The Difference Between...Anapsids, Synapsids, Diapsids and Euryapsids

Simplified skull diagrams of anapsid, synapsid, diapsid and euryapsid.
Image taken from Benton 2005

You will come across various references to amniote skull types such as synapsid and diapsid, these are the more commonly used ones. So for this post I will go through how to tell which is which by looking at the skull.

(a) Anapsid Skull: Skulls that lack openings, known as temporal fenestrae, are anapsids. These include turtles, modern and prehistoric, as well as extinct reptile species.

(b) Synapsid Skull: There is a single temporal fenestrae situated below the postorbital bone, in a similar position to the lower opening of a diapsid. Synapsid reptiles are now extinct but mammals are also synapsid and believed to be descendants of these reptiles.

Dimetrodon Skull, an example of a synapsid. Image credit:
mercyhurst.edu

(c) Diapsid Skull: Perhaps the most famous diapsids are the dinosaurs, but diapsid also covers snakes, crocodiles, lizards and birds. There are two temporal fenestrae behind the orbit. One is inferior (smaller) and one superior (bigger).

(d) Euryapsid Skull: This is probably the least known of the amniote skull. Although it appears to be similar to the synapsid skull it differs as it is positioned above the postorbital bone rather than beneath it. The Euryapsids include Ichthyosaurs and Plesiosaurs.

Palaeoart: Island Dwarfism

I have chosen this artwork by Mark Witton because of the interesting ecology that lies behind it.

This artwork shows us the giraffe sixed pterosaur Hatzegopteryx feeding on what appear to be juvenile sauropods. Its a natural assumption, however the sauropods pictured here are called Magyarosaurus and they are in fact adult dinosaurs. 

In the late Cretaceous, where modern day Romania is, there is an isolated island in the Tethys Sea, this is Hateg Island. It is a brilliant case study in palaeontology. It is an example of island dwarfism. This is an evolutionary trait that is found when herbivores become smaller in size so as not to deplete the vegetation to the point where it will not replenish. As the herbivores get smaller as do the carnivores. They do not need to be so giant now that the prey is small, again this is conserving food so that the herbivores can breed and replenish the food stocks. 

So why are the pterosaurs so giant? This is believed to be due to the fact that they can fly. There is no need to succumb to dwarfism if they can easily leave the island to find more food. Thus the pterosaurs retained their size. 

Hateg Island is not the only example of island dwarfism. Our ancient relatives Homo floresiensis on the Indonesian island of Flores were dwarves around 12,000 years ago, elephants were also dwarves here, both now extinct.

Palaeoart: Mating Display

Because I was so impressed with the artwork I found last night by Emily Willoughby I decided to do another post on her work, this time, as with the last, we see her knowledge of modern birds shining through.

This piece is entitled 'Balaur bondoc is a bird', which it is, and we see that easiest here. Without having to look too closely it is evident that the Balaur on the log is a male from the more colourful plumage around the neck. The other animal is a more neutral colouring and therefore can be assumed to be a female. How can we make these assumptions? By doing what the artist did and taking a look at modern birds. Mallard ducks are a good example, the drake is more decorated than the female in order to compete for mating rights.

While watching pigeons in the street we also see another parallel between this depiction of the male dinosaur. The puffing around the neck, while fending off other males, birds such as pigeons will puff their feathers to appear bigger which also attracts a female. This is most likely what Willoughby is trying to portray here. Even the front limbs are held like wings.

Its safe to say I'm now a big fan of this artist, she brings modern birdlike features to the world of the dinosaurs, making for very interesting artwork. This won't be the last you see of Willoughby as I want to share more of her work on here.

Let me know what your thoughts are on this work in the comments.

The Big Five Mass Extinctions

Mounted Brachiosaurus skeleton at the
Naturkunde Museum in Berlin, Germany. The dinosaurs
were the major casualties of the K/T Extinction. Image
credit: Bill Sellers

As I said in my Devonian post yesterday, I am going to cover the Five biggest mass extinctions in the Earth's history. We will look at these from the one with the least impact on global species to the one with the most impact. You will notice that when reading the statistics for what went extinct that the number of species will be higher than the number of families or genera that were lost, this is because you can have vast numbers of species die out without losing a genera if some species are to survive. For instance, the Sarcopterygii that was discussed in the Devonian post largely have died out but the whole class was not lost as it survives with the lungfish and Coelacanth. I am also using marine life families as some of the extinctions took place when there was little or no life on land.

#5: The Cretaceous Tertiary Extinction 
Also known as the K/T Extinction or K/Pg Extinction, Pg being the Palaeogene period that followed the Cretaceous, is famed for being the extinction that wiped out the dinosaurs and closed the Age of Reptiles. Extensive studies, including the drilling of boreholes, of the Chicxulub crater off the coast of the Yucatan Peninsula in Mexico have given a clearer picture of what happened 66 Ma. An asteroid nearly six miles wide smashed into the earth, this caused a chain reaction of events that doomed the dinosaurs. After the impact, mass volcanism, particularly around the Deccan Traps area in India, polluted the atmosphere and caused the Earth to heat up. Sea levels also fell by 150 metres which could be attributed to the loss of the marine life as many would have depended on shallower seas to survive. 
Marine Families Lost: 16%
Genera Lost: 67%
Species Lost: Approximately 76% including non avian dinosaurs, marine reptiles, pterosaurs and ammonites.

Artist's impression of the Chicxulub Crater. Image credit:
Detlev van Ravenswaay

#4: End Triassic Extinction
Little is known about the causes of this extinction that took place 201 Ma, but we do see evidence of falling sea levels which is potentially the reason behind a larger loss of ocean species, including some marine reptiles. There is also sedimentary evidence for volcanic rifting that took place as Pangaea broke apart. Taking place over where North America, Europe and Africa would have been on the supercontinent, the air would have been toxic to nearby ecosystems, another possible reason for an extinction event. 
Marine Families Lost: 22%
Genera Lost: 53%
Species Lost: Approximately 80% including most mammal-like reptiles and large amphibians, surprisingly plants made it through largely unscathed. 

#3: Devonian Period's Two Extinction Events
There were two separate events of extinction in the Devonian; the first being the Kellwasser, in the late middle Devonian, which pushed corals and jawless fish to extinction as well as reducing trilobite species. The second was the Hangeberg, which took place on the Devonian-Carboniferous boundary, was responsible for the extinction of Placoderms and many early ammonite species. The Hangeberg extinction event is believed to have been the result of global cooling due to increased volcanic activity. There is also evidence of eutrophication in the shallow seas. This is where there is an excess of nutrients, usually caused by the run off water from the land, this causes algal blooms. These blooms are disastrous for marine life as it prevents sunlight from penetrating the water, thus there is no replenishment of the oxygen that the algae removes from the water, which in turn kills the marine life that depend on the oxygen rich waters. The result of this is the coral reefs not making a return for another 100 million years.
Marine Families Lost: 22%
Genera Lost: 57%
Species Lost: Approximately 83% 

#2: End Ordovician Extinction
Taking place between 445 and 440 Ma, it is believed that an intense global ice age was the trigger for the event. As the supercontinent of Gondwana moved further South to take it's place over the South Pole, vast glaciers spawned gradually lowering global temperatures and therefore causing a fall in sea levels. It is believed that the sea levels fell by between 70 and 100 metres. 
Marine Families Lost: 26%
Genera Lost: 60%
Species Lost: 85%

#1: End Permian Extinction
The largest extinction event in Earth's history took place at the end of the Permian period and the end of the Palaeozoic Era around 252 Ma. Also known as the "Great Dying", the causes are unknown for certain, however, we already know that Pangaea was incredibly hot and dry which would push a great many of species to the brink. But we also see a spike in greenhouse gases such as Carbon Dioxide and Methane that would have been released from frozen stores in the oceans. Combined with one of the biggest volcanic eruptions ever and we can start to see why so many species were lost at the close of the Permian. 97% of all species that were present on Earth in the Permian were wiped out 252 Ma, all life that followed, the majesty of the dinosaurs, the radiation of mammals and eventually the success of Homo sapiens can all be traced back to the 3% of species that clung to survival at the end of the Palaeozoic Era.
Marine Families Lost: 51%
Genera Lost: 82%
Species Lost: 97%

I hope you find this helpful and interesting, let me know what you think in the comments.

Palaeoart: Dakotaraptor Hunt

Seeing as I haven't got as much done today as I would have liked I found a nice piece of artwork to have a look at. This one comes from an artist I haven't come across before, this is a depiction of the dromaeosaur, Dakotaraptor with an unknown ornithomimid in it's cluthces and is created by Emily Willoughby.

Let's start with the art itself. The textures of the feathers on these dinosaurs are beautiful, you really get the feeling that these are bird ancestors. I think we can agree that this is an incredibly accurate representation of this dinosaur, I really am impressed. 

I did a little research on the artist. Emily Willoughby is a bird photographer and palaeoartist, looking at her work it is evident that she has a talent for blending her knowledge of modern ornithology with the prehistoric animals that she resurrects in her art. 

In my opinion, this is the way that artists should look at theropods and ornithopods, by looking at the decedents; the birds. By studying modern birds; their plumage, their posture and behaviour, we can start to understand the way that dinosaurs may have looked and behaved. 

In this piece we can see direct parallels with modern birds. For instance the posture. If we look at the way the head of the Dakotaraptor is being held its very similar to eagles and vultures of today, the neck is also S-Shaped. The forearms are held more like wings than forearms of many bipedal dinosaurs. The artist here has made these arms look more like wings with the long feathers similar to those that enable flight. The hind legs are grasping the ornithomimid, again, much like birds of prey in the present day. 

Just a fantastic piece, I highly recommend that you take a look at her other work, I'll leave a link to her website below. Just a brilliant representation of the theropod dinosaurs. What do you think of this, let me know in the comments below. 

emilywilloughby.com

The Devonian Period

An artist's impression of the Devonian landscape. Image credit:
Karen Carr

The Devonian period began 416 Ma and came to a close around 358 Ma. It is commonly referred to as the Age of Fishes, despite plants and insects taking great leaps forward in evolution. 

In the Devonian, Gondwana had begun its drift into lower latitudes, set on a collision course with Euramerica. By the end of the Permian these two continents will collide and form the supercontinent Pangaea. The Caledonian Orogeny was continuing in Euramerica, however, the mountains were being rapidly eroded, this caused vast deposition in shallow ocean basins. The climate was also warming up and so the planet was quite dry. 

Because of the continuation of the formation of shallow sea environments, extensive reef building could be found on the perimeter of the continents, the reefs were continuing to thrive from the Silurian Period. 

The Placoderms that first appeared in the Silurian grew to great lengths, up to 10 metres. This made them the top predators of the oceans. The most famous of which is

Skull of Dunkleosteus. Note the bony extensions at the
front of the mouth, these are not teeth. Image credit:
cmnh.org

Dunkleosteus, this fish did not have crushing teeth instead these were extensions of bone from the armour on the animal's head. The trilobites and brachiopods were joined by the coiled molluscs; these were the first ammonites. By the close of the period we also see the emergence of sharks and rays that diversified from cartilaginous fish. 

Fish also underwent massive evolutionary success. Here ray finned fish (Actinopterygii) and lobe finned fish (Sarcopterygii) had evolved. These fish had evolved true bones, teeth, swim bladders and gills. Actinopterygii have fins supported by thin bones whereas the Sarcopterygii fins were fleshy and had phalanges that were joined to an ulna and a radius on the pectoral fin and a fibula and tibia on the pelvic fins. These two bones where then joined to a humerus on the pectoral fin and a femur on the pelvic fin. You'll notice that these are the same bones that we have in our limbs. This is because Sarcopterygii fish are widely accepted as the common ancestor for all tetrapods. But despite being the more numerous in the Devonian, the Sarcopterygii widely died out, except for the Coelacanth and lungfish that still exist today. 

Plants had taken hold of the land in the Devonian. Ferns, lycophytes and horsetails had evolved from the primitive plants of the Silurian. Plants were evolving incredibly quickly, their size and lifestyle was changing completely. A good example of this is

Artist's impression of Archaeopteris. Note
that the leaves are not true leaves they are
in fact fern-like in appearance. Image credit:
go2add.com

Archaeopteris which grew to a massive 30 metres with a 3 foot diameter. From the fossils of this plant we can see that it shed its fern like branches, a change in lifestyle from the primitive Cooksonia of the Silurian. Archaeopteris was the first deciduous tree. The expansion of greenery across the landscape meant that Carbon dioxide levels fell and Oxygen soared, this was a key characteristic of the following period the Carboniferous. 

The earliest true insect appeared in the Devonian, Rhyniella praecusor was a flightless hexapod that evolved between 412 and 391 Ma. Tetrapods also began to crawl out of the water, the first tetrapods are more closely related to amphibians. Tiktaalik rosae is believed to be the link between the Sarcopterygii and the Tetrapods. This animal was mostly aquatic but had powerful hind limbs that were jointed to a fish-like pelvis. This enabled the animal to propel itself while out of the aquatic environment. It was also able to breathe air through nostrils, an adaptation not previously seen in animals. 

The Devonian period was one of the big five extinctions in geological history (I will cover the big five extinctions in a separate post tomorrow). It is hypothesised that this extinction was two prolonged events rather than a single instantaneous eradication of species. Firstly, the Keilwasser Event which took place in the late middle Devonian. This is where great amounts of corals, the jawless fish went extinct, whilst the number of trilobite species were dramatically reduced. The second event, the Hangeberg Event, took place on the Devonian-Carboniferous boundary. Here the Placoderms and many species of early ammonite were pushed to extinction. Despite 70% of invertebrate life going extinct, vertebrates and plants were relatively untouched by these two events. The extinctions are believed to have been caused by global cooling and the first forest fires caused by Carbon dioxide depletion.  

Palaeoart: Super Croc Ambush Part 2

Further to what I said in the previous post about crocodiles generally being subdued by the dinosaurs. In North America at the end of the Cretaceous period we find another leviathan; Deinosuchus. Here it is depicted, again by the incredibly talented Raul Martin, launching what can only be described as a surprise attack on an unsuspecting Albertosaurus. This shows once again that perhaps dinosaurs were destined for their downfall before Mother Nature took control of their fate. Was evolution kicking other groups of animals into overdrive in order to combat the dinosaurs' reign.

Let me know what you think in the comments section below, it would be interesting to see what you think.

Paleoart: Super Croc Ambush

Raul Martin is a well known paleoartist, creating some true masterpieces over the years, I've chosen this one because it shows two key concepts that I will discuss on this post.

This scene depicts a confrontation between two African giants. Two different animals sharing the same lifestyle. The first concept I like about this is the fact that dinosaurs, even large predators such as Suchomimus tenerensis, are threatened by crocodiles that elsewhere is the world are subdued by the dinosaurs, with the exception of Deinosuchus at the end of the Cretaceous period. As the spinosaur is believed to have primarily fed on fish these two massive predators would have come in to regular contact, making confrontations frequent. Sarcosuchus imperator would have posed a genuine threat to even the biggest of African dinosaurs, with the stealth of modern crocodiles and massive, powerful jaws, the odds of surviving would be very little. This shows that in some places around the world, the dinosaurs did not have absolute rule over their territory.

Secondly, we are seeing an ecological struggle. Suchomimus has evolved to feed on fish, a niche that few other theropod dinosaurs had filled. However, this created competition with the aquatic predators such as Sarcosuchus. So despite escaping competition with other dinosaurs, Suchomimus is no better off as the super croc has grown to titanic proportions in order to reign supreme over the waterways of Africa.

To summarise, the most important thing to take from this is that the dinosaurs were not always at the top of the food chain and that even the largest most specialised theropods could become prey.

The Difference Between...Bivalves and Brachiopods

Diagram of Bivalve morphology. Image credit: keyword-suggestions.com

This is a group of fossils that I struggled to get to grips with initially, but hopefully this will make it easier to identify which one you have.

Both bivalves and brachiopods are very similar at first glance. They both have calcium carbonate, hinged shells that are opened and closed by muscles and ligaments in order to get oxygen and nutrients. They both have relatively sessile lifestyles

Diagram of Brachiopod morphology. Image credit 

and are extensive throughout the fossil record. However, these two organisms belong to different phyla. Brachiopods have their own phyla; the Brachiopoda, and bivalves belong to the phyla Mollusca.

There are many noticeable differences between the two, once highlighted it is clear that they belong in different phyla. I will go through the differences that will aid in identifying the fossil of either a bivalve or a brachiopod.

First, there is size. Bivalves can be much larger than brachiopods, growing anywhere between 1 millimetre and 1 metre, the largest being the Giant Clam. Brachiopods on the other hand only grow between 2 centimetres and 10 centimetres. I your shell is considerably larger than 10 centimetres, chances are you have a bivalve. There are more ways to increase your certainty.

Symmetry is one of the best ways to tell the difference between bivalves and brachiopods. Bivalves have a line of symmetry that runs along a plane between the two valves, meaning that they have symmetrical valves. BrachiopodsGryphaea arcuata which only has one valve, these are often called Devil's Toenails.

An example of a brachiopod from my own collection note
the larger pedicle valve overreaching the brachial valve.
Genus is Terebratula

are bilaterally symmetrical, from umbo to anterior edge of the pedicle valve. Thus if your specimen is complete and one valve is larger than the other you have a bivalve. An exeption to this is

If observing these animals in life it may be useful to know that the right and left valves are hinged by a ligament on the dorsal surface in bivalves. In brachiopods, the pedicle valve, the ventral valve, is larger and projects beyond the brachial valve, the dorsal valve. This is to allow the pedicle to emerge from the pedicle opening and anchor the brachiopod to a substrate at the posterior. The bivalves also have a foot that is released through the posterior by opening the valves.

I hope you find this useful when identifying bivalves and brachiopods, this works for extant species as well as extinct ones.

The Silurian Period

The Silurian period stretches from 443.4 to 419.2 Ma, it is a relatively short period.

Map of the Palaeo continents during the middle Silurian.
Note the continents on the equator are Laurentia,
Baltica and Avalonia colliding during the Caledonian
Orogeny. Image credit: silurian.stratigraphy.org

But despite it's length this was a time of great biological advances.

During this time Gondwana had continued to drift south and covered much of the southern latitudes. The northern hemisphere was mostly ocean with the exception of two continents, Laurentia and Baltica, during the dawn of the Silurian. As the period passed, Gondwana rifted further, the continent of Avalonia separated and drifted North. The middle Silurian is characterised by mountain building, known as the Caledonian Orogeny. This was when Avalonia, Baltica and Laurentia collided near the Equator. This collision formed the Irish and Welsh Mountains as well as the Grampians, Northern Appalachians and the Norweigian and Swedish Mountain ranges.

The land masses were still at a low altitude and the sea levels remained high. Shallow sea continued to provide new habitats for an evolving fauna. Light had the ability to penetrate the water in the shallow sea environment. The evidence provided for this comes from the great amount of coral reef fossils that we find in the Silurian sediments.

In the early Silurian, the jawless fish discussed in the Ordovician post still dominated. However, as the middle of the period arrived so did the jawed fish. Placoderms, named Romundina, had evolved. Placoderms are armoured fish with cartilaginous skeletons. The evolution of a jaw enabled these fish to become refined hunters in the Silurian waters.

However, fish were still in their infancy. The Eurypterids were the top predators during the Silurian. The sea scorpions had become larger and more common, developing a spiked tail which allowed for the injection of venom into prey.

The climate was also beginning to stabilise after the extensive glaciation during the Ordovician. It is believed that Lichens were the first photosynthetic organisms to move onto land. This would be a logical assumption because the first plants to colonise the land would have needed a softer soil to flourish. Decaying Lichens produced acids that broke down rock into soils. This paved the way for the primitive plant Cooksonia to take control of the banks of deltas and rivers. Cooksonia was the first upright plant to evolve. Cooksonia show it had bulbous tips. This suggests it may not have been photosynthetic due to the lack of leaves, but it is theorised that spores could have been ejected from the stalks. Despite the lack of leaves, this pioneering plant was the first to have vascular tissues.

The fossil of Cooksonia sp. alongside an artist's impression
of the plant. Image credit: tes.com

This revolutionised growth in plants, by growing vertically rather than laterally, plants could start competing better for sunlight with each other as well as the mosses and algae. The fossil of Cooksonia show it had bulbous tips. This suggests it may not have been photosynthetic due to the lack of leaves, but it is theorised that spores could have been ejected from the stalks. Despite the lack of leaves, this pioneering plant was the first to have vascular tissues. 

We also see further diversification of brachiopods, molluscs, crinoids and trilobites. Graptolites, an animal that puzzles palaeontologists on what they may have looked like when alive, are one of the more common fossils of the Silurian, for this reason they are used to date the Silurian strata. This is because they change their morphology so frequently, like ammonites during the Mesozoic. 

Graptolite fossils. Image credit: geology.gsapubs.org

Animals also began to take their first steps onto land by the mid Silurian. Pseumodesmus, a genus of ancient millipede was among the first animals to venture onto land. The predatory arachnids and myriapods that occupied the land are the very start of the terrestrial food web, being the top predators. They may have fed on undiscovered detritivores and mircoscopic grazers, this was a hypothesis that was put forward by Andrew Jeram et al in 1990.

To summise, the Silurian saw a terrestrial revolution as plant and animal both made their first tentative steps onto the barren wastelands. While these organisms battled the elements above the waves, in the oceans life continued to thrive because of shallow sea habitats and a stable climate.

Palaeoart: North Africa in the Cretaceous

Today, I have chosen artwork from Mohamad Haghani. A depiction of North Africa in the late Cretaceous featuring two of the world's largest predators.

I like this piece because we are seeing two different lifestyles of Cretaceous predatory dinosaurs. The two Carcharodontosaurus' are shown feeding on an Ornithopod, whilst Spinosaurus is in the river catching the giant sawfish, Onchopristis. Spinosaur dinosaurs are generally regarded as ichthyophagous now due to their crocodilian features, thus it would be rare, but not impossible, to find Spinosaurus hunting large prey when fish is plentiful as this was the prey they were best adapted to hunting. However, having said this there is evidence for other members of the Spinosaur family hunting prey other than fish, an Irritator was found in a pterosaur vertebrate, whilst evidence of Baryonyx eating Iguanodon has been found in England. Carcharodontosaurus on the other hand has very large blade like teeth that are perfect for cutting through flesh. Studies revealed that the skull of Carcharodontosaurus could not withstand a great deal of strain, and therefore not wrestle large prey to the ground, the dinosaur would thus have to rely on dealing a devastating wound and simply wait for the animal to die of shock and blood loss.

Although this is a very nice piece of art, I do have some problems with it. Before I get to that I understand that this art is now getting old and that our theories on dinosaurs are changing rapidly, so these are not faults per say but just areas that I want to highlight. Firstly there is the Spinosaur itself. Spinosaurus is the world's first semi aquatic dinosaur, being adapted for a life in the water and not stalking the African plains in search of food as previously thought. We now also know that the animal was quadrupedal not bipedal as shown above. But this was of course discovered after the creation of the art. Also these two giants would not come into close contact very often. Spinosaurus was best suited to the swampy deltas, whereas Carcharodontosaurus was adapted to actively hunting. Both animals would need a massive territory to sate their apetites. It was only in times of hardship, for instance drought, that the two would be in direct competition with each other for food.

But I respect the artist's decision to put the dinosaurs in the same location, it highlights that despite being the top predators and two of the largest carnivorous dinosaurs to walk the Earth, they had very different lifestyles. Spinosaurus being water based, relying on swarms of fish to hunt and Carcharodontosaurus depending on herds of herbivorous dinosaurs to feed. That, I think, is probably the most interesting thing about this artwork despite being inaccurate.

The Difference Between...Rugose, Tabulate and Scleractinian corals

This is going to be a series of posts that look at fossils that are either difficult to

Rugose coral. Image credit: paleo.cortland.edu

differentiate or can be easily confused.

This post will look at three types of corals; rugose, tabulate and scleractinian.

First of all, there is the geological context of these corals, in partcular what age the sediments will be that you find them in. Rugose corals are found in Ordovician to Permian sediments, being wiped out at the Permian extinction. Tabulate corals also have the same range, so this would not be useful if you were trying to differentiate the two using geology. However, scleractinian corals have a younger range, from the Triassic to recent times. giving a feature to differentiate this coral from the other two.

Tabulate coral. Image credit: fossillady.wordpress.com

Scleractinian coral. Image credit: hoopermuseum.earthsci.carleton.ca

When trying to identify if your coral is tabulate or not, look at whether or not your fossil is colonial or solitary. Tabulate fossils are almost exclusively colonial. It's difficult to differentiate Scleractinian and Rugose fossils this way as both have colonial and solitary species.

Scleractinian and Rugose corals both also have well developed septa, so this cannot be used to tell the difference. But again, tabulate corals have weak or absent septa. The tabulae can be used to identify Scleractinians easily as they are usually absent in these corals. They are well developed in tabulate and most rugose possess tabulae.

Symmetry is useful for differentiating Rugose corals from tabulate and scleractinians. The symmetry in rugose is bilateral, meaning that two identical halves can be created, humans are bilaterally symmetrical. However, tabulates and scleractinians have radial symmetry.

Scleractinian skeletons are made from aragonite which is unstable in fossilisation, whereas the tabulate and rugose corals have calcite skeletons.

Summary:
Rugose: Ordovician to Permian. Well developed septa. Bilaterally symmetrical. Colonial and solitary. Most possess tabulae. Calcite skeleton.

Tabulate: Ordovician to Permian. Weak or absent septa. Radial symmetry. Always colonial. Well developed tabulae. Calcite skeleton.

Scleractinian: Triassic to Recent. Well developed septa. Radial symmetry. Colonial and solitary. Absent tabulae. Aragonite skeleton.

Did you find this helpful? Let me know what you think in the comments.

The Ordovician Period

The Ordovician is the second geological time period of the Palaeozoic era, spanning from 485.4 to 443.4 Ma. The Ordovician is named after the Celtic tribe the Ordovices. This period was the stage for a number of revolutions in the world's flora and fauna.

Ordovician oceanscape. Image credit: dustdevil on DeviantArt

For most of the Ordovician, the climate was warm and wet. This caused the sea levels to rise 600 metres above todays levels, this created new habitats such as inland seas and freshwater areas.

The fauna still dominated the planet's oceans. After the Cambrian extinction, coiled cephalopods, called a Nautilus, exploited the empty niche and became successful and effective predators. A straight cephalopod also evolved to become one of the larger predators of it's time, this was the Orthocone. Trilobites and cnidarians also continued to thrive.

Fossil fish became more abundant in the Ordovician. The jawless mouths of these fish are found positioned on the ventral surface of the head. This suggests that they sucked up their food from the sea floor rather than being active and swift predators. We also find the early evolution of armour plating in fish in the Ordovician, the fish depicted above have bony armour plates on their heads. These fish are the ancestors of lampreys and hagfish that we have today.

Crinoids also find their origins in the Ordovician. They pinnules filtered the Ordovician waters for plankton. To read more about Ordovician crinoids, see my post 'My Collection #1' where I discuss a crinoid fossil that I have.

Life also began to make advances on land as well. Hard bodied arthropods; Eurypterids, also known as sea scorpions. could survive on land for short periods of time. This was due to the ability to diffuse gases across their exoskeleton. The living fossil Horseshoe crabs are also believed to have ventured onto land to spawn as they still do today.

Horseshoe crabs spawning, scenes like this would have
been common during the Ordovician. Image credit:
capeandislands.org

The very first terrestrial plants are seen in the Ordovician. They likely evolved from green algae. They appeared as tiny non vascular plants, that resemble Liverworts. Evidence for these plants comes from not only their fossils, but the fossils of their spores that have been identified in Upper Ordovician sediments. This shows that the plants were immediately exploiting the land, using reproductive methods that allowed for rapid expansion across the barren landscape.

The Ordovician was closed with the second largest mass extinction in the Earth's history. It is believed that this event took place between 447 and 444 Ma.

Chronostratigraphical Timescale of the
Ordovician. Image credit:
keyword-suggestions.com

A massive 49% of marine fauna was pushed to extinction, while other phyla saw individual numbers fall dramatically. This is commonly attributed to an ice age. Research by Page et al states that temperate climates did not return until the end of the Silurian. The ice age's trigger is disputed, the more popular hypothesis is that as Gondwana drifted over the South Pole, ice caps formed over where Africa would have been location on the supercontinent. This locked up vast amounts of the Earth's water, sea levels consequently dropped, destroying shallow sea habitats. The falling temperatures also pushed tropical species to extinction. An alternative hypothesis that was put forward by Melott et al in 2004 suggested that a gamma ray burst of a mere 10 seconds destoryed the ozone layer. This exposed the life on Earth to great amounts of radiation. This radiation is believed to have triggered a sharp fall in global temperatures, trigging an ice age.

Palaeoart: Brachylophosaurus in the river

I wanted to highlight this piece of artwork by Julius C. Csotonyl because of its palaeontological importance and the reason for its creation.

This piece shows a dead hadrosaur, Brachylophosaurus canadensis, on a sand bank in a turbulent river. Not only is the artwork beautifully executed with real force coming through in the torrents of the river, but this was actually created because of an important discovery. Numerous mummified brachylophosaurs have been discovered, the best preserved, named Leonardo, exhibits remnants of a ceratinous beak, skin impressions showing a scaly covering. Also an interesting adaptation of extra thick muscle around the neck, possibly to make it more difficult for predators to make a kill. We can also see that the animals were dominated by parasitic worms because of this specimen. The mummy is on display in the Children's Museum of Indianapolis. 

The best way that a mummy like this could have been created is if the carcass of the dinosaur was left untouched and then rapidly covered with sediment. This would explain why the skin impressions survived the process of fossilisation. This environment for preservation is best provided by a river, preferably a powerful one, as depicted above. 

This piece is therefore interesting to me because it shows a key study in palaeontology; taphonomy. Taphonomy is the study of what happens to an animal between death and discovery, so basically looks at the mechanisms of fossilisation. 

What do you guys think? Is this interesting piece to see or is there another artwork that you find even more fascinating? Let me know in the comments.

My Collection #1

So in this feature I want to share the fossils and rock that I have in my collection, give you a little information about each piece. Hope you enjoy reading it.

I thought a good place to start was with the first fossils that I received as a present, and the first fossils I owned. There is a range of fossils in this box ranging from the Ordovician to the Eocene.

Scyphocrinites elegans stems.

Artist's impression of Scyphocrinites elegans
with loboliths. Image credit: Terry McKee

Firstly is a piece that features numerous crinoid stems. There are approximately 625 species of crinoid, both extinct and extant. Crinoid origins officially date back to the Ordovician, however there is one species known from the Cambrian Burgess Shale, Echmatocrinus, but it is unclear as to whether this fossil is a crinoid or an octocoral. Crinoids are typically found attached to a substrate on the sea floor, there are some exceptions as some species anchor themselves to driftwood and reside at the surface. These simple organisms are filter feeders, they use tiny structures called pinnules that line the brachials to catch tiny plankton, this is where the colloquial name of 'sea lillies' comes from as the brachials make them look like flowers, despite being a member of the echinodermata. Crinoids have also been known to create 'forests', with individuals of varying heights. This particular species has a geological range between 416.0 to 412.3 Ma, placing this fossil in the opening of the Devonian period. It had a structure called a lobolith instead of a holdfast, this was a flotation device meaning that these crinoids floated on the surface, as shown in the artist's impression, the brachials can then been seen hanging in the water at the end of the stem, the stems are what is preserved in this fossil. This specimen comes from Erfoud, Morocco.

Orthoceras sp. in Moroccan Limestone.

Orthoceras sp. on Devonian limestone, from Cumberland House
Museum, Portsmouth

Orthoceras is a genus of straight cephalopod with a geological range between 471.8 to 205.6 Ma (Early Ordovician to Late Triassic). These fossils, like the one above, are commonly found in marine limestones. In rare occasions Orthoceras can be found in monospecific assemblages, previously theorised to be mass deaths after mating rituals, it is now, after sedimentological and taphonomical studies, widely accepted that the shells were deposited over time rather than during a single event. The assemblages are more common throughout the Ordovician until the early Devonian. Orthoceras did not grow to massive sizes like other straight cephalopods, reaching about 6 inches in length. This fossil is often confused with the Cretaceous ammonoid, Baculites. A key difference that helps to identify each fossil is that the Baculites exhibits the complex ammonitic sutures whereas Orthoceras has a simple suture. Some specimens have a medial line between the anterior and the posterior of the shell. This is called the siphuncle, a tissue that allows for the disposal of water from the formation of new chambers as the shell grows. This is done through osmosis. It also allows for a change in density, taking in more water to sink, and releasing water to become more buoyant. The two Orthoceras fossils are from Erfoud, Morocco dating back to around 400 Ma in the Early Devonian. The fossil pictured right is from the Cumberland House Museum in Portsmouth, definitely worth a visit if you're in the area.

Goniatites sp. from the Moroccan limestone

Goniatite fossil with sutures. Image credit: educationalfossils.com

Goniatites are ammonoid cephalopods that occupied the oceans of our planet between the early Devonian, 391.9 Ma, to the Permian extinction 251.4 Ma. These cephalopods are morphologically similar to ammonites in the sense that they have a series of gas filled chambers to allow for buoyancy and a single living chamber. A major difference between the two shelled creatures is their suture patterns, the ammonite suture is incredibly complex, the suture of the Goniatite is quite simple, more of a zig-zag. It is clearer to see on the image on the left. There is little to no evidence to how this animal lived, nor is there evidence of a calcified jaw, similar to the ammonite, which eliminates shellfish as a food source. The fossil pictured above is again from Erfoud, Morocco, dating back to the late Devonian, 360 Ma.

Heliophora orbiculus

This interesting fossil is known as a sand dollar. These are highly modified sea urchins that reside on sandy sea floors. These sea urchins are found mostly in shallow tropical waters and temperate seas. With a geological range of 9 Ma to recent times. The odd outline of the outer edge of the echinoid that you can see in the photograph has no official explanation to its use in life. Some hypotheses suggest that they aided feeding, while others state they allow the creature to anchor itself in the sand to prevent the current from carrying it away. This particular specimen comes from Morocco and dates back to the early Pleistocene 2 Ma.

Terebratula sp.

This is an example of an epifaunal brachiopod, epifaunal meaning that it lives on the surface of the sea floor. This genus of brachiopod is a suspension feeder, like the crinoids they feed on plankton and other microscopic organisms. The hole that you see in the larger valve of the photograph above is known as the pedicle opening. This is where the pedicle emerges to attach the brachiopod to a substrate. It is common that bivalves and brachiopods get mixed up as they are similar at first glance. However, for the most part bivalves are symmetrical, with the exception of Gryphaea. Brachiopods have one valve larger or a different shape to the other. Also bivalves don't have a pedicle opening as their pedicle comes from between the valves to feed. This species of brachiopod first evolved approximately 268 Ma in the late Permian surviving until 0.781 Ma in the Pleistocene. This particular specimen dates back to around 120 Ma in the early Cretaceous, it was then discovered in Agadir, Morocco. 

Flexicalymene ouzregi

This small trilobite dates back to around 450 Ma in the late Ordovician, it is named after the location of it's discovery, Ikhf-n-Ouzreg, Morocco. The geological range of this species of trilobite is from the middle Ordovician, 463.5 Ma, to the late Silurian, 426 Ma. It is common to find this species of trilobite enrolled, this is hypothesised to have been a defense mechanism. This was more likely to be due to an external stimulus, possibly a predator or environmental hazard. The cephalon (head) of this specimen is better preserved than the more damaged pygidium (posterior). The eyes are visible, however it is not possible to determine whether they are holochroal or schizochroal. For an explanation on holochroal and schizochroal take a look at my post on the Cambrian period. 

Trinucleus fimbriatus

Another species of trilobite and also my oldest specimen in my collection, this is the cephalon of a 460 My old trilobite from Llanfar, Wales, UK. A geological range of between 466 to 455.8 Ma places the trilobite in the middle to late Ordovician. This species lacks the typical compound eyes that most trilobites exhibit. Instead there are small pits lining the outer edge of the cephalon, it is believed that these are sensory pits that could detect movement in the water, helping to hunt and evade predators. This is a likely use for the pits as the trilobite lived approximately 200 metres beneath the surface of the oceans, light cannot penetrate this far down and so eyes would be useless. 

Toxaster peroni

This is another example of an echinoid. This specimen is from the early Cretaceous, 118 Ma, from Agadir, Morocco. This echinoid survived the Mesozoic world between the early Cretaceous 140.2 Ma to the start of the late Cretaceous 99.7 Ma. This differs from the sand dollar shown earlier in the fact that this is an infaunal echinoid, meaning that it lived within the sediment itself rather than on it. It was also a detritivore rather than a filter feeder. 

Placosmilia sp.

Placosmilia is an example of a scleractinian coral of the phylum cnidaria. Placosmilia originate 167.7 Ma in the middle Jurassic, becoming extinct only 5.332 Ma in the Pliocene. This particular coral is solitary, scleractinian corals are known for being colonial and solitary. These corals build themselves a hard skeleton that is topped with the mouth surrounded by tentacles. This specimen was discovered in Lleida, Spain, and dates back to 80 Ma in the late Cretaceous. 

Otodus obliquus

This tooth is from the top predator of it's time. A genus of extinct Mackerel Shark, Otodus lived between the early Palaeocene, 61.7 Ma, to the middle Miocene 13.65 Ma, this particular specimen comes from 55 Ma, this is the Ypresian stage of the early Eocene. The morphology of this shark is unknown because, as with most other sharks, the skeleton is composed primarily of cartilage which doesn't fossilise, therefore very few skeletal structures are known of this genus. The largest tooth however, measured 104mm, and shows signs of the evolution of serrated teeth in sharks. Studies on the vertebral centrum of these sharks put length estimates between 9.1 and 12.2 metres long, meaning this shark dominated the oceans on a global scale during it's reign. 

Three ammonites, the bottom two from Madagascar and the top from Deux Sevres in France.

Ammonite fossil showing complex sutures. Image
credit: fossilmall.com

Ammonites are by far the most common Mesozoic marine fossils that can be found, so common that they are used in relative dating of Mesozoic rocks. Ammonites have a massive geological range between 400 Ma in the Early Devonian to the KT Boundary at the end of the Cretaceous 66 Ma. These coiled cephalopods are related to the Goniatite shown above. Ammonites survived the massive Permian extinction but not the extinction that wiped out the dinosaurs and other reptiles of the Mesozoic. In life the shells of the ammonites would be made of aragonite but this is more unstable than calcite and therefore the shells change their chemical composition to become more stable. The fossils we find are actually casts of where sediment has entered the chambers of the shell and the shell has consequently broken down leaving a cast behind. It is sometimes possible to find the complex ammonitic sutures on the fossils, as shown in the photograph on the right. 

Diplomystus dentatus from Kemmerer, Wyoming, USA

Possibly the most impressive fossil on this post, this is a brilliantly preserved fish in a fossil lagerstätte from 55 Ma, this fossil therefore comes from the early Eocene. This is a genus of freshwater fish that is related to herrings and sardines that swim in our oceans today. The upturned mouth of this specimen and genus as a whole is indicative of a surface feeding fish. It is relatively conclusive that Diplomystus fed on smaller fish called Knightia as the bones of Knightia have been found in the stomach of Diplomystus. The geological range of this fish is very short, from 55.8 to 50.3 Ma, this genus of fish evolved and became extinct in the Eocene. 

So that's it for now, please do share any interesting specimens you have in your collection or just share your thoughts in the comments below.