Brachiosaurus

Type Species: Brachiosaurus altithorax

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

Time Period: Late Jurassic 

Location: United States and Europe

Diet: Herbivore 

The sauropod Brachiosaurus traveled in herds in the western United States during the Late Jurassic. Its stomping grounds consisted of low-lying drainage basins that swallowed runoff from the emergent Rocky Mountains to the west. These lowlands were scarred by crisscrossing streams and rivers and were dotted with swampy lowlands, lakes, river channels, and floodplains. (Brachiosaurus remains have also been allegedly found in Portugal). This infamous sauropod 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. Its name means ‘arm reptile,’ in reference to the fact that its arms (forelegs) were longer than its rear legs. 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. 

Brachiosaurus’ neck reached vertical rather than horizontal like diplodocids. This gave it a feeding advantage: whereas most of its sauropod contemporaries were low-browsing diplodocids, Brachiosaurus could browse foliage up to fifty feet off the ground to feed on high conifers and ginkgoes. Air sacs along the neck and trunk of Brachiosaurus lightened the strain needed to keep its neck vertical. These air sacs connected to its lungs, thus lowering the body density. Brachiosaurus couldn’t chew its food, as its jaws were only capable of opening and closing (it couldn’t move its jaws side-to-side in a grinding motion). Its 52 spatulate (spoon-like) teeth cropped conifer needles, palm-fronds, ginkgo leaves, and even towering horsetails that grew along the many waterways of the Morrison. It would’ve needed to consume up to 440 pounds of food each day, and this food was swallowed unchewed and passed into a gizzard where gastroliths (stomach stones) crushed the food to a pulp for digestion. 

Fossils similar to those of North America’s Brachiosaurus were discovered in Africa’s Tendaguru Formation in 1914; scientists believed the fossils to represent a new species of Brachiosaurus, but further study indicated significant morphological differences, so the fossils became a new genera altogether: Giraffatitan. Giraffatitan’s crest bone, rising from the top of the skull, is much larger than that in Brachiosaurus (interestingly, most modern depictions of Brachiosaurus include a crest bone more in line with that of Giraffatitan than Brachiosaurus). While it was once believed Brachiosaurus’ nostrils were set atop its skull crest, modern reconstructions place them lower down on the high forehead, right above the eyes, in a kink that angled from the forehead into the low snout. This reconstruction has led some scientists to postulate that the crest was a resonating chamber that could’ve amplified Brachiosaurus’ vocalizations. 

a scene from the Morrison Formation; Brachiosaurus in the foreground,
Camarasaurus in the background, and early ornithopods along the forest floor

Dysalotosaurus

Type Species: Dysalotosaurus lettowvorbecki

Classification: Dinosauria – Ornithischia – Ornithopoda – Iguanodontia – Dryosauridae 

Time Period: Late Jurassic 

Location: Africa

Diet: Herbivore   

The ‘uncatchable lizard’ lived in Africa during the Tithonian stage of the Late Jurassic. This gazelle-like ornithopod traveled in herds and lived in the shadow of larger herbivores such as the stegosaur Kentrosaurus and the sauropods Dicraeosaurus and Giraffatitan. As flocks of Dysalotosaurus scurried about the semi-arid coastal environment laced with lagoons and brackish rivers and lakes, they would need to keep an eye out for predators such as the spinosaurid Ostafrikasaurus and the carcharodontosaur Veterupristisaurus. This small ornithopod was only eight feet long and weighed 180 pounds, and it lacked the thumb spikes associated with later iguanodonts. It was adapted for running about on two legs, as implied by its short front limbs, powerful and long hind limbs, and long, counter-balancing tail. That this lithe ornithopod was numerous is seen in the thousands of bones and fragments that have been recovered from the Tendaguru Formation in Tanzania; some scientists believe these remains are from a herd that died and was buried in a cataclysmic event (not too noteworthy, given the intense volcanism of the Jurassic). Interestingly, all rather complete specimens of this dinosaur belong to juveniles; from their specimens we can determine that their dentition (teeth and jaws) changed as they grew, changes that would make sense if juveniles had an omnivorous diet whereas more mature individuals were herbivorous. Bone analysis indicates that their growth rates were similar to that of a modern kangaroo. In one specimen, evidence of scoliosis was present; while all vertebrates are known to suffer this defect, Dysalotosaurus was the first dinosaur to have evidence of it.

For much of the 1900s, Dysalotosaurus was believed to be synonymous with its closely-related cousin Dryosaurus of North America; more recent studies, however, have determined that it was its own genera. It’s classified as a dryosaurid, a type of primitive iguanodont. Iguanodonts belong to a clade that includes most ornithopods, as well as the duck-billed hadrosaurs. The iguanodonts became the most widespread and diverse herbivore lineage of the Cretaceous, but in the Jurassic they were Little Leaguers compared to the stegosaurs and sauropods. 

Gargoyleosaurus

a Gargoyleosaurus takes its stand against an Allosaurus 

Type Species: Gargoyleosaurus parkpinorum

Classification: Dinosauria – Ornithischia – Thyreophora – Ankylosauria – Nodosauridae

Time Period: Late Jurassic 

Location: North America

Diet: Herbivore   

Gargoyleosaurus is one of the earliest ankylosaurs, and it shared its habitat with another smaller ankylosaur named Mymoorapelta. Gargoyleosaurus had an eleven-inch skull and reached up to thirteen feet from its head to tail. As a nodosaur it lacked the tail club associated with many ankylosaurs. Gargoyleosaurus was a common low-browsing herbivore in the western United States, as three specimens have been discovered. Its armor – consisting of plates and conical spikes across its back and sides – would’ve served as a deterrent against contemporary predators such as Allosaurus. 

Kaatedocus

Type Species: Kaatedocus siberi

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

Time Period: Late Jurassic 

Location: North America

Diet: Herbivore   

Until 2012 this sauropod was believed to be a variant of Barosaurus; only when it was determined by intense study that the remains belonged to a new genera (albeit one closely related to Barosaurus) was this sauropod coined. Kaatedocus was fifty feet long, making it much smaller than its cousin Diplodocus, which could reach up to ninety feet in length. Kaatedocus had a gracile body, a whip-like tail, a very long neck, a small head, and a toothy grin thanks to overly large teeth. Its teeth were pencil-shaped like those of other diplodocids, but they were much larger, giving Kaatedocus a clownish appearance. The pencil-like teeth were designed to strip foliage off plants rather than to chew the plant material; the ‘chewing’ happened in Kaatedocus’ gut where gastroliths – swallowed stones – worked to pulverize the plant material for further digestion.  

Galeamopus

an unfortunate Galeamopus succumbs to the circle of life

Type Species: Galeamopus hayi

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

Time Period: Late Jurassic 

Location: North America

Diet: Herbivore   

Until 2015, the nearly complete skeleton with an associated skull of a certain diplodocid of the Morrison Formation was assumed to be a species of Diplodocus; the change came when researchers determined that these skeletal remains had enough differences from Diplodocus – at least eight! – to determine it as a new species. Thus Galeamopus was born. This sauropod closely resembled its contemporary Diplodocus, and they share the same family group. Galeamopus was lightly-built and most likely had a whip-like tail capable of cracking the sound barrier. Researchers believe this sauropod also had a series of short keratinous spines running down the length of its body, as these are present in many other species of diplodocid sauropods. Galeamopus’ long neck was probably held close to the ground, swinging in crescent-shaped arcs as it fed on low-growth foliage in the wetlands and savannahs of Late Jurassic North America. 

Mymoorapelta

a Mymoorapelta is flanked by a pair of Ceratosaurus

Type Species: Mymoorapelta maysi

Classification: Dinosauria – Ornithischia – Thyreophora – Ankylosauria – Nodosauridae 

Time Period: Late Jurassic 

Location: North America

Diet: Herbivore   

Mymoorapelta is one of the earliest ankylosaurs along with Gargoyleosaurus. Mymoorapelta was the first Jurassic ankylosaur to be discovered in North America, though scientists ponder its exact placement within Ankylosauria. Because it lacks a tail club, most scientists consider it to be a nodosaur (one of the ‘branches’ of Ankylosauria; these ankylosaurs lacked tail clubs). Some believe it to be a polacanthine ankylosaur, a ‘middle-ground’ between the clubbed ankylosaurs and the non-clubbed nodosaurs; others believe it is a basal ankylosaur that doesn’t fit into Ankylosauridae nor Nodosauridae. At only ten feet in length snout-to-tail, Mymoorapelta is the smallest herbivore known from the Morrison Formation. It was a low browser, feeding on ferns and cycads and other low-growing plants. Its armor would’ve given it decent protection against predators such as Allosaurus, but it may not have been an invulnerable deterrence, as predators were known to go after the plated and spiked stegosaurs in the same environment. Being so small and low to the ground, Mymoorapelta’s first line of defense may have been one of hiding among foliage to escape detection. 

a cast of well-preserved Mymoorapelta remains

Tanycolagreus

Type Species: Tanycolagreus topwilsoni

Classification: Dinosauria – Saurischia – Theropoda – Tetanurae – Coelurosauria

Time Period: Late Jurassic 

Location: North America

Diet: Carnivore   

Tanycolagreus was your average, run-of-the-mill Jurassic coelurosaur theropod. It grew to about thirteen feet in length and likely weighed under three hundred pounds. This agile, quick-footed predator lived in the shadow of much larger theropods such as Torvosaurus, Allosaurus, and Ceratosaurus. It had long, lightly-built legs and a large, elongated head that was rectangular in profile. It likely preyed on smaller dinosaurs of the Morrison Formation such as Camptosaurus and Dryosaurus. 

Turiasaurus

Type Species: Turiasaurus riodevensis

Classification: Dinosauria – Saurischia – Sauropoda - Gravisauria – Eusauropoda – Turiasauria 

Time Period: Late Jurassic 

Location: Europe (Spain)

Diet: Herbivore   

Turiasaurus was the largest land animal ever known to have lived in Europe. It was one hundred feet long – the length of ten cars! – and weighed as much as eight elephants. Its upper forearm bone was the length of a human adult, and it bore a sickening thumb claw the size of a rugby ball. Its vertebrae suggest that it had a row of spikes or at least a ridge running down its back. Its skull was less than thirty inches long; scientists believe a larger skull would’ve put too much pressure on the neck at the risk of snapping it. Turiasaurus thundered through the wooded islands of what is now eastern Spain, eating tough plant matter like leaves, stems, and shoots. Its teeth were heart-shaped and covered in a wrinkled enamel that would’ve helped it grind up tough plant matter. 

Lourinhanosaurus

Type Species: Lourinhanosaurus antunesi

Classification: Dinosauria - Saurischia - Theropoda - Carnosauria - Megalosauroidea

Time Period: Late Jurassic 

Location: Europe (Portugal)

Diet: Carnivore   

The theropod Lourinhanosaurus prowled the wooded islands of southwest Europe during the Late Jurassic. Contemporary dinosaurs in this environment included the theropods Lusovenator (a carcharodontosaur), Torvosaurus, and Allosaurus; the sauropods Oceanotitan, Supersaurus, and Zby; the stegosaurs Dacentrurus and Miragaia; and the ornithopods Draconyx and Dryosaurus. Lourinhanosaurus’ classification is murky: was it an allosaur? a megalosaur? something in between? The current consensus has swung towards it being a megalosaur. The holotype specimen, discovered in Portugal, belonged to a juvenile around fifteen years old and stretched fourteen feet snout-to-tail. Adults may have grown up to twenty-six feet in length. Dinosaur eggs and embryos, believed to belong to Lourinhanosaurus on the grounds that they were found near the Lourinhanosaurus type specimen, have been discovered; these eggs were around thirteen centimeters long, and the nest contained over a hundred of them!

The juvenile specimen had gastroliths in its abdominal cavity. While gastroliths are common in herbivorous dinosaurs, they’re rare in theropods. One explanation is that the Lourinhanosaurus accidentally swallowed them when feasting on the stomach of dismembered prey; another theory is that Lourinhanosaurus used gastroliths to tenderize meat that had been swallowed (since predatory dinosaurs weren’t great at chewing and thus would’ve swallowed large chunks of meat, tendons and gristle and all whole); or, perhaps, Lourinhanosaurus was a specialized predator that fed on crustaceans and shellfish. The latter would’ve been abundant among the island ecosystem, and other megalosaurs appear to be specialized towards this end. Gastroliths would’ve been helpful in demolishing tough shells in the dinosaur’s gut. Perhaps a juvenile Lourinhanosaurus employed such a diet until they became older and were unable to subsist off what could be dredged from the tidal shallows; some scientists speculate that adults shed this ‘marine’ diet and began hunting other dinosaurs. In this manner, the two generations – the juveniles and the adults – wouldn’t be competing against each other for the same resources. In an island community, resources were scarcer, and such niche partitioning would ensure the survival and flourishing of the species. 

Aviatyrannis

Type Species: Aviatyrannis jurassica

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

Time Period: Late Jurassic 

Location: Europe (Portugal)

Diet: Carnivore   

The tyrannosaurs had their genesis in the Jurassic Period – the earliest being the Middle Jurassic Proceratosaurus – but these were a far cry from their giant ancestors. The tyrannosaurs of the Jurassic were small and lithe; Aviatyrannis was the size of a dog, and its name means ‘tyrant’s grandmother.’ Aviatyrannis’ bones were collected at Guimarota, an abandoned coalmine that has become famous for its Jurassic mammal fossils. During the Late Jurassic, this was a warm and dry wooded island. Other dinosaurs in the environment included sauropods, troodontids, and other small theropods such as Compsognathus. 

Veterupristisaurus

Type Species: Veterupristisaurus milneri

Classification: Dinosauria – Saurischia – Theropoda - Carnosauria – Allosauroidea – Allosauria – Carcharodontosauria – Carcharodontosauridae 

Time Period: Late Jurassic 

Location: East Africa

Diet: Carnivore

This carcharodontosaur of Africa indicates that the carcharodontosaur lineage – whose jaws are reminiscent of those belonging to sharks – stretched back into the Late Jurassic (though bigger members carried the stage in the Late Cretaceous). The thirty- to forty-foot-long Veterupristisaurus stalked the muddy banks of a lagoon in Late Jurassic east Africa. Though it’s already noteworthy for being so large – undoubtedly the top predator in its environment – some scholars believe the remains we have actually belong to a juvenile, which would make Veterupristisaurus even larger in adulthood! 

Europasaurus

Type Species: Europasaurus holgeri

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

Time Period: Late Jurassic 

Location: Europe (Germany)

Diet: Herbivore   

Europasaurus was a tiny sauropod that, in adulthood, reached only twenty feet in length, stood as tall as an eight-year-old human at the hips, and whose head reached only ten feet above the ground. Its small size has been attributed to ‘insular dwarfism,’ in which animals evolve to shrink in size in order to cope with diminished resources. Germany at this point in the Late Jurassic was mostly underwater; higher elevations emerged from the sea in a string of island archipelagos, the largest of which was only 120,000 square miles. Even an island that large likely couldn’t support a herd of normal-sized sauropods; hence Europasaurus grew smaller in order to survive. Bone analysis shows that while gigantic sauropods reached their massive size by growing quickly, Europasaurus had an unusually slow rate of growth. Other instances of ‘insular dwarfism’ have been documented from Europe around this time; in Romania, for example, we’ve discovered a dwarf titanosaur Magyarosaurus and a dwarf hadrosaur Telmatosaurus. 

Europasaurus’ remains were found in a richly marine environment that faced a large German island coated with conifers, ferns, and cycads. Pterosaurs flew about among the trees, hopping island-to-island, and early mammals scurried in the underbrush. Fossilized turtles, fish, hybodont sharks, and marine crocodylomorphs are common. At least 450 bones from Europasaurus were recovered from the Langenberg Quarry, and about a third of them had tooth marks. These tooth marks match the teeth of fish, sharks, and marine crocodylomorphs, but none were made by theropods. Scientists believe that a herd of Europasaurus were crossing a tidal zone and drowned. Other dinosaur material in the vicinity includes remains from an unknown diplodocid, a stegosaur, and multiple indeterminate theropods. Isolated teeth show that there were at least four different types of theropods living on the island, including the megalosaur Torvosaurus as well as an indeterminate megalosaur, an allosaur, and a ceratosaur. Interesting, teeth that seem to belong to Velociraptorinae, which would put the genesis of this dromaeosaur subgroup in the Late Jurassic rather than the (proposed) Early Cretaceous. 

this graphic highlights European bone-beds with their Late Jurassic counterparts
The Langenberg Quarry is #7

Dinosaur footprints preserved at the quarry have led researchers to propose a reason for Europasaurus’ eventual demise. Footprints located sixteen feet above the Europasaurus burial ground shows that 35,000 years after their burial (well into the Cretaceous), sea level dropped and allowed for what’s called a ‘faunal overrun.’ The theropods that coexisted with Europasaurus were, by and large, about thirteen feet in length; but the theropods that were able to cross to the former island via a land bridge revealed by sinking sea levels were around twenty-five feet in length (based upon their footprints). These larger theropods made windfall on the previously-isolated island: the creatures who had grown small to survive amid diminished resources were now easy pickings for large Cretaceous predators. Europasaurus wouldn’t have stood a chance in the bloodletting. 

Torvosaurus

Type Species: Torvosaurus tanneri

Classification: Dinosauria - Saurischia - Theropoda - Carnosauria - Megalosauroidea - Megalosauria - Megalosauridae - Megalosaurinae

Time Period: Late Jurassic 

Location: North America and Europe

Diet: Carnivore   

The massive-bodied Torvosaurus was the largest predator in its environment. Its remains have been found in both North America and Spain. The specimen from the Morrison Formation lived in an environment that had rivers flowing westward into a giant, saline alkaline basin lake surrounded by wetlands. Other dinosaurs of this environment included plentiful sauropods such as Apatosaurus, Diplodocus, and Camarasaurus; ornithopods such as Dryosaurus and Camptosaurus; the stegosaur Stegosaurus; and the early ankylosaur Gorgoyleosaurus. Other large theropods, namely Allosaurus and Ceratosaurus, also lived in the area. 

Researchers believe that Torvosaurus and Ceratosaurus preferred to prowl waterways; their lower, more sinuous bodies would give them an advantage in forest and underbrush terrains; meanwhile, Allosaurus – with its longer legs – was faster but less maneuverable, and may have preferred to hunt in dry floodplains. Torvosaurus may have hunted large land animals whereas Ceratosaurus, in the same watery environment, preferred to hunt marine organisms such as fish, amphibians, and crocodylomorphs. Some scientists believe that because of its huge size, it would’ve been a clumsy hunter and instead scavenged the large dinosaur carcasses of the Morrison Formation. The idea is that it could use its ‘bulk and brawn’ to scare other theropods away from their kills and then steal the meat. However, other scientists point out that Torvosaurus’ size would be a boom in preying on larger dinosaurs; the Morrison Formation had plenty of prey – stegosaurs and ornithopods were numerous, and large sauropod herds were common – so Torvosaurus could ‘pick and choose’ what it hunted. It may have preferred to hunt juvenile or sick sauropods; one kill could fill its stomach for days. 

Torvosaurus grew up to thirty-three feet long and weighed as much as a hippo. It was the same size as Allosaurus but more massive. Its short, powerful arms were capped by large claws. Its skull – which may have been five feet long, at least according to some Portuguese remains – was elongated with a narrow snout. It had a kink in its profile just above its nostrils, and the lacrimal bone had a distinctive lacrimal horn. In 2005 Torvosaurus eggs were discovered in Portugal and dated to the Tithonian stage of the Late Jurassic. This find was remarkable for a number of reasons: first, these eggs contained the most primitive dinosaur embryos yet known; second, they were the only basal theropod embryos known; third, fossilized eggs and embryos are rarely found together; and fourth, it represents the first evidence of a one-layered eggshell for theropod dinosaurs. Because the eggs were abandoned due to unknown reasons, it’s unknown whether Torvosaurus provided parental care to its eggs and young or abandoned them shortly after laying. 

Elaphrosaurus

Type Species: Elaphrosaurus bambergi

Classification: Dinosauria – Saurischia – Theropoda – Ceratosauria – Neoceratosauria – Abelisauroidea – Noasauridae – Elaphrosaurinae 

Time Period: Late Jurassic 

Location: Africa

Diet: Carnivore   

The lithe theropod Elaphrosaurus has a storied taxonomic history. It’s known from a single nearly-complete specimen from the Kimmeridgian stage in Africa, but this specimen lacks a head – and heads are notoriously helpful when it comes to classification. Elaphrosaurus had anatomical features similar to different theropod lineages; was it a ceratosaur? a coelophysoid? was it, perhaps, the ancestor of the later Cretaceous ostrich-mimic theropods? The current consensus is that Elaphrosaurus was a ceratosaur closely related to the beaked Limusaurus of the earlier Oxfordian stage of the Late Jurassic. Because we lack Elaphrosaurus’ skull, and because it’s assumed to have a close relationship with the omnivorous or herbivorous Limusaurus, Elaphrosaurus’ dietary preferences are dense with speculation; but, as we shall see, evidence from its long neck may give us a clue. 

Elaphrosaurus is known from the African Tendagu Formation, but possible remains have been discovered in North America, hinting at a wide distribution throughout Gondwana and western Laurasia. This theropod was twenty feet long with slim, long legs; slender forelimbs with three digits each; a lightweight, shallow-chested body; a long, stiff tail; and a long, relatively stiff neck. This was the shortest theropod dinosaur in stature, at least when you go by the height of the hips compared to the creature’s overall length. Several Coelophysis-like teeth were discovered among Elaphrosaurus’ remains; though these have been attributed to Elaphrosaurus (and they may very well belong to Elaphrosaurus!) most scientists believe these were deposited by scavengers enjoying this specimen’s long-lost flesh. Although Elaphrosaurus’ neck was long, the design of the neck vertebrae indicate that I was much less flexible than those of other theropods. It likely supported a rather small skull. These traits argue against Elaphrosaurus being a predator of large prey; perhaps it hunted early ornithopods? The other theory is that Elaphrosaurus, like its (assumed) close relative Limusaurus, was omnivorous or even herbivorous. 

a pack of Elaphrosaurus attack a juvenile sauropod in Late Jurassic Africa
(this is assuming, of course, that Elaphrosaurus was a predator!)

Allosaurus

Type Species: Allosaurus fragilis

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

Time Period: Late Jurassic

Location: North America and Europe

Diet: Carnivore   

Allosaurus’ name means ‘different lizard,’ and it refers to its ‘unique’ concave vertebrae (only ‘unique’ in quotes because, since its discovery, many theropods have been discovered with such vertebrae). Allosaurus was described in 1877 by paleontologist Othniel Charles Marsh, and as it was one of the first well-known theropod dinosaurs, it’s long been popular in paleontological and cultural circles (though we must emphasize that Allosaurus was not the ancestor of the later, and bigger, Tyrannosaurus). Interestingly, for over half of the 1900s, Allosaurus was known as Antrodemus; only later did the name Allosaurus come back to prominence to be established as one of the best-known dinosaurs!

Allosaurus lived from the Kimmeridgian to the Tithonian stages of the Late Jurassic. Though its primary stomping ground was the Morrison Formation of western North America, its remains have also been discovered in Portugal. Radiometric dating puts the age of the Morrison Formation and its associated fossil-beds to between 156 and 146 million years ago, safely nestled in the Late Jurassic and including the late Oxfordian stage, the Kimmeridgian stage, and the early Tithonian stage of the period. The Morrison Formation was a semiarid environment with distinct wet and dry seasons. The Morrison Basin stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains. These environments were dominated by herbivorous sauropods such as Camarasaurus, Brachiosaurus, Apatosaurus, and Diplodocus; other herbivorous dinosaurs included the plated Stegosaurus and ornithopods such as Camptosaurus and Dryosaurus. Other large theropods, in addition to Allosaurus, were the equally-sized Torvosaurus and the smaller Ceratosaurus. The top predator of the area was Allosaurus, which accounts for up to seventy-five percent of theropod specimens. Non-dinosaurian organisms included ray-finned fishes, frogs, salamanders, turtles, lizards, terrestrial and aquatic crocodylomorphs, and several species of pterosaurs. Fossilized flora of the Morrison Formation includes green algae, fungi, mosses, horsetails, cycads, ginkgoes, and conifers. The Morrison Formation was a wide tract of territory with sub-environments that included river-lined forests of tree ferns and ferns (called ‘gallery forests’); swampy ‘backwaters’; lakeside ‘resorts’; and fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.

The bulky, well-muscled Allosaurus was the top predator in its environment: it grew between thirty and forty feet in length and weighed between 1200 to 1500 pounds. It had a barrel-chested ribcage, giving it a bulkier appearance in contrast to other theropods such as its smaller contemporary Ceratosaurus. It had a wishbone. Its forearm was shorter than its upper arm, but its arms were powerful and capped with three fingers per hand, each finger equipped with ten-inch long strongly curved, pointed claws. Its legs were built for running, though not to the same extent of the later tyrannosaurs; Allosaurus’ top speed has been estimated between twenty and thirty-four miles per hour.  Its feet claws were less developed, too, and more hoof-like than those of earlier theropods. Each foot had three weight-bearing toes and an inner dewclaw, which some scientists have speculated was used for grasping in juveniles. It also had a splint-like remnant of a fifth toe that was perhaps used as a lever between the Achilles tendon and foot. 

Its massive skull attached to a short, S-shaped neck. Allosaurus had a pair of horns above and in front of the eyes; these horns were composed of extensions of the lacrimal bones, varied in shape and size among specimens, and would’ve been covered in a keratinous sheath in life. There were also lower paired ridges running along the top edges of the nasal bones that led to the horns. The function of the horns has been debated: they may have been used for display, for interspecies combat between rival males fighting for territory or females, for species recognition, or even as sunshades for the eyes! They would’ve been too weak and fragile to be used in any serious combat, however. There’s evidence for salt glands in the lacrimal bones. The eyes ‘shaded’ by these horns were placed on the skull in such a way that Allosaurus had binocular vision, though it was limited to twenty degrees. This meant that Allosaurus needed to keep it prey directly in front of it, because if the prey turned sharply, the prey could break from the hunter’s cone of vision. When this happened, Allosaurus could see the prey but only with one eye, and it would lack depth perception which could lead to a failed strike. Particularly agile prey may have been able to dodge Allosaurus’ bites by keeping itself out of its narrow binocular vision. Studies of Allosaurus’ braincase indicate its brain was similar to those found in crocodiles. Allosaurus had large olfactory bulbs, but the area associated with assessing smells was undeveloped. Scientists believe this meant that Allosaurus had a great sense of smell but the ability only to recognize a few, perhaps those of prey animals, carrion, or other members of its species. The design of its inner ear implies it was best suited to hearing low frequency sounds; the design of its vestibular system – which controls balance – shows that its head was usually held horizontally level to the ground. The braincase roof was thin, perhaps to improve thermoregulation for the brain. 

Allosaurus’ skull was massive and armed with dozens of sharp, serrated teeth up to four inches long. Each premaxilla of the tip of the snout held five teeth; each maxilla in the upper jaw had between fourteen and seventeen teeth. Each tooth-bearing cone of the lower jaw had between fourteen and seventeen teeth, as well. The teeth became shorter, narrower, and more backwards-curved toward the back of the skull. All of Allosaurus’ teeth had saw-like edges. Its teeth were shed easily and were replaced continually, making them common fossils in the Morrison Formation. The skull and lower jaws had points that permitted motion; in the lower jaws, the bones of the front and back halves loosely articulated, enabling the jaws to bow outward and increasing Allosaurus’ gape. Allosaurus’ hunting methods and preferred prey may have changed with age. Juvenile specimens had proportionally longer legs than adults; they would be ‘quick on their feet,’ perhaps the speediest dinosaurs of the Morrison Formation. They would’ve likely preyed on smaller animals, such as early mammals and ornithopods. As Allosaurus matured, it needed more sustenance – and thus it turned to the larger dinosaurs. As Allosaurus grew, its legs became shorter and more robust, which made them better able to handle the stresses in tackling large prey. For such large prey, high speed wouldn’t be needed, and longer legs would’ve made Allosaurus more susceptible to injury. An adult Allosaurus, at the top of the ‘feeding pyramid,’ would’ve been the terror of ornithopods, stegosaurs, and even sauropods.

There’s plenty of evidence that Allosaurus tackled stegosaurs; we have evidence of an Allosaurus tail vertebra with partially healed puncture wounds that fit the spikes of a Stegosaurus thagomizer, and the neck plate of one Stegosaurus specimen has a U-shaped wound that correlates well with an Allosaurus snout. Many sauropod bones have scrapings that fit Allosaurus teeth, and we even have shed Allosaur teeth present with many sauropod bones. Does this mean, then, that Allosaurus could take down fully-crown sauropods? Many scientists are doubtful. In comparison to an adult Brachiosaurus, for instance, Allosaurus wouldn’t be much of a threat. Perhaps the evidence of Allosaurus feeding on sauropods is due to scavenging; a sauropod carcass could be a windfall for a predator. Another theory is that Allosaurus did indeed hunt full-grown sauropods, and it was able to do this because it was a pack hunter (we will examine that concept in a moment). If Allosaurus hunted alone, it may have preyed upon sick or young sauropods, but attacking a healthy, full-grown adult would’ve been tantamount to foolishness. Because ornithopods were common in the Morrison Formation, they were likely a staple in the Allosaurus diet. Allosaurs may have subdued them by using an attack similar to that of modern big cats: grasping the prey with their forelimbs and then making multiple bites on the throat to crush the trachea. Allosaurus’ forelimbs were strong and capable of restraining prey with the three-fingered claws, so this hunting method seems likely.

The precise methodology of an ‘Allosaurus attack’ has been the subject of fierce debate. The renowned paleontologist Robert Bakker compared Allosaurus to Cenozoic saber-toothed carnivores and noted similar adaptations, such as a reduction in jaw muscles and increase in neck muscles, and the ability to open the jaws wide. Bakker suggested that in the absence of ‘saber teeth,’ Allosaurus’ short teeth became small serrations on a saw-like cutting edge that ran the length of the upper jaw. Allosaurus would use the length of its jaws to execute slashing attacks against much larger prey in the hope of weakening the prey by pain, hewn muscle, and blood loss. Other paleontologists have suggested that Allosaurus used its skull like a machete against prey: it would attack open-mouthed, slashing flesh with its teeth, and tearing the flesh away without splintering bone. The strength of the skull would’ve helped Allosaurus withstand the impact forces associated with repeated attacks against prey. Building upon this theory, some scientists have suggested that Allosaurus would attack large prey such as full-grown sauropods but without the intent of actually killing them; in this scenario, the fleet-footed Allosaurus would lunge up, take a bite of flesh out of the Brachiosaurus haunch, and then retreat to feed in peace (leaving the wounded Brachiosaurus moaning with a chunk of flesh missing). Such a strategy would enable Allosaurus to fill its stomach while also preserving the prey to be fed upon another day. Once Allosaurus brought down prey – whether a juvenile sauropod, a Stegosaurus, or a hapless ornithopod – how did it eat? A 2013 biomechanical study showed that Allosaurus could make rapid, forceful vertical movements with its skull. This suggested that Allosaurus ate by vertical movements in a manner akin to that of modern falcons: Allosaurus could have gripped the prey with its skull and feet, then jerked back to tear flesh from bones. This method of eating was different than that envisioned for tyrannosaurs, which probably tore flesh with side-to-side shakes of the skull, similar to the prey-handling of crocodiles.  

were allosaurs family-friendly pack hunters?

Many scientists believe that Allosaurus worked in family groups or packs to take down large prey. This concept was promoted during the 1970s and has become a staple of theropod studies. Robert Bakker extended social behavior in hunting to parental care; he interprets shed allosaur teeth and chewed bones of large prey animals as evidence that adult allosaurs brought food to lairs for their young to eat until they were grown. Evidence for ‘pack hunting’ – or at least gregarious behavior among Allosaurus – comes from multiple bone-beds that include multiple Allosaurus specimens in varying stages of growth. However, another explanation for these ‘family’ bone-beds is that they are fossilized scenes of territorial infighting or even cannibalism run amuck. That allosaurs didn’t always get along is evident, as we have interspecies injuries recorded in allosaur pathologies, such as allosaur bite wounds to Allosaurus skulls. Head-biting may have been a quick way to establish dominance in a pack or to settle territorial disputes among rogue allosaurs. There’s significant evidence of cannibalism among Allosaurus: these include allosaur teeth among allosaur rib fragments, allosaur tooth markings on allosaur bones, and even fully-cannibalized allosaur skeletons among the bones at Bakker’s ‘lair sites.’ The large bone-beds of ‘family groupings’ may not represent family groups but feeding sites. Most carnivores are territorial and will kill or cannibalize intruders of the same species; young organisms of the same species are often killed by older organisms when they become too bold. The accumulation of multiple Allosaurus remains may be due to individual allosaurs gathering at the same site not due to pack hunting but to feed on other disabled or dead allosaurs; in the ‘feeding frenzy’ other allosaurs were killed, as well – and in a domino effect, the situation gets worse and worse as more bodies start piling up. This could explain the high proportion of juvenile and sub-adult allosaurs present, since they are disproportionally killed at modern group feeding sites of modern predators like crocodiles and Komodo dragons. This may be what was taking place at Bakker’s ‘lair sites’ (in which case, Bakker’s ‘paternal’ allosaurs become frenzied baby-killers). Whether or not Allosaurus was a family-friendly pack hunter (as Bakker thinks) or a bloodthirsty killer with no qualms about killing members of its own kind (as others think) is still a matter of debate. 

or were they loners who had a tendency to fight and kill one another? jury's out!

Yingshanosaurus

Type Species: Yingshanosaurus jichuanensis

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

Time Period: Late Jurassic

Location: China 

Diet: Herbivore   

The Chinese stegosaur Yingshanosaurus was on the smaller side of things, growing to about sixteen feet snout-to-thagomizer, and it’s known for a pair of broad, wing-like spines on its shoulders that were flat like the bony plates on its back. These shoulder spines had large, flat, trapezoidal bases; after a sudden kink, they were reduced to a more narrow straight shaft that remained flat but with a protruding ridge on the outer side. The plates on its back were small and relatively low, and they were triangular or fin-shaped. The largest plates were only about five inches high and seven and a half inches long. These plates were uniformly flat with a rough, veined surface. As a low browser, Yingshanosaurus plodded through the Jurassic forests of prehistoric China munching on cycads and ferns. 

Dacentrurus

Type Species: Dacentrurus armatus

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

Time Period: Late Jurassic

Location: Europe 

Diet: Herbivore   

The stegosaur Dacentrurus was initially discovered in England, though fragmentary remains have been found in France, Spain, and Portugal (in which fossilized eggs are attributed to Dacentrurus), indicating a wide distribution among the islands and archipelagos of northeastern Laurasia. We know that stegosaurs were regularly attacked by large theropods in North America (Stegosaurus and Allosaurus had a long-running feud), and it’s believed that Dacentrurus faced similar opposition on its own turf; however, the precise identity of its larger theropod assailants is unknown, as the larger European theropods of the Jurassic date back to the Early and Middle Jurassic (such as Dubreuillosaurus and Poekilopleuron). If the Oxfordian theropod Metriacanthosaurus continued into the Kimmeridgian, it's likely it and Dacentrurus duked it out a time or two. This stegosaur was initially named Omosaurus, but since that name had already been given to a species of extinct crocodile, the name was changed to Dacentrurus.

a Dacentrurus defends against a Ceratosaurus (never mind these two likely didn't coexist!)

Dacentrurus was a large, heavily-built stegosaur that grew up to thirty-two feet in length and clocked in around five and a half tons. It had a broad gut and a massive rump. Its hind-limbs were short, but the forelimbs were long; thus Dacentrurus had the same general proportions as its North American cousin Stegosaurus, though their ‘plate armor’ was different. Dacentrurus had eight pairs of triangular plates that ran from the neck to the end of the hip; these ‘double-rowed’ plates were followed by four pairs of large spikes that ran down to the thagomizer. Dacentrurus’ stagomizer consisted of four more pairs of spikes that pointed to the side, and these tail spikes had sharp cutting edges on the front and rear sides. The arrangement of ‘plate and spike’ armor is reminiscent of its African cousin Kentrosaurus. Though Dacentrurus is often portrayed with a spike growing near the shoulder, this is artistic license based upon the fact that many primitive stegosaurs – i.e. those that had a mix of both plates and spikes – employed such shoulder spikes. 

Dicraeosaurus

Type Species: Dicraeosaurus hansemanni

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

Time Period: Late Jurassic

Location: Africa (Tanzania) 

Diet: Herbivore   

The small-sized sauropod Dicraeosaurus lived in eastern Africa in what is now modern Tanzania. Its remains have been uncovered in the Tendago Formation, which dates from the Middle Jurassic to the Early Cretaceous and which is divided into six ‘zones’ corresponding to different time periods. The Tendagu Formation of the Late Jurassic was located in the subtropical southern hemisphere, and it would’ve been a semi-arid environment with seasonal rainfall. The Tendagu has given us a wealth of fossils from this period in earth’s history, not only dinosaurs but also early mammals, crocodylomorphs, amphibians, fish, invertebrates, and flora. The environment in which Dicraeosaurus lived included a coastal region of beaches and lagoons; further inland were coastal plains with brackish lakes and ponds. Dicraeosaurus lived among other herbivores such as the brachiosaurid Giraffatitan and the stegosaur Kentrosaurus; it may have been hunted by the carcharodontosaur theropod Veterupristisaurus. 

Dicraeosaurus’ name means ‘two forks’ in reference to the neural spines of the backbone that branched (or ‘forked’) in two. In life, this was likely a ridged back of fleshy skin. This type of backbone design is rare, and it’s far more pronounced in the later Amargasaurus. The ridged back came from the neural spines that projected upwards from its backbone, running from its tail to its neck. Each spine opened out at the top to form a ‘Y’ shape to which muscles were attached. Some scientists believe these were bony anchors for a thin, low, sail-like structure. The sail would’ve made it look bigger in profile as a deterrent to predators; or it may have served as a display for species recognition or attracting mates, in which case it was likely brightly colored or vibrantly patterned; another theory is that the sail would’ve served for thermoregulation. In the latter case, the large area of the sail, when positioned at a right angle to the rising sun, would’ve absorbed warmth and passed it, via the blood flowing through it, into the animal’s system. This would quickly raise the animal’s body temperature to allow more and faster activity after the cool of night; conversely, standing in the shade and at a right angle to the breeze would cool the body. 

Dicraeosaurus had a relatively short, wide neck with only twelve vertebrae, less than any other late Jurassic sauropods other than Brachytrachelopan. Its tail had the typical diplodocid ‘whiplash,’ though it was nowhere near as ‘whippy’ as more derived (and larger) diplodocids. Its eyes were set high atop its skull; its snout was long, low, and horse-like; and its teeth were fine and pencil-shaped, set in two curved clusters toward the front of the jaws. These teeth were designed for stripping foliage. The design of its neck – coupled with its low stature – meant that it fed at ground level up to ten feet off the ground.

Ceratosaurus

Type Species: Ceratosaurus nasicornis

Classification: Dinosauria - Saurischia – Theropoda – Neotheropoda – Ceratosauria – Neoceratosauria – Ceratosauridae

Time Period: Late Jurassic

Location: North America

Diet: Carnivore   

The ‘horned lizard’ Ceratosaurus is one of the main theropods that prowled North America during the Late Jurassic. This dinosaur was discovered early in paleontology, and so its name was given to one of the major theropod subgroups, the Ceratosauria, a sister taxon to the ‘stiff-tailed’ tetanurans. Members of Ceratosauria had robust skulls with increased ornamentation or height and a shortening of the arms. Ceratosaurs are identified as theropods closer in relation to Ceratosaurus than to birds; indeed, it was the tetanuran line that eventually diversified into modern birds. Though Ceratosauria diverged from the rest of theropoda – and its sister taxon Tetanurae – in the Early Jurassic, most ceratosaurs were from the Late Jurassic (with a few identified in the Cretaceous). 

Three nearly complete Ceratosaurus specimens have been uncovered (along with a host of fragmentary remains) in the North American Morrison Formation. Though possible remains have also been found in Africa, South America, and Europe, the identification of these fossils as belonging to Ceratosaurus is dubious; thus, while some would like to push Ceratosaurus’ domain southward and eastward from North America, more research is needed before this can be done in good faith. What is not in doubt is that Ceratosaurus was a ‘staple theropod’ of the Morrison Formation. Radiometric dating puts the age of the Morrison Formation and its associated fossil-beds to between 156 and 146 million years ago, safely nestled in the Late Jurassic and including the late Oxfordian stage, the Kimmeridgian stage, and the early Tithonian stage of the period. The Morrison Formation was a semiarid environment with distinct wet and dry seasons. The Morrison Basin stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains. These environments were dominated by the herbivorous sauropods, though it was also home to the plated Stegosaurus and early ornithopods such as Camptosaurus. The top predator of the area was Allosaurus, which accounts for up to seventy-five percent of theropod specimens. Non-dinosaurian organisms included ray-finned fishes, frogs, salamanders, turtles, lizards, terrestrial and aquatic crocodylomorphs, and several species of pterosaurs. Fossilized flora of the Morrison Formation includes green algae, fungi, mosses, horsetails, cycads, ginkgoes, and conifers. The Morrison Formation was a wide tract of territory with sub-environments that included river-lined forests of tree ferns and ferns (called ‘gallery forests’); swampy ‘backwaters’; lakeside ‘resorts’; and fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum. 

Ceratosaurus reached between seventeen and twenty-three feet in length and weighed up to a ton. Researchers have called it the ‘dragon’ of the theropods, because it had a striking resemblance to dragons of lore: it had a short, ridge-like horn on the tip of its snout, horny ridges near its eyes, and a jagged crest of osteoderms running down its neck. Fossil remains of the nasal horn include only the horn core; in life, the core would’ve been supported by a keratinous sheath. While the base of the nasal horn was smooth, its upper two-thirds were wrinkled and lined with grooves that contained blood vessels in life. In the holotype specimen, the horn core was five inches long and three-quarters of an inch wide at its base, but it narrowed to only half an inch wide further up the snout. It was just under three inches in height. In another specimen, it was longer and lower in the skull; this may be an episode of sexual dimorphism (perhaps males had larger horns than females?). These horns would’ve been larger in life due to the keratinous sheath. Though scientists used to believe the horn was used as a weapon while hunting prey, more studies have shown it was too small and weak to be used as a weapon. Though a few researchers believe it was used in interspecies combat between males – perhaps to establish territory or to determine mating rights – most scientists believe its function was strictly for display. When the nasal horn fused in maturity, it may have signaled the male’s readiness to mate. In this scenario, the nasal horn was primarily a function for males. It may have been richly colored in life. Ceratosaurus also had smaller, semicircular, bony ridges in front of each eye, similar to those of Allosaurus. These ridges were formed by the lacrimal bones. In juveniles, all three horns were smaller than in adults, and the two halves of the nasal horn didn’t fuse until later in life. Ceratosaurus’ further ornamentation included small, elongated, and irregularly formed osteoderms (skin bones) that ran along the midline of its body, likely forming a continuous row that extended from the base of the skull to most of the tail. 

Ceratosaurus’ arms were short but strong and capped with four fingers on the hands (a primitive condition, as more ‘developed’ theropods would be three-fingered or even two-fingered). Its powerful rear limbs made it at a capable runner, and its skull was two feet long. It had massive fanged teeth set in deep jaws; the maxillary bones of the upper jaw were lined with fifteen blade-like, serrated teeth on each side. The first eight of these teeth were long and robust, but from the ninth tooth onward they gradually decreased in size. Ceratosaurus’ skull was unique in that it had cranial kenesis, in which the bones were so loosely connected that the skull bones could move side-to-side when eating; this enabled Ceratosaurus to swallow large pieces of meat. Ceratosaurus’ hunting methods have been a significant debate, largely because it shared its environment with larger theropods such as Allosaurus and Torvosaurus. Because it shared its environment with ‘bigger and badder’ theropods, scientists believe these predators practiced niche partitioning, in which they didn’t directly compete for food. One suggestion is that Ceratosaurus, being the smaller theropod of the Morrison ‘big-wigs’, hunted smaller ornithopods and stegosaurs whereas Allosaurus and Torvosaurus hunted larger herbivores such as the sauropods. Other scientists have proposed two more ‘developed’ theories regarding how niche partitioning may have played out between these theropods, and these theories have been promoted, embraced, and fought over; the first categorizes Ceratosaurus as a terrestrial hunter, and the second categorizes Ceratosaurus as an aquatic hunter who no doubt scavenged large dinosaur carcasses when the opportunity arose.

In 1998 paleontologist Donald Henderson suggested that Ceratosaurus lived alongside two separate potential species of Allosaurus. The first Allosaurus ‘morph’ had a shortened snout, a high and wide skull, and short, backwards-angled teeth; the second Allosaurus ‘morph’ had a longer snout, lower skull, and long, vertical teeth. Henderson attributed these morphological differences to variation in feeding strategies, so that the short-snouted Allosaurus occupied a different niche than both the long-snouted Allosaurus as well as Ceratosaurus. The short-snouted Allosaurus would’ve had reduced movement when biting, resulting in increased bite force, similar to what we see in cats. The long-snouted Allosaurus and Ceratosaurus would’ve used their fang-like teeth to deliver quick, slashing bites; their narrower skulls resulted in a generally weaker bite force. Because the long-snouted Allosaurus and Ceratosaurus would’ve had similar feeding strategies, Henderson suggested they would’ve been in direct competition in their environment; because only one species could reign supreme, the ‘loser’ would have to find elsewhere to hunt. Henderson argues that this is precisely what happened, and the larger long-snouted Allosaurus was triumphant. He shows how Ceratosaurus remains are rare in environments that include the long-snouted Allosaurus, but Ceratosaurus and the short-snouted Allosaurus – both employing different feeding strategies – could be found together. While this theory is intriguing, some oppose it by arguing that the two Allosaurus ‘morphologies’ may not be as ‘cut and dry’ as Henderson thinks. Bolstering skeptics’ cause, a 2010 study suggested that short-snouted Allosaurus were actually cases of individual variation rather than a separate species. 

Henderson’ theory assumes that Ceratosaurus was a terrestrial predator, but a 2004 study by Robert Bakker and Gary Bir went another direction: “What if Ceratosaurus specialized in aquatic prey, feeding on fish and crocodiles and turtles?” They pointed out how shed teeth from fifty different localities in the Morrison Formation belong to both Ceratosaurus and megalosaurs tend to show up in habitats in and near water sources such as wet floodplains, riverine locations, lake margins, and swamps. While allosaurids were common in both terrestrial and aquatic environments, Ceratosaurus was predominantly found in the latter. Bakker and Bir argued that Ceratosaurus and megalosaurs preferred to hunt near and in bodies of water (though they no doubt fed on scavenged dinosaur carcasses; Ceratosaurus tooth marks have been found on sauropod bones that it likely scavenged). They pointed out how Ceratosaurus and megalosaurs in general had long, low, and flexible bodies. Compared to other Morrison theropods, Ceratosaurus had taller neural spines on the foremost tail vertebrae, which were vertical rather than inclined toward the back; these, when combined with the deep chevron bones on the underside of the tail, indicate a deep, ‘crocodile-like’ tail that may have been designed for swimming. Allosaurids, in contrast, had shorter, taller, and stiffer bodies with longer legs; Allosaurus and its ilk were designed for rapid running in open terrain and preying upon larger sauropods and stegosaurs. The Morrison Formation, resplendent with swamp-lands and lakes and river valleys, would’ve been a prime environment for a primarily aquatic hunter such as Ceratosaurus. Perhaps, if we were to step back in time and walk along the shore of a Jurassic river, we would see a Ceratosaurus sculling its way through the current on the hunt for crocodilians and fish.