placoderms, and also kept Dicranurus from sinking into the mud at the bottom of the ocean.

Dicranurus lived in the shallow ocean between Gondwana (a supercontinent) and Euramerica (north Europe and North America). This shallow sea is now Oklahoma and Morocco, which is where Dicranurus fossils have been found.

Dicranurus was a lichid trilobite, which were very spiny trilobites that lived from the Ordovician to the Devonian. It is distinguished by the two spines on its head.

Prototaxites.

Prototaxites (pro-toe-tax-eye-teez) is a mysterious genus of life form that lived from the Silurian to the Devonian Period. Prototaxites was first believed to be a conifer-like plant, but is now believed to be a giant fungus or huge liverwort. It was up to about 30 feet tall and could be three feet wide. Prototaxities was the biggest life form on land of its time.

Prototaxites looked like a giant tree trunk with no branches or leaves. It's possible that Prototaxities was so tall so its spores could move far away so that it would not have to compete with other Prototaxities for what it needed.

Prototaxites was worldwide and died out when vascular plants took over.

Furcacauda.

Furcacauda is a genus of thelodont from the Silurian to Devonian Periods. It had a large caudal fin which made it look very odd. Furcacauda was closely related to the Silurian thelodont Lanarkia.

Since the largest thelodont, Thelodus, was 30 cm, Furcacauda was smaller than that. Furcacauda and other thelodonts were jawless. Scientists have found a fossilized part of Furcacauda that looks like a stomach. So Furcacauda could have had the first stomach of any vertebrate.

This image shows a fossil of Furcacauda on the bottom, and the top fossil is Lanarkia. Although Furcacauda didn't look anything like Lanarkia, they were still both thelodonts. Thelodonts were covered in tooth-like scales rather than having armor on their head like most jawless fish did.

Drepanaspis.

Drepanaspis is a genus of heterostracan (which is a jawless placoderm with two plates of armor on its head) from the Devonian Period. Drepanaspis means "sickle shield." It probably swam along the bottom in search of food, but its mouth pointed up. The main mystery about Drepanaspis is that, if its mouth pointed up, how could it be a bottom feeder? It may have eaten bits of dead animals and plants that drift down to the bottom called "marine snow." Or maybe it could have stirred the sand up so much that the food came flying up, and then Drepanaspis would be able to suck it in. But those are just my hypotheses.

This image shows Hemicyclaspis in the lower right-hand corner, which is the one with the headshield that looks like half an oval. Astraspis is in the lower left-hand corner, and is the one that only has a caudal fin and a shield that looks like half of a medicine capsule. Anglaspis is similar to Astraspis, because it has two plates of armor, and the only fin it has is a caudal fin. Anglaspis is the one in the upper right-hand corner. The other two fish in this image are Pterapis, the one in the upper left-hand corner with the long, lower lobe on the caudal find and the beak-like rostrum, and Drepanaspis, which is the one with one of its pectoral fins scraping the bottom.

Drepanaspis was usually about six inches long, but it could grow up to one foot long. Drepanaspis had a flattened, ray-like body with two wide pectoral fins.

Terataspis.

Terataspis grandis can be translated to "grand monster shield," because of its huge size and monstrous appearance. Although no complete skeleton of Terataspis has been found, many fragments of the exoskeleton have been found, so scientists have gradually been able to reconstruct Terataspis with every fragment they've found.

Terataspis was a strange genus of trilobite from the Devonian Period. Its body was completely covered in small barbs, possibly as a defense against huge predators such as Eusthenodon, Eusthenopteron, and Dunkleosteus.

This scale shows the five largest species of trilobite, largest on the right, and smaller on the left. Terataspis grandis is the third biggest species of trilobite. Terataspis was found in New York State and Ontario, Canada. It lived in the Devonian Period.

Scientists believe that Terataspis was a detritivore, meaning it ate edible particles of dead plants and animals. But Terataspis may have predated upon other animals if they were easy to catch.

Click image for larger size.

This model is based on the fragments of Terataspis so that scientists can try to learn more about it with a recreation. It can be hard to learn about a fossil if it's in pieces.

Some of Terataspis's relatives are Selenopeltis and Odontopleura. Unlike its relatives, Terataspis had the bars sticking out of the abdomen with barbs on them. Terataspis was also much bigger than those relatives.

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."

Bothriolepis.

Bothriolepis was the most common placoderm in the Devonian Period. It was about one foot long. Bothriolepis was world-wide. There were 100 species of Bothriolepis.

Bothriolepis means "pitted scale" or "trench scale," because Bothriolepis had pits and trenches in its armor. Bothriolepis, like all placoderms, even had its eyes covered with armor.

Bothriolepis had its eyes almost touching each other, and looked straight ahead like a person, unlike many other fish, which evolved one eye on either side of the head like a horse.

Bothriolepis had armored front fins to push it off the sea floor, because if it tried to swim up, it would immediately fall back down because of the weight of its armor. This image shows Bothriolepis canadensis on the sea floor.

Some scientists think that it is possible that Bothriolepis migrated like salmon into fresh water to mate. Unlike salmon, Bothriolepis is believed to have spent most if its life in freshwater.

The reason why Bothriolepis was so successful is unknown.

Palaeospondylus.

Palaeospondylus was a mysterious worm-like fish which has been described as a larval tetrapod, lungfish, unarmored placoderm, and agnathan.

Palaeospondylus was discovered in Scotland and is 2" long. This image shows Coccosteus attacking four Palaeospondylus.

Palaeospondylus may have been a parasite or an early lungfish.

Palaeospondylus had a weird basket-like formation in the skull, but the use for this basket-like formation is unknown.

Walliserops.

Walliserops is a weird genus of lower-to-middle Devonian trilobite with a trident sticking out of its head. There are six species of Walliserops: Walliserops trifurcatus, Walliserops hammii, Walliserops tridens, and three undescribed species.

The use for the trident is unknown. Maybe it's for defense, maybe it's for detecting food under the sand (sort of like a built-in radar), or maybe it's for fighting other males to mate and the female doesn't have a trident, so it might be thought to be a different kind of trilobite.

This well-preserved fossil of Walliserops trifurcatus shows every detail, so scientists don't need to reconstruct it learn about it. Walliserops had to avoid predators such as Shinderhannes bartelsi, Dunkleosteus, Eusthenodon, and Eusthenopteron.

The family of trilobites which was wiped out in the Permian must have been very successful because all other families of trilobites were wiped out in either Ordovician or Devonian.

Walliserops isn't the only trilobite with a weird head. The Permian trilobite Keryopigee had a head shaped like a pointy top hat. But Walliserops probably isn't related to Cheiropyge because Cheiropyge only had one spike in the front of its head. Walliserops had a lot more spikes all over the body.

Walliserops trifurcatus was the only species of Walliserops with a long trident. The others had the trident directly attached to the head and not on a pole-like spike like trifurcatus.