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.

Alcovasaurus

Type Species: Alcovasaurus longispinus

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae – Dacentrurinae

Time Period: Late Jurassic

Location: North America

Diet: Herbivore

The North American stegosaur Alcovasaurus grew up to eighteen feet in length; this medium-sized stegosaur would’ve been a low browser in prehistoric North America. Its main enemies would’ve included the theropods Allosaurus, Torvosaurus, and perhaps Ceratosaurus. Much of Alcovasaurus’ anatomy is unknown, but because what we do know is similar to the African Kentrosaurus, most reconstructions make it similar to its African contemporary. Alcovasaurus was originally identified as a species of Stegosaurus. This classification was questioned, however, due to five significant anatomical differences, not least its long dermal spikes. Alcovasaurus had two tail spike pairs as its thagomizer that were slender and elongated and ninety percent of the thighbone length. Some scientists argued that these larger spike pairs weren’t indicative of a different species but of sexual dimorphism used for display; perhaps, the argument went, male stegosaurs had flashier thagomizers. Other scientists argued that this stegosaur was less closely related to Stegosaurus and had more affinity with the African Kentrosaurus. Serious studies of this dispute were hampered when the type specimen was damaged by water after a pipe burst at the University of Wyoming; studies couldn’t continue until more specimens were recovered. Recently those scientists who argued for Alcovasaurus being a different genera won out, and Alcovasaurus is now differentiated from its contemporary Stegosaurus.

Archaeopteryx

Type Species: Archaeopteryx lithographica

Classification: Dinosauria – Saurischia – Theropoda – Coelurosauria – Maniraptora – Paraves – Avialae – Archaeopterygidae

Time Period: Late Jurassic 

Location: Europe 

Diet: Carnivore

Archaeopteryx’s name means ‘Ancient Wing/Feather’, and for a long time it was thought to be the oldest known member of the Avialae (‘birds’), at least until earlier specimens were unearthed in China as far back as the Middle Jurassic. This Late Jurassic paravian lived among the cycad- and conifer-dotted wooded islands of prehistoric Germany, mingling with small lizards, pterosaurs, other paravians, and small theropods such as Compsognathus. Multiple specimens have been uncovered in what’s known as Solnhofen Lagoon, which during the Late Jurassic was interspersed with dozens of small islands. Archaeopteryx was similar in size to a Eurasian magpie, though larger individuals could reach the size of a raven. The largest species grew to about one and a half feet in length and would’ve weighed just over two pounds. Though originally considered to be the first bird, many paleontologists decry this statement, for Archaeopteryx had more in common with non-avian theropods – particularly dromaeosaurs and troodontids – than with birds. Just for beginners, it had toothy jaws, three clawed fingers on each hand, a lony bony tail, and hyper-extendable ‘killing claws’ on its feet. Though it had feathers, these are a shared morphology between birds and many different theropod classes. Because it’s morphologically closer to non-avian dinosaurs than modern birds, many have considered it a ‘transitional fossil’ between non-avian dinosaurs and avian dinosaurs and their modern-day descendants. Ironically, this ‘transitional fossil’ appears millions of years after more advanced paravians such as Serikornis and Anchiornis.

Archaeopteryx’s feathers were similar in structure to modern-day bird feathers. Its feathers were asymmetrical and showed the same structure as modern birds’ flight feathers: vanes given stability by a barb-barbule-barbicel arrangement. The tail feathers, too, were assymetrical with firm vanes. Its thumb didn’t yet bear a separately movable tuft of stiff feathers. Serious studies of Archaeopteryx feathers have been done one specimen dubbed ‘the Berlin specimen’. In this species, its legs had ‘trousers’ of well-developed feathers that are firm and capable of supporting flight. Pennaceous feathers ran along its back; these were asymmetrical and firm, though not as stiff as the flight-related feathers; thus these were similar to the contour feathers of the body plumage of modern birds. Aside from these feathers, the rest of the Berlin specimen was covered in a type of ‘proto-down’ similar to that found in the Early Cretaceous Sinosauropteryx. This ‘proto-down’ was decomposed and fluffy, and it may even have resembled fur in real life (though the fact that it wasn’t fur would be clear up-close under a microscope). This ‘proto-down’ went as far as the lower neck. In all species, the upper neck and head are clear of feathers. This is explained in one of two ways: either Archaeopteryx simply lacked feathers or proto-down on the upper neck and head, or this is an artifact of preservation. In the latter scenario, Archaeopteryx indeed had feathers (or, more likely, proto-down) on its upper neck and head, but these features were lost in death. Scientists believe most Archaeopteryx specimens became embedded in anoxic sediment after drifting for quite some time on their backs in the sea; in these anoxic waters, their corpses wouldn’t be scavenged, for marine life would be limited to smaller organisms that can survive such oxygen-depleted waters. While drifting on the waves, the head, neck, and tail bent downwards, with the body floating atop. They began to rot before they sank under the waves, resulting in loosening tendons and muscles resulting in the infamous ‘death pose.’ The skin, already softened by decay and by underwater friction, wouldn’t be able to keep hold of feathers or proto-down. Before the corpse settled to the seabed, those parts underwater – the neck, head, and tail – would begin to lose their feathers. The more firmly attached body feathers would’ve remained intact by the time the corpse settled on the seabed to be covered with sediment and fossilized for our enjoyment. 

Scientists have used electron microscopy and energy-dispersive X-ray analysis to detect the structure of the melanosomes of one of Archaeopteryx’s wing feathers and compared them with those of over eighty modern bird species; the conclusion was that Archaeopteryx’s original feather color was black with heavier pigmentation in the distal tip. In 2013 another study was done that indicated that Archaeopteryx’s flight feathers had complex light- and dark-colored plumage with heavier pigmentation in the distal tips and outer vanes. This type of coloration is consistent with many modern birds in which black melanosomes have structural properties that strengthen feathers for flight. This leads, of course, to the ultimate question: ‘Was Archaeopteryx capable of powered flight?’ Some scientists doubt that it could fly on its own, insisting that it was a ‘glider’ who would climb high into a tree, launch off, and glide to another tree or to the ground. Others argue that it was indeed capable of flight, though its flight mechanisms would’ve differed from those seen in modern birds. That it was capable of some sort of flight is undisputed. The fact that its feathers are asymmetrical hints at flight, for flightless birds tend to have symmetrical feathers; however, some flightless birds have asymmetrical feathers similar to those of Archaeopteryx. However, the degree of asymmetry in this dinosaur’s feathers more closely resemble those of slow-flying birds than flightless ones. If Archaeopteryx was capable of flight, it would’ve been more ungainly than what we’re used to; for instance, recent studies of flight feather barb geometry reveal that modern birds possess a larger barb angle in the feather’s trailing vane, and Archaeopteryx, lacking this large barb angle, would’ve been a weaker flier. Furthermore, the lack of a bony breastbone upon which flight muscles could attach also testifies to weak flying capabilities; detractors from this conclusion speculate that its strong flight muscles may have attached to the thick, boomerang-shaped wishbone, the plate-like coracoids, or even to a cartilaginous sternum. However, even if it had strongly-anchored flight muscles, its shoulder anatomy made it unable to lift its wings above its back, a requirement for the upstroke used by modern flying birds. However, it may have utilized a downstroke for powered flight. If it were capable of powered flight, its power would’ve been hindered by its large wings, which would’ve resulted in a low stall speed and reduced turning radius. The short, rounded shape of the wings would’ve increased drag, but scientists point out that it would’ve also improved its ability to fly through cluttered environments dense with trees and brush. Such heightened aerial mobility would’ve been improved by its hind wings on its legs. 

While much of the debate over Archaeopteryx’s flying ability (or lack thereof) revolves around its feather and anatomical structure, in 2004 some scientists took a different approach, asking themselves, ‘Did Archaeopteryx have a brain suited for flying?’ By analyzing a detailed CT scan of the braincase of an Archaeopteryx, the scientists found that its brain was proportionately much larger than those of most dinosaurs. The regions associated with vision took up nearly a third of the braincase, and other well-developed areas included hearing and muscle coordination. These are all factors seen in modern birds and necessary for aerial locomotion. The scientists also examined the inner ear and discovered that it more closely resembled the ears of modern birds than those of non-avian dinosaurs. Archaeopteryx had a cerebrum-to-brain-volume ratio 78% on the way to modern birds from the condition of non-coelurosaurian dinosaurs such as Allosaurus, which had a crocodile-like brain and inner ears. All this together suggests that Archaeopteryx had the keen sense of hearing, balance, spatial perception, and coordination needed to fly. The studies of Archaeopteryx’s braincase were revolutionary in the debate over its place in the sky, and in 2014 a team of dedicated scientists reported that their consensus was that Archaeopteryx was indeed capable of powered flight, but in a manner distinct and different from that of modern birds. Its modern equivalents would be pheasants and other burst flyers. 

If we were to step back in time to the Late Jurassic Period in Germany, we would find ourselves in the Solnhofen Lagoon among scattered low-lying, semi-arid, sub-tropical islands. The vegetation of these islands consisted of low-lying shrubs and cycads; interestingly, the islands of this lagoon seem to have lacked conifers. Few trunks have been found in the sediments, and tree pollen is absent. It was in this environment that Archaeopteryx lived, and it was a prime environment for a pheasant-like burst-flying hunter. It most likely hunted small prey, seizing it with its jaws if it was small enough, or with its claws if it was larger.  

Sciurumimus

Type Species: Sciurumimus albersdoerferi

Classification: Dinosauria - Saurischia - Theropoda - Carnosauria - Megalosauroidea

Time Period: Late Jurassic 

Location: Europe 

Diet: Carnivore

The small bipedal theropod Scuirumimus lived among the large islands and archipelagos of prehistoric France and Germany. During the Late Jurassic, much of modern western Europe was submerged by the Oxford Sea and shallow sea armlets of the Tethys Sea that were ringed with coral reefs. Emerging from this vast spider-web network of waterways were dry, forested islands cut by streams and lagoons. These islands catered to smaller terrestrial organisms: lizards, mammals, and a number of small-fry dinosaurs, Scuirumimus among them. This theropod lived alongside the compsognathids Compsognathus and Juravenator, as well as a number of paravians, such as Ostromia, Wellnhoferia, Alcmonavis, and of course the infamous Archaeopteryx.

Sciurumimus’ name means ‘Squirrel-mimic’ for its tail’s resemblance to that of the modern tree squirrel. It’s known from a single juvenile specimen, so its adult length is unknown. While classified as a megalosaurid, this classification is hotly debated. The single specimen was preserved with traces of feather-like filaments. The specimen’s body proportions – the short forelimbs, the lack of fusion in the skeleton, as well as the fact that its skull is 156% the length of the femur – indicate that it was a juvenile and perhaps as young as a hatchling. 

Juravenator

Type Species: Juravenator starki 

Classification: Dinosauria – Saurischia – Theropoda – Tetanurae – Coelurosauria – Tyrannoraptora – Compsognathidae   

Time Period: Late Jurassic 

Location: Europe 

Diet: Carnivore

The small bipedal theropod Juravenator lived among the large islands and archipelagos of prehistoric France and Germany. During the Late Jurassic, much of modern western Europe was submerged by the Oxford Sea and shallow sea armlets of the Tethys Sea that were ringed with coral reefs. Emerging from this vast spider-web network of waterways were dry, forested islands cut by streams and lagoons. These islands catered to smaller terrestrial organisms: lizards, mammals, and a number of small-fry dinosaurs, Juravenator among them. This theropod lived alongside its larger cousin Compsognathus, the squirrel-like theropod Sciurumimus, and a number of paravians, such as Ostromia, Wellnhoferia, Alcmonavis, and of course the infamous Archaeopteryx. Juravenator is known from a single juvenile specimen that was twenty-nine inches head-to-tail. This fleet-footed hunter likely preyed on lizards, mammals, and insects. The scleral rings of Juravenator resemble those of nocturnal birds, suggesting that it was a night-time hunter (but some believe these scleral rings are due to the fact that it was a juvenile and that adults would’ve been daytime hunters). A patch of Juravenator’s skin shows dinosaur scales as well as traces of proto-feathers. 

Compsognathus

Type Species: Compsognathus longipes

Classification: Dinosauria – Saurischia – Theropoda – Tetanurae – Coelurosauria – Tyrannoraptora – Compsognathidae   

Time Period: Late Jurassic 

Location: Europe 

Diet: Carnivore

The small bipedal theropod Compsognathus lived among the large islands and archipelagos of prehistoric France and Germany. During the Late Jurassic, much of modern western Europe was submerged by the Oxford Sea and shallow sea armlets of the Tethys Sea that were ringed with coral reefs. Emerging from this vast spider-web network of waterways were dry, forested islands cut by streams and lagoons. These islands catered to smaller terrestrial organisms: lizards, mammals, and a number of small-fry dinosaurs, Compsognathus among them. This theropod lived alongside its smaller cousin Juravenator, the squirrel-like theropod Sciurumimus, and a number of paravians, such as Ostromia, Wellnhoferia, Alcmonavis, and of course the infamous Archaeopteryx. Compsognathus itself may have island-hopped all the way down to Portugal, for teeth that may belong to this dinosaur have been found in the Lourinha Formation. 

Compsognathus is known from two nearly complete specimens, one from France and one from Germany. The French specimen was forty-nine inches long, and the German specimen was 35 inches long. This lithe theropod likely weighed as little as seven pounds full grown. Compsognathus had long hind legs and a long tail, which it used for balance while running; some scientists have postulated that it could reach speeds up to forty miles per hour. Its forelimbs were smaller than its hindlimbs, and each hand bore two large clawed digits and a third, smaller digit that may have been non-functional. Their delicate skulls were long and narrow with tapered snouts. Its eyes were large in proportion to the skull, indicating that it was a visually-oriented predator that relied more on sight than smell for hunting. Its long neck enabled it to move its head side-to-side without moving its body, helping it spy out prey; and the long neck would’ve come in handy when plunging its head into the undergrowth to root out hiding prey. This dinosaur was designed for catching small and fast-moving prey like lizards that would’ve scurried into the undergrowth as soon as they were seen. Compsognathus’ speed is attested by a proportionately small humerus when compared to the lower legs, a trademark of a fast runner. It balanced itself on its toes rather than the flat of its foot, another design appropriate for speed; this digitigrade stance meant that the main foot bones extended the length of the leg and thus increased its stride. Its tail, held erect off the ground, would’ve served as a balancing aid as it chased prey through the wooded islands of prehistoric western Europe. Its small, sharp teeth were suited for a diet of small vertebrates and perhaps even insects. Its frontmost teeth were unserrated, but those farther back in the jaw were flattened and recurved. The specimens we have preserve part of its diet: in the French specimen, the remains of unidentified lizards and sphenodonts (lizard-like reptiles) are found in its thoracic cavity; in the German specimen, the articulated remains of a full lizard are in plain view. These lizard remains were originally thought to belong to an embryonic Compsognathus, which would’ve rewritten the book on dinosaur reproduction, but further research showed that it belonged to a Bavarisaurus lizard. This lizard was fast and agile, which meant that Compsognathus would’ve also needed to be fast and agile in order to hunt it. Compsognathus may also have preyed on small mammals, as its close Early Cretaceous relative Sinosauropteryx has been discovered with the remains of small mammals in its stomach. 

Some artistic renditions depict Compsognathus with feathers while others do not; this is because the presence of feathers or feather-like features on this theropod is hotly debated. While some of Compsognathus’ relatives have been preserved with the remains of simple feathers covering the body like fur, this isn’t the case with Compsognathus. Archaeopteryx, found in the same sediments as Compsognathus, is preserved with plenty of feathers, which means that the environment was suitable for feather preservation. A patch of fossilized skin from the tail and hind-limb of its close relative Juravenator show mainly scales, though there is some indication that simple feathers were present in some areas. There are thus three possibilities when it comes to Compsognathus: it may have been featherless, it may have had partial feathers such as may be the case with Juravenator, or it may have been fully feathered like its more distant cousins. The jury is out until more evidence comes in. 

a Compsognathus perches atop a dead juvenile dwarf sauropod

Miragaia

Type Species: Miragaia longicollum

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae – Dacentrurinae

Time Period: Late Jurassic 

Location: Europe 

Diet: Herbivore

The stegosaur Miragaia was closely related to its contemporary cousin Dacentrurus. Miragaia could grow eighteen to twenty feet in length and would clock in at around two tons. Paired triangular plates ran down the midline of its neck; these plates were asymmetrical with a convex outer side and a concave inner side. They were obtuse but lightly hooked at the front. A long, narrow, and straight spike has been preserved; some paleontologists believe this was a shoulder-spike seen in some stegosaurs, but others believe it was part of the tail. Miragaia’s tail anatomy isn’t known, but it’s usually reconstructed with a four-spiked thagomizer like that seen in its near relatives. Because Miragaia’s front limbs were almost as high as the rear limbs, its overall posture was more horizontally level to the ground than what we find in most other stegosaurs, whose bodies slope down to the ground so that their heads were better situated for low browsing.

Miragaia is noteworthy for its elongated neck, which was built by seventeen vertebrae. It had the longest neck of any known stegosaur, and most scientists believe this represents the pinnacle of a trend toward longer necks in stegosaurs. Thyreophorans – the dinosaur clade to which stegosaurs belong – originally had nine neck vertebrae, and one of the most basal stegosaurs, the Chinese Huayangosaurus of the Middle Jurassic, had nine, as well. While more advanced stegosaurs such as Stegosaurus had twelve or thirteen vertebrae, Miragaia outdoes them – and it even outdoes most sauropods of its time. Only a few Chinese sauropods – such as Euhelopus, Mamenchisaurus, and Omeisaurus – had as many neck vertebrae as Miragaia; most sauropods of the Late Jurassic had only twelve to fifteen widely-spaced vertebrae. Scientists have come up with two explanations for Miragaia’s elongated neck. The first holds that it developed due to sexual selection: if longer-necked stegosaurs of this species were seen as more attractive, then it makes sense that necks would get longer over time. Another theory, and one which is more likely, is that the long neck developed as an aide to niche partitioning. Miragaia lived alongside the obviously low-browsing Dacentrurus (and Stegosaurus may have even ocean-hopped to reside in Portugal); because of this, these two species would be in direct confrontation. Niche partitioners coexist by eating different foods, and it may be that Miragaia evolved as a medium-browser, able to reach foods inaccessible to other stegosaurs. Its limb structure, which indicates a shift away from a low-browsing stance, supports this theory for the origin of Miragaia’s long neck. 

Lusotitan

Type Species: Lusotitan atalaiensis

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

Time Period: Late Jurassic 

Location: Europe 

Diet: Herbivore

The Late Jurassic sauropod Lusotitan lived in prehistoric Portugal as part of Portugal’s Lourinha Formation, which resembled North America’s Morrison Formation and which emerged as a result of the genesis of the Atlantic Ocean. This brachiosaurid was related to the North American Brachiosaurus, and it grew up to seventy to eighty feet in length. Lusotitan walked on four pillar-like legs; its front legs were longer than its back legs, so that its body sloped downwards towards its short tail. Some scientists believe it could rear back on its hind legs to reach super high foliage, though some believe it kept its four legs on the ground at all times. Lusotitan’s neck reached vertical rather than horizontal like diplodocids. This gave it a feeding advantage: whereas most of its sauropod contemporaries were low-browsing diplodocids, Lusotitan could browse foliage up to fifty feet off the ground to feed on high conifers and ginkgoes. It undoubtedly practiced niche partitioning alongside the low-browsing diplodocid Dinheirosaurus. As part of the Lourinha Formation, it also lived alongside large predators such as Allosaurus and Torvosaurus, stegosaurs such as Dacentrurus and Miragaia, the early ankylosaur Dracopelta, and numerous early ornithopods. 

Dinheirosaurus

Type Species: Dinheirosaurus lourinhanensis

Classification: Dinosauria – Saurischia – Sauropoda – Gravisauria - Eusauropoda - Neosauropoda - Diplodocoidea – Flagellicaudata – Diplodocidae – Diplodocinae

Time Period: Late Jurassic 

Location: Europe 

Diet: Herbivore

The Late Jurassic sauropod Dinheirosaurus lived in prehistoric Portugal as part of Portugal’s Lourinha Formation, which resembled North America’s Morrison Formation and which emerged as a result of the genesis of the Atlantic Ocean. Dinheirosaurus had the general diplodocid form: a slender body, long neck carried low over the ground, and a long, whip-like tail. Its squared snout, similar in appearance to its North American relatives Diplodocus and Supersaurus, indicates that it was a non-specific low-browsing herbivore. It grew up to eighty feet in length, the same length as Diplodocus but smaller than Supersaurus, to whom it was more closely related. Dinheirosaurus is one of the few sauropods for whom gastroliths have actually been found alongside the type specimen. This sauropod lived alongside large predators such as Allosaurus and smaller ones such as Aviatyrannus (the latter of which could be squashed under Dinheriosaurus’ feet if it lacked spatial awareness). Other herbivores of the environment included the stegosaur Dacentrurus, the early ankylosaur Dracopelta, and numerous early ornithopods. 

Supersaurus

Type Species: Supersaurus vivianae

Classification: Dinosauria – Saurischia – Sauropoda – Gravisauria - Eusauropoda - Neosauropoda - Diplodocoidea – Flagellicaudata – Diplodocidae – Diplodocinae

Time Period: Late Jurassic 

Location: United States 

Diet: Herbivore

Supersaurus was a Late Jurassic diplodocid of the Morrison Formation. Though remains have been discovered from several individuals, these remains have been scanty, and so little is known about Supersaurus apart from its length and weight. From this scientists have deduced that it was the largest sauropod of the Morrison Formation, reaching up to 112 feet in length and weighing up to forty tons. We can assume that it behaved like other diplodocids, traveling in herds across the floodplains and savannahs of Late Jurassic western North America and feeding nonstop in order to provide enough energy for its massive size. It would’ve had few predators, as it would’ve dwarfed even Allosaurus and Torvosaurus, but Supersaurus would’ve been vulnerable in its early growth stages. Given its sheer size, it may be that Supersaurus herds were greedily eyed and followed by roving theropods looking to pick off the aged or weak. A Supersaurus carcass could’ve fed dozens of large theropods. 

Marshosaurus

Type Species: Marshosaurus bicentesimus

Classification: Dinosauria - Saurischia - Theropoda - Carnosauria - Megalosauroidea

Time Period: Late Jurassic 

Location: United States 

Diet: Carnivore

While little is known about Marshosaurus, it’s noteworthy as the only medium-sized theropod of the Kimmeridgian stage of Late Jurassic North America. At fifteen feet in length and around five hundred pounds in weight, it was significantly larger than the smaller Coelurus and Ornitholestes of its habitat whilst being overshadowed by the much larger theropods Allosaurus and Torvosaurus. Unlike its smaller counterparts, Marshosaurus was built for strength: it had a robust skull and its powerful arms were built for holding onto and subduing prey. It’s likely that Marshosaurus preyed on medium-sized dinosaurs such as Camptosaurus but may have also hunted young, sick, or weak sauropods. 

Ornitholestes

an artistic depiction of Ornitholestes with a nasal horn

Type Species: Ornitholestes hermanni

Classification: Dinosauria – Saurischia – Theropoda – Tetanurae – Coelurosauria – Tyrannoraptora – Maniraptoromorpha  

Time Period: Late Jurassic 

Location: United States 

Diet: Carnivore

The ‘bird robber’ Ornitholestes is known from a single partial skeleton with a badly crushed skull found in Wyoming at the turn of the 20th century (making it the first theropod discovering of the 1900s). Ornitholestes was a short-bodied theropod that grew to about eight feet in length and stood three feet tall at the hips. It had a relatively short neck with a slight sigmoidal (or S-shaped) curve. Its tail was long and whip-like and accounted for half its length. Its skull was proportionally smaller than that of most theropods, but it remained heavily built with a short snout and robust lower jaw. Its front teeth were conical-shaped with few serrations whereas the back teeth were recurved and sharply serrated like those of most theropods; the teeth didn’t extend as far back as its eyes, and neither tooth row spanned more than a third of the skull length. It’s likely that Ornitholestes used its front conical-shaped teeth for tearing flesh from its prey while the recurved back teeth were used to slice through the meat before swallowing. Ornitholestes’ forelimbs were relatively long, slightly under two-thirds the length of its hind legs. The first and second fingers of its three-clawed hands were the same size, but the claw bone was likely stunted. Ornitholestes was able to bend its forearm at an angle more acute than ninety degrees, which is characteristic of maniraptors but absent in more primitive theropods such as Coelophysis and Allosaurus. When Ornitholestes bent its elbow, its arms moved inwards towards its body; this would’ve increased in grasping ability. Though Ornitholestes is often portrayed as a fast, agile runner, its lower limb bones were relatively short. Some scientists believe that its innermost toe was larger than its other toes and suggest that it may have had a sickle claw similar to those of the dromaeosaurs. Many modern reconstructions depict Ornitholestes with a covering of feathers; this isn’t because feathers for this dinosaurs have been discovered but because they are present in so many of its kin that it’s thought by many that all coelurosaurs (to which Ornitholestes belongs) had some sort of rudimentary feathery covering. These feathers would’ve have been used for flight but for display, insulation, or for brooding eggs. Early depictions of Ornitholestes show it with a nasal horn akin to a chicken’s comb. When the specimen was discovered, it had an area of broken bone near the nostril that appeared to bulge upwards. Paleontologist Gregory S. Paul interpreted this as a nasal horn, but this interpretation has been rejected; the upward flare of crushed bone was likely due to post-mortem crushing of the skull. Below is a modern depiction of Ornitholestes - covered in fur, eating an early mammal, and lacking a nasal horn:

Debate swirls around Ornitholestes’ diet. When it was first discovered, it was argued that it utilized its grasping ability and the balancing power of its tail to catch birds. Though this theory had its detractors – a simultaneous theory was that its strange tooth design indicated a ‘transitional’ stage between a carnivorous and herbivorous diet – the original theory gained steam and became the dominant theory (hence the meaning of Ornitholestes’ name, ‘Bird Robber’). Over the decades, both the ‘bird robber’ and transitional diet theories have faded out of vogue. Most modern paleontologists believe that Ornitholestes preyed upon small terrestrial vertebrates such as mammals, lizards, frogs, and even dinosaur hatchlings. Another theory is that Ornitholestes used its front conical teeth to catch fish in the many streams, rivers, and lakes of the Morrison Formation, and some scientists  believe that Ornitholestes engaged in pack hunting behavior to bring down medium-sized prey such as the ornithopod Camptosaurus. Some argue that Ornitholestes and its slightly larger contemporary Coelurus lived side-by-side by utilizing niche partitioning in which Coelurus hunted at night and Ornitholestes hunted during the day. 

Hesperosuchus

a mother Hesperosaurus defends its child against an Allosaurus

Type Species: Hesperosaurus mjosi  

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae

Time Period: Late Jurassic 

Location: United States 

Diet: Herbivore

The infamous Stegosaurus wasn’t the only stegosaur roaming the Morrison during the Kimmeridgian; its slightly smaller cousin Hesperosaurus was present, too (though it was likely more closely related to Dacentrurus of Europe). Hesperosaurus grew up to twenty to twenty-two feet in length – making it slightly smaller than Stegosaurus, which could grow up to thirty feet long – and weighed two to three tons. Like Stegosaurus it had two rows of plates running along its back; asymmetrical bases imply that the rows were staggered rather than symmetrical. Hesperosaurus’ plates were wider than those of Stegosaurus but not as tall, and its skull was deeper than that of its Morrison kin. Like Stegosaurus, Hesperosaurus had a four-spiked thagomizer on its tail; the front pair was thicker than the latter pair, and the latter were more horizontally directed towards the rear. Hesperosaurus’ tail spikes angled slightly backwards, pointing away from the body, implying that they were used in defense against predators such as Allosaurus and Torvosaurus. At least one Allosaurus specimen shows damage to its vertebrae that seems delivered by a stegosaur’s tail spike. 

CAT-scans on Hesperosaurus’ plates show that they had thin but dense outer walls and were filled with thick but spongy bone. This bone shows signs of being remodeled during the growth process. The plate bones were supplied with blood via long and wide arterial vessels. CAT-scans of the tail spikes show that they have thicker walls than the plates, and the interior spongy hollows are smaller. Each spike had a single artery that ran along the longitudinal axis. Skin impressions from Hesperosaurus give us a glimpse of what it looked like enfleshed: a part of the lower flank preserves rows of small, hexagonal, non-overlapping convex scales; higher on the flank are rosette structures with large central scales. Impressions of the back plates show no scales but a smooth surface with low parallel ridges; these likely represent the horn sheath covering the plate, and if so, these represent the first direct proof of such plate sheaths in stegosaurs. The horn sheath on the plates indicate that they had a defensive function, as the horn layer would not only strengthen the bony plate but give it sharp cutting edges. Simultaneously, the display function seems plausible, as these plates would likely be brightly colored in real life. Horn sheaths are a blow to those who believe the plates served a thermoregulatory function, as the sheaths would’ve hampered the plates’ ability to thermoregulate; however, the theory cannot be wholly rejected, for some cattle and ducks use horns and beaks to dump excess heat despite horn coverings. 

Dryosaurus

a family group of Dryosaurus drink at a river beside a Stegosaurus
(never mind the presence of grass, which had yet to evolve)

Type Species: Dryosaurus altus  

Classification: Dinosauria – Ornithischia – Ornithopoda – Iguanodontia – Dryomorpha – Dryosauridae 

Time Period: Late Jurassic 

Location: United States 

Diet: Herbivore

Dryosaurus was an iguanodont ornithopod, though it was formerly classified as a hypsilophodont. Its name means ‘tree lizard,’ referring to the forested environment it inhabited (some people erroneously believe the name refers to its vague oak-leaf shaped cheek teeth). Dryosaurus could grow between eight to fourteen feet in length and could weigh up to two hundred pounds; because all known specimens are of creatures in various stages of growth, the maximum adult size is unknown. Dryosaurus had a long neck, slender legs, and a long, stiff tail that acted as a counterbalance when running. Its short arms had five fingers on each hand. Dryosaurus had a horny beak and cheek teeth, and some paleontologists believe it had cheek-like structures to prevent the loss of food while chewing. Living in the Morrison Formation, Dryosaurus was dwarfed by its titanic herbivorous brethren, sauropods such as Diplodocus, Brachiosaurus, and Supersaurus; larger ornithopods such as Camptosaurus; and massive stegosaurs such as Stegosaurus. It likely used speed as its best defense against large predators such as Allosaurus and Ceratosaurus, and it’s speculated that with its small size, it stuck to the overgrown conifer forests that would be difficult for larger animals to navigate. Thus if we were to step back in time to the Late Jurassic western United States and tour a deep conifer forest cut by streams with overgrown banks and littered with deep ponds teeming with crocodylomorphs and early amphibians, we might spy small herds of Dryosaurus roaming like deer through the trees and munching on ferns and cycads, safely tucked away from the giant theropods roaming the neighboring floodplains and valleys. 

Camarasaurus

Type Species: Camarasaurus supremus  

Classification: Dinosauria – Saurischia – Sauropoda - Gravisauria - Eusauropoda - Neosauropoda – Macronaria – Camarasauridae 

Time Period: Late Jurassic 

Location: United States 

Diet: Herbivore

Camarasaurus was the most common sauropod of the Morrison Formation; vast herds roamed the floodplains and valleys of Late Jurassic North America. Herding behavior is attested in the fossil record: a group of two adults and a forty-foot-long juvenile died together around 150 million years ago in what is now Wyoming. It appears their bodies were washed by a flooding river and buried in sediment. This find implies that Camarasaurus traveled in herds or at least in family groups, though the discovery of Camarasaurus eggs laid in lines rather than nests suggests that Camarasaurus didn’t tend to its young. It’s possible that Camarasaurus embraced an R-strategy for survival, in which overwhelming numbers of young were hatched in the hope that some of them made it to adulthood. Juveniles, having survived the many predators of the Morrison Formation, may have ‘linked in’ with roving herds for safety. The size of herds is pure speculation, for unlike some ceratopsians of the Cretaceous, vast Camarasaurus bone-beds haven’t been discovered. 

Camarasaurus could grow up to sixty feet in length, though some specimens reached up to seventy-five feet. Skeletal studies indicate that these sauropods reached sexual maturity around twenty years of age. Camarasaurus had a blunt, box-like head that, despite its bulldog appearance, was filled with lots of air cavities (called fenestrae) which helped lighten the skull’s weight. Its teeth were seven and a half inches long, and they were stronger than those of most sauropods. These sturdy, spoon-like, deep-rooted teeth extended nearly into the cheeks, in contrast with the front-only teeth of some sauropods such as Diplodocus. Studies on the plentiful teeth have revealed that they were used vigorously in chewing and were replaced on average every two months; the lack of gastrolith fossils in the numerous specimens indicate that Camarasaurus chewed its food down to a pulp prior to swallowing. When scientists performed clumped isotope thermometry on the enamel covering the teeth of several genera of Jurassic sauropods, including Camarasaurus, it revealed temperatures of 90.3-98.4 degrees Fahrenheit, comparable to that of modern mammals. Its neck was held up high so that the head were at a level where Camarasaurus could eat from the tree canopy like its contemporary cousin Brachiosaurus; the numerous fenestrae in its skull would’ve lightened the weight, enabling it to hold it higher off the ground. 

Camarasaurus’ legs were about equal length (the forelegs were only slightly shorter than the hind-legs), unlike Brachiosaurus’ long forelegs and Diplodocus’ longer hind-legs. The fact that its forelegs were slightly shorter than the hind-legs would’ve made its back slope forward, but its high shoulders off-balanced this so that its body ran nearly parallel to the ground. Its neck and tail were relatively short for sauropods, and like most sauropods its inner toe bore a large, sharp claw. Camarasaurus’ name comes from the Greek word for ‘chamber,’ referring to the chambers discovered in its vertebrae. These air-filled cavities made its bones pneumatic, and their purpose has been approached in two ways: the air-filled cavities (pleurocels) may have served to reduce the weight of its skeleton, or they may have even been air sacs that were part of the sauropods’ respiratory system. These features are found in plenty of other sauropods as well as in theropods; it may very well be a common feature of the saurischian lineage that leads to the avian respiratory system in which birds use similar air sacs to increase their breathing potential. If this is the case for Camarasaurus, the air sacs would’ve provided a super-efficient airflow down the long neck so that the fresh air went down one network of sacs whilst oxygen-depleted air went up another. This would result in a constant supply and exchange of breathable air despite the distance of the lungs from the mouth and nostrils.