Paleo Profiles: Pterygotus

A Pterygotus in the National Museum of Scotland

It has been sometime since our last Paleo Profile so I thought we should look at an extinct animal closer to home. Throughout the planet's history the arthropods have been the most diverse type of animal including in their numbers the insects, arachnids, and crustaceans with all their diversity. One interesting order among the arthropods, now long extinct, were the eurypterids, or as they are better known as, sea scorpions. As you can probably tell eurypterids were named thanks to their similarity to scorpions although we now know that they are most closely related to horseshoe crabs; ironically modern scorpions are also more closely related to horseshoe crabs than they are eurypterids. Nevertheless, eurypterids and scorpions were so similar, likely thanks to convergent evolution, that it is not uncommon for them to be mistaken as one another (or their cousins); a giant spider called Mesothelae was depicted in the BBC documentary Walking with Monsters only for them to find out close to the end of production that palaeontologists had made a mistake, Mesothelae was actually a eurypterid called Megarachne. Making matters even more confusing not all sea scorpions lived in the sea, and there are many examples of freshwater eurypterids. Today, we'll be looking at one of the best known eurypterids: Pterygotus. Pterygotus was one of the most common and largest eurypterids being found everywhere. Currently, I attend the University of Edinburgh which has its main campus next to the National Museum of Scotland which contains various Pterygotus fossils - some of the photos on this post today are ones which I took in the museum.

Discovery and Fossils

It is no mistake to say that Pterygotus is a common fossil. We are lucky to have several full specimens of Pterygotus, as well as parts of their bodies including legs, tails, and chelicera (front appendages). They have also been found across the world in four different continents: Europe, Australia, North America and South America. In particular, New York and Scotland have produced some of the richest deposits of Pterygotus fossils. However, when Pterygotus was first discovered the remains were not well preserved so it was believed to be a fish - Pterygotus is Latin for 'Finned One' or 'Winged Animal' depending on the translation. The first Pterygotus, as often with fossils, were not discovered by palaeontologists but by workers in an English quarry. Swiss-American naturalist Louis Agassiz, whom we encountered when we discussed the giant shark megalodon, named the fossil Pterygotus problematicus in 1839. After finding more fossils from the Old Red Sandstone in Scotland Aggasiz realised that Pterygotus was really an arthropod so reclassified it in 1844 - P. problematicus was renamed P. anglicus in 1849 after the discovery of the Eurypterus. Initially both Eurypterus and Pterygotus were believed to be crustaceans, although as more and more fossils were discovered the realisation came that eurypterids were related to, but different from, crustaceans. In 1859 James Hall discovered a new species of Pterygotus from New York - this was important as it was the first Pterygotus to be discovered outside Scotland. Since then New York has become one of the most important places to find Pterygotus fossils. Palaeontologists have continued to find new species across the world from Ukraine to Bolivia to Czechia. 

Biology

A sea scorpion is the best way to describe the overall body shape of a Pterygotus, and most over eurypterids for that matter. Naturally there are several key differences - Pterygotus had more limbs. It had eight 'traditional' legs used for walking along the sea bed, two legs which whose ends were flattened for propulsion, and two very large chelea (claws). These claws were large, some exceeding 30 cm, around 11 inches, in length and were powerful. Pterygotus had a surprisingly small mouth so its claws were designed to crush and tear up prey into smaller pieces to devour.

A Pterygotus claw in the National Museum of Scotland

Like many arthropods Pterygotus was covered in a hard scale-like exoskeleton which they would likely shed as they grew. Tracks from eurypterids have been found in Pennsylvania indicating that eurypterids may have came onto land to shed their skin out of the reach of potential predators. However, as we'll later see this was not an option for Pterygotus. Pterygotus had compound eyes and a 2015 paper by a series of palaeontologists, including Victoria McCoy, used this to determine how they lived. Traditionally, eurypterids in the family pterygotidae were seen as being active hunters with McCoy and others wanting to challenge this interpretation. Their results found that different pterygotids had different hunting styles - Pterygotus had many compounds in its eyes and the way its eyes were angled gave it very good eyesight letting it be an active predator. To help catch their prey Pterygotus had a paddle-like tail. Many arthropods have a division on their posterior called a telson which can vary in size, shape, and purpose - they form the sting of scorpions and tail fans of lobsters as examples. The Pterygotus telson was used as both a rudder and a paddle (as well as the two front appendages) - they helped steer the eurypterid while also giving it a boost in speed. Pterygotus was adapted to a life underwater.

A sketch of the paddle by Henry Woodward

What makes Pterygotus stand out is its size. Arthropods could get very large when Pterygotus swam the seas and Pterygotus showed this. The smallest species, like P. kopaniensis, measured 50 cm (20 inches) in length to put into perspective the size of the largest Pterygotus. The largest grew to over 1.75 metres in length, or 5 foot 7 inches, rivalling the size of an alligator. Edinburgh's National Museum of Scotland has models of P. anglicus which are around the size of a labrador or retriever. Pterygotus was not the largest eurypterid around, Jaekelopterus averaged 2.5 metres, 8.2 feet, in length. However, Pterygotus was likely the top predator in most habitats it happened to inhabit.

When and Where

Pterygotus lived in a time long before the dinosaurs - it lived even before there was life on the land. When they appeared the first jawed fish and land plants had yet to appear. Eurypterids had arrived on the scene during the Ordovician 467 million years ago, (to put it into context one of the first land plants, Cooksonia, evolved around 433 million years ago), and Pterygotus arrived during the Late Silurian - around 428 million years ago. During the Late Silurian the Pterygotus lived in a very warm world - the mean CO2 concentration in the atmosphere was sixteen times that of the atmosphere when humans arrived, and the surface temperature was three degrees Celsius above modern levels. Sea levels were also higher so warm, shallow seas covered large tracts of the Earth - including Scotland and New York. The Pterygotus managed to survive into the Early Devonian - around 391 million years ago - which had similar warm temperatures. Many of the Scottish fossil sites containing Pterygotus fossils actually come from this time period. The temperature was very hot - there may have been no glaciers and the mean surface temperature was double that of the Silurian. Due to these warm temperatures and shallow seas the Pterygotus managed to spread across the world producing around 20 species. Scotland, Wales, New York, Ohio, Ukraine, Prague, Australia, and Bolivia are just some of the regions where they have been discovered, and in each region they adapted to their local environment.

Habitat and Neighbours

A model in the National Museum of Scotland of a Pterygotus in its habitat

With around 20 species the Pterygotus lived in a wide range of habitats as a result. Due to their large size and adaptation to a purely marine life they could afford to not live in shallow water - they could safely mate, breed, and shed their exoskeleton in the ocean. An Australian species has been found to have even lived in particularly deep water instead of the reefs that others have been found in. Pterygotus lived in a diverse habitat alongside other eurypterids, even other species of Pterygotus along the Silurian sites on the Welsh border, molluscs, fish, trilobites, cephalopods, and the first ammonites and sharks. During the Devonian 'armoured' fish evolved, perhaps as a defence against the claws of eurypterids, and McCoy found that Jaekelopterus had managed to puncture the armour of these fish, so it is likely that Pterygotus could have as well. As a side note Jaekelopterus was once thought to be a species of Pterygotus. Warm waters with ample prey allowed Pterygotus to be a widespread and common animal. Why then did it go extinct? Palaeontologists are not entirely sure - for many extinct animals we cannot pinpoint why (and sometimes when) they went extinct. With Pterygotus we have a few ideas. One possible reason is climate change. By the mid-Devonian the first forests had managed to evolve which reduced the planet's CO2 levels, and with it, reducing global temperatures. Habitats are dependent on climates remaining the same so even the slightest changes can have drastic consequences - we can see this playing out right now with the extreme weather of the last decade thanks to human caused climate change. There are other theories, and possible contributions, about the extinction. The Devonian has been nicknamed the 'Age of Fishes' thanks to the explosion of fish diversity. Armoured fish and the first sharks emerged offering fast-swimming rivals, and also rivals who could bite back. Possibly, large, jawed fish and climate change led to the extinction of Pterygotus. The eurypterids lived on. Unlike the armoured fish they managed to survive the Devonian extinction between 376 and 360 million years ago (although just barely). It took until the planet's worst mass extinction marking the end of the Permain around 251 million years ago for the eurypterids to finally vanish.

Thank you for reading. For other Paleo Profiles we have a list. The sources I have used are as follows:

-'Pterygotus', Prehistoric-Wildlife.com, [Accessed 30/11/2018]

-Erik N. Kjellesvig-Waering, 'A Synopsis of the Family Pterygotide Clarke and Ruedemann, 1912 (Eurypterida)', Journal of Palaeontology, 38:2, (1964), 331-361

-Derek Briggs and W.D. Ian Rolfe, 'A Giant Arthropod Trackway from the Lower Mississippian of Pennsylvania', Journal of Palaeontology, 57:2, (1983), 377-390

-Simon Braddy, 'Eurypterids from the Early Devonian of the Midland Valley of Scotland', Scottish Journal of Geology, 36, (2000), 115-121

-Victoria E. McCoy, James C. Lamsdell, Markus Poschmann, Ross P. Anderson, and Derek E. G. Briggs, 'All the better to see you with: eyes and claws reveal the evolution of divergent ecological roles in giant pterygotid eurypterids', Biology Letters, 11:8, (2015)

-Randall Miller, 'Pterygotus anglicus: Agassiz (Chelicerata: Euryptida) From Atholville, Lower Devonian Campbellton Formation, New Brunswick, Canada', Palaeontology, 50:4, (2007), 981-999

-W.J. Salter, 'Description of Pterygotus problematicus, Agass', Quarterly Journal of the Geological Society, 8:1-2, (1852), 386-388

-Trey the Explainer, 'Paleo Profiles - Sea Scorpions', Youtube, 13/09/2016, [Accessed 30/11/2018]

Thank you for reading and I hope you found it interesting. Paleo Profiles is an interest of mine instead of a field of expertise so if I got anything wrong, or missed something out, please feel free to mention it. For future blog updates please see our Facebook or catch me on Twitter @LewisTwiby.

Paleo Profiles: Muttaburrasaurus

A Muttaburrasaurus from Queensland Museum

Australia is not well known for its dinosaurs. When one thinks of palaeontology and Australia we normally think of the megafauna which went extinct within the last ten thousand years. However, Australia has a plethora of dinosaurs from largely the Cretaceous period which shows the variety of dinosaurs which once roamed the world. We'll look at one of them today: Muttaburrasaurus. The Muttaburrasaurus was a herbivorous dinosaur which would have remained very obscure if not for the famous BBC documentary from 1999 Walking with Dinosaurs. 

Discovery and Fossils

Naturally Muttaburra is proud of its famous local

Muttaburrasaurus was discovered in 1963 just outside the town of Muttaburra in Queensland by a grazier (sheep/cattle farmer) called Doug Langdon. It is rare that a dinosaur skeleton has most of the bones through various reasons regarding preservation so it was a surprise that one would be found by accident in Australia. Due to this word spread fast that a dinosaur had been discovered so locals wanting a souvenir went out to take pieces of the fossil. As a result it took until 1981, and a general amnesty for those who took the bones, for the dinosaur to be formally described. This dinosaur was well preserved with it having a nearly complete skull, vertebrae, parts of the pelvis, and parts of the limbs. This doesn't sound well preserved but it is extremely rare to find this amount of bones belonging to one dinosaur - the weather, scavengers and soil can prevent fossilisation never mind leaving it for millions of years. Taking almost twenty years to be described in 1981 Alan Bartholomai and Ralph Molnar would name this dinosaur Muttaburrasaurus langdoni - Muttaburrasaurus with it coming from Muttaburra and langdoni after its discoverer. Since then several other skeletons, or parts of it, have been discovered making it one of the best known dinosaurs from Australia. Most happen to be teeth from Queensland and northern New South Wales and in 1987 a possible second skull, called the 'Dunluce Skull', was found by a fourteen-year old in Queensland. However, to this day the skull offers confusion about what it means as it resembles the first skull, but it also has some differences. The Dunluce Skull is slightly older than the Muttaburra one possibly indicating that as the dinosaur got older the crest on the skull changed; another theory suggests that one could be male and the other female; and a final theory, suggested by Molnar, that it could be a different species of Muttaburrasaurus. Muttaburrasaurus is the genus, not the species. If it turns out that the two skulls are from different species then it would be similar to a difference between a wild horse and a zebra.

Biology

A Muttuburrasaurus in Queensland Museum

What type of dinosaur was Muttaburrasaurus? First off Muttaburrasaurus was in the group Ornithopoda which was an incredibly diverse group of herbivorous dinosaurs which included the Camptosaurids and the very famous duck-billed dinosaurs, or Hadrosaurs like Parasaurolophus. Originally Muttaburrasaurus was assigned into a family called Iguanadontidae which was named after the second dinosaur to ever be described, Iguanodon. As a result Muttaburrasaurus was often recreated to resemble Iguanodon including giving it a thumb spike similar to Iguanodon - these spikes have never been found so they were eventually taken out of reconstructions. However, it was debated and a 2010 paper determined that Muttaburrasaurus was in fact part of a family closely related to iguanodontids called Rhabdodontids. Ornithopods shared several key biological similarities with many being both bipedal and quadrupedal. The forelimb of the Muttaburrasaurus has hands perfect for supporting weight indicating that it would spend large amounts of times on all fours, and the structure of the pelvis adds to this. Similar to Iguanodon it had a long tail held stiff by strong tendons to act as a counterbalance essential for bipedalism. However, this was noted when it was believed that Muttaburrasaurus was an iguanodontid; Iguanodon was capable of bipedalism and quadrupedalism. The Rhabdodontids were more quadrupedal than bipedal, with some incapable of bipedalism, so Muttaburrasaurus was likely more bipedal than quadrupedal. We also have a question of was it warm-blooded and did it have feathers? The debate about both is skill going on. In 2014 a paper by John Grady and other palaeontologists suggested that non-avian dinosaurs were mesothermic - neither warm or cold-blooded. The debate still rages on, however, and at times gears more towards mesothermy while at other times endothermy. Protofeathers have been discovered on primitive Ornithiscians, (the order containing Ornithopods and other groups including stegosaurids and ceratopsians like Triceratops), called Tianyulang and Kulindadromeus. These were not feathers as you see on a modern bird but more like filaments and fuzz. As a result, more and more palaeontologists are believing that all dinosaurs could have some level of filaments mixed with scales. If you find this hard to believe remember that elephants, rhinos and whales all have hair. We can imagine that Muttaburrasaurus may also have had some form of filaments on its body.

The Muttaburrasaurus with its unique crest

Muttaburrasaurus was a medium sized herbivore reaching around 7 metres, or just under 23 foot, in length and being about 2 metres, or six and a half feet, tall. The most interesting thing about Muttaburrasaurus is its skull. Rising from the front of the snout is a large, hollow nasal crest. One theory has it that it was a large cavity for smell; something useful to smell out potential predators. However, the more recognised theory, and the one shown in Walking with Dinosaurs, that this crest acted as a resonating chamber allowing it to make various unique calls that can be heard over a wide area. The calls could indicate an approaching predator, to a greeting, to possible mating calls. Furthermore, the crest potentially could have been brightly coloured if used for communication - individuals could have different colouring or it could help attract a potential mate. As tissue very rarely preserves it is difficult to know. The two skulls we have have slightly differently shaped crests indicating that it could be differently aged animals, sexes, or species. Finally, we have the teeth. Cretaceous ornithopods normally had teeth adapted to grinding plant matter, and the later hadrosaurs evolved the ability to chew, but Muttaburrasaurus had different teeth. The teeth of Muttaburrasaurus were adapted to sheering and the dinosaur was unlikely able to chew. Molnar originally hypothesised that Muttaburrasaurus was partially omnivorous relying heavily on scavenging. In the 1990s Molnar would re-evaluate the scavenging hypothesis instead noticing the similarities to the ceratopsians, like Triceratops. Ceratopsians had teeth adapted to sheering tough vegetation, mainly cycads, so Muttaburrasaurus could be an example of convergent evolution - like ceratopsians it needed to sheer through hard foliage so evolved teeth and jaws to do exactly that.

When and Where

Cretaceous Australia

As mentioned earlier Muttaburrasaurus was from the Cretaceous; all the Australian dinosaurs that we know of come from either the Jurassic or Cretaceous. The Cretaceous was the last period in which non-avian dinosaurs existed in lasting from 145 million years ago to 66 million years ago. Muttaburrasaurus existed in the Albian and early Cenomanian of the Cretaceous which was near the start of the period with it existing from 112 until 99 million years ago. The Australia which Muttuburrasaurus existed in was very different to the Australia of today. Australia was drifting apart from the continent of Gondwana and up to 50% of today's Australia was covered in shallow seas. This potentially could explain why the Muttaburrasaur fossils we have are well preserved. Plant fossils indicate that Australia was covered in ferns and conifers, all hard foliage indicating Muttaburrasaurus's sheering teeth. Part of southern Australia was attached to Antarctica and was slowly splitting off forming a large rift valley and was in the polar regions. Was Muttaburrasaurus a polar dinosaur? The answer is possibly no. Southeast Australia was in the polar regions and Muttaburrasaurus so far has only been found in the north. Furthermore, Muttaburrusaurus has been found in formations near formations, geographically and in age, where sauropods (long-necked dinosaurs) are found. This is important as sauropods favoured warmer climates. Therefore, we can imagine that at least some parts of the year Muttaburrasaurus lived in a warm climate. Due to the Australia's proximity to Antarctica and an inland sea the climate would not be too warm - Muttaburrasaurus lived in a climate not too dissimilar to Central Europe or New Zealand today, warm in the summer and cold in the winter. Quite possibly to keep warm in the colder periods Muttaburrasaurus had thicker filaments on their bodies. By the Late Cretaceous the inland sea started to vanish and temperatures changed which likely led to its extinction.

Neighbours

Walking with Dinosaurs had Muttaburrasaurus and Leaellynasaura co-existing 

With a habitat that was not too warm or too cool the Muttaburrasaurus had several notable neighbours. The ferns and conifers of Cretaceous Australia had the newly evolved flowering plants growing alongside them allowing for a wide range of dinosaurs to feed off of them. Muttaburrasaurus fossils have not explicitly been found next to other dinosaurs but based on where they have been found and the time they lived we can make guesses. Among them include the ankylosaurid Kunbarrasaurus and various sauropods including Wintonotitan. Pterosaurs flying between the various seas and looking over the rivers would have been a common sight. We know of a few carnivorous dinosaurs from Australia, such as the Australovenator which existed four million years after Muttaburrasaurus went extinct, so we can imagine that some form of carnivore hunted Muttaburrasaurus. Walking with Dinosaurs portrayed them as being migratory existing in the polar regions during the summer and moving north during the winter; this is not too far-fetched but we will have to wait to see if more are unearthed. If future ones are found exclusively in the north we'll know that they didn't migrate and only existed in warmer climates. Only time will tell.

Thank you for reading. The sources I have used are as follows:

-'Muttaburrasaurus', Prehistoric-Wildlife.com, (Accessed 30/08/2018)

-'Australia in the Cretaceous', Western Australian Museum, (Accessed 30/08/2018)

-A. Bartholomai and R.E. Molnar, 'Muttaburrasaurus: a new Iguanodontid (Ornithischia: Ornithopod) dinosaur from the Lower Cretaceous Queensland', Memoirs of the Queensland Museum, (1981), 20:2, 319-349

-Andrew T. McDonald , James I. Kirkland, Donald D. DeBlieux, Scott K. Madsen, Jennifer Cavin, Andrew R. C. Milner, and Lukas Panzarin, 'New Basal Iguanodonts from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs', PLoS ONE, (2010), 20:2

-Andrew T. McDonald, 'Phylogeny of Basal Iguanodonts (Dinosauria: Ornithischia): An Update', PLoS ONE, (2012), 7:5

-John M. Grady, Brian J. Enquist, Eva Dettweiler-Robinson, Natalie A. Wright, and Felisa A. Smith, 'Evidence for Mesothermy in Dinosaurs', Science, (2014), 344:6189, 1268-1272

-Walking with Dinosaurs, (1999), BBC, 1 November

Thank you for reading. If you felt I should add something, disagree with what I have written, or just fancy having your say please leave a comment. For other Paleo Profiles we have our list and for future blog updates please see our Facebook or catch me on Twitter @LewisTwiby.