Spotlight: Pachycephalosaurus

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Pachycephalosaurus wyomingensis — Wyoming’s thick-headed reptile

Specimen Name: Gracy (female)
Specimen Height: 1.67m
Specimen Weight: 450kg
Specimen Length: 4.98m

One of the most striking things about Pachycephalosaurus is the character that this species is named for — its skull. At the thickest point, the bone was close to 22cm (~9 in) thick. This initial observation sent scientists running to the quickest conclusion they could make: the head was a weapon. Though some doubt has been cast in the time after the initial hypotheses were formed, a well-constructed analysis by Peterson et al. suggests that pachycephalosaurids with dome heads (as opposed to the flatheaded varieties/morphs) frequently confronted one another in antagonistic behaviors. In this study, the same kind of skull lesions/fractures were found between many different pachycephalosaurs across different geographic areas. In addition, Horner et al. found that the skull dome was made of bone known to have fibroblasts (cells that aid in rapid bone regeneration). Plenty of head injuries + a means to heal them => something ahead of its time.

Pachycephalosaurus is also one of the last non-avian dinosaurs to have ever existed. Specimens are known to be found in America’s Hell Creek Formation — a fossil bed known for specimens such as Tyrannosaurus rexTriceratops prorsus, and so on. All of these taxa existed right until the very end of the Cretaceous, to the event known as the K-T boundary extinction. It and its famous contemporaries struggled and failed to survive the aftermath.

Artist Notes:

Pachycephalosaurus is an animal that I’m not unfamiliar with. This is actually my…sixth(?) or seventh time restoring one. For reference, this was my most recent pachy otherwise:

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Some of the things I’ve retained from this to the new pachy are as follows:

  • The color palette (primarily yellow and tan)
  • The cluster of filaments at the end of the tail, accented with a bit of blue and white
  • Filaments on the forearms

The quills/filaments/feathers on this animal are largely speculative. As far as I know, we’ve no direct skin impressions from a pachycephalosaur (I’m writing this 3 March, 2017. If any developments/discoveries are made, I’ll update this.), so integument is largely a task left to phylogenetic bracketing. Ceratopsids and pachycephalosaurs are placed in their own monophyletic group, dubbed “Marginocephalia.” Basal ceratopsids such as Protoceratops and Psittacosaurus are known to have long bristle-like filaments on the tail. Assuming the common ancestor of both pachycephalosaurs and ceratopsids had similar traits, it’s not so strange to think a pachycephalosaur could retain at least some bristle ornamentation.

I made the clumps of bone at the back of the skull pointier in the March ’17 pachy. This is to reflect more recent findings of pachycephalosaur development, particularly in the skull shape. In life, I assume these sharp pseudo-horns(?) would be used to cause superficial injuries to an opponent. Assuming the animal swung its head (as opposed to the straightforward impact as seen in modern rutting animals) like a club, the additional movement of pulling the skull back to a neutral pose had the potential to scrape/cut as well. The head dome is also very brightly pigmented, which is simply something of my own design.

Gracy is depicted in a near-tripodal pose, crouching on her legs to rear her upper torso high. She’s bleating, sending a call to fellow pachycephalosaurs. I don’t imagine these to be exactly social animals, which might’ve formed loose family-based clusters, at best. She would only be vocalizing to ward off intruders to her territory, to find mates, or simply to check if there are others of her kind in the area. The snarl/bleating of the Jurassic Park Pachycephalosaurus is fairly close to what I envision for my renditions

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Spotlight: Triceratops

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“This one was always my favorite as a kid, and now I’ve seen one, she’s the most beautiful thing I ever saw.”

Triceratops is an herbivorous ceratopsian dinosaur from the Upper Cretaceous. Near the top of the list of every 5th-grade poll of “What’s your favorite dinosaur?”, Triceratops has earned her spot through more than a century of study, scrutiny, and debate. The striking three horns, husky frame, and solid frill completes the image of an animal set out to be a warrior against the menacing jaws of Tyrannosaurus.

Since its discovery in 1889 by fossil hunter Othniel Marsh, Triceratops has always been the knight of the Cretaceous, so it were. The first fragmentary remains were of its two long orbital horns, and Marsh thought them to belong to some kind of ungulate. Eventually identifying the remains as belonging to a dinosaur, the genus was named Triceratops – meaning “three-horned face.” There are currently two species of Triceratops formally recognized by paleontologists: Triceratops horridus (meaning “horrible three-horned face”) and Triceratops prorsus (meaning “straightforward three-horned face”). The illustrations I generate are of T. horridus, based in simple personal preference in addition to a plethora of available references for the dinosaur.

The trike is relatively unchanged since its initial restorations. Anatomical discoveries/changes from the 19th century to now include, but are not limited to:

  • More suitable vertebral attachments from the head to the rest of the spine
  • A tail that, while still on a downward slope, is suspended off the ground
  • The discovery of integument; Triceratops had a pattern of non-overlapping scales in addition to large “nipple-like” bumps/scutes along the torso
  • Numerous specimens that enable paleontologists to generate growth series

My Triceratops incorporates elements from Asian elephants; notice the pigmentation on the bottom of the body and along the snout. This provides a gentle counter-shade for the animal as well. I’ve tried to tether the coloration to some of my behavioral hypotheses for Triceratops, which I’ve made analogous to moose. You have a large herbivore that’s perfectly capable of fending for itself. However, any form of reduced attention is more beneficial than not. Some Triceratops restorations favor flashy frills and heads; I’ve stepped away from such a notion.

I did give the trike eyespots on the frill and the lower back, however. Whether this is an effective way to deter a Tyrannosaurus attack or purely species identification is up to the interpreter. Another speculative structure I’ve gifted the trike are quills on the back. There is direct evidence of at least basal ceratopsids boasting some form of quills/bristles on the back. Triceratops does not have direct evidence of bristles, but it’s entirely in the realm of possibility.

That about does it for this animal spotlight. Be on the lookout for more in the future!

Until next time.

Skeletal references: 1, 2