Dinosaurs and Barbarians

Home » Posts tagged 'dinosaur'

Tag Archives: dinosaur

Panphagia, the Oldest-Known Sauropodomorph Dinosaur

For decades, South America has been regarded by paleontologists as the place where dinosaurs originated. It is here that we have our clearest record of what the oldest dinosaurs looked like. Specifically, Brazil and Argentina hold the record for the countries that possess the oldest-known dinosaur fossils. Based upon the fossils that have been uncovered in Brazil’s Santa Maria Formation and Argentina’s Ischigualasto Formation (in particular a locality known as “the Valley of the Moon”), dinosaurs are believed to have appeared during the middle of the Triassic Period about 235-230 million years ago.

Prior to the appearance of dinosaurs in the middle Triassic, smaller dinosaur-like animals scurried about within the jungles of South America. These proto-dinosaurs are known as “dinosauromorphs”. They first appeared during the early Triassic Period, and continued into the late Triassic, well after dinosaurs had appeared and established themselves. Probably the most well-known of these early dinosauromorphs is Lagosuchus, a small reptile about the size of a chicken. What made Lagosuchus and its kind different from the other reptiles which were around at the time was the fact that Lagosuchus and its close relatives ran around on two legs instead of four. This would be a major innovation which would be exploited by the earliest dinosaurs.

File:Marasuchus.JPG

The skeleton of Marasuchus, an advanced “dinosauromorph” from Argentina, dated to the middle Triassic Period about 235 MYA. It has been hypothesized that Marasuchus and Lagosuchus are in fact the same animal. Photograph by Michelle Reback (July 28, 2008). Public domain image, Wikimedia Commons.
https://commons.wikimedia.org/wiki/File:Marasuchus.JPG

For a long time, our idea of what the earliest dinosaurs looked like was shrouded in mystery. However, it seemed that the first dinosaurs were carnivores. From the 1950s until the very early 1990s, creatures like Staurikosaurus of Brazil and Herrerasaurus of Argentina were the oldest-known dinosaurs, and they were also believed to be the most evolutionarily primitive. Still, despite their supposedly archaic nature, these were fairly large animals – Staurikosaurus reached 6 to 8 feet long, and Herrerasaurus was even bigger, reaching 12 feet long. Both of these animals, and Herrerasaurus in particular, clearly would have been formidable competitors to the other carnivorous four-legged reptiles which were alive at the time. This was quite an upgrade from small chicken-sized creatures like Lagosuchus, which had existed only a short time earlier. Considering the very short time difference between the appearance of small creatures like Lagosuchus and the subsequent appearance of large meat-eating dinosaurs like Herrerasaurus, it appeared as though one of two options applied here: either dinosaurs managed to evolve into a large size within a very short length of time, or there was some intermediate species which hadn’t been discovered yet. Was it possible that there was another dinosaur, as yet undiscovered, which could fill the gap between the primitive dinosauromorphs and creatures like Herrerasaurus?

In 1991, the skeleton of a new dinosaur was discovered in Argentina by Dr. Ricardo Martinez, a paleontologist from the University of San Juan. This animal was far smaller, and it seemed more primitive, than Herrerasaurus. It measured only 3 feet long, and it appeared to have an anatomy which was less advanced than either Staurikosaurus or Herrerasaurus. In 1993, the animal was named Eoraptor, “the dawn thief”. For nearly two decades, this little animal held the title of being the oldest-known dinosaur.

However, complications arose. A closer examination of the skeletons of both Herrerasaurus and Eoraptor created doubts as to whether or not Eoraptor really was the oldest and most primitive dinosaur ever found. For example, the fewer sacral vertebrae an animal has, the more primitive it’s believed to be. Eoraptor possessed three sacral vertebrae, but Herrerasaurus had only two. This indicated that Herrerasaurus, despite being five times larger, was actually more primitive than Eoraptor. Another point of contention was the structure of the lower jaw. When Eoraptor was first discovered and described, it was believed that it possessed a less-evolved jaw structure than Herrerasaurus, but this turned out to be false. Gradually, concerns began to be raised that Eoraptor, despite its small size, was actually not as primitive as it first appeared to be. Special attention was given to the skull and the teeth. Eoraptor possessed different kinds of teeth in its mouth, indicating that it was an omnivore. A close examination of both the skull structure and the teeth made some wonder if Eoraptor was as primitive as we initially believed. In fact, there were some aspects of its anatomy that bore a bit of a resemblance to the sauropodomorph dinosaurs – the long-necked long-tailed creatures that we typically associate with the word “dinosaur” – rather than the fleet-footed meat-eating theropod dinosaurs.

In 2011, Dr. Ricardo Martinez (the same man who had found Eoraptor’s skeleton in 1991) re-classified Eoraptor as a primitive sauropodomorph. This claim was met with skepticism by the scientific community. In a subsequent study, Martinez changed his mind again and stated that Eoraptor was so archaic that it could not be placed into any definite group of saurischian dinosaurs and ought to be placed at the very base of Saurischia. However in 2013, Dr. Paul Sereno did his own evaluation of Eoraptor’s skeleton and concluded that indeed it was a primitive sauropodomorph, distantly related to other prosauropods like Plateosaurus and Anchisaurus. Even so, the overwhelming majority of the scientific community has refuted this claim. Numerous studies have been conducted on Eoraptor since it was discovered and named, and most of them state that Eoraptor is either a very primitive theropod dinosaur or else it is the earliest saurischian, appearing before the saurischians split into theropods and sauropodomorphs.

All of this raises an interesting question. If Eoraptor was not the earliest sauropodomorph, then what was?

In 2006, Dr. Ricardo Martinez was once again exploring the middle Triassic rock layers of the Ischigualasto Formation, dated to 228.3 million years ago, when he found another skeleton. It looked similar to Eoraptor, but it was noticeably larger, measuring 4.25 feet (1.3 meters) in length; Martinez thought that the skeleton was of a juvenile, and that the adult would be larger, say perhaps 6 feet long. The skeleton was incomplete, including only a partial skull. Teeth were only found in the lower jaw. The skull was clearly similar to Eoraptor’s, but it also showed some features which can be seen in very primitive sauropodomorphs like Plateosaurus. For example, the lower jaw curves downwards towards the front, which is a tell-tale feature of that group. The teeth were also very similar to those seen in prosauropods. Based upon the skull structure and the shape of the teeth, this animal seemed to be more closely related to sauropods than theropods. In 2009, the animal was named Panphagia, which is ancient Greek for “eats everything” in reference to its supposedly omnivorous diet.

Reconstruction of the skeleton of Panphagia protos. Photograph by Eva Kröcher (December 5, 2010). Creative Commons “Attribution Non-Commercial Non-Derivative 3.0 (US)”, GNU Free Documentation License (GFDL), and Free Art License. https://commons.wikimedia.org/wiki/File:Panphagia_fossil_DSC_6168.jpg.

A complete skull was not found with the skeleton, but we have enough of the bones to give us an idea of the skull’s outline. Below is an illustration that I made of what the complete skull of Panphagia might look like, based upon what was seen in the photograph that you see above. The drawing was made with a black Crayola marker.

Skull of Panphagia protos. © Jason R. Abdale (February 9, 2021).

Based upon this skeleton and the description that Ricardo Martinez and Oscar A. Alcober gave in their paper on this animal, I have reconstructed what the entire animal might look like. The creature bears a slight resemblance to prosauropods like Plateosaurus and Anchisaurus. No hands were found with the specimen. However, the illustration which accompanied Martinez and Alcober’s paper showed Panphagia sporting hands with four fingers, although the fourth digit was so small that it was probably incorporated into the wrist and wasn’t seen on the outside. The fingers themselves were longer the more distal they were to the body (in other words, the middle finger was longer than the thumb, and the pinky was even longer than the middle finger), and this was repeated in the skeletal reconstruction seen above. Since this was the reconstruction seen in both sources, I incorporated it into my own illustration.

I think that there are two issues with the illustrated reconstruction of Panphagia’s skeleton seen in the scientific paper and in the physical reconstruction seen in the photo above. Firstly, I think that the tail is too short. The animal looks conspicuously front-heavy, and the tail ought to be longer to give it better balance. Secondly, I believe that the hand structure is incorrect. Prosauropods like Plateosaurus, Massospondylus, and Anchisaurus had hands with five fingers and large thumb claws. However, it must be noted that all three of those species came from the late Triassic and early Jurassic Periods, nearly twenty to thirty million years after Panphagia’s appearance, and their hand structure may have been more evolved than that seen in archaic animals like Panphagia. However, until a more complete specimen of this animal is found, I think my reconstruction is going to remain as it is.

My drawing was made with No. 2 pencil on printer paper.

Panphagia protos. © Jason R. Abdale (February 14, 2021).

 

For more information, please read Martinez’ and Alcober’s paper on this animal, which you can see here:

Martínez, Ricardo N.; Alcober, Oscar A. (February 16, 2009). “A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha”. PLoS ONE, volume 4, issue 2. Pages 1-12. doi:10.1371/journal.pone.0004397.

https://storage.googleapis.com/plos-corpus-prod/10.1371/journal.pone.0004397/1/pone.0004397.pdf?X-Goog-Algorithm=GOOG4-RSA-SHA256&X-Goog-Credential=wombat-sa%40plos-prod.iam.gserviceaccount.com%2F20210301%2Fauto%2Fstorage%2Fgoog4_request&X-Goog-Date=20210301T093333Z&X-Goog-Expires=3600&X-Goog-SignedHeaders=host&X-Goog-Signature=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.

 

Keep your pencils sharp, everyone.

 

More photos of Allosaurus from the AMNH

Greetings friends. In an earlier post from 2014, I put up some photographs which I took of the two Allosaurus skeletons that are on public display in the American Museum of Natural History (or AMNH for short) in New York City. I’ve recently uncovered some other photos which I took during a visit there in March 2019, and so I’m posting them here. Enjoy!

 

 

News: Brian Franczak, famous paleo-artist, dead at 65

It is with a heavy heart that I announce that Brian Franczak, one of the all-time greats of paleo-art, died on August 1, 2020 in New Britain, Connecticut. He was 65 years old. The cause of death is unknown.

Brian Franczak was one of the greatest paleo-artists of the second half of the 20th Century. In fact, he might be one of the greatest ever. The man was staggeringly prolific. Churning out hundreds of artworks over his life, his drawings and paintings (especially his paintings) were featured in numerous books about dinosaurs throughout the 1980s and 1990s. He even painted the designs for the cards that came with the Jurassic Park toys in 1993. It also helped that his artwork had a very distinctive style. Nobody, absolutely NOBODY, could mistake a Franczak painting or drawing for anyone else’s.

By the late 1990s or early 2000s, Brian Franczak had essentially disappeared from public life. Information about what had happened was scarce, and all that was really known for sure was that he was living in Connecticut. By 2017, it was revealed that Brian Franczak had been diagnosed with dementia, and it was rumored that he was suffering through severe health issues.

R.I.P. Brian Franczak (January 19, 1955 – August 1, 2020). Your work and your legacy will not be forgotten.

Stegosaurus

Introduction

There are over a thousand species of dinosaurs that are known to science today. Kids, it seems, are more disposed to remember these names than adults, and I have encountered several examples of children trying to impress people by rattling off as many dinosaur names as possible. In fact, it embarrasses me to state that I used to be one of these pint-sized paleontological know-it-alls. Of all of these names, there are about twenty or so that nearly everybody knows straight off the top of their heads, and Stegosaurus is unquestionably one of them.

Stegosaurus is one of the most well-known and easily-recognized dinosaurs out there. It is the definitive Jurassic armored plant-eater that everybody knows and loves. It has been consistently featured in nearly every children’s dinosaur book going back as far as the 1950s and it is a favorite subject of paleo-artists. Ask practically anybody what a Stegosaurus is, and they can describe what one looks like for you: four legs, plates on its back, spikes on its tail, and a brain the size of a walnut.

However, there are a lot of misconceptions about this iconic Jurassic armored tank, not only regarding its intelligence but also its appearance. Paleo-artists have regularly portrayed Stegosaurus as a massive hulking brute, but new science suggests that this animal was much slimmer and elegant than how it’s commonly portrayed.

 

Discovery

The first Stegosaurus fossils were discovered in Colorado during the 1870s as part of the “Bone Wars”, an intense scientific feud between Prof. Edward D. Cope of the Philadelphia Academy of Natural Sciences and Prof. Othniel Charles Marsh of Yale University in their quest to become THE paleontologist of the late 19th Century by discovering and naming more species than the other guy. When the fossils were first uncovered, Marsh looked at the large back plates and thought that they were pieces of an enormous turtle shell; it wasn’t until later that he realized that they actually came from a dinosaur. In 1877, the fossils were officially given the name Stegosaurus armatus “the armed roof lizard”, because the back plates reminded Marsh of roof shingles.

As the Bone Wars continued, more specimens of Stegosaurus were discovered. However, O. C. Marsh was not working with complete specimens – only with partial skeletons or fragments. Therefore, whenever he found a specimen that did not look EXACTLY like something that he had already seen, he automatically assumed that it was a different species. Consequently, numerous species were ascribed to Stegosaurus such as S. armatus, S. affinis, S. duplex, S. laticeps, S. sulcatus, S. ungulatus, and probably the most well-known of all of them, S. stenops. A few of these were later determined to by synonymous. However, after a long and thorough examination of the finds, it appears that there were indeed three or maybe four distinct species.

Of all of the species that have been named, Stegosaurus stenops is probably the most widely recognized simply because more skeletons have been found of this particular species than any other. Stegosaurus stenops, therefore, might have been the most common species of its genus. However, prehistoric population percentages are extremely difficult to determine because the studies tend to be very subjective rather than objective. There might also be preservation biases in fossilization which would lead to some species being more likely to fossilize than others. The number of fossils, therefore, should not always be automatically correlated to population numbers.

Illustration of the skull of Stegosaurus stenops. Illustration from The Dinosaurs of North America by Othniel Charles Marsh. Washington D.C.: U.S. Government Printing Office, 1896.

Stegosaurus stenops might be the most well-known Stegosaurus species due to the sheer number of fossil specimens that have been found, but it wasn’t the largest member of its kind. Stegosaurus stenops reached about 25 feet long, while another species named Stegosaurus ungulatus was slightly larger, reaching 30 feet long. In fact, S. ungulatus is the largest stegosaur species that we know of in the entire world. However, a stegosaur from Europe named Dacentrurus may challenge that title. The problem is that this animal is known only from partial remains, so its total length is difficult to determine. Most sources that I have seen identify it as a medium-sized animal measuring 15 to 20 feet long, and there are only a handful of finds which hint that it might have grown larger. So, for the time being, S. ungulatus still holds the world record of “biggest stegosaur ever”.

 

Anatomy

Stegosaurus has been intensely studied ever since its discovery, partly due to its novel appearance. Even so, there are a lot of misconceptions about how this animal looked which have been perpetuated over the years.

Previous restorations have shown Stegosaurus as having a short compressed body with a highly arched back, short front legs, freakishly tall back legs, and a tail that’s substantially shorter than what you would expect. This image has been copied for decades and it has become so engrained into our consciousness that we automatically assume that this is how a Stegosaurus is supposed to look. One of the things that needs to be considered is that this image was completely contrary to the majority of other stegosaur species found elsewhere in Europe, Africa, India, and China, which had longer necks, shorter legs, smoothly-curving backs, and long tails. However, we just assumed that Stegosaurus was weird and didn’t fit with the majority of stegosaur anatomy, until some new discoveries were made in the 2000s.

While a complete specimen of Stegosaurus has never been found, a skeleton of a sub-adult Stegosaurus which was discovered in 2003 in Wyoming helped to substantially change our perceptions of this animal. Named “Sophie”, this 18-foot-long skeleton was 80% complete, making it the most complete Stegosaurus skeleton ever found. It took many years to clean the skeleton up, measure it, and mount it for public display in 2014. When all of the work was done, Sophie had some noteworthy aspects to her anatomy which did not fit with the traditional image, and this compelled scientists to update their reconstructions of how Stegosaurus was supposed to look. The revised image showed this animal as having much shorter back legs, a lower back, a longer stretched-out neck, and a longer tail. The resulting image is much more sinuous and streamlined than the previous image of the brooding bruising hulk that’s been around for ages.

Below is a rough sketch that I had made sometime during the late 2000s of Stegosaurus stenops based upon the information that I had at the time. This shows how Stegosaurus was believed to appear since at least the 1980s, with its conspicuously high-arched hump back, very long rear legs, and a rather short tail.

Now, here is an updated version of how Stegosaurus stenops would have looked based upon our current understanding of this animal’s anatomy. The neck is slightly longer because this creature had more cervical vertebrae than we had previously thought. The back legs aren’t as tall as we once thought they were, and this makes the back much lower and less strongly arched. Finally, the tail is noticeably longer. The resulting image is much more in-line with what we know about other stegosaur species and doesn’t make Stegosaurus appear as freakish as it once was. This drawing was made with No.2 pencil on printer paper and was made in 1:20 scale. From the tip of its nose to the tip of its tail, this drawing measures precisely 15 inches long, which would make it 25 feet long in real life.

Stegosaurus is instantly recognizable due to its back plates and tail spikes. These physical features are, anatomically-speaking, highly transformed osteoderms. The word “osteoderm” literally means “skin bone”, and it refers to any bone object which is embedded within the skin or is visible on the body’s exterior rather than forming a part of the structural skeleton. Technically, a stegosaur’s plates and spikes are osteoderms because they are attached onto the body rather than being incorporated as part of its skeleton.

While the plates and spikes may be the most obvious features to Stegosaurus’ anatomy, there were other, more subtle aspects that provided it with a certain measure of protection. Notably, there existed a series of marble-like osteoderms covering the underside of the neck where the neck connects to the skull and extending backwards for about half of the neck’s length. This almost certainly evolved as a means to protect the carotid artery and jugular vein from being torn open by a predator, yet it’s perplexing that it would only extend halfway down the neck rather than covering the entire neck. This pebbly structure forms the equivalent of a chain-mail pixane, a type of armored throat protector which was worn by Medieval knights. My gracious thanks to Mr. Ian LaSpina for his wonderful video series on Medieval armor which let me know of the existence of such an object. Please check out his website on Medieval clothing, armor, and weapons here or his YouTube channel here.

Medieval armor researcher Ian LaSpina wearing a pixane (also called a pisan or a standard), a chain-mail collar meant to protect the throat. Image courtesy of Ian LaSpina (2014), used with permission.

As stated earlier, Stegosaurus was a genus composed of three or four species, and each of them had a slightly different appearance not only in terms of their overall size but also in their body proportions, including the size and shape of the dorsal plates. The plates of Stegosaurus ungulatus are much smaller and narrower than those of Stegosaurus stenops, and they come to a pronounced sharp point at the tip. By contrast, the plates of Stegosaurus stenops were large, wide-based, and they have somewhat rounded ends.

The number of plates that Stegosaurus possessed is difficult to determine. Various sources give numbers ranging from seventeen to twenty-two plates in total. This probably has to do with the fact that most sources lump all species of Stegosaurus together, not taking into account that different species have different appearances, including different numbers of plates running along the back. It also might be partially to do with the fact that a 100% complete specimen of Stegosaurus has never been found, and therefore we cannot be entirely certain of how many plates it indeed had. The finished drawing of Stegosaurus stenops which you see above has a total of nineteen plates.

One of the topics which has generated a sizeable amount of academic debate is how the plates were arranged on the back. The earliest reconstruction of this animal shows the plates lying down on the back like overlapping fish scales. Some artists depicted this animal as having a double row of plates with the plates arranged in pairs. For much of the late 1800s and into the early 1900s, Stegosaurus was shown with the plates arranged in a single line running down the middle of the back. However, the most common arrangement that you will see nowadays is a double line of staggered alternating plates. How far apart were these two rows from each other? That, also, is a subject of conjecture. Some reconstructions show them butted up against each other along the top of the animal’s spine, forming a V-shape when seen from the front. Other artists put a gap in between the two rows, with the wideness being largely personal interpretation.

 

Depiction of Stegosaurus ungulatus made in 1896 showing it with eight tail spikes and a single line of back plates. Public domain image, Wikimedia Commons.
https://commons.wikimedia.org/wiki/File:Stego-marsh-1896-US_geological_survey.png.

 

Depiction of Stegosaurus ungulatus by Charles Knight (1901) showing it with a double row of paired plates. Public domain image, Wikimedia Commons.
https://commons.wikimedia.org/wiki/File:Stego.jpg

 

Depiction of Stegosaurus ungulatus by G. E. Roberts (1901) showing it with a double row of alternating plates. Public domain image, Wikimedia Commons.
https://commons.wikimedia.org/wiki/File:Stegosaurus_ungulatus_Roberts_1901.png

 

One of the things that you’ll notice in my drawing is that the plates are non-symmetrical. Not only are they arranged in a staggered formation along the back instead of being arranged in pairs, but also the plates on one side are of a different size and shape to the plates on the opposite side; no two plates on any Stegosaurus’ back look exactly alike to each other.

While some older sources on dinosaurs claimed that Stegosaurus’ plates were used in defense, this idea is false. Defensive armament would be better served if the plates were lying flat upon the body like overlapping armor plates, and being substantially thickened. However, the plates stand erect upon the animal’s back, leaving the sides completely unprotected. The plates are also very thin in cross-section and they would have been easily broken if they were impacted by something. Rather, the plates were almost certainly used for display. The plates extending upwards from the animal’s spine also would have made the animal look far larger than it actually was, likely as a means to deter predators.

In life, the back plates would not have been exposed bone. Instead, they would have been covered with a protective layer of keratin – the same stuff that your fingernails are made out of. Based upon the texture of the plate’s surface, it seems highly probable that these plates were not covered in scaly skin.

In addition to the dorsal plates, another distinctive feature of Stegosaurus are the four spikes on the end of its tail. While there is no official anatomical term for this feature, this weaponized tail is nowadays commonly referred to as a “thagomizer”. The name is based upon a 1982 comic from The Far Side by Gary Larson in which the tail was named in honor of a caveman named Thag Simmons who met his maker by it. Since then, it has gained popularity within the scientific community and is now an unofficial anatomical vocabulary term. It was even referenced in the fourth episode of the 2011 BBC documentary series Planet Dinosaur.

Similar to the academic debate concerning the placement and arrangement of Stegosaurus’ dorsal plates, there has likewise been an argument concerning the placement of the tail spikes. Based upon the shape of the base of these spikes, nearly all people can agree that they were angled backwards, pointing towards the tip of the tail rather than pointing forwards or directly sideways. Unfortunately, there’s not much else that we know about the spikes’ position on the body, and this has led to a lot of varying interpretations over the years. Some reconstructions and paleo-art show the spikes sticking virtually straight up, while others show them positioned outwards horizontally; this latter position has become somewhat trendy recently. However, the vast majority of 2D and 3D reconstructions show the left and right spikes positioned in a V-shape at varying degrees, with the angle being either narrower or wider depending upon the supervising museum curator, fossil preparator, or artist. So far, nobody has been able to definitively say how the tail spikes ought to be positioned. Perhaps the only way in which this debate may be settled is if a mummy is found or if a Stegosaurus specimen is found preserved in three dimensions similar to the infamous “Dueling Dinos” find.

While no skin impressions have been found in association with Stegosaurus fossils, they have been found with a related species called Hesperosaurus. It’s based upon this find that we can make inferences about what the skin of Stegosaurus would have looked like.

In 1985, the remains of a stegosaur skeleton were discovered in north-central Wyoming in rocks dated to approximately 156 MYA, in a rock layer that marks the lowest and oldest layer of the Morrison Formation. Upon careful examination of the skeleton, it was determined that this did not belong to any known species of Stegosaurus, but was instead a previously unknown genus. In 2001, it was named Hesperosaurus, “the western lizard”. Hesperosaurus differed from Stegosaurus in that it was slightly smaller (20 feet long instead of 25-30 feet) and its plates were smaller and a bit more rounded in shape. Hesperosaurus might have been the direct ancestor of the more famous Stegosaurus, but more evidence is needed before this claim can be definitively proven.

In 1995, another stegosaur skeleton was discovered in northern Wyoming in rocks dated to approximately 155-150 MYA. This skeleton was remarkable not only due to the fact that it was nearly complete, but it also contained one spot on its body with preserved skin, located on the animal’s right side in between its front right and back right legs. It wasn’t until September of 2010, fifteen years after the skeleton was discovered, that a description of this specimen was published. It was identified as belonging to Hesperosaurus.

The skin impression from Hesperosaurus consists of small non-overlapping scales which are either round, oval, or polygonal in shape. The further up the back you go, the larger the animal’s scales become, with some of the scales becoming large, oval-shaped, and surrounded by a ring of smaller scales. Most of the body’s hexagonal scales measured 2-7mm in diameter, but the oval scales higher up on the flanks are much larger than that. One rosette measured 8x10mm in area, and another further up on the back measured 10x20mm in area. These larger scales are noticeably more rounded in texture, forming distinctive “lumps”, arranged in rows lengthwise down the body. Technically these are not true osteoderms because they do not have a bony core. Instead, they could be considered as “dermal scutes”, which are nothing more than scales, like other body scales, which just happen to be unusually large and thick compared with other scales on the body. Although it cannot be proven, it’s possible that Stegosaurus had a similar skin texture to its relative Hesperosaurus.

 

Color Patterns

While skin texture can be speculated upon with a certain degree of accuracy, skin color is something that falls entirely into the realm of guesswork. To date, no preserved pigment cells have been discovered in any stegosaur fossil. Traditionally, Stegosaurus has been depicted as being green with the back plates colored in red, orange, or pink. This color scheme has been around since the 1950s, and it has been copied so many times that many people automatically think of this image whenever they hear the word “Stegosaurus”. This contrasting color scheme of green plus some color on the red end of the spectrum is visually striking and appealing to the eye, and may be the reason why it is so commonly seen to the point of it being considered a “paleo meme” to use Darren Naish’s term. But how probable is it that Stegosaurus was colored in this way? There’s really no way to tell.

Below is a colorized rendition of my updated Stegosaurus drawing showing it garbed in a traditional color scheme consisting of a mottled green with reddish plates.

One argument can be made that Stegosaurus was probably colored in more muted tones given it lived in an environment which was dry and arid for much of the year. Such a color scheme can be seen in Fred Wierum’s artwork in which he gives his Stegosaurus a distinctly desert-themed coloration of tan and brown. Unfortunately, I was not able to gain permission to use his work on this website; you can see his painting here.

Paleo-artist and children’s author Patricia Bujard has also liveried her Stegosaurus in various desert-themed color patterns. Below are a series of Stegosaurus illustrations that she has made dated, left to right: November 9, 2016. August 2, 2017. January 4, 2018. All images © Patricia Bujard. All images are used with permission. Please check out her wonderful website, Pete’s Paleo Petshop, to view more of her lovely illustrations.

steggySteggy_update2Steggy_update3

It has also been proposed by Patricia Bujard that Stegosaurus, and possibly all stegosaurs, might have been decked out with bright color patterns that are similar to venomous snakes, poison arrow frogs, or poisonous insects. Such colors would loudly advertise that it is a dangerous animal and it would serve as a warning to potential predators to back off. A color scheme which evokes this idea is a painting of Tuojiangosaurus, a stegosaur from China, made by Brian Franczak during either the late 1980s or early 1990s. In this painting, the animal is vividly portrayed in contrasting colors of black and yellowish-orange.

Here is another colorized version of my Stegosaurus drawing portraying it in a much more un-orthodox color scheme of bright black and orange stripes with a bold yellow underside, and with plates that are patterned with red, a black edge, and bright yellow “eye spots” in the center, and with black-and-yellow striped tail spikes. The message here – Stay away from me! The stripes on the body are formed by the lines of dermal scutes that are arranged on the animal’s sides. Since we only have a small patch of preserved skin from one Hesperosaurus specimen, we cannot know how extensive these scutes were on the animal’s body or if they were arranged in any kind of pattern. However, if they were arranged in a series of horizontal lines, or at least lines that more-or-less followed the body’s contours in a front-to-back arrangement, then it’s possible that these lines of scutes might have demarcated different color areas on the body. It’s just a thought. The resulting coloration is remarkably reminiscent of Brian Franczak’s painting, even though it wasn’t intended to be.  My gracious thanks to Madame Bujard for helping me with this.

Finally, here is a colorized rendition of a Stegosaurus showing a combination of the two color patterns which you see above. It has the stereotypical mottled green body, but it has the more vibrantly-colored plates seen in the second drawing. Personally, I like this one the best.

It has come to my attention that I have quite a few illustrations portraying dinosaurs patterned in broad longitudinal black stripes, including Dryosaurus and Camptosaurus. Hmmm. I don’t like making my dinosaurs look too similar to each other, but honestly, I cannot imagine these two species looking any other way. After all, both Dryosaurus and Camptosaurus are supposed to be related to each other, being primitive iguanodonts. However, the similarity of the stripes on Stegosaurus with the previously-mentioned species was entirely coincidental.

I hope you enjoyed this article. Please like, comment, and subscribe, and as always, keep your pencils sharp.

 

Allosaurus, revised

Greetings, all. For those who regularly visit this website, you will know that this post has been a long time coming. Years ago, I mentioned that I was planning on re-doing my Allosaurus drawing so that it would be more accurate. However, that project always seemed to be shuffled onto the back-burner in place of other things that I was working on. Well not anymore. I recently completed a detailed drawing of an Allosaurus head (another one of the projects on my to-do list that I never seemed to get around to doing) which you can look at here, and I’m happy to state that after a long delay, I’ve finally completed my updated full-body Allosaurus.

Below is an Allosaurus drawing which I made in July of 2013 and which I posted to this website at that time. This portrays Allosaurus in a color scheme based upon that seen in the 1999 BBC series Walking With Dinosaurs. I must state that, as flawed as this illustration is, this piece was actually itself an updated version of a drawing that I had made a couple of years earlier. Even so, upon reflection, while it was an improvement on my previous work, it still needed more improvement.

And here is my revised Allosaurus drawing, made in July of 2020. This drawing was made in 1:20 scale, which is my preferred scale for illustrating prehistoric animals. From the tip of its nose to the tip of its tail, this drawing measures precisely 21 inches long, which would make the real-life animal 35 feet long; this measurement is regularly given as the maximum size for Allosaurus fragilis. This drawing was made with No.2 pencil on printer paper.

Finally, here is a colorized version of the new drawing. Again, the color scheme is based upon that seen in Walking With Dinosaurs, but the coloration and the color patterns differ slightly from the original image seen at the top. The picture was colored using Crayola colored pencils and No.2 pencil for re-shading.

Nearly everything about my previous drawing was altered in order to make this present artwork. This includes:

  1. The head was changed to be more accurate in appearance. Designing the head took most of the research time.
  2. The shape of the eye’s pupil was changed from a sort of oval slit to being a circle.
  3. The neck was made thicker, more muscular, and not as strongly S-curved.
  4. The body was made deeper.
  5. The arms were slightly enlarged and the hands were changed to be more anatomically accurate.
  6. The legs were thickened to provide extra weight support.
  7. The orientation of the hip bones was shifted.
  8. The tail was thickened to provide better balance to the front of the body. The previous drawing was conspicuously front-heavy.
  9. The tail was slightly elongated.

As you can see, one of the major changes to this drawing was the addition of dermal scutes along its back and sides. Unlike osteoderms, dermal scutes are scales which are enlarged and unusually thick compared to other scales on the rest of the body. There is evidence from preserved skin impressions from stegosaurs and ceratopsians that their skins possessed patterns of dermal scutes, sometimes arranged in lines, and it is therefore possible that theropods had such a feature to their outward appearance as well. It also gives this particular Allosaurus a distinctly reptilian look to it. I decided not to include any type of feathering or some other filamentous structures to the skin.

I also chose to portray this animal in a walking pose rather than running. I think that too many of my drawings of bipedal dinosaurs portray them running Gregory Paul-style, and I wanted to show something more natural. Also, unlike Scott Hartman’s illustrations, the legs are not splayed so widely apart from each other that they’re halfway to performing a split. Mostly, a normal walking stride is about three times the length of the foot. In fact, I actually practiced walking back and forth in front of a mirror, bending my legs theropod-style, in order to get a rough idea of how the leg position on this drawing ought to look.

Keep your pencils sharp, everyone.

Allosaurus head

Hello everyone. Here is a drawing of the head of Allosaurus fragilis, the top predator of the Morrison Formation of Late Jurassic North America. This drawing has been on my to-do list for quite some time, and I’m happy that it’s finally finished. The drawing was made with No. 2 pencil on printer paper.

Some Morrison Formation Sauropods: Apatosaurus, Barosaurus, and Diplodocus

Hello everyone. Here are some simple sketches of three Late Jurassic sauropod dinosaurs from the Morrison Formation of western North America: Apatosaurus, Barosaurus, and Diplodocus. All three of these sauropods are members of the family Diplodocidae, which includes the eponymous Diplodocus and any other sauropod that’s more closely related to Diplodocus than to any other sauropod group. The “diplodocids”, as these species are sometimes called, are distinctive for having long peg-like teeth in the fronts of their jaws (good for raking and stripping, but not well-suited for biting), a nares (the hole in the skull that contains your nostril openings) that’s located on the top of the skull, and long tapering whip-like tails.

The first is Apatosaurus louisae, which measured around 75 feet long. Like all diplodocid sauropods, Apatosaurus had a long whip-like tail, but it also had a massive thickly-built neck. Some paleontologists hypothesize that Apatosaurus used its neck in whacking contests during the mating season like modern-day giraffes. You can read more about that here.

Apatosaurus louisae. © Jason R. Abdale. May 11, 2020.

 

Next is Barosaurus lentus, which measured around 85 feet long. This animal was made famous by the impressive display in the entrance hall of the American Museum of Natural History in New York City. Notice that the neck and the tail are almost the same size; the tail is only slightly longer.

Barosaurus lentus. © Jason R. Abdale. May 11, 2020.

 

Finally is Diplodocus carnegii, which measured around 90 feet long. For a long time, this animal held the record as the longest dinosaur ever, until it was challenged by Supersaurus, Seismosaurus (which is almost certainly another species of Diplodocus), and various titanosaurid sauropods from South America. Of all of the diplodocid sauropods, Diplodocus itself had the longest tail. Some have speculated that the long ribbon-like tails of Diplodocus and its kind were used like whips, and it was even calculated that they could be cracked like a modern-day bull-whip. In the early 1990s, a partial skeleton of a Diplodocus-like dinosaur was found in Howe Quarry, Wyoming which had preserved skin impressions, including a series of keratin spikes similar to those seen on the back of an iguana lizard. An article was published about this discovery in 1992, which you can read here, although it wasn’t expressly stated within the report that the creature in question was indeed a Diplodocus. However, many paleo-artists ran with the idea anyway, and it was even incorporated into the 1999 BBC television series Walking With Dinosaurs. Since this is the prevailing trend, I decided to outfit my Diplodocus razorback-style as well.

Diplodocus carnegii. © Jason R. Abdale. May 11, 2020.

 

Next is an image showing a size comparison between Apatosaurus (75 feet), Barosaurus (85 feet), and Diplodocus (90 feet). For some people, it can be difficult to mentally grasp the size and the anatomical differences of these animals just by looking at numbers on a page. Perhaps by looking at this picture, you can truly appreciate the differences in the size proportions. Apatosaurus is a muscular beast. Barosaurus looks like a see-saw with legs. Diplodocus‘ tail measures three-fifths of its whole body length. So, as you can see, not all sauropods are the same.

A size comparison between Apatosaurus (75 feet), Barosaurus (85 feet), and Diplodocus (90 feet). © Jason R. Abdale. May 11, 2020.

Keep your pencils sharp, everyone.

Evidence of Therizinosaurs in North America during the Late Cretaceous Period

Introduction

For many years, paleontologists have known about the presence of therizinosaurs (formerly classified as segnosaurs) in Asia, especially within what’s now Mongolia and China. However, Asia and North America were linked during a considerable portion of the Cretaceous Period, and this resulted in an interchange of faunas between the two continents, notably ceratopsians, pachycephalosaurs, tyrannosaurs, and maniraptorans. Could therizinosaurs, which had hitherto been exclusively Asian, have lived in North America as well?

A pair of Tarbosaurus attacking a herd of Therizinosaurus somewhere in Mongolia, approximately 80 million years ago. © Gregory S. Paul (1988). Image used with permission.

 

During the early 2000s, that question was answered with a definitive “yes”. Two genera of therizinosaurs have been described from North America, named Falcarius and Nothronychus. Falcarius represents possibly the earliest stage in therizinosaur evolution, dated to the early Cretaceous Period, while Nothronychus is much larger and more advanced and is dated to the middle Cretaceous. The presence of these two creatures clearly shows that therizinosaurs existed in North America, but so far they have only been found in rocks dated to the early and middle parts of the Cretaceous Period. One wonders if therizinosaurs managed to stay in North America right up until the end of the Mesozoic, 66 million years ago. Would they have kept evolving, becoming larger and more advanced? Would they have lived alongside Triceratops and Tyrannosaurus? (1)

It just so happens that there are a few pieces of evidence here and there which suggest that therizinosaurs did survive past the middle Cretaceous within North America, and that they kept living in North America up to the end of the Cretaceous Period.

 

The Evidence

The idea that there were therizinosaurs in late Cretaceous North America was first proposed by the German paleontologist Hans Sues in 1978. Specifically, he was writing about a particular specimen that had been uncovered in the Dinosaur Park Formation, located in Alberta, Canada, in rocks dated to the Campanian Stage of the Cretaceous Period. The specimen in question was a single “frontal” bone, which forms part of the skull. Today, this specimen is in the collections of the Carnegie Museum of Natural History, categorized as “CMN 12355” (NOT 12349 as you’ll sometimes see in internet searches). In his paper, Sues thought that this frontal bone belonged to a “raptor” dinosaur, and listed it as “gen. et sp. indet.”, which is an abbreviated Latin way of saying “genus and species undetermined” (2).

“CMN 12355”: A frontal bone which may belong to a therizinosaur. Left top: ventral view. Right top: dorsal view. Left bottom: lateral view. Right bottom: medial view. © Tracy Ford. Image from Paleofile.com. Used with permission. http://www.paleofile.com/Dinosaurs/Theropods/Segnosaurincertae.asp

 

Saying that this bone belonged to a raptor is understandable, since the dromaeosaurs and the therizinosaurs are related to each other. Both groups are located in a clade called the “maniraptorans”, which includes the ornithomimids, the oviraptorosaurs, the therizinosaurs, and famously, the dromaeosaurs and troodontids – the so-called “raptors” with their famous killing claws.

The second piece of evidence came in the early to mid 1980s. A single bone called an “astragalus”, which forms part of the ankle, was found in the Hell Creek Formation in rocks dated to the very end of the Cretaceous Period. In 1984, the Canadian paleontologist Dale Russell listed this single peculiar find in a long list of specimens uncovered in the Hell Creek Formation during the middle 1980s. However, this particular specimen has never been analyzed or described in a publication exclusively devoted to this bone. It is simply listed as “therizinosaurid indet.”. In 1992, Kenneth Carpenter looked at this bone, and concluded that it actually belonged to Tyrannosaurus, not a therizinosaur (3).

In 1987, the Canadian paleontologist Philip Currie, who is widely acknowledged as the world’s expert on meat-eating dinosaurs, took a second look at the frontal bone which Sues had examined in the late 1970s, and concluded that Hans Sues had made a mistake. It wasn’t a raptor, but was instead a “segnosaur”, which was the way therizinosaurs were called back then. Currie stated that the bone looked similar to the frontal bone of an Asian therizinosaur called Erlikosaurus, and so he reclassified the bone as “cf. Erlikosaurus” (4).

In 1992, Philip Currie did a more thorough examination of possible therizinosaur finds in Canada. He again wrote about the frontal bone which was initially described in 1978, but he also added two more specimens to the discussion table, both of which were housed in the collection of the Royal Tyrell Museum of Paleontology (RTMP). These specimens were given the identification codes “RTMP 81.16.231” (again, Currie classified this specimen as “cf. Erlikosaurus”) and “RTMP 79.15.1” (a “pedal ungual”, or foot claw, which was classified as “cf. therizinosaurid”) (5).

“RTMP 79.15.1”: A foot claw which may belong to a therizinosaur. © Tracy Ford. Image from Paleofile.com. Used with permission. http://www.paleofile.com/Dinosaurs/Theropods/Segnosaurincertae.asp

 

In 2001, Michael Ryan and Anthony Russell conducted their own analysis of North American therizinosaur finds. They confirmed Currie’s claim that the frontal bone found in 1978 did indeed come from a therizinosaur. They also wrote about a neck vertebra found in the Scollard Formation (specimen identification code is “RTMP 86.207.17”), which dates to the very end of the Cretaceous Period, and which they classified as “Therizinosauridae indet.” (6).

Body fossils of therizinosaurs may be rare in North America, but footprints which may belong to therizinosaurs are more abundant. The first footprints were discovered in the 1990s in the Harebell Formation of northwestern Wyoming. According to an article published in 1996, these footprints were unique because they looked like theropod prints except that they had four toes instead of three – unique among theropods, therizinosaurs have four main toes. The authors postulated that the footprints belonged to an animal whose physical remains had not yet been discovered (7).

In 2011, a single therizinosaur footprint was discovered in Denali National Park, Alaska. The rock that the footprint was found in was part of the Cantwell Formation, which spans 80-65 MYA, and the footprint was placed in a layer dated to about 71-69 MYA. Depending upon which source that you read concerning geological dating, this date of 71-69 MYA either marks the boundary between the where the Campanian Stage ends and the Maastrichtian Stage begins, or else it is the earliest phase of the Maastrichtian Stage. In 2012, Anthony R. Fiorillo of the Perot Museum of Nature and Science (located in Dallas, Texas) published an article concerning this peculiar footprint (8). You can see a photo of it here.

In 2013 and 2014, Anthony R. Fiorillo and a team of other researchers returned to the site in Denali National Park and found a total of thirty-one therizinosaur footprints, along with numerous hadrosaur footprints as well. Like the first footprint that had been found in 2011, all of the other footprints were in rock dated to 71-69 MYA. The fact that footprint trackways of both hadrosaurs and therizinosaurs were found together might indicate that these animals traveled together, possibly for mutual protection. An article was published in August 2018 detailing these discoveries (9).

 

Species Identification

As we have seen in the previous section, there is some evidence in the way of footprints and a handful of isolated bones which suggests that therizinosaurs inhabited North America during the late Campanian or early Maastrichtian Stages of the Cretaceous Period. However, is there any way that we can identify which particular genus or species that these fossils belong to?

The subject of identification has been especially contentious concerning the footprints that were found in Wyoming and Alaska. So far, footprints form the majority of finds that are attributed to late Cretaceous therizinosaurs within North America. The problem is that it is difficult to identify a particular genus or species based solely on footprints, unless the shape of the footprint is extremely distinctive. Another problem is that while footprints are abundant, very few body fossils have been found, and none of them are highly diagnostic. Most researchers who examined them determined vaguely that the creature was a therizinosaur, but they couldn’t be more specific than that, with the exception of Philip Currie who proposed that they might belong to Erlikosaurus or a creature very similar to it.

Because it is so difficult to match a footprint with a particular animal, paleontologists often ascribe footprints their own genus and species names. This is what is referred to as an “ichnogenus”, which is a genus of animal known only from trace fossils, such as footprints, rather than actual physical body fossils.

In the 1996 article which discussed the unusual footprints found in Wyoming, the footprints were ascribed to the ichnogenus Exallopus (pronounced as Ex-ALLO-pus, meaning “from different foot” due to its unusual shape) and its species name was given as Exallopus lovei. The type specimen is identified as “DMNH 5989”, and it was identified as a coelurosaur. According to the website Fossilworks, “Its type locality is Whetstone Creek tracksite, which is in a Maastrichtian terrestrial sandstone in the Harebell Formation of Wyoming” (10). The following year in 1997, the genus name was changed from Exallopus to Saurexallopus (SORE-ex-ALLO-pus), because the name Exallopus was already taken by a species of marine worm (11). Another species, Saurexallopus zerbsti, was named in a 2003 article. The type specimen is identified as “CUMWC 224.2”. According to Fossilworks, “Its type locality is Zerbst Ranch Tracksite, which is in a Lancian fluvial sandstone/sandstone in the Lance Formation of Wyoming” (12). In 2014, a third species was named called Saurexallopus cordata based upon a single footprint fount in British Columbia, Canada, and dated to the Wapiti Formation of the late Cretaceous Period (13).

While all of the scientific articles concerning Saurexallopus identify it as a theropod, there has been some dispute as to what particular type of theropod it is. The original article which was written in 1996 identified it as a coelurosaur. In 2012, Anthony Fiorillo and Thomas Adams identified Saurexallopus as a therizinosaur (14). In an article written in 2015, Saurexallopus was identified as an oviraptorid (15). In an article written in 2018, Saurexallopus was simply identified as a theropod without any specific affinity (16). The website Fossilworks identifies Saurexallopus as a therizinosaur (17).

 

Reconstructing Saurexallopus

During the late 1980s and early 1990s, Philip Currie made comparisons between the various finds in North America with the Asian species Erlikosaurus. According to a phylogenic analysis of therizinosaur genera which was conducted in 2019, Erlikosaurus was closely related to Nothronychus, a therizinosaur which lived in North America during the middle Cretaceous Period. Since Saurexallopus is believed to be physically similar to Erlikosaurus, it is likely that it was genetically related as well, and as such would have been genetically related to Nothronychus. It is therefore quite possible that Erlikosaurus, Nothronychus, and Saurexallopus would have been similar in appearance (18).

Erlikosaurus skull and foot.jpg

Upper jaw and right foot of the Asian therizinosaur Erlikosaurus. Saurexallopus was probably similar in appearance to this genus. Illustration from Rinchen Barsbold and Altangerel Perle (1980) “Segnosauria, a new infraorder of carnivorous dinosaurs”. Acta Palaeontologica Polonica, 25 (2): pages 187-195. https://www.app.pan.pl/article/item/app25-187.html. Creative Commons Attribution License.

 

We can guess that Saurexallopus reached a similar length to Erlikosaurus, measuring about fifteen to twenty feet long (Holtz claims that Erlikosaurus was smaller than other authors do, although his estimate of Nothronychus is in fitting with the size bracket mentioned above) (19). Unlike the eponymous Therizinosaurus, which possessed long scythe-like finger claws (hence its name, which translates to “scythe lizard”), Nothronychus possessed shorter hook-shaped claws, which looked very similar to the stereotypical talons that are seen on carnivorous dinosaurs like Allosaurus and Torvosaurus. These claws were only one-third the size of the claws of Therizinosaurus, but they were well-suited for pulling down branches, for digging (if they could pronate their hands, but that’s a whole other argument), and for smacking the daylights out of any would-be predator. Thomas R. Holtz Jr. has compared therizinosaurs to the large ground sloths of the Cenozoic Era, and the analogy has some merit (20). Saurexallopus and other therizinosaurs likely lived a similar lifestyle and occupied a similar ecological niche, with the possible exception of Falcarius, which may have had a more cursorial lifestyle similar to early coelurosaurs like Ornitholestes.

Based upon their place within the dinosaur family tree, as well as from fossil finds, we are fairly certain that therizinosaurs were feathered. Therefore, it is almost certain that Saurexallopus would have had some form of feather covering as well, although whether it was over the entire body or only partially cannot be determined.

Below is a drawing that I made of Saurexallopus, based upon Erlikosaurus and Nothronychus. The erect mane running down the middle of its neck, back, and tail are just artistic conjecture.

Saurexallopus. © Jason R. Abdale. May 7, 2020.

 

Conclusions

So where does all of this information lead us? So far, there is some evidence which suggests that therizinosaurs were living in Alberta, Canada and Alaska, USA during the late Campanian Stage or early Maastrichtian Stage of the late Cretaceous Period up until about 70 MYA or thereabouts. As such, they would have lived side-by-side with creatures such as Albertosaurus, Edmontosaurus, and Hypacrosaurus. There is only one piece of evidence, a single neck vertebra, which suggests that therizinosaurs existed in North America during the Maastrichtian Stage of the Late Cretaceous. However, no specimens that can be definitely and unquestionably identified as belonging to a therizinosaur have been found in the Hell Creek Formation. Therefore, as far as our current evidence goes, it is unlikely that therizinosaurs lived side-by-side with Triceratops and Tyrannosaurus. However, this may change in the future if more body fossils are discovered.

 

Sources

  1. Utah’s Dino Graveyard; When Dinosaurs Roamed America.
  2. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172.
  3. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172; Dinosaur Mailing List. “Re: Yet even more questions (and I’m sure there’ll be more…)”, by Mickey Mortimer (June 22, 2002). http://dml.cmnh.org/2002Jun/msg00369.html; Theropod Database. “Therizinosauroidea”. http://theropoddatabase.com/Therizinosauroidea.htm.
  4. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172.
  5. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172; Dinosaur Mailing List. “Re: Yet even more questions (and I’m sure there’ll be more…)”, by Mickey Mortimer (June 22, 2002). http://dml.cmnh.org/2002Jun/msg00369.html.
  6. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172.
  7. J. D. Harris, K. R. Johnson, J. Hicks and L. Tauxe (1996). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming”. Cretaceous Research, 17: 381-401.
  8. Anthony R. Fiorello and Thomas L. Adams (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400.
  9. Anthony R. Fiorello and Thomas L. Adams (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400; “The Lower Cantwell Formation and Its Fossils”; “Therizinosaur: prehistoric predator set standard for ‘weird’ in Alaska”; “First North American co-occurrence of Hadrosaur and Therizinosaur tracks found in Alaska”.
  10. Fossilworks. “Saurexallopus lovei”. http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=65844.
  11. J. D. Harris, K. R. Johnson, J. Hicks and L. Tauxe (1996). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming”. Cretaceous Research, 17: 381-401; J. D. Harris (1997). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming: a correction”. Cretaceous Research, 18: 139.
  12. Martin G. Lockley, G. Nadon, and Philip J. Currie. (2003). “A diverse dinosaur-bird footprint assemblage from the Lance Formation, Upper Cretaceous, eastern Wyoming; implications for ichnotaxonomy”. Ichnos, 11: 229-249; Fossilworks. “Saurexallopus zerbsti”. http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=81011.
  13. R. T. McCrea, L. G. Buckley, A. G. Plint, Philip J. Currie, J. W. Haggart, C. W. Helm, and S. G. Pemberton (2014). “A review of vertebrate track-bearing formations from the Mesozoic and earliest Cenozoic of western Canada with a description of a new theropod ichnospecies and reassignment of an avian ichnogenus”. In Lockley Martin G.; Lucas, Spencer G., eds. New Mexico Museum of Natural History & Science. Bulletin 62: Fossil Footprints of Western North America. Albuquerque: New Mexico Museum of Natural History & Science, 2014. Page 87.
  14. Anthony R. Fiorello and Thomas L. Adams (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400.
  15. R. T. McCrea, D. H. Tanke, L. G. Buckley, M. G. Lockley, J. O. Farlow, L. Xing, N. A. Matthews, C. W. Helm, S. G. Pemberton and B. H. Breithaupt (2015). “Vertebrate ichnopathology: pathologies inferred from dinosaur tracks and trackways from the Mesozoic”. Ichnos, 22 (3–4): 235-260.
  16. Martin Lockley, Gerard Gierlinski, Lidia Adach, Bruce Schumacher, and Ken Cart (2018). “Newly Discovered Tetrapod Ichnotaxa from the Upper Cretaceous Blackhawk Formation, Utah”. In Spencer G. Lucas and Robert M. Sullivan, eds. New Mexico Museum of Natural History and Science. Fossil Record 6, Volume 2: Bulletin 79. Albuquerque: New Mexico Museum of Natural History and Science, 2018. Pages 469-480.
  17. Fossilworks. “Saurexallopus”. http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=65843.
  18. Scott Hartman, Mickey Mortimer, William R. Wahl, Dean R. Lomax, Jessica Lippincott, and David M. Lovelace (2019). “A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight”. PeerJ, 7: e7247. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6626525/.
  19. David Lambert, The Dinosaur Data Book (New York: Avon Books, 1990), page 61; Don Lessem and Donald F. Glut, The Dinosaur Society Dinosaur Encyclopedia (New York: Random House, 1993), page 184; Peter Dodson, The Age of Dinosaurs (Lincolnwood: Publications International Ltd., 1993), page 142; Thomas R. Holtz Jr, Dinosaurs: The Most Complete, Up-To-Date Encyclopedia for Dinosaur Lovers of All Ages (New York: Random House, 2007), page 382.
  20. Thomas R. Holtz Jr, Dinosaurs: The Most Complete, Up-To-Date Encyclopedia for Dinosaur Lovers of All Ages (New York: Random House, 2007), page 147.

 

Bibliography

Books:

  • Dodson, Peter. The Age of Dinosaurs. Lincolnwood: Publications International Ltd., 1993.
  • Holtz Jr., Thomas R. Dinosaurs: The Most Complete, Up-To-Date Encyclopedia for Dinosaur Lovers of All Ages. New York: Random House, 2007.
  • Lambert, David. The Dinosaur Data Book. New York: Avon Books, 1990.
  • Lessem, Don; Glut, Donald F. The Dinosaur Society Dinosaur Encyclopedia. New York: Random House, 1993.

Articles:

  • Fiorello Anthony R.; Adams Thomas L. (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400.
  • Fiorillo, Anthony R.; McCarthy, Paul J.; Kobayashi, Yoshitsugu; Tomsich, Carla S.; Tykoski, Ronald S.; Lee, Yuong-Nam; Tanaka, Tomonori; Noto Christopher R. (August 3, 2018). “An unusual association of hadrosaur and therizinosaur tracks within Late Cretaceous rocks of Denali National Park, Alaska”. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-30110-8. https://www.nature.com/articles/s41598-018-30110-8.
  • Harris, J. D.; Johnson, K. R.; Hicks, J.; Tauxe; L. (1996). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming”. Cretaceous Research, 17: 381-401.
  • Harris, J. D. (1997). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming: a correction”. Cretaceous Research, 18: 139.
  • Hartman, Scott; Mortimer, Mickey; Wahl, William R.; Lomax, Dean R.; Lippincott, Jessica; Lovelace, David M. (2019). “A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight”. PeerJ, 7: e7247. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6626525/.
  • Lockley, Martin G.; Nadon, G.; Currie, Philip J. (2003). “A diverse dinosaur-bird footprint assemblage from the Lance Formation, Upper Cretaceous, eastern Wyoming; implications for ichnotaxonomy”. Ichnos, 11: 229-249.
  • Lockley, Martin; Gierlinski, Gerard; Adach, Lidia; Schumacher, Bruce; Cart, Ken (2018). “Newly Discovered Tetrapod Ichnotaxa from the Upper Cretaceous Blackhawk Formation, Utah”. In Spencer G. Lucas and Robert M. Sullivan, eds. New Mexico Museum of Natural History and Science. Fossil Record 6, Volume 2: Bulletin 79. Albuquerque: New Mexico Museum of Natural History and Science, 2018. Pages 469-480.
  • McCrea, R. T.; Buckley, L. G.; Plint, A. G.; Currie, Philip J.; Haggart, J. W.; Helm, C. W.; Pemberton, S. G. (2014). “A review of vertebrate track-bearing formations from the Mesozoic and earliest Cenozoic of western Canada with a description of a new theropod ichnospecies and reassignment of an avian ichnogenus”. In Lockley Martin G.; Lucas, Spencer G., eds. New Mexico Museum of Natural History & Science. Bulletin 62: Fossil Footprints of Western North America. Albuquerque: New Mexico Museum of Natural History & Science, 2014. Pages 5-94.
  • McCrea, R. T.; Tanke, D. H.; Buckley, L. G.; Lockley, Martin G.; Farlow, James O.; Xing, L.; Matthews, N. A.; Helm, C. W.; Pemberton, S. G.; Breithaupt, B. H. (2015). “Vertebrate ichnopathology: pathologies inferred from dinosaur tracks and trackways from the Mesozoic”. Ichnos, 22 (3–4): 235-260.
  • Zanno, Lindsay Elizabeth. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008.

Websites:

Videos:

  • Utah’s Dino Graveyard. The Discovery Channel, 2005.
  • When Dinosaurs Roamed America. The Discovery Channel, 2001.

 

Coelurus again

Coelurus is one of my favorite theropod dinosaurs, and has been since I was young. It’s not as well-known as other Jurassic theropods like Allosaurus, Ceratosaurus, and Ornitholestes, partly because it is only known from fragmentary evidence. Yet I’m always intrigued by animals that we only have fragments of because that gives my imagination room to play. This dinosaur had pretty high popularity during the 1980s and early 1990s – it was featured in nearly every dinosaur book during that time, right alongside the more famous names that everybody knows. Since then, Coelurus has largely dropped off of the radar and has become a rather obscure species.

Coelurus had a much thinner build than its Morrison Formation coelurosaurid counterpart Ornitholestes, and it was also bigger. Ornitholestes measured 6 feet long and scarcely 2 feet tall, while Coelurus measured 8 feet long and 3 feet tall. Note the unusually long metatarsal bones. With its long lanky legs, Coelurus was probably a very good runner. I imagine it having the same ecological niche as a Secretary Bird today on the African Savannah.

I have made four previous drawings of this animal, but all of them were inaccurate in one way or another, or I was simply not satisfied with the way that the end product looked. Therefore, I decided that I needed to re-do my Coelurus yet again. This is my fifth iteration of this animal’s design, and this time I think I’ve more-or-less got it right. Made on printer paper with No. 2 pencil. The colorized version was made with Crayola and Prismacolor colored pencils.

The final image that you see below is a size comparison showing Coelurus fragilis (8 feet long) and its counterpart Ornitholestes hermanni (6 feet long) in order to give you a greater appreciation of their anatomical differences.

 

Keep your pencils sharp, everyone.

 

Camptosaurus

This is Camptosaurus dispar, a 20 foot long herbivorous dinosaur from the Morrison Formation of western North America during the late Jurassic Period. In most paleo-art, it seems that the only purpose in life for this unfortunate animal is to be Allosaurus‘ lunch! It’s not hard to see why – a large meaty animal with little or no defenses.

Camptosaurus was a primitive member of the iguanodonts, a group of ornithopod ornithischians which could chew their food. This act helped them to process their food better which in turn helped their digestive systems to extract more nutrients. One of the most well-known features of the iguanodonts was the presence of a thumb spike. On Iguanodon, the thumb spike was rather large. Being a primitive member of the iguanodont family, Camptosaurus also had a thumb spike, but it was comparatively tiny, almost the same size as its other finger claws, and would have been pretty much useless as a weapon. But hey, we all have to start off somewhere.

Paleontologists are still arguing whether Camptosaurus was primarily bipedal or quadrupedal. Personally, while I believe that Camptosaurus was capable of going down on all fours (making it a “facultative quadruped”), I think that it was bipedal most of the time.

Below are three stages of the same drawing: an outline, an outline with the color patterns drawn in, and finally a finished colored drawing. The drawing was made on printer paper with No. 2 pencil, Crayola colored pencils, and Prismacolor colored pencils.

Related article: