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Brachiosaurus

There are some dinosaurs that everybody thinks of when they hear the word “dinosaur”. Among these is a very large sauropod which was the reptilian analog of a giraffe. I am, of course, talking about Brachiosaurus.

Brachiosaurus is one of the more famous dinosaurs. This animal was the iconic “giraffe of the Jurassic”, and for a while it held the record of being the largest dinosaur known. It has been featured in countless books and TV documentaries about dinosaurs, and got a major role in the 1993 movie Jurassic Park. But how much do we really know about it?

Brachiosaurus makes its debut appearance in Jurassic Park (1993).

Considering that Brachiosaurus is one of the more familiar dinosaur names, we actually know surprisingly little about it. This largely has to do with the fact that fossils of this animal are extremely rare. Our total knowledge about this animal’s anatomy comes from bits and pieces of several skeletons that were found here and there across much of the Rocky Mountains within the states of Wyoming, Utah, and Colorado, as well as one location in the extreme westernmost parts of the Oklahoma pan-handle. That’s it.

Map of locations where Brachiosaurus fossils have been found, as of 2020:
1) KU Quarry, Wyoming (KUVP 129724; KUVP 133862; KUVP 142200; KUVP 144767)
2) Freeze-out Hills, Wyoming (one caudal vertebra, undescribed)
3) Reed’s Quarry 13, Wyoming (undescribed specimen)
4) Jensen/Jensen Quarry, Utah (FHPR 17108)
5) Fruita, Colorado (undescribed specimen)
6) Riggs’ Quarry 13, Colorado (FMNH P 25107) (this is the holotype)
7) Dry Mesa Quarry, Colorado (BYU 9462; BYU 12866; BYU 12867; BYU 13023)
8) Potter Creek, Colorado (BYU 4744; USNM 21903)
9) Felch Quarry 1, Garden Park, Colorado (USNM 5730)
10) Kenton Pit 1, Oklahoma (OMNH 01138)

The discovery of Brachiosaurus dates back to the very beginning of the 20th Century. In 1900, a few very large bones were discovered in western Colorado near the small town of Fruita, located only a short distance away from the Utah-Colorado border. There wasn’t much to go on: some vertebrae, one hip bone, one femur, one humerus, and part of the shoulder. Still, the bones were distinctive enough from other sauropod dinosaurs known from the Morrison Formation to warrant classifying it as a new genus. In 1903, the creature was officially named Brachiosaurus altithorax, “arm lizard with a wide chest” by Elmer Riggs.

In 1909, a German paleontological expedition led by Wilhelm von Branca were exploring in the German colony of Tanzania when they discovered some large bones near a site called Tendaguru, meaning “steep hill” in the Mwera language. Excavations revealed that it was a partial skeleton, and similarities were soon observed between these bones and the bones that had been unearthed by Elmer Rigg’s team in Colorado several years earlier. In 1914, these bones were classified as another species of Brachiosaurus, named Brachiosaurus brancai. It helped that there was a lot more of the skeleton in this specimen, and for decades afterwards, the African species of Brachiosaurus served as the model for the North American species. However, beginning in the 1980s, doubts arose whether these animals were, in fact, two species of the same genus. A thorough compare-and-contrast analysis showed that there were actually more differences noted in each bone than similarities. Consequently in 1988, the African species was re-named as Giraffatitan brancai.

Both genera had similarities. Both Brachiosaurus and Giraffatitan were very large animals, both of them belonged to the sauropod group known as “Macronaria”, both of them had necks which could be held vertically or near-vertically rather than the horizontally-oriented necks of many other sauropods, both of them had arms which were longer than their legs (hence Brachiosaurus‘ name) which resulted in high shoulders and the back sloping downwards towards the hips, and the neck was longer than the tail. Now that we have established what they had in common with each other, how different was Brachiosaurus from Giraffatitan? Since neither skeleton is complete, and in fact Brachiosaurus is known from scant remains, it is impossible to do a comprehensive 100% compare-and-contrast analysis of both of their skeletons. However, based upon the remains which we do have, we can draw a few conclusions.

First, it appears that either A) Giraffatitan was larger, or B) Both animals were the exact same length but Giraffatitan was more physically massive. Brachiosaurus is estimated to have reached a length of 70 feet long or thereabouts with a 30 foot neck. By contrast, Giraffatitan may be the same length, but differences in body proportions (which I will describe later) meant that it was bulkier than its North American counterpart. Other estimates state that Giraffatitan exceeded Brachiosaurus in size, measuring 75 to 85 feet long.

Second, the skull shape was different. When most people imagine what the head of a Brachiosaurus looked like, they are actually imagining the head of a Giraffatitan, with its high firefighter-helmet crest. Only one partial skull of a Brachiosaurus has been found near Garden Park, Colorado; it was found in 1883, but it wasn’t identified as belonging to a Brachiosaurus until decades later. Although the skull is not complete, enough of it was preserved to indicate that it was not as tall as the skull of Giraffatitan. It appears to have had a much lower crest, sort of in-between the low curvaceous skull of an Apatosaurus and the tall crested skull of a Giraffatitan.

Skulls of Brachiosaurus altithorax (A) and Giraffatitan brancai (B). Carpenter, Kenneth; Tidwell, Virginia (1998). “Preliminary description of a Brachiosaurus skull from Felch Quarry 1, Garden Park, Colorado”. Modern Geology, volume 23. Page 73 (Pages 69–84).

Third, Brachiosaurus had larger and bulkier shoulders compared to Giraffatitan, despite the fact that Giraffatitan seems on the whole to have been larger and more robustly-built than Brachiosaurus. However, Brachiosaurus might (emphasis on “might”) have had a wider chest than its African counterpart.

Fourth, Brachiosaurus may have had a longer chest compared to Giraffatitan. This cannot be stated with 100% certainty because we have not yet found a complete vertebral column or a complete ribcage of Brachiosaurus which could give us a clear picture of the animal’s body proportions. However, if it is true that Brachiosaurus had a longer torso, it would mean that its back would have had a much gentler slope than its African counterpart.

Fifth, Brachiosaurus might have had a longer tail. Only one tail vertebra of Brachiosaurus has been found so far. However, based upon its features, it has been hypothesized that the tail would have been substantially longer than that of Giraffatitan.

The scarcity of remains hints that Brachiosaurus might have been a rare animal out on the Jurassic plains. Other sauropods such as Camarasaurus were far more common.

Like Camarasaurus, Brachiosaurus was a member of a group of sauropod dinosaurs called the “macronarians”, meaning “the large nostrils”. The skull likely acted as a resonating chamber, able to produce loud low frequency long-range noises, which would be very helpful for communicating over the vast expanses of the Morrison Formation plains. If it is true that Brachiosaurus was rare, or perhaps even a solitary animal by nature, it would still need to communicate with other members of its kind, especially during the mating season. Being able to produce such sound, which could travel over long distances, would help these animals to communicate with each other even if individuals were located miles apart from one another.

Unlike the diplodocid sauropods of the Morrison Formation such as Apatosaurus, Barosaurus, and Diplodocus, Brachiosaurus did not hold its neck in a horizontal position. Instead, it held its neck either vertically or at a diagonal angle. The act of the head sticking far above the ground would minimize the chance that the sounds that it produced would be broken up and dissipated due to ground clutter, such as rocks, trees, and even other dinosaurs. This head attached to a long vertical neck would act like a submarine’s periscope, enabling it to see for long distances, and also enabling other members of its kind to spot it from a long distance away. To make sure that it could be seen from long distances away, it is possible that the head and the neck were very brightly and vividly colored while the rest of the body was comparatively drab. It’s also possible that the head might have sported some type of decoration to further ensure that it could be spotted from miles away by other members of its species – perhaps a frill or a mane of quills or baleen-like bristles. However, color and adornment are only hypothetical conjecture and should not be taken as fact.

Below are a pair of drawings that I made of Brachiosaurus altithorax. I have adorned the top part of the neck with a series of long quills forming a mane, and I also made its head bright red in order to stand out amidst the Morrison landscape. As to the remaining colors of grey with blue stripes, I based this on the Brachiosaurus model made for the Carnegie Collection in the 1980s. The drawings were made with No. 2 pencil, No. 3 pencil, and assorted Crayola and Prismacolor colored pencils.

Brachiosaurus altithorax. © Jason R. Abdale (April 26, 2021).

Keep your pencils sharp, everyone.

List of Articles about the Morrison Formation

The Morrison Formation of western North America is my favorite geological / paleontological formation to study. Within these rock layers, which are dated to the late Jurassic Period from approximately 155 to 145 million years ago, are found the fossils of some of the most famous dinosaurs known, such as Allosaurus, Brachiosaurus, Stegosaurus, and Diplodocus. However, dinosaurs were not the only animals which lived here. This was a vibrant ecosystem home to all kinds of fish, amphibians, reptiles, and mammals.

Since I set up this website in 2013, I have written several articles concerning the animals which lived in the Morrison Formation. It can be a bit difficult for me to keep track of what I’ve already written about and what I haven’t yet, so I’ve decided to compile all of my articles here into a comprehensive list. That way, it’s easy for myself and indeed anybody to quickly use this as a reference guide to look up info about the animals of late Jurassic North America.

FISH

REPTILES

MEAT-EATING DINOSAURS

PLANT-EATING DINOSAURS

Ceratodus: The Iconic Lungfish of the Mesozoic Era

Ceratodus was a genus of prehistoric lungfish which existed on Earth for a surprisingly long time, from the middle of the Triassic Period approximately 227 million years ago to the beginning of the Eocene Epoch of the Tertiary Period about 55 million years ago – a jaw-dropping span of 172 million years! That’s impressive by ANYBODY’S standards!

Lungfish as a whole are a primitive group of fish. They first appeared during the early Devonian Period about 416 million years ago (MYA), and it’s believed that they represent an evolutionary “missing link” between fish and amphibians. The closest relatives of the lungfish are the coelacanths, meaning “hollow spines”. That’s not surprising, considering that both lungfish and coelacanths have prehistoric origins as well as that both groups are classified as “lobe-finned fish”.

Lungfish do not have individual teeth like many fish today. Instead, they have four large bone plates (two in its upper jaw, and another two in its lower jaw) that were ridged in texture and crowned with thick triangular projections, and were used for crushing and cracking. Many species of modern lungfish feed on worms, freshwater snails, crustaceans, small fish, and amphibians.

Today, there are only six surviving species of lungfish, and all of them are found in hot tropical environments. With the exception of one species found in the Amazon Jungle and another species found in northern Australia, the remaining lungfish species are found in Africa.

  1. The South American Lungfish (Lepidosiren paradoxa), found in the Amazon River.
  2. The Marbled Lungfish (Protopterus aethiopicus), which is found throughout much of eastern and central Africa.
  3. The Gilled Lungfish (Protopterus amphibius), which is also found in eastern Africa.
  4. The West African Lungfish (Protopterus annectens), which is found, not surprisingly, in western Africa.
  5. The Spotted Lungfish (Protopterus dolloi), which inhabits the Congo Jungle of central Africa.
  6. The Australian Lungfish, also called the Queensland Lungfish (Neoceratodus forsteri), found in northeastern Australia. Of all of the extant lungfish species, this one is believed to be the most primitive.

Special attention must be given to the Australian Lungfish (Neoceratodus forsteri), for not only is this species regarded as the most archaic of all of the extant lungfish, but it was once believed to be the sole surviving member of the prehistoric lungfish genus Ceratodus alive in modern times.

Skeleton of Neoceratodus forsteri. From Günther, Albert. “Description of Ceratodus, a Genus of Ganoid Fishes, Recently Discovered in Rivers of Queensland, Australia”. Philosophical Transactions of the Royal Society of London, volume 161 (1871). Plate XXX. https://www.jstor.org/stable/pdf/109041.pdf.

The lower jaw of Neoceratodus forsteri, seen from above. From Krefft, Gerard. “Description of a gigantic amphibian allied to the genus Lepidosiren from the Wide-Bay district, Queensland”. Proceedings of the Zoological Society, volume 16 (April 28, 1870). Page 222. https://ia800405.us.archive.org/16/items/biostor-107043/biostor-107043.pdf.

The genus Ceratodus was established in 1837 by the famed Swiss ichthyologist Louis Agassiz based upon teeth which were found in European rock layers dated to the Triassic and Jurassic Periods. Most Ceratodus fossils that are found consist of isolated tooth plates, and different species have been named based largely upon difference in tooth morphology. Twenty-two species of Ceratodus have been named since the genus was first described in 1837. For a long time, Ceratodus was what is known as a “waste basket taxon” – all North American lungfish fossils were ascribed to this genus, regardless of how different they were from each other. Recently, a careful re-examination of lungfish fossils have revealed that these animals are remarkably different from each other and may constitute numerous genera, not just one. If that’s the case, then the overall lifespan of Ceratodus as a genus may be dramatically shorter than was previously supposed (Günther, Albert. “Description of Ceratodus, a Genus of Ganoid Fishes, Recently Discovered in Rivers of Queensland, Australia”. Philosophical Transactions of the Royal Society of London, volume 161 (1871). Page 512).

File:Ceratodus.jpg

Ceratodus, painted by Heinrich Harder. From Animals of the Prehistoric World (1916). Public domain image, Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Ceratodus.jpg.

Ceratodus’ length varied depending on the species. Most sources which I have seen give an average length of 3 feet long. However, one species of Ceratodus may have reached truly gigantic proportions, possibly reaching 10 to 12 feet long. This estimate is based upon a single bone plate, which is the largest-known of any lungfish. The tooth plate was found in central Nebraska in rocks dated to the Miocene or Pliocene Epochs of the Tertiary Period. Shimada and Kirkland hypothesized that the tooth had been carried into central Nebraska by river from older rock layers that were located further to the west within Wyoming, in rocks dated to either the late Jurassic or early Cretaceous Periods. However, the tooth isn’t as banged up as you would expect from such a long journey. It’s possible that the tooth is endemic to central Nebraska, and if that is the case, 1) Ceratodus was alive in North America for a much longer geologic time span than previously supposed, or 2) This species is mis-identified and belongs to a new un-described genus of giant lungfish which lived in central North America about 5 million years ago, or 3) This was a species which happened to have unusually large teeth within its jaws, and the overall length of the animal was much smaller than the 4 meter estimate given by Shimada and Kirkland. Unfortunately, only one tooth plate has been discovered. Until more specimens are found, everything that we have to say about this specimen needs to be taken with a great degree of skepticism. (Kenshu Shimada and James I. Kirkland, “A Mysterious King-Sized Mesozoic Lungfish from North America”. Transactions of the Kansas Academy of Science, volume 114, issue 1 (2011). Pages 135-141. https://www.researchgate.net/publication/261964060_A_Mysterious_King-Sized_Mesozoic_Lungfish_from_North_America).

For the artwork accompanying this article, I decided to change up my style. For this drawing, I chose to evoke the whimsical style of the paleo-art of Patricia Bujard. If you don’t know who Patricia Bujard is, then I highly recommend that you check out her work. She is a children’s author and illustrator with a love for prehistoric life, and I find her artwork adorable. There aren’t too many people who can make an Allosaurus “cute”, but dag-nabbit, she somehow manages to pull it off. You can see her artwork on her WordPress page, Pete’s Paleo Petshop. My own drawing, which you can see below, was made with an ordinary Crayola black marker.

Ceratodus © Jason R. Abdale. February 9, 2021.

Keep your pencils sharp, and in this case, also keep your markers properly stored so they don’t dry out.

Fruitachampsa, the crocodile-bear-cat of the Morrison Formation

Meet the Jurassic Period’s analog of the common house cat. This is Fruitachampsa callisoni, a prehistoric reptile which inhabited western North America during the late Jurassic Period. However, this was not a dinosaur. In fact, Fruitachampsa was a distant relative of crocodiles.

The fossils of this animal were discovered by James M. Clark and George Callison near Fruita, Colorado during the middle and late 1970s within the rocks of the Morrison Formation dated to about 150 million years ago (MYA). By the late 1980s, this creature was unofficially known by the name “Fruitachampsa”, but since it had not been officially named or described in any scientific research article, this name could not yet be used. It wasn’t until 2011 that the animal was officially classified under the name Fruitachampsa callisoni, “George Callison’s Crocodile from Fruita”.

Clark, James M. “A new shartegosuchid crocodyliform from the Upper Jurassic Morrison Formation of western Colorado”. Zoological Journal of the Linnean Society, volume 163, issue supplement 1 (December 2011): S152–S172.

Fruitachampsa belonged to a group of reptiles which were related to crocodiles known as the “shartegosuchids”. These reptiles are known from the late Jurassic and early Cretaceous Periods, and all known specimens have been found in North America, Europe, and Asia. Shartegosuchids have distinctive skull features, including:

  1. A lack of anteorbital fenestrae (the hole between the nostril and the eye socket) in the upper jaw.
  2. Within the upper jaw’s palate, the choanae (the holes that connect the nostril to the inside of the mouth) are set within a deep depression in the center of the palate.
  3. The palatal bones, which form most of the inside of the mouth of the upper jaw, are joined together medially.
  4. The teeth in the lower jaw never extend posteriorly past the mandibular fenestrae.
  5. The edges of the teeth in both the upper and lower jaws are ridged with serrations – quite unlike the smooth cone-shaped teeth that are often associated with crocodilians.

The shartegosuchids are visibly similar to earlier primitive crocodyliforms such as Protosuchus, and have even been ascribed to the same family as that genus. However, they appear to be slightly more advanced than Protosuchus and other members of Protosuchidae, and may represent the next evolutionary development of crocodilians.

Fruitachampsa measured three feet long, and its body was more-or-less about the same size as a cat. Like a cat, it also had large eyes, and was therefore possibly nocturnal, preying upon the small rodent-like mammals which inhabited the Morrison Formation.

Fruitachampsa also possessed unusually long legs in proportion with the rest of its body. However, like a crocodile, it walked in a “plantigrade” style, walking on the flats of its feet like a human or a bear, rather than walking “digitigrade”, on its toes, like a cat. So perhaps we should think of Fruitachampsa less like a cat and more like a pygmy-sized long-legged bear.

Fruitachampsa possessed a double-row of rectangular osteoderms which ran down the middle of its back, in which the row in front slightly overlapped the row behind, like roof shingles or an ancient Roman legionnaire’s body armor.

Fruitachampsa callisoni. © Jason R. Abdale. December 19, 2020.

Keep your pencils sharp, everybody.

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!

 

 

Caturus

This is Caturus, a prehistoric fish which swam in the oceans during the Mesozoic Era. Fossils of this saltwater fish have been found in North America, Europe, northern Africa, and as far as China within rocks spanning from the beginning of the Triassic Period about 250 million years ago (MYA) up to the middle of the Cretaceous Period, about 100 MYA. However, most Caturus fossils have been found in Europe within rock layers dated to the middle and late Jurassic Period, about 170-150 MYA.

Despite a superficial resemblance to a salmon, Caturus was actually more closely related to a bowfin (Amia calva), which is a rather primitive ray-finned fish.

So far, paleontologists have identified fourteen species of Caturus. The largest species, Caturus furcatus, which lived in the Tethys Sea (the shallow sea that covered much of Europe during the middle Jurassic to the middle Cretaceous Period), reached three feet long; other species were much smaller. One species, Caturus dartoni, is known from North America in rocks dated to the middle Jurassic Period, about 165 MYA. Only two skeletons of this particular species have been found, the largest measuring 15 inches long.

Caturus. © Jason R. Abdale. September 5, 2020.

This drawing was made on printer paper with No. 2 pencil, No. 3 pencil, Crayola colored pencils, Prismacolor colored pencils, and Artist’s Loft colored pencils.

Pantosaurus

Hello everyone. Several years ago, I wrote a short article for Prehistoric Times magazine about the Sundance Sea. This was a shallow saltwater sea which covered much of central North America during the middle to late Jurassic Period. One of the illustrations that I made which accompanied that article was a drawing of a pair of plesiosaurs chasing after a school of belemnites. The plesiosaurs in question were called Pantosaurus. This species was a member of the “cryptoclidid” family of plesiosaurs, and measured about 20 feet long.

I thought that I had posted that drawing onto this website at that time, but looking through my portfolio, it appears that I neglected to do so. Well, better late than never! Unlike many of my other drawings, which are mostly made with No. 2 pencil or colored pencils, this one was made with a black ballpoint pen and a black marker.

Pantosaurus with belemnites. © Jason R. Abdale. November 18, 2014.

Please also look at these related articles:

Baptanodon

This is Baptanodon, an ichthyosaur which lived during the middle and late parts of the Jurassic Period about 165-155 million years ago. During this time, the central part of North America was covered with a body of saltwater known as the Sundance Sea, and Baptanodon was one of the creatures that swam in this inland ocean. It measured 20 feet long, it had freakishly huge eyes, and, as far as I have been able to learn so far, it had small teeth only in the front half of its mouth while the rear half was completely toothless. The presence of grooves running along the sides of its jaws indicate that it probably had lips and the teeth would not have been visible when the mouth was closed.

Baptanodon was closely related to the European ichthyosaur Ophthalmosaurus. In fact, for a while it was believed that Ophthalmosaurus and Baptanodon might be the same animal. However, phylogenic studies indicate that they are indeed separate.

Baptanodon shared its habitat with numerous other forms of marine life including oysters, ammonites, belemnites, hybodont sharks, as well as the 20 foot long plesiosaur Pantosaurus and the 25 foot long pliosaur Megalneusaurus.

This drawing was made on printer paper with No. 2 pencil, Crayola colored pencils, and Prismacolor colored pencils.

Baptanodon. © Jason R. Abdale. August 12, 2020.

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.

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

Champsosaurus: The Croc-Lizard of the Cretaceous

When most people hear the words “aquatic reptile”, they usually think of two things: turtles and crocodilians. Some clever people might mention sea snakes, and others might mention marine iguanas. Those who are keen on impressing you may bring up some obscure species like the water monitor, the basilisk lizard, and other species of snakes which venture into water.

In prehistoric times, the list of options that you could choose from was much more expansive. In fact, there were animals around then which aren’t around today which fit into this category. One such group of prehistoric water-going reptiles was known as the “choristoderans” (pronounced as Kore-RISS-toe-DEER-rans).

The choristoderans were a group of semi-aquatic reptiles which lived during the Mesozoic Era. Although not as well-known as other non-dinosaurian reptiles of the Mesozoic such as pterosaurs and ichthyosaurs, they nevertheless shared their environments with dinosaurs for a span of approximately 110 million years and even survived the dinosaur extinction. Choristoderans first appeared during the middle of the Jurassic Period about 175 MYA. The oldest-known genus which is recognizably a choristoderan was Cteniogenys, which measured just one and a half feet long and was very lizard-like in appearance. In life, it probably resembled a small monitor lizard and it likely filled a similar ecological niche. However, the heyday for the choristoderans occurred during the early Cretaceous Period from about 144 to 100 MYA, after which they went into decline. They were fortunate to survive the K-T Extinction, but they were always second fiddle to their crocodile neighbors. Most of the surviving species went extinct about 50 MYA, with the remainder just barely hanging on. The last of the choristoderans completely went extinct around 20 MYA.

The choristoderans belonged to a group of vertebrates called the “diapsids”, meaning that they had two holes in their skull behind each eye socket. Lizards, snakes, crocodilians, pterosaurs, dinosaurs, and birds are all classified as diapsids.

At first glance, choristoderans might be mistaken for crocodiles. However, despite their crocodile-like appearance, they are more closely related to lizards than to crocodiles, at least according to a study made by Mike Lee in 2013 (“Turtle origins: insights from phylogenetic retrofitting and molecular scaffolds”). Their placement in the reptile tree is primarily based upon the structure and arrangement of their ear bones, which is more advanced than those seen in lizards but not as advanced as those seen in crocodilians and birds. Also, the skulls of choristoderans are structurally more lizard-like than crocodilian.

The order Choristodera is divided into four families: Champsosauridae, Hyphalosauridae, Monjurosuchidae, and Simoedosauridae. The more primitive the species, the more lizard-like it is in form. The more derived, then the more crocodilian it is in appearance. The most primitive choristoderans were the monjurosuchids, which looked similar to the modern-day Water Monitor Lizard (Varanus salvator). Even at this early stage in their development, there is fossil evidence that some species like Monjurosuchus possessed webbed fingers and toes. Already, they were adapted to living a semi-aquatic lifestyle.


Skeleton of Monjurosuchus splendens, a primitive choristoderan from China. Photograph by Jonathan Chen (June 13, 2019). Creative Commons Attribution-Share Alike 4.0 International license. https://commons.wikimedia.org/wiki/File:Monjurosuchus-Beijing_Museum_of_Natural_History.jpg

Even more advanced were the hyphalosaurids, which bear a remarkable resemblance to the earlier nothosaurs and thalattosaurs of the Triassic Period. Form tends to follow function in evolution, and these creatures almost certainly led a similar lifestyle. The act of species from completely different groups evolving into more-or-less the same shape is called “convergent evolution”.

The champsosaurids and the simoedosaurids are the most crocodile-like in appearance, and together they form the super-family Neochoristodera. Like crocodiles, these creatures were almost certainly living as shallow-water ambush predators, fitted with long slender jaws lined with small conical teeth. Like modern-day gharials, they may have been primarily or even exclusively fish-eaters.

Probably the most famous choristoderan genus was Champsosaurus (pronounced as CHAMP-so-SORE-us). It first appeared about 90 MYA during the Turonian Stage of the late Cretaceous Period, persisted through the K-T Extinction, and finally went extinct during the Paleocene Epoch of the Tertiary Period about 56 MYA. Impressive. Most genera don’t last that long.

Champsosaurus was named by the famed paleontologist Edward D. Cope in the year 1877. Despite not having an easily-recognizable name (most members of the general public have likely never heard of it), it has been rigorously studied by paleontologists ever since then. For example, three academic articles were published about it just in the year 2010, and another article was recently published in April 2020. So, from an academic standpoint, interest in this animal has been pretty consistent.

There are seven species which have been ascribed to the genus Champsosaurus. Most of them measured 5 feet long or thereabouts, but the largest, which was appropriately named Champsosaurus gigas, reached 10 feet long. Most Champsosaurus fossils have been found in south-central Canada and the north-central United States within rocks dated to the late Cretaceous Period from 90 to 66 MYA, but a few have also been found in Belgium and northern France in rocks dated to the Tertiary Period.

Champsosaurus skeleton from Montana, USA on display in the Royal Ontario Museum. Photograph by Daderot (November 21, 2011). Public domain image, Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Champsosaurus_sp.,_Montana,_USA,_Late_Cretaceous_-_Royal_Ontario_Museum_-_DSC00088.JPG.

 

Upper jaw of Champsosaurus, above view (left) and underside view (right). The skull’s length measures about 13 inches. Illustration by Samuel W. Williston. From The Osteology of the Reptiles (1925). Public domain image, Wikimedia Commons. https://commons.wikimedia.org/wiki/File:The_Osteology_of_the_Reptiles_p76.png.

Champsosaurus appears to have been able to tolerate both freshwater and saltwater environments. Fossils of a species called Champsosaurus laramiensis have been found in rocks from the Fox Hills Formation, a geological layer which represents a coastal or estuary environment on the edge of the Western Interior Sea. Fossils of mosasaurs and dinosaurs including Tyrannosaurus have also been found in these rocks.

Preserved skin impressions show that, unlike many lizards, choristoderans like Champsosaurus did NOT have overlapping scales. Instead, the skin consisted of tiny non-overlapping scales, with no crocodile-like dorsal scutes, giving it a very smooth-skinned appearance when seen from a distance.

Unlike crocodiles, which have their nostrils on the top of their upper jaw, Champsosaurus had its nostrils on the front tip of its upper jaw. Perhaps they would use their long nose like a snorkel, sticking just the tip out of the water’s surface in order to stay as concealed as possible.

Champsosaurus had a pair of long thin gharial-like jaws lined with tiny conical teeth. Because of its close affinity towards lizards than to crocodiles, it is highly likely that Champsosaurus had lips and a fully enclosed mouth. But that’s just speculation based upon phylogenic relationships to other reptiles. In terms of hard physical evidence, the teeth themselves are quite small, and are inset from the edge of the jawline rather than standing on the rim of the jaw like a crocodile. This suggests that Champsosaurus had lips covering its teeth like a lizard, unlike crocodiles which don’t have lips.

Compared with crocodilians, the eye sockets of choristoderans are positioned much further forwards on the skull, located halfway or two-thirds of the way back from the tip of the snout. This provides more space for jaw muscles, and the temporal fenestrae (the holes in the back of the skull that accommodate the jaw muscles) were very large in proportion with skull size. Champsosaurus, in particular, had very large temporal fenestrae, which indicates that it had strong jaw muscles and could quickly snap its mouth shut within a fraction of a second – an important adaptation if your diet consists primarily of small fish.

Unlike lizards, Champsosaurus might not have had external ears. Analysis of its skull structure shows that Champsosaurus had internal ears, similar to turtles. This is an important adaptation if you are spending much of your life in the water. Therefore, you would not have seen a pair of ear holes on a Champsosaurus head. Instead, there likely just would have been a slight depression (or maybe not even that) on the side of the head marking where the tympanum (the part of the ear that vibrates in order to make a sound) would have been.

If you spend much of your life in the water, walking really isn’t an issue. Therefore, the limbs of choristoderans are not well-developed. In fact, the more “advanced” the species, the weaker its limb bones appear to be. Champsosaurus is no exception to this – its legs are downright puny in comparison with its body. The bones that make up the arms and legs are short and stumpy, and the hands and feet are small, although the feet are noticeably bigger than the hands. The fingers and toes are thin and end with very tiny claws. This was an animal that would have had a hard time pushing itself onto land. However, there is some evidence that females had more robustly-built limbs than the males due to the need to haul themselves onto land in order to lay their eggs.

The tail of Champsosaurus was flattened, and looked more like that of a crocodile or even a mosasaur than to a lizard. Even so, this animal was definitely not a power-swimmer. If it was, then one would expect the tail to be both longer and broader. Instead, the tail seems to be peculiarly under-developed. Keep in mind, though, that this was likely not an animal that was actively chasing after its prey. If all it was doing was hunkering down on the bottom of a lake or river and waiting motionless for fish to carelessly swim by, then it doesn’t need a well-built tail that’s designed for plowing through the water.

Skeleton of Champsosaurus laramiensis. From “The Osteology of Champsosaurus”, by Barnum Brown (1905). Memoirs of the American Museum of Natural History, volume 9, part 1. Public domain image. http://commons.wikimedia.org/wiki/File:Large_williston_champsosaurus.jpg.

Below is a drawing made of Champsosaurus laramiensis drifting about in a murky pond or stream somewhere in Montana during the late Cretaceous Period. This five-foot-long piscivore would have shared this environment with alligators, crocodiles, turtles, large freshwater fish like gars, sturgeons, and bowfins, and of course dinosaurs like Triceratops and Tyrannosaurus. The drawing was made with No.2 pencil on printer paper.

Anyways, keep your pencils sharp.