Level: Introductory

Many kinds of creature which lived in the past, have no living representatives today. Definitely the most famous fossils in our part of the world, are the dinosaurs. Like reptiles, they had backbones and four limbs, but their posture was not sprawling like reptiles such as crocodiles. Also dinosaurs moved on two or four legs. Moreover they were typically much bigger than reptiles and all lived on the land. The name for dinosaur came from the Greek for “fearful lizard”, but they are not really like lizards.  They are a whole different group.

There are two basic designs for the dinosaur body: the lizard hipped and the bird hipped. In each category we find totally different body plans and life styles. Among the lizard hipped we find sauropods (those gigantic four footed plant eaters like Apatosaurus (otherwise known as Brontosaurus) and the fast frisky two footed meat eating predators called theropods. The bird hipped dinosaurs are all plant eaters and these include armoured stegosaurs (with triangular shaped plates along the back), ankylosaurs and nodosaurs (all armoured), horned dinosaurs like Triceratops, domed dinosaurs, and bird footed dinosaurs including duckbill dinosaurs.

Bird hipped dinosaurs 

Includes most exciting dinosaur fossil ever found. Read on to find out the story of the nodosaur fossil carcass.

All the bird hipped dinosaurs ate plants. The stegosaurs and ankylosaurs were heavy, slow, creatures covered in hard plates. They moved on four feet. The horned dinosaurs, on the other hand, had huge frills attached to the skull and horns on the face. They too moved on four feet. The dome headed dinosaurs were small and bipedal (moved on two feet). Similarly the duck bill dinosaurs were bipedal but they were large.

Armoured dinosaurs

Some of the most famous armoured dinosaurs are the stegosaurs. Every young person knows about Stegosaurus and how funny they looked! They had triangular plates along the backbone and spikes on the tail. These were four footed animals with hind legs longer than the front ones, so they looked slightly tipsy. Up to 21 ft long (6.5 m), these animals are particularly noteworthy for their small heads and small brain.  

The ankylosaurs are also armoured dinosaurs. Their four legs are much shorter than those of the stegosaurs. These animals were covered in heavy bony plates so that they seem built like tanks. They were big too, averaging about 6-8 m (20-26 ft) long. One book on The Great Dinosaurs by Alberta’s dinosaur expert Philip Currie and Zdenek Spinar says about the ankylosaurs: “Because of the great weight of their armour, they would have had great difficulty in swimming because they would have a tendency to roll over onto their backs and sink.” (1994 p. 126) This statement applies not only to the ankylosaur armoured dinosaurs but also to the nodosaur armoured dinosaurs which were a bit smaller than the ankylosaurs. [See footnote about a swimming dinosaur.]         

It is a nodosaur fossil that is particularly exciting. The story goes like this.

Good fossil remains of armoured dinosaurs are rare, so it was an exciting day when a new nodosaur fossil was discovered near Fort McMurray, Alberta in 2011 in the Suncor Millenium oilsands mine. More amazing however was the condition of the dinosaur remains. There was a fully three-dimensional body with the exterior skin, armour, and spikes preserved as they would have been in life. Even more amazing, its stomach contents were preserved. It seems that this animal preferred ferns. Have you ever heard of such an amazing fossil? No? Neither had anyone else!!

Scientists from the Royal Tyrrell Museum were very surprised to discover that this newly discovered specimen was a land dwelling dinosaur and not a sea dwelling reptile like a plesiosaur. No land animal had ever previously been discovered in the oilsands. Many people wondered how this heavy (about 1.3 metric tons) animal, about 5.5 m long (18 ft) ended upside down in sediments typical of the ocean.

As with many other armoured dinosaur fossils, it seems that this creature was overtaken by rushing waters that tipped him over and carried him in the fast moving current. Eventually the animal sank to the bottom and its body further sank into soft sediments which perfectly protected its three-dimensional shape. Soon buried by other sediments, the whole thing hardened into a most unusual perfectly preserved fossil. This creature Borealopelta markmitchelli is a dramatic testimony to the power of unique flood waters to sweep away and bury heavy dinosaurs.  

Horned Dinosaurs

This is another popular group of bird hipped dinosaurs.

Although there were some heavy four footed dinosaur designs found worldwide that feature sharp beaky mouths and skulls that stretch backward and upward into a small frill, nevertheless North America is definitely the place to find dramatic horned dinosaurs. Protoceratops, for example, from China, is an example of an animal with a small frill but It did not have any horns.

Western North America however is unique for two groups of particularly dramatic horned dinosaurs. These two groups appear suddenly in the same rock levels. The one group of fancy horned dinosaurs features a short face and a short frill, and the other exhibits a long face with a long frill. The centrosaurs with the short face, feature highly ornamented frills. There may or may not be a horn over the nose. Pachyrhinosaurus is an example in this group. The chasmosaurs, with a long face, feature a short horn over the nose and long horns over the eyes. Their long frill is plain in appearance, but under the skin there are large holes in the bone. This drastically cuts down on the weight of this object. Triceratops is the only known horned dinosaur with three horns and a relatively small frill with no holes.

Not surprisingly, these large heavy four footed animals had a major problem in that the skull with frill was almost one third of body length. Moreover, that frill was heavy and bulky, even with large holes in it. In order to manage with such a heavy head, the horned dinosaurs had a unique design feature which allowed them to turn their heads easily. At the base of the skull (where it joins the backbone), there was a highly unusual ball and socket joint. Attached to the base of the skull was a perfectly round ball of bone which rotated in a socket made of bones in the backbone joined together to make the socket. The ball of this joint was impressive. It could be as large as a small grapefruit.

The bones and skeletons of horned dinosaurs are particularly common in bone beds. (Bone beds are deposits which can extend for many kilometres which contain the individual bones and some skeletons of often a single herd of dinosaurs.) That horned dinosaurs are common in such beds is surprising since these animals were so heavy and so solid on their feet. The amount of force needed to sweep away such animals must have been very different from what we see today in bodies of moving water. The Centrosaurus bone bed in Dinosaur Provincial Park is featured in the Royal Tyrrell Museum and the Pachyrhinosaurus bed of Pipestone Creek near Grande Prairie, is featured in the Philip J. Currie Museum in Wembly, Alberta.

Duckbill dinosaurs

The other major group of bird hipped dinosaurs in Alberta are the duckbills of which we find lots of variety. Some of these were buried so quickly that portions of their skin was preserved in the rocks.

Lizard hipped dinosaurs

The dinosaurs with this body design came in two very different formats/body plans. Firstly there were the gigantic four footed plant eating sauropods, and the fierce and frisky two footed meat eaters, the theropods.

Some of the sauropods grew up to about 50 m (150 ft) long, or more! These were the largest land animals ever. Their bodies looked very heavy, positioned on four stocky legs. Their necks were long, sometimes extremely long, but they held their heads and tails up in the air. How did they manage all this on a diet of plants only? It turns out that they enjoyed some design features which helped them to reduce weight. The long bones in the legs had large cavities that were filled with fat, much lighter than bone or muscle. The component bones of the neck were extremely light, since the bones were gas filled. These bones were like air-filled helium balloons. The bone was so thin these structures were amazingly light but strong. The shape of the individual bones in the neck and back also provided bracing, so that the neck would not droop down to the ground. Obviously, these animals were wonderfully designed to manage with long necks and large size. It is  important to notice also that the reason we know about such creatures is that rushing waters quickly and permanently buried some of them in sediments that turned to rock. Would you like to calculate how much sand or gravel you would need to bury such an animal so deeply it could not be dug up or later exposed by wind or water? Flooding carried that kind of load which buried these animals.

The theropods navigated on two feet. They chased other creatures and ate them. Because they had to be fast on their feet, many displayed delicate bones. For example, Coelophysis is a carnivorous meat eating dinosaur found in Canada’s maritime provinces and elsewhere. It had hollow fat filled leg bones and gas filled cavities in the back bone. This animals grew to about 3m (10 ft) long and weighed only about 40 kg (88 lbs). That was certainly slim and trim!

One famous group of carnivorous dinosaurs in Alberta were the dromaeosaurs. These are famous for large wicked looking sickle-shaped claws held upright on the innermost toe of each foot. Saurornitholestes and Dromaeosaurus albertensis were such species found in Dinosaur Provincial Park. The discovery of such a claw made scientists realize that these species must have hunted victims by leaping through the air and slashing their sides. That was a very energetic lifestyle! There were other much larger and more solid looking meat eating dinosaurs like Albertosaurus and Gorgosaurus and Tyrannosaurus rex, all found in Alberta. All theropods had fat filled leg bones and perhaps similar cavities in their large skulls.

Summary of dinosaurs

Like the large reptile fossils, the dinosaurs were clearly overtaken by catastrophic flooding. Entire carcasses of heavy animals, bones still attached as in life, skin preserved, and bone beds of whole herds, all demonstrate the terrible widespread quality of the flooding that lead to these creatures being preserved in rock until today.

Footnote: A 5 minute video clip from the Royal Tyrrell Museum called A swimming dinosaur: The tail of Spinosaurus talks about Spinosaurus a dinosaur skeleton found in Morocco. It is said to be the longest and largest theropod (carnivorous dinosaur). An article in Nature vol. 581 May 7, 2020 by Nizar Ibrahim and others (pp. 67-70) also describes this new fossil find. The recently discovered skeleton is the only one that exists. The only other specimen ever found was destroyed during World War II. Based on the anatomy of its tail, the scientific team concludes that this dinosaur lived part of the time in water chasing fish. Apparently, this conclusion is controversial in some circles which consider that all dinosaurs lived land-based lives.  It is worthy of note that this dinosaur, whether swimming or not, was much less likely to get trapped by sediments in water than were the armoured dinosaurs which have been found around the world.

A specialist from the Royal Tyrrell points out that all theropod dinosaurs had very buoyant bodies which would insist on floating. This specialist does not think that Spinosaurus did anything other than stay at the surface of the water, if that! This shows how different specialists can emphasize different features of an organism and come to different conclusions. See Computer Models: A Tool for Palaeontological Biomechanics Studies

Book Reference: Tim Clarey and Brian Thomas. Guide to Dinosaurs. ICR. 117 pp.                                 Ken Ham. Dinosaurs for Kids. Master Books. 64 pp.