Merry Xmas!

Very dirty Mazon Creek fossils for Xmas!

A subscription to Deposits magazine.
This issue: The Geology and Terrestrial Life of the Carboniferous.

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

Field Museum birthday update: 20%!

Thanks to generous contributions from readers and various friends of the blog, Art is 20% closer to reaching the Field Museum for his 8th birthday. The museum has generously offered free admission and a special tour, including the possibility of a peek behind the scenes with a fossil dude. Sincere thanks to everybody who is helping to make this trip a reality for Art.

Titanichthys.

Titanichthys was a giant Devonian placoderm which was about twenty feet long. Since the tooth-like gnathal plates in its mouth were small and dull, it is believed that this fish fed on tiny zooplankton and tiny fish.

Fossils have been found in North America, Morocco, and Poland. Some specimens are found in the Cleveland Shale of Ohio, and shared the same area with Cladoselache, Dunkleosteus, and many other strange fish.

The fossil below shows the upper part of a Titanichthys skull. Although it doesn't look like it, it's a well-preserved specimen. The only downsides are that it does not preserve the bottom half of the skull, and it was flattened during fossilization. But what's amazing is that it's complete to a certain extent. The front of the skull is facing upwards, while the neck plates in the back of the skull are facing downwards. Also note the strange diamond-shaped hole in the middle of the skull. This is the neck joint that gave these so-called arthrodire placoderms their name. "Arthrodire" means "jointed neck."

Titanichthys was one of the largest placoderms. In fact, it was the second largest, after Dunkleosteus terrelli. When Titanichthys was first discovered, some scientists thought that the pieces of bone were from a dinosaur. But after more study, it was discovered that they were actually from a placoderm fish.

References:

http://geology.cwru.edu/~huwig/catalog/ohiogeology.html#cleveland%20shale

http://dinosaurs.about.com/od/tetrapodsandamphibians/p/titanichthys.htm

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

http://tanystropheus.wordpress.com/2010/04/02/weekly-spotlight-titanichthys/

http://gsa.confex.com/gsa/2011NE/finalprogram/abstract_185308.htm

Cladoselache.

Cladoselache (CLAD-oh-SELL-uh-key and CLADE-oh-SELL-uh-key) is a genus of late Devonian shark which is known from extremely well-preserved fossils from the Cleveland Shale in Ohio. Some of the specimens even have gut contents. They most commonly have small, ray-finned bony fish in their guts, but some of them have shrimp-like creatures, conodonts, and one even has another shark in its stomach.

One of this shark's most notable features is its lack of scales. It only had scales on particular places, such as around the eyes and mouth. Its teeth do not seem to be suited for ripping and tearing up prey, so they seem more likely to have grasped prey and allowed the shark to swallow it whole, tail first. The presence of gut contents with the posterior of the prey facing Cladoselache's posterior, (instead of facing just any old way, as in most sharks) suggests that Cladoselache swallowed its prey tail first.

Cladoselache also had enormous pectoral fins, which it probably used to glide through the water as it searched for food or pursued its prey. It had a short, blade-like spine in front of its dorsal fin, which was not as advanced as the spike-like spines of Xenacanths, Hybodonts, and Ctenacanths.

Cladoselache was about six feet long, and was probably prey for giant placoderms such as Dunkleosteus.

Cladoselache had a large mouth in front of its head. More advanced forms, such as Cretoxyrhina (the Cretaceous "Ginsu shark") and the modern Great White, have a smaller mouth under the snout.

References:

http://geology.cwru.edu/~huwig/catalog/slides/1006.Ga.24.jpg

http://www.elasmo-research.org/education/evolution/ancient.htm

http://www.elasmo-research.org/education/evolution/cladoselache_feeding.htm

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

http://dinosaurs.about.com/od/tetrapodsandamphibians/p/cladoselache.htm

Royal Ontario Museum Burgess Shale Fossil Gallery.

I first found The Royal Ontario Museum Burgess Shale Fossil Gallery before it was even finished being made, because I'm always using the internet to research fossils. The Royal Ontario Museum had to keep people from going to the website for a while because they were not done with it. But now they are done and it is amazing. 


I love that this fossil gallery tells you maximum size, supposed diet, abundance, classification, and morphology. It also has pictures of fossils, drawings, and even some videos. You can zoom in on the fossils and drawings to see them up close. At first it seems blurry, but then it clears and you can see amazing details. The Royal Ontario Museum Burgess Shale Fossil Gallery is the best place to find information and pictures of Burgess Shale fossils. The Gallery even features fossils that were discovered last year, in 2010. 

One of the most notably strange animals in the Burgess Shale that is featured in the ROM Fossil Gallery is Herpetogaster collinsi, which is weird. It had a flexible and extendible stalk, with a disc to anchor it to sponges. It had a sea cucumber-shaped body on top of the stalk. The body had thirteen segments, a circular mouth on top, and two branching tentacles on top of the head on either side of the mouth. Its maximum length was 48 mm. One amazing specimen of Herpetogaster collinsi shows many individual specimens attached to a single Vauxia gracilenta sponge. 

© ROYAL ONTARIO MUSEUM. PHOTOS: JEAN-BERNARD CARON

Another amazing animal in the ROM Fossil Gallery is Odontogriphus omalus. The fossil shown below preserves Odontogriphus grazing on mats of the cyanobacteria Morania. Odontogriphus omalus was an early slug-like mollusk, related to the more heavily armored Wiwaxia. 

© ROYAL ONTARIO MUSEUM. PHOTOS: JEAN-BERNARD CARON

A strange ctenophore that is featured in the ROM Fossil Gallery is Xanioascus canadensis. It looked like a balloon with eggs inside of it. It also had twenty-four comb rows, which are the rows of cilia that propel a ctenophore through the water. Modern ctenophores only have eight comb rows. Fossils of X. canadensis are usually found torn, suggesting that these ctenophores were very fragile and could be easily torn. One of the coolest things about the ROM Fossil Gallery is that they feature some very obscure animals and show a lot of information that most people cannot find anywhere else on the internet. Xanioascus canadensis is one of the very obscure creatures in the ROM Fossil Gallery. 

© MARIANNE COLLINS

I recommend that anyone searching for obscure Burgess Shale animals, or even non-obscure Burgess Shale animals, should go to the ROM Fossil Gallery. They have a lot of information, even the meaning of the names, which is something that I love to know. This Gallery has a wide range of Burgess Shale life, even cyanobacteria and algae. In my opinion, it's the best place to find information on Burgess Shale fossils. 


References:

http://burgess-shale.rom.on.ca/en/fossil-gallery/list-species.php
"Materials for this virtual exhibit – called 'The Burgess Shale' – were produced and/or compiled by Parks Canada (for the Parks Canada section) and the Royal Ontario Museum (for all other sections) for the Canadian Heritage Information Network (Virtual Museum of Canada program) for the purposes of providing the public with information about the Burgess Shale."

The Bear Gulch Limestone.

The Bear Gulch Limestone is an amazing fossil bed that dates to the Mississippian epoch of the Carboniferous Period. Some of the most notable specimens are of fish. The Bear Gulch fish are extremely diverse. They include sharks, rhizodonts, petalodonts, and even a lamprey.

The Bear Gulch is a fresh and brackish water deposit, suggesting that the environment was similar to the Mazon Creek and was an estuary or a lagoon connected to the sea.

Since some of the fossils show signs of stress during death, and rarely show signs of decay and scavenging, scientists believe that they were buried rapidly, similar to how the Burgess Shale fauna were buried.

To me one of the most amazing fish skeletons from the Bear Gulch is a fossil of a pair of Falcatus that I believe are mating:

Lund, Richard, and Grogan, E.D., 2005 Bear Gulch website,
www.sju.edu/research/bear_gulch, accessed by lifebeforethedinosaurs.com on
11-27-2011, page referenced last updated 02-01-2006.

It's possible that one of the top predators in the Bear Gulch was a colossal rhizodont called Strepsodus. Scales of this fish found in the Bear Gulch Limestone were up to 6 cm in diameter. Huge, especially for fish scales, and would point to Strepsodus being a massive fish:

Lund, Richard, and Grogan, E.D., 2005 Bear Gulch website,
www.sju.edu/research/bear_gulch, accessed by lifebeforethedinosaurs.com on
11-27-2011, page referenced last updated 02-01-2006.

An amazing fossil from the Bear Gulch is Hardistiella, a very early lamprey. It is not the oldest, however. The oldest lamprey discovered so far is Priscomyzon, which was found in Africa and dates to the late Devonian Period, 360 million years ago. Hardistiella is quite strange compared to other lampreys because it has a body shaped more like a lancelet's, and no signs of a bloodsucking structure in the mouth. Scientists do not know if the Hardistiella fossil shown here is an adult or not, probably because it could possibly be the only known specimen:

Lund, Richard, and Grogan, E.D., 2005 Bear Gulch website,
www.sju.edu/research/bear_gulch, accessed by lifebeforethedinosaurs.com on
11-27-2011, page referenced last updated 02-01-2006.

Invertebrates in the Bear Gulch limestone are diverse, but not as diverse as fish, which are one of the most varied groups of organisms found in the Carboniferous Bear Gulch Limestone. This is similar to the Devonian Period, when fish were extremely diverse. But Bear Gulch fish probably weren't as diverse as Devonian fish, because many kinds of fish went extinct at the end of the Devonian, including placoderms, armored jawless fish, the so-called "fishapod" forms, and thelodonts.



References:

http://www.sju.edu/research/bear_gulch/

http://www.cas.umt.edu/paleontology/rc_beargulchlime.htm

http://www3.amherst.edu/~jwhagadorn/publications/Lag4.pdf

http://rstb.royalsocietypublishing.org/content/327/1242/595.short

http://www.scienceinafrica.co.za/2007/february/lamprey.htm

http://www.fossilmuseum.net/Fossil_Sites/beargulch.htm

Happy Thanksgiving!

Skeemella made from foil off chocolate coins. 

Research trip. Wanna help?

We're planning a trip to the Field Museum in Chicago to celebrate Art's eighth birthday. He's never seen the Field Museum, and their exhibit "Evolving Planet" looks excellent. We've added a ChipIn widget to the blog to help pay for the trip. Art will definitely blog about the experience, and I'll take a ton of pictures.

Thanks to everyone who reads the blog and supports Art's work. He lives for this stuff!

-The Mom

The Field Museum: Evolving Planet

Anomalocaris (Part 2).

I've written about this animal before, but there is more information that I would like to talk about.

Anomalocaris was a very widely distributed Cambrian animal. Their remains have been found in at least China, Australia, Nevada, Pennsylvania, California, Georgia, Utah, Canada, and Greenland. Adults were normally about three feet long, but some could have grown up to six feet. Fossils of Anomalocaris canadensis show that it had a skinny head and long eye stalks, so it could have been able to turn its head and swivel its eyes while it was hunting for prey.

Some scientists believe that Anomalocaris ate trilobites. This evidence comes from Anomalocaris briggsi coprolites found in Australia, which contain pieces of trilobite exoskeletons, as well as trilobites with bite marks in them, which are found in many places. Some scientists don't believe that Anomalocaris normally ate trilobites because its mouth parts may not have been hard enough to penetrate trilobite exoskeletons. Anomalocaris mouth part fossils do not show any signs of being worn down by trilobite exoskeletons. But to some scientists this just points to the spines on the mouth parts being pliable but hard. So it's possible that Anomalocaris did still normally eat trilobites.

Anomalocaris fossils are most commonly found as disarticulated pieces, but well-preserved juveniles and some well-preserved adults are known.

Although A. canadensis had its claws curled up under its head. A. saron had its claws stretched out sideways in front of its face so they would have acted like scissors, where the spikes on one claw faced the spikes on the other claw. But there are other differences between the two species. A. saron had legs and cerci, while A. canadensis did not. But they did share the same basic structure. Some scientists believe Anomalocaris pennsylvanica was just a non-Canadian A. canadensis, but they might be different species.

References:

http://www.trilobites.info/anohome.html

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

http://whyevolutionistrue.wordpress.com/2010/11/17/a-new-anomalocaris-mystery/

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

Happy Halloween!

Diania cactiformus costume? Yes.

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

Archimylacris.

Archimylacris was a Carboniferous genus of insect. Even though it looked like one, it was not a cockroach, but an ancestor. The first true cockroaches appeared in the Jurassic period, and the first modern cockroach appeared in the Cretaceous period. But the paleozoic "cockroaches" are not cockroaches but Blattopterans, which are ancestors of cockroaches, termites, and mantises.

Archimylacris was very large, reaching up to 9 cm in length and 4 cm in width. It looked like a modern cockroach, except it was much bigger. It had slight differences, such as sticky pads on its legs called euplantulae and a long ovipositor. (Only the female had the ovipositor). The euplantulae may have helped it crawl on smooth surfaces, such as leaves, or possibly help it walk upside down like some modern insects do. This may have allowed it to escape from forest floor predators such as amphibians and early reptiles and allow it to climb tall plants.

Archimylacris lived in the swamp forests of Europe and North America about 300 million years ago. It probably scurried along the forest floor and acted like a modern cockroach. The video below shows an animated CT scan of one of the fossils.

http://www.sciencecodex.com/creepy_crawly_cockroach_ancestor_revealed_in_new_3d_model

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

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

http://palaeoblog.blogspot.com/2010/04/ancient-cochroach-ancestor-in-3d.html

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

Belantsea

Belantsea (bull-ANT-see-uh) was a kind of cartilaginous fish from the Carboniferous period that was related to the Permian Janassa. Both of these fish are chondrichthyans called Petalodonts. I first read about Belantsea in Paleo Sharks by Timothy J. Bradley.

Belantsea had a large, lobe-shaped fin on its ventral side, right behind the mouth. I believe that this may have helped Belantsea steer. Even though Belantsea could steer and move very well, it probably could not move very fast because of its shape, which was not hydrodynamic.

Belantsea had large teeth probably used to crush and eat hard-shelled animals such as corals and sponges. Fossils of Belantsea have been found in Montana and reach 2 feet in length. Fossils of Belantsea are rare.

References:

http://www.sju.edu/research/bear_gulch/pages_fish_species/Belantsea_montana.php

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

Paleo Sharks: Survival of the Strangest by Timothy J. Bradley

Deiphon.

Deiphon is a Silurian trilobite which had long, conical spines on its body. It had a very large, round glabella, or middle cheek. Some scientists believe the glabella was filled with fat or oil, to keep the trilobite buoyant. But others think Deiphon was predatory and that it stored prey inside the glabella. 

My interpretation of Deiphon on the Silurian sea floor. 

Deiphon's spines may have made it hard for larger predators to swallow it. Deiphon was either planktonic and ate phytoplankton, or was benthic and predatory.

Deiphon had long, curved spines along its thorax, and two spines that formed a v-shape on its pygidium, or tail. It also had two spines on its cephalon, one on each side. Deiphon's thorax was much skinnier than that of most other trilobites. All these odd features would have made Deiphon a very strange trilobite.

Click image to see more of Christian Richet's illustrations.

References:

http://www.britannica.com/EBchecked/topic/692300/Deiphon

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

Skeemella.

Skeemella is a Cambrian animal that is found in Utah and is known from one specimen. The specimen has two halves: a posterior half and an anterior half. Although some scientists in China believe Skeemella is an arthropod, some American scientists believe it is a Vetulicolian.

Anterior half of Skeemella.
[Source: University of Kansas Division of Invertebrate Paleontology]

Skeemella had a long, skinny tail with two flukes that formed a paddle at the end of the tail. This picture shows Skeemella, the large elongate animal, and a group of the trilobite Peronopsis. The Peronopsis are probably searching for carcasses of Elrathia kingii, because they were some of the most common food sources that a scavenger like Peronopsis would be able to eat.

I believe that Skeemella may have been nocturnal, because its long tail would drag behind and in the day could be seen and grabbed by a predator. But in the nighttime, the big predators were either sluggish, inactive, or could not see well in the darkness, so Skeemella could be safe. But that's just my hypothesis.

My interpretation of Skeemella with a group of Paronopsis.

Skeemella had a tough carapace shaped like a fingernail, a beak-shaped mouth, no eyes, and two lobe-like extensions on the glob-like anterior part of the body.

Skeemella swimming slowly above the Cambrian sea floor in search of detritus or plankton.

References:

http://kumip.ku.edu/cambrianlife/Utah-Vetulicolians.html

http://www.fossilmuseum.net/Fossil_Sites/Chengjiang/Vetulicolia-Fossils.htm