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The Hell Creek Formation of the north-central United States is famous for its dinosaur fossils, notably those of Tyrannosaurus, Triceratops, and others whose names are well-known to children and adults. However, this fossilized environment was home to more than just dinosaurs. The Hell Creek Formation was home to a wide range of fish, amphibians, reptiles, and mammals. One of the animals that called this landscape home during the late Cretaceous was Habrosaurus.
Despite its name, Habrosaurus was not a dinosaur, and it wasn’t even a reptile. It was, in fact, an amphibian, and a large one at that. Habrosaurus dilatus was a three-foot long siren, a type of salamander that bears more of a resemblance to an eel than the lizard-like forms that we associate salamanders with. Unlike most salamanders, sirens are fully-aquatic amphibians that retain gills throughout their whole lives, unlike other amphibian species that possess gills only in the early development stages of their lives. Sirens also possess small rudimentary lungs, and are able to breath air. There are four species of sirens that are alive today, and all of them are found within North America. Depending upon the species, they can have one to three gill slits on each side of the head. They have completely lost their hind limbs, and their front limbs have shrunk considerably, with three or four short stubby fingers on each hand. Sirens have tiny eyes and no eyelids, and possess a long tail reminiscent of an eel or a sea snake – ideal for swimming. Sirens prefer to live in slow-moving or static bodies of water with lots of underwater vegetation and muddy bottoms. They might occasionally come onto land during the night if the ground is wet or if it’s raining.
Habrosaurus is, to date, the oldest-known siren genus. So far, there are two species known: H. prodilatus, which was found in Alberta, Canada in rocks dating to the Campanian Phase (83-70 MYA) of the late Cretaceous, and H. dilatus, which is much more widespread in the western United States, being found in Montana and Wyoming (with more specimens being found in Wyoming) and dating to the Maastrichtian Stage (70-65 MYA) of the late Cretaceous, as well as being found in the early Paleocene Epoch of the Tertiary Period. This means that H. dilatus was one of several species to survive the K-T Extinction, if only for a short while. It may be possible that H. dilatus is simply the evolved form of H. prodilatus.
Habrosaurus dilatus was named by the eminent paleontologist Charles W. Gilmore in 1928. To my knowledge, six specimens have been found of this animal, and all of them have been found in stream channel deposits. The presence of this type of animal, as well as its impressive size of three feet in length, indicates the presence of large bodies of fresh water, such as slow-moving rivers or ponds. However, the possibility of a dry year was ever-present, and for a fully-aquatic or mostly-aquatic animal like Habrosaurus, that could spell doom. During dry periods or droughts, modern-day sirens are able to dig burrows into the mud and encase themselves in a cocoon, like a lungfish, and Habrosaurus might have adopted the same strategy.
Habrosaurus had rows of blunt teeth arranged in the roof of its upper jaw, which indicates that these jaws were designed for crushing rather than grabbing. Presumably, it fed upon tiny mollusks and arthropods, such as snails and shrimp. Modern-day sirens feed mainly upon worms, aquatic snails, shrimp, and occasionally algae. Like fish, sirens possess lateral lines to find prey by indicating differences in water pressure and underwater vibrations.
An appropriate modern-day analog for the three-foot long Habrosaurus dilatus is the Greater Siren (Siren lacertina), which also grows to three feet long and is the largest siren species in the world today.
Below is a simple drawing of a Habrosaurus that I made with a felt-tipped marker. This style is a considerable departure from my usual style of highly-detailed pencil drawings, but I wanted to do some artistic experimenting.
The image of Nature “red in tooth and claw” is a compelling vision which appeals to the popular imagination. Time and again, paleo-art illustrations depict dinosaurs and other prehistoric animals actively engaged in fighting, hunting, and killing. It’s a well-known fact that violence sells, and it’s also a well-known fact that the animal kingdom can sometimes be very brutal. But was the Mesozoic world really a landscape of perpetual violence and bloodshed with animals constantly engaged in the savage business of survival?
Most naturalists, biologists, and animal behaviorists today would say “probably not”. Animals do not engage in a perpetual brawl-fest with each other. Even so, animals do have violent interactions, not only among different species (inter-species combat), but also within the same species (intra-species combat). The dinosaurs were no exception to this, and we have many pieces of evidence that individuals within certain dinosaur species engaged in violent behavior towards each other.
Before I get into the particulars of the paleontological evidence, it’s important to establish some ground rules as to the sort of intra-species combat that animals engage in today, and what the dinosaurs likely engaged in during the past. Physical combat between individuals or at least physical harm inflicted by one individual upon another is typically rooted in either social or environmental causes. Animals hurt each other for a variety of reasons, but seldom is it done purely for the hell of it – only people do that. Social reasons for intra-species combat include violence associated with mating and with mate selection. Bighorn sheep rival males cranially collide with each other until one contestant or another gives up. Other individuals within numerous animal species fight each other in order to assert their right to mate. Mating-based violence can also include some very rough love – some males within certain shark species will actually bite the females in order to assert their power over the female. Speaking of this, asserting dominance is also one of the main causes for intra-species violence, regardless of whether or not mating is involved. This involves dominance within a hierarchy system, such as a lion pride or a wolf pack. Other reasons for intra-species combat are environmental, and are usually tied to the availability of food and other resources. Territorial defense in a strong motivator in this behavior, and this is strongly tied to yet another reason, which is competition of food.
Now that we have established some of the motivating factors behind why modern animals hurt each other, let’s examine the sort of intra-species combat that dinosaurs would have engaged in. For instance, many animals will kick either out of aggression, self-defense, or purely to express annoyance. One dinosaur that possibly engaged in combative kicking was the late Cretaceous ornithopod Parksosaurus. This small speedy herbivore possessed unusually long scythe-like claws on its feet. One may hypothesize that Parksosaurus engaged in kicking contests like in cockfights, or like the modern-day Australian cassowary bird. Then again, Parksosaurus could have also used these long claws for better traction when running, like the cleats on a runner’s shoes, or could have used them like digging tools to scratch into the dirt to search for food or water.
Of course, when people imagine kicking dinosaurs, the first thing that likely pops into their minds are the “raptor” dinosaurs, such as Deinonychus, Velociraptor, and Troodon. Did raptor dinosaurs, with their killing claws, do the same? The large hook-shaped toe claws were certainly used for a specific function, either ripping prey open or pinning it to the ground. I can easily imagine two bird-like raptors squabbling with each other and kicking out with their feet, like a pair of roosters, but this is purely speculative as there is no hard evidence for raptors engaging in kicking each other.
Acheroraptor. © Jason R. Abdale. July 16, 2014.
Years ago, it was proposed that another meat-eater, the late Jurassic carnivore Ceratosaurus, could momentarily balance itself on its thick tail like a kangaroo and kick out. However, this idea has since been disproven. In order for this kicking behavior to work, the tail has to be very thick and muscular and at the same time be very flexible. Ceratosaurus’ tail was deep, but thin in cross-section, more like a crocodile’s tail than a kangaroo’s. Furthermore, it only had limited up-down flexibility. For the most part, the tail was held stiff for balance, and its range of flexibility was largely confined to side-to-side motion, not up-and-down.
Ceratosaurus. © Jason R. Abdale. April 23, 2012.
Ceratosaurus is famous for having a prominent horn on the end of its nose, hence its name. However, the horn was very thin and blade-like in form, and was certainly used for display rather than offensive action. However, there were dinosaurs and other animals in the past that likely used their heads as weapons. “Head-butting”, when animals engage in combat by using their heads as hammers, possibly occurred in earlier animals, such as the dinocephalians of the Permian Period. They had thick flattened skulls, and either pressed and shoved against one another or might have collided cranium against cranium. The dinosaurs which are most associated with head-butting are the marginocephalians, “the wide skulls”, the group that includes pachycephalosaurs and ceratopsians. At first glance, their skulls seem to have been specially designed for head-on physical combat. The eponymous Pachycephalosaurus had a rounded skull that was a solid foot thick, and many scientists have automatically assumed that such skulls were used in head-butting contests, like with modern-day bighorn sheep. A recent study by the University of Wisconsin has found that 20% of pachycephalosaur skulls exhibit head trauma, suggesting with some certainty that the pachycephalosaurs did indeed engage in head-butting behavior.
Pachycephalosaurus. © Jason R. Abdale. October 19, 2013.
But what about the other members of the marginocephalians? The ceratopsians, “the horned faces”, which include the likes of Triceratops and Styracosaurus, have also been assumed to have been highly combative animals, with their spikes, horns, and frills. In recent years, the idea of these horned behemoths duking it out with each other or impaling predators on their sharpened horns has come under intense criticism. Many of their frills are dominated by wide holes which served to lighten the weight but also made them practically useless for protection. Some scientists think that the frills and horns were primarily there for display and species recognition, and their use in defense was only an afterthought.
Chasmosaurus. © Jason R. Abdale. March 31, 2016.
As you’ve probably seen by now, most of the animals which have physical features that can be used in combat are herbivores. Why? Because they sometimes have to physically fight in order to stay alive and avoid being eaten by carnivores. Aside from teeth and claws, the meat-eating theropod dinosaurs don’t seem to have much in the way of special features that would be involved in fighting, not just eating. Ceratosaurus’ nasal horn was too thin and flimsy for attacking something, and so too were the eyebrow horns of its larger contemporary Allosaurus. However, another carnivore did possess eyebrow horns which very well might have been used in fighting – Carnotaurus, one of my personal favorites. Ever since its discovery in the 1970s, paleontologists and paleo-artists have imagined this dinosaurian toro engaged in head-butting clashes with other members of its kind. However, based upon the build of the skull, it seems more likely that it was engaged in cranial “shoving matches”, in which both competitors would press their skulls against one another (hence the Velcro-like arrangement of bumps and nodules on the top of their heads in between the horns) and proceed to push and shove in a demonstration of pure muscular strength until one side or another decided that their opponent was too strong, and retreated.
While predators might not necessarily have physically struck each other with their skulls, they could have used their heads in another way that is far more common among carnivorous animals of all sorts today – face-biting. Face-biting is a way to assert dominance among individuals, especially in communal or pack-hunting societies. Several modern carnivorous animals, such as lions, foxes, and wolves, engage in this behavior. The infamous creature known as “Jane”, who might be either a Nanotyrannus or a juvenile Tyrannosaurus (to this day, nobody is exactly sure), has evidence of face-biting. Since many animals today who engage in face biting do so in order to assert their position of dominance in a pack society, this could be further evidence that this animal was itself a pack hunter, at least as a juvenile. At least one specimen of a juvenile Daspletosaurus also has evidence of face-biting. Sue the T. rex possesses marks on the jaw which were previously thought to have been the result of bites, but were later proven to have actually been caused by a bone infection.
Predators aren’t the only animals today that engage in face-biting, so there may have been herbivorous dinosaurs that engaged in the same behavior. The most likely candidate for this is the small African herbivore Heterodontosaurus. The tusks on this creature could have been wielded in actual biting, or they could have been used for fang-bearing contests like modern baboons. Many animals bear their fangs or canines when aggressive, and Heterodontosaurus possibly did this to intimidate rivals and scare off predators. Another animal that can be compared with Heterodontosaurus is the musk deer. However, their long saber-like canine teeth are grown for display, not combat. Musk deer grow huge teeth instead of growing antlers in order to over-awe rival males and to impress females.
Another possibility for serious dinosaur fights was among the sauropods. With their massive builds, any hit, no matter how light, likely would have caused some kind of damage. One modern long-necked animal that uses its body in sheer brute force is the giraffe – a rather placid-looking animal, but don’t make it angry. During the mating season, male giraffes will proceed to whack each other, swinging their long stiffened necks around like baseball bats, with the short stumpy horns on the tops of their heads inflicting some serious pounds-per-square-inch. Some sauropods, like Apatosaurus, had very massive thick necks in proportion with their body size. This leads some to speculate that Apatosaurus and its ilk used their bruiser builds to inflict bruises on others.
Apatosaurus louisae. © Jason R. Abdale. May 11, 2020.
But what about the opposite end of a sauropod? For many of them, the tail was just as long, or longer, than the neck. Tails can be effective weapons. Crocodilians and monitor lizards engage in tail whacking as a way to ward off threats. Many sauropods had thick tails, but others, like Diplodocus, have very long thin tails, and some believe that these long whip-like tails were indeed used like whips. A sharp crack across the side would make any Allosaurus wary.
Diplodocus carnegii. © Jason R. Abdale. May 11, 2020.
Of course, there are dinosaurs that almost certainly used their tails specifically for combat: the stegosaurs and the ankylosaurs. Evidence has been found for injuries inflicted by these animals upon predators, but I’m not certain if any evidence exists for stegosaur spikes or ankylosaur clubs being used upon members of their own kind. However, I can’t imagine it NOT happening.
Well, if you don’t have any biological weaponry on your side, like fangs, horns, spikes, clubs, or whatever, then raw physical force is your go-to option. There is evidence that predator species tangled with prey. The famous fossil find of a Velociraptor and a Protoceratops perpetually locked in a mutual mortal combat proves this. But this is likely an example of an attack-gone-wrong. Did dinosaurs of the same species physically grab onto and grapple with each other? Did dinosaurs wrestle, the way that some lizard species do today? Monitor lizards are a prime example of this, when two males will attack each other by essentially doing reptilian ju jitsu. Did dinosaurs wrestle? I’m not sure, but I’m leaning towards no, especially for the larger ones. Many small dinosaurs had thin delicate bones that could be easily broken, and many of the larger dinosaurs simply did not have the arm dexterity to do rough-and-tumble wrestling maneuvers the way that you see monitor lizards doing today. Furthermore, with their large size, being body-slammed to the ground would have done a lot of damage. As they say, the bigger they are, the harder they fall. Many dinosaurs show signs of physical trauma, including broken bones. Many led a very brutal life, with some skeletons being covered with injuries. For those reasons, I would say that most dinosaurs wanted to avoid intense physical combat.
Sometimes, the violence goes to its absolute extreme, and animals deliberately kill each other. Like intra-species fighting, intra-species killing has several motivating factors, both environmental and social. Animals kill each other to either reduce or totally eliminate competition over limited resources. Animals will also kill rivals to increase their own chances for mating, as well as killing the offspring of rivals to increase their own offspring’s chances for survival. As an example, new male lions that take over an existing pride will often kill all of the pride’s cubs in order to completely eliminate the legacy of the preceding male leader.
The most extreme form of intra-species combat is killing followed by cannibalism. Although it is largely taken for granted that prehistoric carnivorous animals ate their own kind under certain circumstances, there is little evidence to support this hypothesis. Some animals will kill and eat the young of other individuals in order to improve the chances of survival for their own young. Others may kill and eat their own kind out of starvation. Still others, like alligators, may view other members of their own kind as a legitimate food source, no different than any other prey item, and actively hunt, kill, and eat each other.
For a long time, it was believed with the firmest dogmatic conviction that the late Triassic dinosaur Coelophysis practiced cannibalism. However, this long-held belief has come into question upon closer examination of the famous Ghost Ranch specimens. It now appears that many of the bones which were previously believed to be inside the ribcages of others were actually lying underneath the ribcages. Furthermore, some of the bones previously identified as juvenile specimens have recently been re-identified as belonging to other reptile species. For the record, I am not stating that Coelophysis never engaged in cannibalism. I am stating that the evidence for cannibalism in this species is not as clear-cut as once believed and needs to be taken with a certain degree of doubt. If the study of paleontology has taught me anything, it’s that there is no such thing as dogma.
Coelophysis. © Jason R. Abdale. April 26, 2015.
Although there’s questionable evidence for cannibalism in Coelophysis, there is more compelling evidence in another dinosaur from the opposite end of the Mesozoic spectrum – Majungasaurus, an abelisaurid from Madagascar who lived at the very end of the Cretaceous Period. In 2007, scientists published findings that tooth marks discovered on some Majungasaurus bones matched the teeth in Majungasaurus’ jaws. So far, this is the only conclusive proof that a theropod species killed and/or ate the flesh of its own kind. I would like to say one thing, though: just because there’s evidence that an animal was cannibalized, that doesn’t necessarily mean that this individual was killed by the animal feeding off of it. As said before, scavengers will sometimes eat the dead bodies of their own kind. To them, meat is meat, no matter where it comes from. Others will not usually eat their own kind, but will do it if they’re desperate enough and cannot find other sources of food. As an example, most humans who have engaged in cannibalism do it out of necessity, not out of habit.
In conclusion, animals will hurt each other and kill each other for a variety of reasons, not only between species but also within species. Competition for mates, competition for food and territory, and establishing your position within the social hierarchy are all seen within the modern animal kingdom, and it’s highly likely that dinosaurs did the same.
Chasmosaurus was a common genus of ceratopsian dinosaur found in North America, especially Alberta, Canada circa 75 MYA. This creature is so recognizable due to its rectangle-shaped frill that it has given its name to a whole slew of other ceratopsians that are related to it – the “chasmosaurine” ceratopsians.
Made with regular No. 2 pencil on plain white printing paper. The actual drawing of the creature from the tip of the beak to the tip of the tail measures just a smidge over seven inches. Scanned at 600DPI to show as much of the detail as possible.
Keep your pencils sharp, everybody.
Triceratops was the last and largest of the ceratopsians, the “horn-faced” dinosaurs – other familiar members of this group include Chasmosaurus, Styracosaurus, and Protoceratops. Triceratops existed from about 70-65.5 MYA, and measured 30 feet long. There are currently two confirmed species: T. horridus and T. prorsus; the first one is the more famous and numerous of the two. They can be distiguished by their short nasal horns. Triceratops horridus has a short fat nasal horn, positioned a considerable way up the snout, and sticks more or less straight up, perpendicular to the line of the skull. Triceratops prorsus has a somewhat longer and thinner nasal horn, it is positioned more to the front of the nose, and it is angled forward.
There’s also been a dispute raging over the past few years as to whether or not another ceratopsian species named Torosaurus is actually another older age stage of Triceratops. This is really complicated, so I won’t even bother to get involved in this academic brawl. All I can say is that this subject appears to be just as hotly and intensely debated as the whole dispute regarding T. rex as a predator or scavenger.
The drawing which you see here is Triceratops horridus. One thing that you’ll notice is how large the head is in proportion with the rest of its body. This is not artistic license – the head really was that big! The second thing that you’ll notice is the lack of detail on the skull, showing instead a scarred but still mostly smooth surface. Paleontologists including Jack Horner and Peter Larson suspect that the top of Triceratops’ skull, including its distinctive neck frill, was covered in a layer of keratin, the same stuff that your fingernails are made of. This horny / keratinous covering might have been colored dark, as horn tends to be, or it might have been bright red due to the numerous blood vessels which are imbedded into the frill’s structure. Perhaps the males were brightly and vividly-colored, while the females were more drab and subdued.
Triceratops, regardless of which particular species, was a very populous animal. In the Hell Creek Formation, 60% of the dinosaur fossils found there belong to Triceratops.
I started drawing this picture months ago, but I got stalled with my classes and with the publication process of my book, and so I had to stick it on the shelf. These past few days, I’ve tackled it hard and completed it. I used my preferred medium, regular No.2 pencil.
Goodbye, and I hope that all of you had a good holiday.