Monday, 13 August 2012


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:

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.

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