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Ceratosaurus

Ceratosaurus

Ceratosaurus nasicornis was a 20-foot theropod dinosaur which lived in western North America during the late Jurassic Period, about 155-145 million years ago. It is one of the more famous Jurassic meat-eating dinosaurs, along with Allosaurus and Ornitholestes. It is the second-most-common theropod found within the Morrison Formation.

There are several anatomical features which make this animal distinct. Firstly, and most obviously, it has a small flat horn shaped like half of a dinner plate on the end of its nose, as well as a pair of horns over the eyes. These features are almost certainly visual in nature and were not designed for combat. Many paleo-artists, notably Gregory Paul, like to show the horn as being very large and triangular. I might be wrong, but I instead decided to portray the horn as it appears on the skull – low and rounded, not tall and pointy.

This animal also has a single row of scutes or osteoderms – small knobs of bone – running down the middle of its back, extending from the back of the head all the way to the tip of the tail. Many examples of paleo-art show Ceratosaurus with multiple rows of osteoderms, like the South American abelisaurid theropod Carnotaurus. This, however, is not true – Ceratosaurus just had one row of these bony bumps.

Ceratosaurus had unusually large teeth in its upper jaw in proportion to the rest of its head. This is a clue that this particular animal engaged in what is called “hatchet-style” biting and feeding, where the animal opens its jaws as wide as it possibly can, and then forcibly slams its head downward on its prey like a guillotine.

It possessed four fingers on each hand, which indicates that it was of a much more primitive stock than contemporary theropods, which were more advanced and had only three fingers on each hand. Its primitiveness also means that Ceratosaurus was probably less intelligent than other theropods. Granted, big bad Al was no genius either.

Finally, its tail was unusually wide, and some have suggested that because of this, Ceratosaurus might have been a good swimmer.

This drawing was made with a combination of Crayola and Prismacolor colored pencils. No.2 pencil was used for shading.

The Changing Face of Camptosaurus

Camptosaurus dispar was a type of ornithopod ornithischian dinosaur which lived in western North America during the late Jurassic Period. It measured 20 feet long and possibly weighed a ton. Camptosaurus was the largest ornithopod found within the Morrison Formation. Other ornithopods include the 10-foot long Dryosaurus and the 5-foot long Othnielia.

Camptosaurus was discovered on September 4, 1879 by William Reed in Wyoming during the famous “Bone Wars”. Othniel Charles Marsh originally named the animal Camptonotus, but was forced to change it because another animal had already been given this name. In 1885, the dinosaur was re-named Camptosaurus.

For a long time, we thought we knew what Camptosaurus looked like, or at least what its head looked like. Publications as recent as the 1990s depicted Camptosaurus with a boxy rectangular-shaped skull. This is due to paleontologist Charles W. Gilmore. In 1909, Gilmore wrote a description of the genus Camptosaurus and its assorted species. A skull (YPM 1887), referred to in 1886 by Marsh as belonging to Camptosaurus amplus, was re-designated by Gilmore as belonging to Camptosaurus dispar. In 1980, Peter Galton and H. P. Powell stated that C. nanus, C. medius, and C. browni were not separate species, but were instead growth stages of C. dispar, making C. dispar the only valid species. They also used the skull catalogued as YPM 1887 as the skull of Camptosaurus dispar. For many years, this was taken as fact, and this skull was used in many illustrations of Camptosaurus. However in 2006, Kenneth Carpenter and K. Brill found that this skull actually belonged to a different dinosaur. The skull, and the animal associated with it was named Theiophytalia kerri.

Below is the traditional-but-incorrect depiction of what Camptosaurus‘ skull looked like. Image from The Dinosaur Data Book, by David Lambert. New York: Avon Books, 1990. Page 180. The original image has been modified so that the labels have been removed.

So what did Camptosaurus really look like? The skull was more triangular in shape, similar to that of Dryosaurus. However, it was not a close relative. According to current phylogenics, Camptosaurus was more advanced than Dryosaurus, but more primitive than Iguanodon and hadrosaurs.

The illustration which you see below is the current look of Camptosaurus. However, I should state that the old rectangular image is so prevalent that it will take quite some time before old-school paleo-buffs like me learn to disregard it. This drawing was made with regular No. 2 pencil (my favorite medium) on basic computer paper.

Camptosaurus head

Keep your pencils sharp, everyone.

Allosaurus

Allosaurus

Allosaurus fragilis is one of the most famous and easily-recognized dinosaurs. Practically every museum has at least one specimen, either on display or in collections, and absolutely every basic-level children’s book about dinosaurs mentions Allosaurus, usually accompanied with a picture.

Allosaurus lived in western North America during the late Jurassic Period, from 155-145 million years ago. Its fossils have been found in rocks known as the Morrison Formation. It measured a colossal thirty-five feet long (half of it being just the tail), making it the largest carnivore in its environment (Torvosaurus comes in a close second, and Saurophaganax might just be an unusually large Allosaurus). It was also the most numerous. More fossils have been found of Allosaurus within the Morrison Formation than all other theropod dinosaurs combined. In fact, we have so many fossils of Allosaurus, ranging from juveniles up to fully-grown adults, that paleontologists know more about Allosaurus than any other meat-eating dinosaur. In all likelihood, it was the top predator in its environment, sometimes (and appropriately) referred to as “the lion of the Jurassic”.

This drawing was the culmination of years of drafting and revision. As you can tell by the coloration, it is heavily influenced by the color patterns seen on the Allosaurus in Walking with Dinosaurs, but I chose not to make the crests red. The first copy was made when I was just starting college, and that stuck around in my house for a couple of years. Then, I changed the proportions and slightly altered the color scheme. Finally, I added greater textural realism and made the colors substantially darker (on the original and second drafts, the gray was so light that it almost looked white). The hardest thing that I had to work on were the hands – I just couldn’t seem to get them right. When I was volunteering at the American Museum of Natural History, I spent about a half-hour taking numerous photographs of allosaur hands to get the right proportions. I also decided not to make the lacrimal crests too large, but instead kept them exactly as they appeared on the skull – I call them “doorknobs with dimples”. I’m sure that I’ll get some paleo-related flak for my decision NOT to make the characteristic large shark fin-like crests in front of the eyes which many paleo-artists put on their Allosaurus drawings, paintings, and sculptures, but it’s my decision and I like my beast’s head just the way it is.

This drawing was colored using no.2 and no.3 pencils (which I almost NEVER use!) and Crayola colored pencils. I hope you like it.

UPDATE: A revised version of this drawing was created and uploaded in July 2020. You can see it here.

Dromaeosaurus

Dromaeosaurus

Dromaeosaurus albertensis was a six-foot carnivore which lived in western North America during the Late Cretaceous Period. It is a distant cousin of Deinonychus and Velociraptor. Only one fragmentary skeleton was found in Alberta, Canada, although its teeth have been found in a number of localities, including the Hell Creek Formation. Like many members of Maniraptora, it is believed that Dromaeosaurus had feathers.

This drawing was made using that same time-consuming polygonal scale design that I used on my Giganotosaurus and Troodon drawings. I felt that I should make the scales as small as possible for this guy. Keep your pencils sharp.

Pachycephalosaurus

Pachycephalosaurus

Pachycephalosaurus wyomingensis was the last and largest of the so-called “dome-headed” dinosaurs. It measured fifteen feet long and lived 68-65.5 million years ago, right at the very end of the age of dinosaurs. Its fossils have been found in Wyoming (hence its name) and Montana, USA. The latter of the two localities is especially important, because this area is home to the Hell Creek Formation, a geologic formation which dates to the last days of the Mesozoic. It is within the Hell Creek Formation that most fossils of Tyrannosaurus have been found. It is possible that Pachycephalosaurus might have occasionally been prey for T. rex, but the presence of its foot-thick dome of solid bone and its sharp teeth-lined beak make this idea somewhat suspect.

The first remains of Pachycephalosaurus wyomingensis, which means “thick-headed lizard from Wyoming” were discovered during the 1850s in Montana. it consisted of pieces of the back of the skull (the squamosal bone) where there were several bony bumps. The eminent American paleontologist Joseph Leidy described this fossil, identifying it as armor, but he wasn’t sure what sort of animal it might belong to. He christened it Tylosteus (ancient Greek: tylos = “bump”; osteon = “bone”). In the first half of the 20th Century, two other fragmentary specimens were found, and in 1943, the name Pachycephalosaurus was created.

In the 1980s, it was realized that Tylosteus and Pachycephalosaurus were the same animal. According to the rules of the International Code of Zoological Nomenclature, the original name (Tylosteus) takes precedence, and any secondary names (such as Pachycephalosaurus) would have to be declared invalid.  In 1985, paleontologist Donald Baird was able to convince the ICZN to make an exception – to keep Pachycephalosaurus as its legitimate name and to discard the original name. He stated that the name Tylosteus hadn’t been used in over fifty years, and therefore shouldn’t be used. The ICZN granted his request, something that hardly ever happens! Usually, they are very “by the book”.

Pachycephalosaurus and its kind have generated a great deal of confusion and controversy since they were discovered. Most of the debating has pertained to their most obvious feature, their massive thick skulls. For a long time, it was assumed that these thick skulls were used for head-butting, like modern-day bighorn sheep. For years, paleontologists had an academic showdown over this idea, with some claiming that this idea was the only one that made sense, and others claiming that it was physically impossible for the animal to engage in head-butting behavior. For more information regarding this debate, you should watch the following two television programs:

Paleoworld, season 3, episode 3 – “Boneheads”. TLC, 1996.

Bizzare Dinosaurs. National Geographic Channel, 2009.

Now, the issue appears to be settled. Scientists at the University of Wisconsin recently conducted a study of various pachycephalosaur skulls from a number of different genera. If these dinosaurs did engage in some serious head-to-head combat, then their skulls would surely show some damage. After looking at over a hundred skulls, about 20% showed bone damage, specifically a condition called “osteomyelitis”, which is most commonly caused by trauma or injury to the bone. In other words, something hit it. For decades, the hypothesis that pachycephalosaurs engaged in head-butting has been conjecture. Now, we have the first hard evidence to support this idea. You can read more about their research and findings at the website article listed below.

“Study Confirms Head-Butting Behavior in Dome-Headed Dinosaurs”, by Natali Anderson (July 22, 2013). http://www.sci-news.com/paleontology/science-head-butting-dome-headed-dinosaurs-01247.html

The identity problem of Tylosteus and Pachycephalosaurus has resurfaced in recent years, but relating to different species. In the past few years, it has been proposed that two other pachycephalosaurs – Dracorex and Stygimoloch – are actually juvenile forms of Pachycephalosaurus. Watch the following videos for more information:

Dinosaurs Decoded. National Geographic Channel, 2009.

Bizarre Dinosaurs. National Geographic Channel, 2009.

“TEDxVancouver – Jack Horner – The Shape-Shifting Skulls of Dinosaurs”. http://www.youtube.com/watch?v=xYbMXzBwpIo

Lastly, it had been believed for many years that pachycephalosaurs belonged to a group of dinosaurs called the ornithopods. This is a very large group within Dinosauria, compsising hypsilophodonts, iguanodonts, and hadrosaurs (commonly known as “duck-billed” dinosaurs). This was because pachycephalosaurs appeared similar to these animals, especially the first on the list, the hypsilophodonts. These animals were bipedal, had beaks, and had front teeth – traits that were also present in pachycephalosaurs. However, recent re-examination of pachycephalosaur skeletons and cladistics have shown that they are not ornithopods at all; they are actually more closely related to the ceratopsians, the “horned” dinosaurs like Triceratops and Styracosaurus.

The drawing that you see here was made using a combination of shading and stippling, similar to my earlier drawing of Albertosaurus, but on a much smaller scale.

Two Triassic Pycnodont Fishes: Brembodus and Eomesodon

Here are color pencil drawings of two genera of prehistoric fish. Their fossils have been found in central Europe in rocks dating to the late Triassic Period. Both of these fish belong to a group called the pycnodonts, and it seems that they fed primarily upon mollusks and small crustaceans. Pycnodonts first appeared during the late Triassic Period, and became completely extinct during the Eocene Epoch of the Tertiary Period.

Brembodus

The first one is called Brembodus ridens. Among its features was a short spike on its back formed by extensions of the skull bones. This might have been meant to deter predators, like a modern-day triggerfish.

Eomesodon

The second fish is called Eomesodon liassicus. It looked remarkably similar to a modern-day tang or surgeonfish, except I’m not sure if the typical surgeonfish caudal blade (a sharp pointed piece of bone, located on both sides of the base of the tail, which could be extended if needed) has been found in association with specimens of this particular genus. As to the color, it’s pure guesswork on my part.

Hope you enjoy, and I look foward to any feedback.