The Iguanodon's Thumb

About six months after my drawing of Iguanodon through the ages, I did another piece taking a closer look at the dinosaur as we now see it, in part because the modern reconstruction was easily the hardest the capture on paper.

 This drawing is strictly of Iguanodon bernissartensis, currently recognized as the only valid species (though ironically, the original Iguanodon bones have now been ascribed to a new genus called Mantellisaurus, in honor of the animal's initial describer Gideon Mantell). Here's a closer look:

The specimen sketched is from the Senckenberg Museum in Frankfurt, Germany.

The term "Swiss Army hand" was coined by paleontology Thomas R. Holtz in the wonderful Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages (Random House, 2007). Even with its impossible-to-live-up-to title, it's a must-own for anyone vaguely curious about dinosaurs.

Growing up, the explanation for Iguanodon's thumb spike was that it was a weapon against predators. As Holtz and other paleontologists have pointed out, this premise makes little sense, since surely an Iguanodon who got close enough to jab at a large theropod with its thumb would also be close enough for this attacker to take a large bite out of the herbivore. Since the animal is now thought to have been mostly quadrupedal, the big claws of the middle three fingers now seem to have been for bearing its weight as it walked, while the dangling pinkie may have been for grasping the branches it fed from. But now that defense has been discarded, the question how Iguanodon used its claw is wide open.

What walks on four legs at dawn, on two legs mid-morning, and then on four legs again at noon?

An Iguanodon. The second dinosaur ever described in scientific literature and one of the genera known from the most specimens, this beast has arguably gone through the most dramatic makeover of any dinosaur, as this drawing from last June demonstrates.

The first iteration of Iguanodon (standing on the left) was conceived by Sir Richard Owen — who envisioned it as an elephantine behemoth — and popularized by Benjamin Waterhouse Hawkins in a series of sculptures unveiled at London's Crystal Palace Park in 1854. An isolated triangular bone was interpreted as a horn that jutted between the nostrils like a modern rhino's.

In 1878, dozens of intact Iguanodon skeletons were discovered near the Belgian town of Bernissart. These remains revealed a much more slender animal along the lines of Hadrosaurus (described in 1858), and like Hadrosaurus, the animal was reconstructed in a tripodal, kangaroo-like position (center). The horn also turned out to be a spiky, ersatz thumb. As a very young child, I remember most dinosaur books, toys, and other dinosaur media conforming to this image, even as other dinosaurs assumed a more balanced, horizontal stance. In addition, I noticed that many of these depictions had also Iguanodon drooping their skulls downward, drawing attention to the back of their heads and making them look like vultures or bald men. Some of these illustrations also gave the animal a set of scaly ridges running down the vertebrae — not completely impossible, given the presence of these structures in the iguanodonts' later relatives and successors, the hadrosaurs.

The most recent reconstruction of Iguanodon (right) was devised by David Norman, who found that it walked primarily on all fours. 

I normally am hesitant about coloring dinosaurs green, worrying it will make them look too lizard-like. For Iguanodon, however, I thought it appropriate to keep the initial, super-reptilian restoration that color. I chose to make the later restorations mostly green as well, but with starker secondary colors and markings to represent our view of dinosaurs becoming more nuanced throughout the ages.

The markings for the modern Iguanodon are actually based on the modern Fiji crested iguana, albeit in a cedar rather than emerald green and with no teal scales. Also like this iguana, I made the skin around the nostrils yellow, although I'm not sure this was the most practical or aesthetically pleasing decision.

Triceratops & Co.

The first two pieces (from last summer) were in response to the still-raging "Toroceratops" controversy. This debate began in the summer of 2010, when paleontologists Jack Horner and John Scannella declared that Torosaurus represented the final growth stage of its better-known contemporary, Triceratops. The same study also found that the even more obscure Nedoceratops represented a transition from Triceratops as we knew it to the mature, formerly-known-as-Torosaurus stage. Contrary to hyperbolic headlines from that summer, this study concluded that the names Torosaurus and Nedoceratops — not Triceratops — were scientifically obsolete and ought not to be used.

Not every paleontologist agreed with this assessment and as an amateur enthusiast, I'm still not sure what to make of it. Here's how I attempted to tackle the questions of growth, species separation, and genus determination:

1) Baby Triceratops (species unknown) from the University of California Museum of Paleontology.
2) Juvenile Triceratops (species unknown) from the Burpee Museum of Natural History.
3) Adult Triceratops horridus (the older and more southerly species) from the Peabody Museum of Natural History at Yale (YPM).
4) Adult Triceratops prorsus (the younger and more northerly species), also from the YPM.
5) Nedoceratops from the National Museum of Natural History. Currently known from just this skull, so it's unclear whether it's a separate genus or an outlier among Triceratops individuals. Colored version favors the latter interpretation.
6) Torosaurus from the Academy of Natural Sciences. Cited by opponents of Horner and Scannella's study as proof that Torosaurus was a separate genus.
7) Torosaurus from the YPM. Cited by Horner and Scannella as proof that Torosaurus was actually a fully-mature Triceratops.

Colored version:

The different coloration of the two Torosaurus represents these two interpretations.

NOTE: Not illustrated to scale.

Below is much more recent sketch of Eotriceratops, a earlier relative of its namesake. The white chunks represent the known bones of this animal, which in size was on par with the largest known Triceratops, if not slightly bigger.

As far as I'm aware, only Gregory S. Paul has synonymized Eotriceratops with Triceratops thus far (see The Princeton Field Guide of Dinosaurs). Until this view gains more support, I'm content depicting it as a separate genus with distinct colors and markings.

Happy Memorial Day!

Skinning a hadrosaur 

Gryposaurus head drawing process from May 2014.

At the suggestion of Jason Poole and others, so begins a blog of my paleontology-related artwork.

Up first is some drawings I produced last autumn in Dr. Poole's dinosaur illustration class at the Fleisher Art Memorial and the Academy of Natural Sciences:

 Early draft of Giganotosaurus hunt. Limaysaurus feed and clash in the background.

Final draft of hunt (in progress).