Invertebrates

Welcome to another Mesozoic Mondays blog from Jurassic Forest!  We're going to take a detour from our normal posts as our main blogger, Liz, is away (she is preparing for her thesis defense so wish her luck)!  My name is Kristina and I am another palaeontologist at Jurassic Forest.  Unlike Liz who studies large, flying reptiles, I study fossils that are very small.  Some of them are so small that you need a microscope to see them properly!  Another big difference between the animals that we study is that Liz studies animals that have backbones (vertebrae), and the ones I study do not.  These animals are called invertebrates, and they will be the topic of this week's Mesozoic Monday.

Jurassic invertebrate fossils!

Invertebrate animals have no vertebral column, no bones, and come in countless shapes and sizes.  They represent the most diverse groups of animals on the planet!  It would be impossible for me to give a complete representation of all invertebrates in a blog post, so I am just going to highlight some of the major groups and their evolutionary history.

The first evidence of multicellular animal life comes from fossils in the Ediacaran Period, about 600 - 545 million years ago.  Most of these fossils are from soft bodied creatures, somewhat like jellyfish.  These fossils represent soft bodied creatures that are very different from those seen today so classification of these animals is often very difficult.



Dickinsonia is a classic example of Ediacaran life

The first animals with hard parts appear in the fossil record during the Cambrian Period (about 542 million years ago).  This event is often referred to as the "Cambrian Explosion" because there was such a large radiation of life forms that appeared over a relatively short period of time ("relatively" in geologic terms means about 40 million years).  As well, animals with hard parts fossilize much more easily than soft bodied animals.  

Although most of the fossils from the Cambrian Explosion are very bizzare, most of them are clearly related to modern animal forms.  There are representatives from most major groups of animals, even vertebrates!  Pikaia is thought to be an ancestral form of vertebrate animals.  The most famous fossil site for animals from this event is the Burgess Shale in Yoho National Park, British Columbia.

Animals from the Burgess Shale (Top row: Anomalocaris, Opabinia; Bottom row: Hallucigenia, Wiwaxia, Pikaia), Image by: Matt Martyniuk

In the animal kingdom, there are many different categories of animals.  Vertebrate animals represent only one of these major categories!  The simplest form of animals are the sponges.  Even though they lack true tissue, they are considered animals because they have to eat food (they cannot make their own food like plants), and because they have sperm cells for reproduction.  Unlike other animals that have a digestive system, sponges feed by filtering water through the many pores in their bodies (hence their scientific name is Porifera).

Sponges are animals!

The next major group of animals are called the Cnidaria (pronounced "nye-DARE-ee-a").  They include the jellyfish, corals, and anenomes.  Unlike sponges, cnidarians have their cells organized into true tissues.  They also have special stinging cells, which is what makes some jellyfish so poisonous (please note that not all cnidarians are poisonous).

Anenomes are cnidarians

There are hundreds of different kinds of worms in the animal kingdom, which are usually organized into three major groups: the flatworms, segmented worms, and round worms.  These groups are incredibly diverse, but generally have a poor fossil record.

Worms, such as this tapeworm, can live almost everywhere, including your digestive system!

Molluscs are another incredibly diverse group of invertebrates.  They are one of the most abundant groups of animals in the fossil record and are characterized by a having a special muscle called the "foot".  They include animals such as clams, oysters, snails, slugs, octopi, squid, ammonites, and nautiloids.

Ammonites were one of the top predators in Mesozoic oceans! Photo by: Mike Peel.

By far, the largest, most diverse, and most abundant group of animals on the planet are the invertebrate group called the arthropods.  Arthropods are characterized by  having a hard exoskeleton which they shed (moult) as they grow, and a segmented body.  The arthropods include insects, crustaceans, arachnids, millipedes, centipedes, and a large extinct group called trilobites.

Trilobites first appear at the Cambrian Explosion, and are the only completely extinct group of arthropods.

The next group of invertebrates is one that most people have never heard of, but which were very important in the fossil record.  This group is called the lophophorates (pronounced "LOW-fo-FOUR-ate") and includes two major groups: brachiopods and bryozoans, both of which are still alive today.  They are characterized by a special feeding structure called the lophophore.  The lophophorates were incredibly diverse and abundant during the Paleozoic, but were largely replaced by molluscs during the Mesozoic.  This is the group that I study!

Brachiopods look like clams on the outside, but their internal anatomy is very different! Image by: Didier Descouens

The final major group of invertebrates are called the echinoderms (pronounced "eh-KYE-no-derms").  These animals are the closest relative of vertebrates because most have a special type of internal skeleton.  They are also characterized by a special body plan that has five sided symmetry.  Echinoderms include sea cucumbers, sea urchins, sand dollars, sea stars, brittle stars, sea daisies, crinoids, and an extinct group called the blastoids.

Crinoids are a cool group of echinoderms that are common in the fossil record!

While we are most familiar with vertebrate animals, there are way more invertebrates.  Beetles alone represent more than 28% of all living species of animals!  So for those of you out there that want to study palaeontology: don't forget that there is more that 600 million years of fossil record for you to choose from!  While dinosaurs are one of my favourite groups, there are countless plants, fungi, microfossils, and invertebrate fossils for us to study too.  That is what makes the science of palaeontology so awesome!

Fossils are awesome! Image by: Ghedoghedo 

 References:

Pearse, V., Pearse, J., Buchsbaum, M., and Buschsbaum, R., 1987, Living Invertebrates, Blackwell Scientific Publications, Palo Alto, CA, 848 pp.

http://www.ucmp.berkeley.edu/index.php - This website is a great resource for all things palaeontology and evolutionary biology.  Their invertebrates section is very good and includes some awesome diagrams and animations.
 

Pterosaurs!

This week, I'm going to talk about my personal favourites, and what I do my research on: pterosaurs! As mentioned in my previous post "What is a dinosaur", pterosaurs are flying reptiles that are closely related to dinosaurs (well, depending on who you talk to that is), but are not actually dinosaurs. As such, they are also not closely related to birds. They are a separate group all together that is entirely extinct, the last ones dying out at the same time as the non-avian dinosaurs. Pterosaur wings are different from both bird and bat wings. They are formed mainly from an elongated fourth digit (your ring finger), with a membrane from the end of that digit to its body. They have 3 tiny clawed fingers (digits I-III), as well as a bone only found in pterosaurs: the pteroid, which was likely responsible for controlling the leading edge of the wing membrane. 

Diagram of a pterosaur wing from Wikimedia Commons user ArthurWeasley

Pterosaur evolution is a bit hard to understand because they appear quite suddenly in the fossil record as fully flying pterosaurs during the Triassic. In terms of morphology (the form of the animal), pterosaurs can be divided into two groups: the rhamphorhynchoids, and the pterodactyloids. 

Rhamphorhynchoids

Rhamphorhynchoids are the smaller, more primitive pterosaurs. The had short necks, long tails, and more basic body plans. Dimorphodon comes from the UK. It had a wingspan of 1.2 m, a huge head (20 cm), and long curved claws, suggesting it was a good climber. 

The Early Jurassic pterosaur Dimorphodon 

Another interesting rhamphorhynchoid is Anurognathus, which means 'frog-jaw', for its distinctly froggy jaw. It comes from the amazing Upper Jurassic Solnhofen limestone in Germany, which is known for the amazingly preserved fossils found within. Unlike other rhamphorhynchoids, Anurognathus had a very short tail and a short, squat skull. 

Anurognathus

Rhamphorhynchus

Of course, there is also Rhamphorhynchus, which gives the group its name. Also from southern Germany, England, Switzerland, Africa and maybe the US,  this is one of the most commonly found pterosaur fossils. It has a long tail with a diamond-shaped vane at the end, and lots of pointy teeth used to catch prey. 

Other important or interesting rhamphorhynchoids include Sordes and Jeholopterus, which have shown that pterosaurs were covered in a hair-like material called pycnofibres, and Darwinopterus, which has features from both rhamphorhychoids (characters of the body and wings, like a long tail) and pterodactyloids (characters of the neck and skull, like a crest). This shows that pterodactyloids evolved from rhamphorhynchoids. What a great find! 

Darwinopterus

Pterodactyloids

Pterodactyloids generally include the more well known pterosaurs like Pteranodon, which had no teeth, and flew over the seas and oceans, swooping down to catch fish. They also had large crests, which are different between males and females, suggesting they could be used for sexual displays. These are some of the larger pterosaurs, with the wingspan reaching 7 m. 

A male Pteranodon in front with a large, colourful crest, while a female rests behind, with a smaller crest

Another odd pterodactyloid pterosaur is Pterodaustro, which belongs to a group of pterosaurs known as the 'comb-mouths'. This is because Pterodaustro and its relatives look kind of like a baleen whale. They have over 1000 long, peg-like teeth on their curved lower jaw that they could use to filter small animals out of the water with. 

Pterodaustro from the Early Cretaceous of Argentina

Of course, we can't forget about Quetzalcoatlus, the largest flying animal to have ever lived. This guy was enormous. With a wingspan of about 10-12 m, it is by far the hugest thing to fly. Of course, this has lead to debate about whether or not it was actually capable of flying, but that is for a different day. Unlike the other toothless pterosaurs, this guy may have hunted on land using a 'terrestrial stalking' method, picking up small dinosaurs or other animals as it goes (see Witton and Naish 2008 for details if you're interested). 

Quetzalcoatlus shown using the 'terrestrial stalking'
method eating small sauropod dinosaurs

Size comparison between Quetzalcoatlus, an
average sized person, and a giraffe

Other well-known pterodactyloids include the ornithocheirids Ornithocheirus, and Anhanguera, and the crested Tupandactylus, Tapejara, and Tupuxuara, which all had an enormous crest on their skulls. 

Tupuxuara

Tapejara

 Some important things about pterosaurs to point out. First of all, they are not all toothless. In fact they are far from it as you should have learned. Two groups lost their teeth, the pteranodontids like Pteranodon, and the azhdarchids like Quetzalcoatlus. Another interesting thing about pterosaurs is the debate over where the membrane attached. There are currently three theories: it attached to its ankle, thigh, or hip. There are arguments for all of them, and it's not yet clear which one it was, or if it was different in each pterosaur. Finally, you may have noticed that in all the pterosaurs depicted on the ground, they were not moving around bipedally on their back legs, but quadrupedally using digits I-III to support themselves, while the wing is tucked upwards. This is well supported by pterosaur trackways. Related to this, is the theory that pterosaurs took off not like birds, but by launching themselves quadrupedally, mainly using their forelimbs to produce enough energy to get them off the ground (Habib 2008). A video of this can be seen here. 

UPDATE 3/9:
After I got some feedback about the blog, I found something out that I slightly mis-represented. According to Mark Witton, the membrane attachment issue is much more 'solved' than what I suggested. There is no fossil evidence for the hip-based membrane attachment, and it is highly unlikely that the thigh/knee attachment is correct thanks to another look at the key fossil of Pterodactylus that supported this idea. This leaves the ankle attachment as the only valid thought left. Many different specimens and species show a distal hindlimb attachment in the fossils, so this is most likely it. Thanks Mark for letting me know!

I think pterosaurs are pretty cool. If anyone has any questions about them, please let me know! One last thing I'd like to mention. The majority of these images came from Mark Witton, with permission. Thanks so much for letting me use your pretty pictures Mark! Also, this means that if someone wants to use these images, you need to ask Mark. He's a pretty nice guy and will probably say yes, but they are his and you need permission, so please don't steal them!

References and interesting sites

Habib MB (2008) Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana Reihe B 28: 159-166

WittonMP, Naish D (2008) A reappraisal of azhdarchid pterosaur functional morphologyand paleoecology. PLoS One 3: e2271

Pterosaur.net - Great website for anyone interested in pterosaurs to take a look at. It's run by palaeontologists that work on or specialise in pterosaurs. It has info on their evolution, anatomy, biology, basically everything you want to know!

Mark Witton's images at Flickr and his website - Dr. Witton is a pterosaur palaeontologist as well as a palaeoartist, which means that his images are all scientifically accurate! Definitely take a look at what he's done, but if you want to reproduce or use anything, make sure you ask him because they are all copyrighted!
Musings of a clumsy palaeontologist - specifically, the post on pterosaur mass if you're interested!
Update: Also check out Dave Hone's recent post on pterosaurs. Great read for people not familiar with pterosaurs!

Ornithischians

After a week long hiatus, Mesozoic Mondays is back! Last time, we were explaining what the saurischian dinosaurs were. This week, we will describe the second large group of dinosaurs, the ornithischians. For a review of the difference between the Saurischia (lizard-hipped) and Ornithischia (bird-hipped) dinosaurs, view the Mesozoic Mondays post on the saurischians. 

Most herbivorous dinosaurs are ornithischians, and basically all ornithischians are herbivorous. The early ornithischians look superficially similar to early saurischians, but they evolved later. The earliest ornithischians include dinosaurs like Pisanosaurus from the Late Triassic of South America and Eocursor from South Africa, which lived about 210 million years ago. 

Eocursor,an early ornithischian. (Image from Wikimedia Commons user ArthurWeasley)

Ornithischians are divided into three main groups: the thyreophorans, ornithopods and marginocephalians. What a mouthful! Thyreophorans are the 'shield-bearers', also known as the armoured dinosaurs like ankylosaurs and stegosaurs. They evolved in the early Jurassic and lived right up until the non-avian dinosaurs went extinct at the end of the Cretaceous. Ankylosaurs are divided into 2 groups: the ankylosaurids like Euoplocephalus which have large tail clubs to protect themselves, and the nodosaurids like Edmontonia, which do not have tail clubs. Both groups are characterised by the heavy amount of armour that covers their head, back, and tail to protect them. They are likely the best protected dinosaurs from predation. The stegosaurs include the well known Stegosaurus, as well as other dinosaurs with alternating rows of plates and spikes. Other stegosaurs include the Chinese Huayangosaurus and Tuojiangosaurus. 

Huayangosaurus (image from Wikimedia Commons user ArthurWeasley)

The ornithopods are a very large group. Ornithopod means 'bird foot', with respect to the three-toed feet found in most of these dinosaurs. Although there are many kinds of ornithopods, the main group is the iguanodontians, which includes the hadrosaurids, or 'duck-billed' dinosaurs. The most famous iguanodontid is Iguanodon, which is known for its large thumb spike and is found in Europe. Hadrosaurids are generally divided into two groups: the crested (lambeosaurine) hadrosaurids like Parasaurolophus and Lambeosaurus, and the non-crested (hadrosaurine or saurolophine) ones such as Edmontosaurus. The crests of lambeosaurine hadrosaurids were likely used like a resonating chamber to make sound and to communicate. Hadrosaurids were one of the most successful groups of ornithischians in the Late Cretaceous and lived in Asia, Europe and North America.

Iguanodontian heads (left column then right column): Ouranosaurus, Muttaburrasaurus, Corythosaurus, Lambeosaurus magnicristatus and Lambeosaurus lambei. (image from Wikimedia Commons user FunkMonk)

The final group of ornithischians is the marginocephalians, which are the 'fringe heads'. This group includes the dinosaurs that have some kind of fringe or frill on their skull margin like the pachycephalosaurs and ceratopsians. Pachycephalosaurs, or 'thick-headed lizards' include the very large Pachycephalosaurus, and the small Stegoceras. They may have evolved during the Early Cretaceous, but primarily lived during the Late Cretaceous. Some pachycephalosaurs may have been omnivorous, eating insects as well as plants. Some palaeontologists believe they used their heads to head-butt each other, possibly as a mating display, while others believe that would have resulted in concussions or possibly even broken necks. They argue that pachycephalosaurs were more well suited to flank-butting, where it's a bit more fleshy. 

Skull of Pachycephalosaurus from Wikimedia Commons user  Dudo

The ceratopsians are arguably the most recognisable dinosaurs: the horned dinosaurs. They are an interesting group because they actually have a separate bone on the front of their mouth that makes up the bottom part of their tooth-less beak: the rostrum. No other group of dinosaurs (or animal for that matter) has this bone. Although they are generally known as being horned, not all ceratopsians had horned. Early ceratopsians like Psittacosaurus were bipedal, had no horns and lived during the Early Cretaceous. Recently, a specimen was found that showed barb-like filaments on the tail of Psittacosaurus. Late Cretaceous ceratopsians reached an amazing level of diversity from the three-horned Triceratops, to the spiky Styracosaurus, to the bony boss-covered Pachyrhinosaurus. Although their skulls are very diverse, the rest of their body morphology is fairly common throughout the group. They were all large, quadrupedal, herbivorous dinosaurs. 

Psittacosaurus (image from Wikimedia Commons user ArthurWeasley)

Ceratopsian skull diversity. Some genera include Styracosaurus (bottom left), Centrosaurus (right of Styracosaurus), Achelosaurus (?) (top right of left section), Chasmosaurus (centre), Kosmoceratops (just to the right of center on the bottom with 2 large horns), and Triceratops (?) (top right). Image from Wikimedia Commons from Flickr user Magnus Manske.

Ornithischian fossils are very common in Alberta, especially hadrosaurids and ceratopsians. For a list of some dinosaurs found just in Dinosaur Provincial Park, go here. There are many other places in Alberta where you can find ornithischian dinosaurs including near Grande Prairie (Pachyrhinosaurus, hadrosaurids and more), and right here in the city of Edmonton (Edmontosaurus and more)!

Ornithischians at Jurassic Forest:
Ankylosaurus
Corythosaurus
Edmontosaurus
Hadrosaurus
Iguanodon
Maiasaura
Pachycephalosaurus
Pachyrhinosaurus
Parasaurolophus
Stegosaurus
Styracosaurus
Triceratops

References:
Most of the stuff from this week came from my brain, but some good sites to check out include:
The Paleobiology Database - this site is run by palaeontologists and is a good place to get information on things like dates classification, and where fossils are found. It is a bit technical though.
http://palaeo.gly.bris.ac.uk/communication/boulton/evolution.html