By Jack Wood 

Etymology: Reptile Shield

First Described By: Ostrom, 1970

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Ornithischia, Genasauria, Thyreophora, Eurypoda, Ankylosauria, Nodosauridae, Nodosaurinae

Status: Extinct

Time and Place: Sauropelta lived between 115 and 105 million years ago, from the Aptian to the Albian ages of the Early Cretaceous 

Sauropelta is known entirely from the Cloverly Formation of Montana and Wyoming, specifically the Himes and Little Sheep Mudstone Members 

Physical Description: Sauropelta is a Nodosaurid, a kind of armored dinosaur that featured extensive spikes and other ornaments on their bodies for sexual display. It’s also one of the better known ones, due to its fairly impressive shoulder spikes. While we know the basic structure of this armor due to its bone base, relatives of Sauropelta have helped to indicate that keratin - the same material as hair and nails - probably covered these spikes and made them even longer. This made Sauropelta and animals like it impressive to look at, with increasingly ridiculous spikes and ornaments. 

By Dino Guy 2, CC BY-SA 3.0 

Sauropelta itself was about 5. 2 meters long, making it fairly average size for a Nodosaurid. It was heavily built and squat in size, giving it the general appearance of a tent. It had a triangle shaped head, with a narrow tapering snout. It had a very flat top to its head and a thick skull covered in tightly fused plates, primarily for defense. It had leaf-shaped teeth in both the lower and upper jaws, and a ridge on the inside of its mouth that supported a small beak in the front.

It had a very long tail, half the total length of the body, with bony tendons lining along it to keep it stiff. It had a very wide body, with broad hips and ribs, giving it a very round appearance when looked at head-on. It had short front limbs compared to the hind limbs, arching its back so it was highest over the hips. It had very stout feet and limbs, as well as its shoulders and pelvis, allowing for it to support a great amount of muscle mass and weight.

Sauropelta had rows of small domes - scutes - from the top of the neck to the back of the tail. Over the back and the tail there are small nodules, which separated the larger cone-shaped scutes in parallel rows. On the hips these  nodules and scutes locked together into a shield. Sauropelta had large spines on the sides of the neck, increasing to a peak over the shoulders, and decreasing dramatically before stopping at the hips. Flat plates lined the tail on both sides, pointing out and decreasing in size towards the tail. The spines on the tail and neck were fused, reducing the amount of motion possible for both ends of the body. 

By Emily Willoughby, CC BY-SA 3.0 

Diet: The small, pointed head of Sauropelta means it was a selective browser, eating very specific plant material while foraging rather than indiscriminately eating whatever plants it wanted. It would have been a low-level browser as well, given its short height and limited range of motion in the neck. So, it probably specialized in eating berries; leaves from ferns, conifers, and cycads; and other small bits of vegetation close to the ground or fallen on the ground.

Behavior: Sauropelta is a fairly common animal from its environment and possibly lived in somewhat social groups, either with a few members or many in mixed-species herds, as many other plant eating dinosaurs lived in the same location and may have associated together. It would have been somewhat slow given its squat limb proportions, as opposed to other Nodosaurids such as Hungarosaurus which specialized in quick movements and rapid turns. As such, Sauropelta would have primarily utilized its extensive armor across its back, hips, neck, and head for defense, and may have squatted down against the ground to protect its softer underbelly from attack from predators. This could also have been helped with counter-shading, as found in a close relative Sauropelta. Counter-shading is the use of natural lighting in conjunction with the color of an animal to help disguise it and hide it in the environment, and it is known in Borealopelta, another Nodosaurid; thus, it’s possible that the same would have been found in Sauropelta, or, at least, that Sauropelta would also have been a prey species that needed to hide from predators in its environment. Thus, since Sauropelta didn’t have extensive offensive structures, it probably would have been at least somewhat more skittish than aggressive. 

By José Carlos Cortés

As an Ankylosaur, Sauropelta had a long tongue that it could use to grab food and draw in plant materia, that it would snip off with its narrow beak and jaws. They could breathe while chewing, as well, and probably had a decent sense of smell to aid in seeking out the specific sorts of food it would have preferred.

Sauropelta would probably have taken care of its young, considering that other dinosaurs tend to do so, but there is little evidence present either way for Sauropelta.

Ecosystem: Sauropelta lived in the Cloverly Formation, an Early Cretaceous Western North America ecosystem that showcases the transition from the Late Jurassic to the Late Cretaceous in this region, with many of the features of the more famous Morrison and Hell Creek formations in a weird sort of blender in terms of types of dinosaurs present. This environment lay along the Western Interior Seaway as it began to grow through North America, and extensive rivers ran through the Cloverly Formation to drain into the ocean. These rivers would flood, causing mass burials of animals and leading to the fossils of the formation. The plains were mostly forested, covered in a variety of conifers and cycads. This would lead to flooding causing extensive damage to the forest ecosystem and, as such, leading to mass die-offs of animals. 

This muddy environment transitioned to a more sandy environment, still with some mud, as it aged from the Little Sheep Member of the formation to the Himes Member. This reflected the growth of the seaway and the encroachment of beach sand towards the environment of Sauropelta and others. While many creatures died off in the transition, Sauropelta is present in both layers, indicating that it was fine with the new beachfront property. 

By John Conway, CC BY-SA 3.0 

In the earlier Little Sheep ecosystem, Sauropelta lived alongside dinosaurs such as the medium-level Ornithopod browser Tenontosaurus, the fast-moving low browser Zephyrosaurus, the ambush raptor predator Deinonychus, the Oviraptor omnivore Microvenator, and remains of large sauropods that have not yet been named. There were also non-dinosaurs such as the lungfish Ceratodus, the sharks Polyacrodus and Egertonodus, and many other bony fish, frogs, salamanders, and turtles like Glyptops. There were also mammals such as Gobiconodon, Oklatheridium, Paracimexomys, and Atokatheridium. Crocodilians and lizards were also frequenters of the environment, along with the dinosaurs.

The Himes ecosystem was somewhat different, but in many ways still quite similar to its earlier precursor. Deinonychus, Microvenator, and Tenontosaurus were still around, but there was also the very tall sauropod Sauroposeidon, a poorly known sauropod Rugocaudia, another Nodosaurid Tatankacephalus, and the large predator Acrocanthosaurus, which would definitely have been a thorn in Sauropelta’s side. There may have even been a proto-bird, but that is unconfirmed. There were lizards, frogs, salamanders, crocodilians and more basal crocodile relatives, turtles such as Naomichelys, and an extreme variety of fish and sharks. There were also mammals such as Gobiconodon, Argaliatherium, Corviconodon, Montalestes, Pappotherium, and a wide variety of others.

Sauropelta was an critical fixture of both of these time points, and would have been a defining sight in the Cloverly environment.

Other: Sauropelta may also be known from the Cedar Mountain Formation, a similar environment to the Cloverly, but these remains are largely unconfirmed at this time.

~ By Meig Dickson

Sources under the cut 

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By Ripley Cook

Etymology: Horn Roof

First Described By: Lambe, 1902

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Ornithischia, Genasauria, Neornithischia, Cerapoda, Marginocephalia, Pachycephalosauria, Pachycephalosauridae

Referred Species: S. validum, S. novomexicanum

Status: Extinct

Time and Place: Stegoceras lived between 76.7 and 75.1 million years ago, in the Campanian age of the Late Cretaceous 

Stegoceras is known from the Lower to Middle Levels of the Dinosaur Park Formation, the Fossil Forest Member of the Fruitland Formation, and the Hunter Wash Member of the Kirkland Formation 

Physical Description: Stegoceras is a Pachycephalosaur, a kind of bipedal herbivorous dinosaur made distinctive due to their dome-shaped heads and long, extraordinarily stiffened tails. It is one of the best known Pachycephalosaurs from North America, and one of the few that we actually have remains from non-skull parts of the skeleton. Stegoceras ranged from about 2 to 2.5 meters in length, about the same size as a living goat. This made it about average in terms of Pachycephalosaur size, and about the same general size as any small bipedal Ornithischian. 

By Steveoc 86, CC BY-SA 4.0

It had a very rigid spine, with the vertebrae tightly locked together and then the muscles between the vertebrae being ossified (turned to bone) themselves, making the spine extremely straight and incapable of much sideways movement. It held its neck in an S or U shape curve, like most dinosaurs, which is interesting when combined with this extremely inflexible spine. The tail was even more ossified than the spine, creating parallel and perpendicular rows of fibres that crossed over on each other and created a sort of Chinese Finger Trap of a tail. The reason for this extraordinary rigidity is, so far, unknown. The official term for this structure is a “caudal basket”, which is only found in Teleost fish and Pachycephalosaurs, making Pachycephlosaurs some of the weirdest tetrapods known.

It had long and narrow shoulder blades that twisted in line with the ribs, and it had thin collar bones as well, giving it a fairly slender chest and arm region compared to the rest of its body. It also had weak shoulder muscles, meaning it really wasn’t using its arms and chest area for much in terms of movement and activity. Stegoceras also had very broad hips, which lead some scientists to briefly think it gave birth to live young - but there is no evidence for this and, obviously, much simpler explanations for broad hips than giving birth. It had long, slender legs, which probably would have aided Stegoceras in running. 

By Michael B. H., CC BY-SA 4.0

Of course, one of the most obviously interesting features of Stegoceras is its head. Like other Pachycephalosaurs, it had a large dome on its head, and a little ridge behind the dome itself. The head overall was triangular in shape, and it had a very short and squat snout. The dome was ornamented with little bumps and ridges, as was the shelf, indicating some sort of display was involved with this odd structure. It had large eyes, with heavy bony ridges over the eyes. It also had a shortened and squished brain within its head. It had thick bones around its nose, and its nostrils were large, inflated, and frontward facing on its snout. It also had sinuses in its jaws which then connected with the nostril system; these unique nostrils are actually some of the things that distinguish Stegoceras from other Pachycephalosaurs, along with the ridge on the back of its skull. Despite its weird nose, it didn’t have knobs or other decorations on its nostrils, unlike other members of its group. It had a long, almost jutting-out sort of lower jaw, which was filled with teeth. It also had a small beak in the front of its mouth.

As for teeth, it had a variety of differentiated teeth within its mouth, which is not commonly found in dinosaurs as a general rule (differentiated teeth is more of a mammal thing). It had small, narrow rows of tiny teeth, which only overlapped each other slightly. There is a little bit of space between the frontmost teeth and the back teeth. The front teeth were tall, pointed, and curved, with the lower jaw teeth bigger than the upper jaw teeth. The teeth in the back were more triangular and compressed, with deeper roots.

Skin impressions of Stegoceras are not known. Based on close relatives, it probably would have been primarily scaly; however, given its small size protofeathers are not out of the question, and are even potentially probable. This fluff may have been restricted to the tail, or found elsewhere on the body, if present. It would have aided Stegoceras in maintaining body temperature as well as served as a display structure. 

By José Carlos Cortés

Diet: The small teeth of Stegoceras weren’t really strong enough for eating tough, dry, fibre-filled plants like other dinosaurs at the same time; it’s entirely probable, thus, that Stegoceras was better at eating smaller, softer leaves; seeds; fruits; and even insects. It probably was mostly, if not entirely herbivorous, as it had similar teeth to modern Iguanas. Its jaws mainly moved up and down, shearing the soft plant material, rather than crushing it. Thus, in general, it would have been a low level or ground browser, eating small and soft plants that were on the ground or had fallen to it, especially berries shaken loose by higher-level browsers. Stegoceras also had a very good sense of smell, as indicated by the extensive nasal passages and large sized nostrils, and that would have helped Stegoceras in rooting out food along the ground.

Behavior: Stegoceras, being a common, small herbivore in its environments, probably wouldn’t have been particularly solitary, but lived in groups to forage together and keep an eye out for potential predators. They would have been fairly skittish animals - their small size being a disadvantage in environments with many different types of predators - but also extremely defensive ones, given their large domes on their heads.

There has been an extensive amount of debate over the function of Pachycephalosaur domes in general, and Stegoceras, being one of the better known members of the group, has had a singular place within that debate. The most recent studies on the subject have indicated that extensive damage to the domes actually demonstrate usage of the domes in traumatic situations, with lesions (breaks) found in 22% of Pachycephalosaurs with rounded domes. This is roughly the amount expected for animals that engage in combat within the species - intra-specific combat. These breaks were on the tops of the domes, supporting the idea that Pachycephalosaurs head-butted one another like modern rams - and, indeed, the study compared the breaks in the domes with living sheep and other head-butting animals. So, it seems extremely likely that these animals did, in fact, butt their heads together; despite previous claims that their skulls could not withstand the impact, the actual evidence found on the skulls suggests otherwise.

Still, that doesn’t mean that these skulls weren’t also used in other ways - particularly display. Many defensive & combative structures on animals today are also used for display and species recognition. These could have been mating displays, as well as threat displays, since often displaying a weapon can discourage confrontation. As such, Pachycephalosaur domes may have been differently colored amongst different species or even individuals, in order to look attractive and communicate amongst members of the group.

Thus, Stegoceras would have been a very social animal, living in groups together and fighting amongst one another for mates and resources such as food and territory. They could have used their domes to defend themselves as well, and thus would have probably been fairly aggressive, attacking anything that came too close. And, if that failed - or the threat was too dangerous - it did have long and slender legs to run away with.

As in other dinosaurs, Stegoceras probably took care of its young, though there isn’t really any fossil evidence on that subject either way. Still, closely related dinosaurs such as Psittacosaurus and Protoceratops are known to take care of their young, so that makes it likely that Stegoceras did as well. In addition, Stegoceras - as in other Pachycpehalosaurs - went through extensive change in the dome shape as they aged. Younger Stegoceras had flatter skulls than the older ones, indicating they weren’t involved in combat as adults were until they reached sexual maturity. The knobs on the shelf, however, varied extensively from individual to individual, and weren’t related to the age of Stegoceras like the dome itself was. 

By Jack Wood

Ecosystem: Stegoceras lived at the end of the Campanian epoch in North America, a time of extremely unique living things in North America that characterize the Cretaceous Period in the eyes of many. Unlike the entire rest of the world, North America at this time was filled with many different types of hadrosaurs, Tyrannosaurs, and most especially, Ceratopsids. While some of each of these groups were found elsewhere, especially Asia, this unique cacophony of creatures - and an extensive diversity thereof - is really just a North America thing.

Stegoceras itself lived in a variety of these ecosystems. S. validium lived in the Dinosaur Park Formation, a famous ecosystem with many of the most iconic dinosaurs, up in Alberta, Canada. The environment was a large plain, associated with extensive river systems connected to the Western Interior Seaway, along which the ecosystem extended. Floodplains with rich mud and sand filled the entire area, and it was utterly packed with plantlife, including Ginkgos, Sequoias, Cypresses, other Conifers, Mulberries, Katsuras, Water Cabbage, Plane Trees, Grapes, Buffalo nuts, and a variety of algae, liverworts, mosses, hornworts, club moss, quillworts, ferns, cycads, cypresses, pines, maples, sunflowers, oaks, beeches, birches, alders, mistletoes, elms, lilies, and reeds. This indicates that a forest ecosystem met a more wetland environment - potentially a swamp - with extensive fern fields everywhere else. This would have given Stegoceras a wide variety of soft plant material to feed on, from berries and grapes to soft water plants.

Dinosaur Park is named accordingly, of course - it is utterly filled with a variety of different dinosaurs. Stegoceras, only being known from the lower and middle time periods of this environment, only lived with some of them. Other Pachycephalosaurs it shared its home with included Foraminacephale and Hanssuesia, though those were not as common nor as well known as Stegoceras, which was clearly the most common small bipedal herbivore in the area. There were a lot of large, lumbering Ankylosaurs such as Edmontonia, Panoplosaurus, Euoplocephalus, Dyoplosaurus, Scolosaurus, and Platypelta, at one time or another. Huge, social, loud Hadrosaurs such as Gryposaurus, Prosaurolophus, Parasaurolophus, Lambeosaurus, and Corythosaurus were all there as well - literally, almost all the iconic hadrosaurs lived in the same time and place! There were many kinds of Ceratopsids too, such as Centrosaurus, Chasmosaurus, and Mercuriceratops. One Ornithomimosaur was present in the ecosystem as well, the less famous Rativates. Large Tyrannosaurids such as Gorgosaurus and Daspletosaurus lived in the formation, but they probably wouldn’t have been the main predators of Stegoceras, except maybe as juveniles, given Stegoceras being so, so tiny. Instead, the raptors Saurornitholestes and Dromaeosaurus, and the Troodontid Stenonychosaurus would have been the big problems for Stegoceras, as the predators the little dome-head would have had to look out for.

Interestingly enough, Stegoceras is not known in the upper part of the formation; why it went extinct and was not a part of that ecosystem is not well known.

There were many non-dinosaurs in Dinosaur Park too, of course, including a variety of lizards, pterosaurs, turtles, Crocodilians, Coristoderes, Multituberculate Mammals, Marsupial relatives, and Placental Mammal Relatives. Plus, being associated with the Western Interior Seaway, there were also fish such as sharks, sturgeons, gars, and teleosts. 

By Scott Reid

S. novomexicanum, the other species in this genus, lived much further south - in the Fruitland and Kirtland Formations of New Mexico. The Fruitland Formation is slightly older, and immediately succeeded by the Kirtland Formation. Fewer types of dinosaurs are known from these environments. The Fruitland Formation was next to the Western Interior Seaway as well, and filled with shoreline-associated swampy lowland environments. There were also conifers and flowering plants filling this area, but in general the Fruitland Formation is the most poorly known of the three ecosystems Stegoceras is known from. Dinosaurs present include the Ceratopsid Pentaceratops, the Hadrosaur Parasaurolophus, and the Ornithomimid Ornithomimus. There were also Crocodilians, Multituberculate Mammals, Lizards, and Turtles.

The Kirtland Formation is a little better known, and a little more like Dinosaur Park, with an extensive river system surrounded by floodplains and swamps. There were ferns, conifers, willows, walnuts, beeches, oaks, mulberries, moonseeds, magnolias, laurels, legumes, buckthorns, and grapes. As such, it was extremely similar in terms of plant component to Dinosaur Park, but also quite different, probably due to its more southern location and, thus, likely warmer climate. Still, Stegoceras would probably have enjoyed feeding on berries and grapes in both locations!

In the Kirtland Formation, Stegoceras lived alongside the hadrosaur Kritosaurus, the ceratopsians Pentaceratops and then Titanoceratops, the ankylosaurs Ziapelta and Ahshislepelta, and the smaller Tyrannosaur Bistahieversor that was probably the main predator of Stegoceras. Here there were also turtles, Multituberculates, Crocodilians, and Sharks.

Other: Stegoceras is one of a variety of smaller, more basally derived Pachcephalosaurs separate from things more closely related to Pachycephalosaurus itself. However, this group is very tentative and has not yet been given a name. Where Pachycephalosaurs come from, unfortunately, is a major mystery - they seem to just appear in the fossil record, seemingly out of thin air. More research on this uniquely weird group of dinosaurs is, thus, needed.

Stegoceras is also one of the first known Pachycephalosaurs, and is probably one of the best known today after Pachycephalosaurus itself.

Species Differences: S. validium and S. novomexicanum are mainly differentiated based on location, with the latter occurring in the southwestern part of the United States, and the former in southern Canada. However, S. novomexicanum also is slightly physically different from its northern cousin, specifically in having a smaller, more triangular back of its skull, and being in general more slender.

~ By Meig Dickson 

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By José Carlos Cortés

Etymology: Colossal Iguana

First Described By: McDonald et al., 2010

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Ornithischia, Genasauria, Neornithischia, Cerapoda, Ornithopoda, Iguanodontia, Dryomorpha, Ankylopollexia, Styracosterna

Status: Extinct

Time and Place: Between 129 and 123 million years ago, sometime between the Barremian and Aptian ages of the Early Cretaceous 

Iguanacolossus is known from the Yellow Cat Member of the Cedar Mountain Formation in Utah 

Physical Description: Iguanacolossus was a large, bipedal herbivore, similar in general shape to the earlier Camptosaurus from the same region of North America. As its name would suggest, it was fairly large and robust, reaching 9 meters long and 3 meters in height at the hip - making it longer than the width of a truck and much taller than a person. Known from decent, if scattered, remains, we have parts of the legs, tail, hips, back, and skull. However, we do not have the hands of this dinosaur; though it was touted as being a thumb-spiked dinosaur, we can’t actually be certain it had a large one; most members of the group have reduced thumbs spikes, rather than the large and distinctive structure of Iguanodon itself.

Iguanacolossus had a long, narrow skull, filled with teeth for chewing up plant material, and a beak to aid in snipping off leaves prior to chewing. Its teeth had thickened enamel, to aid in chewing. Iguanacolossus would have slid its lower jaw into its upper jaw to chew, using the serrations created by the closely packed teeth to slice up the plant material. Iguanacolossus would have had a thickened tail to aid in walking, and a thick, muscular neck.

Though only one specimen of Iguanacolossus is officially described, more specimens from juveniles and subadults are known and assigned to the genus in a thesis publication; an official peer-reviewed article is necessary to definitively assign these bones to Iguanacolossus, but for now the association seems likely given they come from the same time and place, and they have similar morphologies. These skeletons indicate that Iguanacolossus went through very rapid growth during development, aiding in reaching such a large size. This also helps to point to Iguanacolossus being warm-blooded and active (as is probably the case for all dinosaurs). In fact, Iguanacolossus shows growth patterns similar to the later Maiasaura, indicating that hadrosaur-like growth and development evolved quickly in their family tree.

Given its large size and relatives with scales, Iguanacolossus would have been mostly, if not entirely, scaly. Any feathers left on its body would have been ornamental - for display only.

Diet: Medium-level browser of plant material; Iguanacolossus would have been able to eat tough vegetation given its increased chewing abilities and strong enamel. 

By Lukas Panzarin, CC BY 2.5

Behavior: Given that Iguanacolossus was found with one single specimen, and its relative Iguanodon was actually a fairly solitary animal, it’s likely that Iguanacolossus would have traveled and fed alone in its environment, only congregating into groups to take care of its young. It’s possible, however, given the probable group of juveniles collected elsewhere, that the young did congregate together until reaching maturity. Their large size at this point would have allowed Iguanacolossus to take care of itself just fine without help from other members of the herd. This would have allowed individual Iguanacolossus to find more food on its own, which, combined with its ability to chew tough plant material, indicates at least some seasonal changes in vegetation that reduced the amount of soft plants to eat.

Ecosystem: Given the presence of extensive mudstone and other evidence of water in the Yellow Cat Member, this represented a fairly wet time in the history of the region, as opposed to other times in the Cedar Mountain Formation or the early Morrison Formation that were marked with extensive arid climates. Lakes and rivers filled the floodplain region and provided a variety of habitats for Iguanacolossus to move around in. Still, it would have been semi-arid, and its possible that the mudstones were the result of seasonal changes in water level.

Iguanacolossus shared its environment with a variety other dinosaurs, including the other Ornithopods Hippodraco and Cedrorestes; the ankylosaur Gastonia; the sauropods Mierasaurus and Cedarosaurus; the early Therizinosaurs Martharaptor and Falcarius; the large (and weird) Dromaeosaur Utahraptor and the somewhat more normal Dromaeosaur Yurgovuchia; the Troodontid Geminiraptor; and the early Ornithomimosaur Nedcolbertia.

Non-dinosaurs were present as well, of course - notably the tuatara relative Toxolophosaurus, turtles such as Glyptops; multiple types of fish; and the mammal Cifelliodon.

Other: Iguanacolossus may have been able to walk quadrupedally, but that’s difficult to determine without forelimb fossils.

~ By Meig Dickson

Sources under the cut 

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