Xuanhuaceratops

Type Species: Xuanhuaceratops niei

Classification: Dinosauria – Ornithischia – Marginocephalia – Ceratopsia – Chaoyangsauridae 

Time Period: Late Jurassic 

Location: China

Diet: Herbivore

Xuanhuaceratops was a small, bipedal herbivore that scurried among the thick forests of Late Jurassic China, dodging predators by hiding in thick undergrowth and running speedily away on two legs. It’s known from four fragmentary skeletons, hinting at a family group. Though it looks alien compared to the later and famous ceratopsians of the Cretaceous Period, Xuanhuaceratops had already developed the classic sharp, cropping beak of the ceratopsians and had the beginnings of the neck frill that would become a trademark of Cretaceous ceratopsians. 

Chaoyangsaurus

Type Species: Chaoyangsaurus youngi

Classification: Dinosauria – Ornithischia – Marginocephalia – Ceratopsia – Chaoyangsauridae 

Time Period: Late Jurassic 

Location: China

Diet: Herbivore

While little remains for this small herbivorous dinosaur have been discovered, those remains indicate that it was an early ceratopsian. Chaoyangsaurus was a small, bipedal herbivore whose lineage lies along the lay-lines that would eventually spawn one of the most dominant dinosaurs of the Cretaceous, the ceratopsians. Chaoyangsaurus is the namesake of the group that includes the earliest ceratopsians, such as Hulianceratops, Yinlong, and Xuanhuaceratops. All are from the Late Jurassic China, and they inform us that the ceratopsian lineage began there before radiating throughout the entire world during the Cretaceous Period. 

Chilesaurus

Type Species: Chilesaurus diegosuarezi

Classification: Dinosauria 

Time Period: Late Jurassic 

Location: South America 

Diet: Herbivore

Chilesaurus is an oddball of a dinosaur. Reaching ten and a half feet in length, it had spatula-shaped, elongated teeth that obliquely pointed forward, a design perfect for eating plants. Its herbivorous lifestyle is also attested by its backward-pointing pubic bone, which made room for a large gut. Its hind limb wasn’t well adapted for running, and its broad feet had a weight-bearing front toe. It had strong arms with a large claw that could be extended outwards, just as is seen in the sauropodomorphs. All this to say, it looks like a cross between a theropod and an ornithischian, and no one really knows where to place it in the dinosaur family tree. 

Those who argue for a theropod lineage point out that it’s not uncommon – although it’s certainly not usual – for theropods to adapt herbivorous lifestyles. We see this with the therizinosaurs, who became herbivorous, and with the ornithomimosaurs, who became omnivorous. Perhaps Chilesaurus is simply a theropod that went vegan. Others, however, consider the mixture of traits between theropods and ornithischians as evidence that we’ve got the dinosaur family tree all wrong. The current cladogram, which subdivides Dinosauria into the lizard-hipped Saurischians and the bird-hipped Ornithischians, wasn’t the only cladogram proposed; another was proposed by Thomas Huxley in 1869 (and revived by some scientists in 2017). Huxley argued that Dinosauria should be subdivided into Saurischia and Ornithoscelida. In his proposal, Saurischia contained all the sauropodomorphs, and Ornithoscelida contained the theropods and the ornithischians. In Huxley’s scheme, theropods are more closely related to ornithischians than to the sauropodomorphs. Proponents of his view point to Chilesaurus as evidence that his thesis is not only justifiable but correct, and that Chilesaurus, despite its relatively late appearance in the fossil record, is evidence of a ‘vestigial’ family line that eventually gave rise to both ornithischians and theropods. 

Kentrosaurus

Type Species: Kentrosaurus aethiopicus

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae

Time Period: Late Jurassic 

Location: Africa

Diet: Herbivore

The African stegosaur Kentrosaurus was closely related to Stegosaurus though it was half its size, clocking in at around fifteen feet in length. Kentrosaurus had a small, elongated head with a beak that it used to sever tough plant material to be digested in its barrel-like gut. Its skin was covered in bony osteoderms, and it had small plates on its neck. These small plates were dwarfed by the plates that ran along its back in a series of fifteen rows. These plates were elongated with a thickened section in the middle, as if they were modified spines, and they were probably covered in horn. These plates gradually merged into spikes on the hip and tail. The longest spikes were on the end of its tail, and it would’ve used its thagomizer as a defensive weapon. It also had a long spike on each shoulder. Because the thigh bones come in two different types, it’s likely that males and females differed in their stoutness (a case of sexual dimorphism). 

Kentrosaurus is considered a low-browsing herbivore, and it likely roamed the thick conifer forests of northern Africa’s inland woodlands and may have even browsed on foliage in the less-lush coastal regions. If it ate while on all fours, it could reach up to five and a half feet off the ground; if it was capable of rearing back on its hind legs to eat, it could access food up to eleven feet off the ground. As a low-browser, it would’ve shared its niche with the iguanodont Dysalotosaurus, leaving the higher foliage to macronarian sauropods such as Giraffatitan. 

Kentrosaurus shared its environment with predators such as Elaphrosaurus, Allosaurus, and Veterupristisaurus. The former was too small to pose any real threat, but Allosaurus and Veterupristisaurus were a different story. The forty-foot-long Veterupristisaurus was the top predator in its environment, and it’s likely that Kentrosaurus would’ve faced-off with this predator on numerous occasions, and those plates and spikes would’ve come in good use. Scientists estimate that it could swing its tail up to speeds of 30 miles per hour, and continuous rapid swings wouldn’t only discourage attacks but could deal massive damage as the spikes ripped open its attackers’ skin, punctured its soft tissues, and broke ribs or facial bones. Repeated blows could even fracture the sturdy limb bones of the stoutest predator. With its ability to pivot quickly round on its hind legs, it would be adept at keeping its spikes pointed towards the attacker. If Kentrosaurus were a herding animal, the family group may have ‘circled-the-wagons’ with their tail spikes facing out to ward off curious predators. Such a wall of spikes would be virtually impenetrable and would likely be enough to discourage even a pack of hungry Allosaurus. Some scientists speculate that a lone Kentrosaurus, when under attack, might have charged backwards, using its tail spines like a spear, much in the manner of modern porcupines. 

Ostafrikasaurus

Type Species: Ostafrikasaurus crassiserratus

Classification: Dinosauria - Saurischia - Theropoda - Carnosauria – Megalosauroidea – Megalosauria – Spinosauridae – Baryonychinae

Time Period: Late Jurassic 

Location: Africa

Diet: Carnivore

Ostafrikasaurus is known only by a single tooth, and yet that lone tooth changed a theropod lineage forever. The single took, discovered in the Tendaguru Formation of Tanzania, is different from those of most theropods and more aligned with the unique teeth of the spinosaurs. Because all other spinosaurs date from the Cretaceous Period, the presence of a spinosaur tooth in the Tendaguru Formation pushed their genesis back into the Late Jurassic. Whereas most theropods have recurved, blade-like teeth with serrations for cutting through meat, spinosaur teeth were straighter, more conical, and had few if any serrations. Ostafrikasaurus’ teeth had a few serrations, indicating that these serrations were lost as the spinosaur family evolved. This may be because spinosaurs embraced a pescetarian (fish-hunting) lifestyle: conical, spear-like teeth are seen in modern fish-hunting gharials, as their design lends them to piercing and maintaining grip on slippery aquatic prey that can be swallowed whole rather than torn apart. The estimated 28-foot-long Ostafrikasaurus likely hunted in the coastal environments of northern Africa, hunting fish and even snagging the occasional pterosaur or two. Though its skull hasn’t been found, it’s likely that it had the crocodile-like snouts of its descendants. However, given its early placement in the spinosaurid family, it may have resembled non-spinosaurid theropods, as well. Until more remains are found, we can only speculate as to what it looked like fleshed-out. 

The spinosaurs are divided into two subfamilies: Baryonychinae and Spinosaurinae. Baryonchines have slightly curved, finely-serrated teeth with more oval cross-sections, whereas spinosaurines have straight, fluted teeth with reduced or absent serrations. Given the fact that Ostafrikasaurus’ teeth are more in line with the former, it’s been placed with the baryonychines and likely represents a primitive form of that subfamily. 

Giraffatitan

Type Species: Giraffatitan brancai

Classification: Dinosauria – Saurischia – Sauropoda - Gravisauria - Eusauropoda - Neosauropoda – Macronaria – Titanosauriformes – Brachiosauridae

Time Period: Late Jurassic 

Location: Africa

Diet: Herbivore

Giraffatitan was originally thought to be a species of Brachiosaurus but has since been given freedom to stand on its own. It was one of the largest sauropods of the Late Jurassic, averaging between 72 and 74 feet in length but capable of reaching up to 85 feet snout-to-tail. Its neck, held vertical, reached up to forty feet in length. It had a giraffe-like build (hence its name) with long forelimbs and a long neck. It had chisel-like ‘spatulate’ teeth and the first three toes on its hind feet were clawed. Its distinctive high-crested skull was once thought to be characteristic of the brachiosaurids, to which Giraffatitan originally belonged; however, it’s possible that many brachiosaurs didn’t have this feature, since this feature is known only from African specimens now assigned to Giraffatitan – all this to say that the classic portrayal of Brachiosaurus may actually not represent Brachiosaurus at all, at least as far as the skull design goes. Like other sauropods, Giraffatitan had a sacral enlargement above the hip; scientists of an earlier age thought this housed a ‘second brain,’ given that sauropods had pretty small brains to begin with, but it’s know believed to be the location of glycogen bodies. Giraffatitan likely roamed the sweeping conifer forests of the Tendaguru Formation, avoiding the coastal environments of brackish coastal lakes, ponds, and pools where vegetation would be harder to come by. 

Giraffatitan’s nostrils were once thought to be located on the top of its head, lending earlier scientists to speculate that it was a water-dweller, snorkeling in the burgeoning North Atlantic. However, studies have shown that the water pressure placed on the rib cage would make it extremely difficult for a submerged Giraffatitan to breathe; extended time submerged would undoubtedly lead to drowning. Studies of the skull in 2001 suggested that while the nasal openings in the skull were above the eyes, this didn’t mean that the nostrils wouldn’t emerge at the tip of the snout. In this case, Giraffatitan’s tall ‘crests’ may have housed a fleshy resonating chamber. 

Australodocus

Type Species: Australodocus bohetii

Classification: Dinosauria – Saurischia – Sauropoda - Gravisauria - Eusauropoda - Neosauropoda – Macronaria – Titanosauriformes – Somphospondyli 

Time Period: Late Jurassic 

Location: Africa

Diet: Herbivore

The 56-foot-long and 8800-pound sauropod Australodocus was originally classified as a diplodocid but has since been reclassified as an early titanosauriform, making it more closely related to Brachiosaurus than Diplodocus. Australodocus is currently considered one of the first specimens of the somphospondyls, a sauropod lineage that would give birth in the Cretaceous to the larger-than-life armored titanosaur sauropods. This ‘large-nosed’ macronarian roamed the dense conifer forests of Africa’s Tendaguru Formation, separated to the south of North America by the widening strip of water that would eventually become the Atlantic Ocean. While the Morrison Formation in North America was dominated by diplodocids, the Tendaguru Formation was dominated by macronarians, likely as a result of the different environments. The Morrison was a savannah-like floodplain cut by lakes and rivers that were forested on the peripheries; the Tendaguru, however, was more densely-packed with thick conifer forests. The low-lying foliage of the Morrison was perfect eating for low-browsing diplodocids whereas macronarians with vertically-oriented necks did better with the plentiful trees of the Tendaguru. 

Saurophaganax

Type Species: Saurophaganax maximus

Classification: Dinosauria – Saurischia – Theropoda - Carnosauria – Allosauroidea – Allosauria – Allosauridae

Time Period: Late Jurassic 

Location: North America 

Diet: Carnivore

Saurophaganax was the largest predator of the Morrison Formation, reaching lengths up to 46 feet snout-to-tail, making it twice as large as its more common and contemporary cousin Allosaurus (because of the similarity between these two theropods, some scientists argue that Saurophaganax is actually a larger species of Allosaurus, but those making these claims are currently in the minority). As the chief hunter of Late Jurassic North America, it’s not surprising that its remains have been scant: the larger the predator, and the greater its competition in the environment, the less prevalent it is. Saurophaganax had lots of predatory competition, principally from the smaller (but still large) Allosaurus and Torvosaurus. Saurophaganax likely hunted large sauropods such as Diplodocus and Brachiosaurus; it may have hunted in groups, like many of its contemporaries, but there’s currently no evidence for this. Some scientists believe that it may even have hunted other theropods, as there have been discoveries of Allosaurus bones with teeth marks matching the size of those belonging to Saurophaganax (it’s noteworthy that these same-sized teeth marks have also been found on the remains of the ankylosaur Mymoorapelta). Because of its large size, some paleontologists argue that Saurophaganax would’ve been slow-moving and would’ve leaned more towards scavenging than hunting. This, too, would explain the presence of its teeth marks on the Allosaurus bones. Given its size, it may have relied on smaller predators taking down prey and then moving in to take over the kill-site; even the mighty Allosaurus would think twice before defending its kill against a predator twice its size. 

a Saurophaganax takes a break from being Top Dog

Stokesosaurus

Type Species: Stokesosaurus clevelandi

Classification: Dinosauria – Saurischia – Theropoda – Tetanurae – Coelurosauria – Tyrannosauroidea – Pantyrannosauria - Stokesosauridae

Time Period: Late Jurassic 

Location: North America 

Diet: Carnivore

Stokesosaurus was a medium-sized theropod from the Late Jurassic Morrison Formation of North America. By the Cretaceous Period, tyrannosaurs would be becoming larger-than-life despite austere beginnings in the Jurassic. Stokesosaurus represents the gradual increase of size among the tyrannosaur lineage; while the earliest tyrannosaurs emerged in the Middle Jurassic small and lithe, as the Jurassic progressed they were growing larger. Stokesosaurus graduated from a small-sized predator to a medium-sized one, clocking in at ten to thirteen feet in length. A fleet-footed predator, this tyrannosaur likely hunted Morrison ornithopods such as Camptosaurus and Dryosaurus, perhaps even wrangling with an occasional stegosaur. The larger predators of its environment, such as Allosaurus and Torvosaurus, likely preyed on the much-larger sauropods. 

Fruitadens

Type Species: Fruitadens haagarorum

Classification: Dinosauria - Ornithischia - Heterodontosauridae

Time Period: Late Jurassic 

Location: North America 

Diet: Omnivore

The heterodontosaur Fruitadens is the smallest known heterodontosaur. It’s known from partial skulls and skeletons from at least four individuals of differing biological ages; the presence of these skeletons in the same locale indicate that this heterodontosaur may have travelled in family packs. Young adults grew to around 26 to 30 inches in length and weighed between a pound and a half. Fruitadens had relatively short arms and long feet and shins. The lower jaws had an enlarged canine-like tooth which corresponded to a gap in the upper jaw. Fruitadens also had a small peg-like tooth in front of its canine-like tooth. It had replacement teeth present in the jaws, a unique find among other heterodontosaurs. Its hind limb bones were hollow like those of small theropod dinosaurs. 

Paleontologists believe Fruitadens was an omnivore, and it lived in an environment rich with food for the plucking. It likely prowled the many riverbeds and streams of the savannah-like Morrison Formation, feeding on plant material in addition to snails, clams, crayfish, and insects. Being on the smaller size, it would’ve been wary of running across crocodylomorphs. While large theropod dinosaurs such as Allosaurus, Ceratosaurus, and Torvosaurus lived in the same environment, Fruitadens would’ve likely evaded these predators by running into heavy thickets or hiding in the gallery forests spreading out from rivers and lakes. 

Barosaurus

Type Species: Barosaurus lentus
Classification: Dinosauria – Saurischia – Sauropoda – Gravisauria - Eusauropoda - Neosauropoda - Diplodocoidea – Flagellicaudata – Diplodocidae
Time Period: Late Jurassic
Location: North America
Diet: Herbivore

The North American Barosaurus was one of the largest sauropods of the savannah-like Morrison Formation during the Tithonian Stage of the Late Jurassic. While most individuals were already larger-than-life, clocking in at 82-89 feet in length and weighing between twelve and twenty tons, at least one specimen may have reached up to 157 feet in length with a 49-foot neck. Barosaurus was closely related to the more popular Diplodocus, though it had some significant differences: it had a longer neck, a shorter tail, and its skeleton was less robust than its contemporaneous cousin. Additionally, Barosaurus’ cervical vertebrae were designed in such a way that it had a lot of side-to-side flexibility at the cost of up-and-down flexibility. This indicates it ate by sweeping its neck in crescent-shaped arcs over the low foliage, which would’ve been a perfect feeding method for the savannah-like conditions of the Morrison Formation. While its neck and skull have not been recovered, it’s assumed that, due to its close relationship with Diplodocus, Barosaurus had a whip-like tail and a skull with an elongated, sloping snout with peg-like teeth.