Gasosaurus

Type Species: Gasosaurus constructus

Classification: Dinosauria – Saurischia – Theropoda – Tetanurae

Time Period: Middle Jurassic

Location: China

Diet: Carnivore

Gasosaurus’ name literally means ‘gas lizard.’ This isn’t because it had swollen bowels and was necessarily gassy, though that would be fascinating if it were true. In reality, it’s named after the gasoline company that found it while doing construction in Sichuan Province, China. The discovery of this carnivorous theropod clued scientists in to a new bone-bed dating to the Middle and early Late Jurassic. During the Jurassic Period, the area had been a forested lakeside environment, and further digs after Gasosaurus’ unearthing have revealed all sorts of sauropods, theropods, and stegosaurs. The bone-bed is known as the Shaximiao Formation, and it’s divided into an Upper and Lower portions. The ‘Upper’ bone-bed correlates with the Oxfordian stage of the Late Jurassic while the ‘Lower’ bone-bed correlates with the Bathonian and Callovian stages of the Middle Jurassic. Gasosaurus emerged at the beginning of the Middle Jurassic and remained a staple of the Asian ecosystem into the beginning of the Early Jurassic; its ten-million-year ‘reign’ lasted from about 170-160 million years (a pretty good run for a single species!). 

Gasosaurus was a ‘stiff-tailed’ tetanuran theropod that measured eleven to thirteen feet and likely weighed around 330 to 880 pounds. It had strong legs but short arms, and it shares characteristics with both more developed tetanuran theropods and earlier non-tetanurans, suggesting that Gasosaurus was near the ‘base’ of the emerging tetanurans. It coexisted with other mid-range theropods such as Chuandongocoelurus and Kaijiangosaurus, both theropods found in the Lower Shaximiao Formation. Though it probably subsisted mostly on small- to medium-sized prey, it could have theoretically taken down the more primitive sauropods in its environment, especially if it utilized pack-hunting. In the artistic depiction below, two Gasosaurus are running in the midst of a Shunosaurus herd. Though Gasosaurus and Shunosaurus co-existed, they did so for only the briefest moment at the twilight of Gasosaurus’ prehistoric career. 

Ohmdenosaurus

Type Species: Ohmdenosaurus liasicus

Classification: Dinosauria – Saurischia – Sauropoda

Time Period: Early Jurassic

Location: Europe (Germany)

Diet: Herbivore

Ohmdenosaurus is one of the few fossilized sauropods found in Europe (most sauropods of the Jurassic tended to gather around the Tethys Sea coastlines). Ohmdenosaurus would’ve reached to about twenty-two feet in length and weighed around 2900 pounds. Its remains were found in an area that had been a series of islands in the region of modern-day Bohemia. These islands were rather large – much like Ireland being an ‘extended island’ of the British Isles – and sported a variety of environments, from seacoasts, river deltas, mangrove-like swamps, lagoons, and brackish waters. These islands were subject to monsoons and large scale rains, which resulted in a vast amount of insect fossils from this time period. Southern summers with humid south-west monsoons resulted in winters hit by dry northeast trade winds. Ohmdenosaurus lived among ocean-going crocodylomorphs such as Platysuchus and lizard-like marine rhynchosaurs such as Palaeopleurosaurus. The fossilized remains of the pterosaurs Campylognathoides and Dorygnathus have also been discovered in the environment.  

Emausaurus

Type Species: Emausaurus ernsti

Classification: Dinosauria – Ornithischia – Thyreophora   

Time Period: Early Jurassic

Location: Europe (Germany)

Diet: Herbivore

Emausaurus is the only known thyreophoran from the Toarcian stage of the Early Jurassic. The remains discovered in Germany belonged to a juvenile whose length was estimated at eight feet and likely weighed 150 to 200 pounds. Adults (whose remains have not been found) may have reached as long as thirteen feet and weighed around 750 pounds. Emausaurus resembled the earlier Laurasian thyreophoran Scelidosaurus, and it was covered in bony armor – called osteoderms. It had at least one spike in its armor. Though infants and juveniles may have been capable of a bipedal stance (perhaps to reach higher foliage), adults were probably confined to a quadruped stance, and as such they were low browsers. The juvenile Emausaurus was recovered in an ancient seashore environment, maybe even a lagoon, and the same rock-beds show Toarcian fauna such as insects, bivalves, sea snails, ammonites, and fish. The remains of marine reptiles, crocodylomorphs, and at least two sauropods have been discovered in the rock-beds, as well. 

Berberosaurus

Type Species: Berberosaurus liassicus

Classification: Dinosauria – Saurischia – Theropoda – Ceratosauria  

Time Period: Early Jurassic

Location: Africa (Morocco)

Diet: Carnivore

Berberosaurus was a moderate-sized theropod whose remains were found in Morocco, Egypt. The remains belonged to a young adult, and they were found amidst the remains of the prosauropod Tazoudasaurus. It’s estimated to have reached sixteen feet head-to-tail and clocked in around 485 pounds in weight. Scientists speculate that this theropod may have been the oldest-known true ceratosaur. 

Lingwulong

Type Species: Lingwulong shenqi

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

Time Period: Early Jurassic

Location: China

Diet: Herbivore

Lingwulong was a sauropod that lived in southern Laurasia sometime between the late Toarcian stage of the Early Jurassic and through the Bajocian stage of the Middle Jurassic. The fossils discovered belong to seven to ten individuals at different stages of growth, indicating that they belonged to a family herd. These sauropods had U-shaped snouts and grew up to fifty feet in length. Lingwulong is considered a ‘neosauropod’ (or ‘new sauropod’), the group to which most sauropods belong. The neosauropods are composed of two subgroups: Diplodocoidea and Macronaria. The neosauropods were the largest land animals to have ever lived, and Lingwulong is the earliest known of the group. It’s considered a dicraeosaurid, a ‘sister group’ to the diplodocids. Dicraeosaurids are differentiated from the diplodocids by their relatively small body size and short necks. 

Segisaurus

Type Species: Segisaurus halli

Classification: Dinosauria – Saurischia – Theropoda – Coelophysoidae - Coelophysidae

Time Period: Early Jurassic

Location: North America

Diet: Carnivore

Segisaurus is known from a single sub-adult specimen from Arizona. The specimen discovered was just under three and a half feet long and would’ve stood just over one and a half feet tall at the hips. It was nimble and likely preyed upon insects, lizards, and small mammals (and there’s no reason to think it wouldn’t scavenge when the opportunity presented itself). Segisaurus had a flexible, elongated neck and stout body; its powerful legs were crowned with three-toed feet; and it had a long tail and long forearms. Segisaurus is remarkable for the fact that it seems to have had clavicles, which are unknown in other theropods from that era. This find demonstrates that the clavicle was primitively present in early theropods and reinforces the theory that modern birds are descended from theropod dinosaurs. 

Dilophosaurus

Type Species: Dilophosaurus wetherilli

Classification: Dinosauria – Saurischia – Theropoda – Dilophosauridae 

Time Period: Early Jurassic

Location: North America

Diet: Carnivore

Dilophosaurus was the apex predator of its time in the Sinemurian and Pliensbachian stages of Early Jurassic North America some 196 to 183 million years ago. Its name means ‘two-crested lizards’ due to the twin sweeping crests atop its skull. Skeletal remains have been found in Arizona, and trackways have been uncovered in Connecticut (thus it’s no surprise that Dilophosaurus is Connecticut’s state dinosaur). The holotype specimen is remarkable in that it showed healed injuries and even signs of a developmental disability. The injuries on the specimen are consistent with those sustained from crushing forces, and there were two pits on the right humerus that may have been from pus-filled abscesses. The holotype specimen had a smaller and more delicate left humerus than the right, but the condition was reverse in its forearms; this may be due to a developmental anomaly called fluctuating asymmetry, often caused by traumatic stressors in the early years of development. Scientists have studied further specimens and have found fractures, tumors, and other anatomical deformities. What they have absolutely not found is a cowl on its neck and the ability to spit venom, as is portrayed Michael Crichton’s novel Jurassic Park and Stephen Spielberg’s cinematic adaptation. So, no, for the umpteenth time, we have no reason to believe that Dilophosaurus was venomous. 

a reconstruction of a 'furry' Dilophosaurus

Dilophosaurus was a medium-sized carnivore analogous to the size of a brown bear. It’s known from plentiful remains and may have been a pack hunter, as several specimens were fossilized together (this is rare for animals that didn’t ‘run together,’ unless they died in a catastrophic event – such as a flood – and were entombed together at the feet of the floodwaters). Dilophosaurus could reach up to twenty-three feet in length and clock in at 880 pounds. It had dual, sweeping crests atop its head, and it was slender and lightly built with a narrow snout. The upper jaw had a gap or kink below the nostril, and the jawbone was slender and delicate at the front but deep at the back. Its teeth were long, curved, thin, and compressed sideways; the teeth in the lower jaw were significantly smaller than those of the upper jaw, and most of the teeth had serrations at their front and back edges. Dilophosaurus had a long neck, and its vertebrae were hollow and light. Its arms were long and slender and powerful. Each hand had four fingers: the first was short but strong with a sickening claw, the second two fingers were longer and slenderer with smaller claws, and the fourth was vestigial. Its thigh bone was robust, its feet were stout, and the toes bore large claws. Trackways in Connecticut show that Dilophosaurus had a six and a half feet stride and that its claws alone made impressions. 

was Dilophosaurus pescetarian? It's a cool idea!

Dilophosaurus’ predatory lifestyle has been the subject of debate over the years. American paleontologist Robert Weems argued that Dilophosaurus had a weak bite and used its teeth for plucking and tearing rather than biting. He theorized that Dilophosaurus was a scavenger rather than a predator, and that if it did kill large prey, it would’ve done so with its clawed hands and feet rather than with its jaws. Later, paleontologist Robert Bakker argued that Dilophosaurus’ massive neck and skull and large upper teeth were expertly designed for killing large prey and robust enough to attack the largest sauropodomorphs in its environment. The paleontologist Paul Sereno also rejected Weems’ arguments for Dilophosaurus as a scavenger, claiming that strictly-scavenging terrestrial animals are a myth. He insisted that Dilophosaurus’ snout was better braced than had been thought and that the large, slender teeth were more lethal than the claws. He argued that Dilophosaurus was fully capable of hunting large herbivores, but that didn’t mean it wouldn’t snap up smaller prey when the opportunity arose. More recently in 2007, it was theorized that Dilophosaurus may have been primarily pescetarian (a fish-eater). Scientists highlighted how the ends of the jaws were expanded to the sides, forming a ‘rosette’ of interlocking teeth. This arrangement is similar to those of the later spinosaurids, which are known to have eaten fish; it’s also similar to modern gharials, which subsists largely on a pescetarian diet. Furthermore, Dilophosaurus’ nostrils were retracted back on the jaws, similar to spinosaurids (though the latter’s nostrils are more retracted). Such retraction of the nostrils may have limited water splashing into the sinus cavities while fishing. Both Dilophosaurus and spinosaurids had long arms with well-developed claws, perfect for catching fish. The Early Jurassic ‘Lake Dixie,’ which extended from Utah to Arizona and Nevada, would’ve provided abundant fish in the post-apocalyptic, biologically-impoverished world following the Triassic-Jurassic Extinction Event. Perhaps Dilophosaurus is a theropod that specialized in tapping into this abundant niche?

gnarly crests bruh

Proponents of the pescetarian Dilophosaurus also point to the head crests. While these wouldn’t necessarily help with a fishing lifestyle – no one is suggesting they were used as lures! – they wouldn’t risk damage in combat. Dilophosaurus’ head crests – similar to a cassowary with two crests – were each made of a curved bony ridge, like a third of a dinner plate, and barely as thick. These thin, fragile crests projecting at an angle above the eyes. The fragility of the crests is a major concern for those who argue for a brutal predatory lifestyle of taking down large prey; they could easily be broken in a scuffle. If Dilophosaurus was a fisher, however, there’s much less chance of them being damaged in the pursuit of food. The purpose of the crests has been debated, and different roles have been assigned to them: were they used for thermoregulation (the regulation of body temperature)? were they used to indimidate rivals or attract mates? were they used to identify one’s own species or even to distinguish between male and female (if the crests were to be smaller, perhaps, on females than males, in a form of sexual dimorphism)? The theory of thermoregulation has been cast aside, since it’s become apparent that dinosaurs were warm-blooded to begin with. Current hypotheses tend towards sexual display or species recognition with an acknowledgement of the distinct possibility of crest differences between genders. 

did Dilophosaurus travel or hunt in family groups? It seems likely!

Dilophosaurus’ fossils were found in the Kayenta Formation of Arizona, which – during the Early Jurassic – was the confluence of several rivers and close to Lake Dixie. By the Middle Jurassic, this area was being encroached upon from the north by a sandy dune field. The animals of the Early Jurassic were adapted to a seasonal climate, and abundant water could be found in streams, ponds, and lakes. The climate experienced rainy summers and dry winters. Dilophosaurus lived alongside large prosauropods such as Sarahsaurus, heterodontosaurs, primitive thyreophorans such as the lightly-armored Scutellosaurus and Scelidosaurus, and smaller theropods such as Coelophysis. The Kayenta Formation has also coughed up microbial or ‘algal’ limestone, petrified wood, plant impressions, freshwater bivalves and snails, various crustaceans, and invertebrae trace fossils. Representatives of the plentiful marine environments – lakes, rivers, and ponds – are common, from hybodont sharks, bony fish, lungfish, salamanders, caecilians, the early frog Prosalirus, and the Early Jurassic turtle Kayentachelys. There are also lizards, numerous crocodylomorphs such as Protosuchus, a panoply of early mammals, and the pterosaur Rhamphinion. It’s safe to say, then, that Dilophosaurus lived in a happening place!

Scutellosaurus

Type Species: Scutellosaurus lawleri

Classification: Dinosauria – Ornithischia – Thyreophora

Time Period: Early Jurassic

Location: North America

Diet: Herbivore

Scutellosaurus has been a riddle in the ornithischian family tree for a long while. Like its European contemporary Scelidosaurus, it’s been paraded as the kind of dinosaur that could’ve evolved into one of the later, better-known groups of thyreophorans (the armored ankylosaurs and plated stegosaurs). Most scientists consider it a common ancestor of both groups and believe it to be closely related to Scelidosaurus and the later Early Jurassic Emausaurus. Though some want to place it in the Scelidosauridae family along with Scelidosaurus, currently it’s viewed as an earlier, more basal thyreophoran (Scelidosaurus is larger and seems to be a more ‘evolved’ thyreophoran with more similarities to the later ankylosaurs and stegosaurs). 

Scutellosaurus is known from two partial skeletons from Arizona. The remains included portions of the skull and lots of detached bony plates called scutes (from which this dinosaur gets its name). The scutes came in a variety of shapes: some were triangular wedges, others were low cones, some were lopsided trimpets, and still others were curved like horns. Hundreds of detached scutes have been found, but because they were detached, the exact pattern on the body is unknown. Scientists estimate that a single individual had anywhere between two hundred and four hundred of these scutes embedded in its skin like small, raised shields. 

a flock of Scutellosaurus flee a pack of Dilophosaurus

Scutellosaurus was relatively small, growing between four to six and a half feet long, and weighing twenty-fifty pounds despite its light armor. It stood about twenty inches tall at the hips. It was small, slim, and long, and it had an unusually long tail, perhaps to counterbalance the weight of its armor. It probably ran rapidly on all fours since the front limbs had broad, sturdy paws. It could rear up on its longer hind limbs to eat higher plant-stuffs, but it’s unlikely that it could’ve run very well bipedally, since its armor would’ve made it top-heavy. Its mouth had a narrow, beak-like front, and its jaws contained several broad incisors and a row of fluted, leaf-shaped cheek teeth designed to crush plant material. Its head was protected by low bony plates. Scientists speculate that, like the similar-sized heterodontosaurs of the Early Jurassic, this early thyreophoran was gregarious in nature, traveling in ‘family flocks’. 

a Scutellosaurus taking a break with an Early Jurassic turtle

Scelidosaurus

Type Species: Scelidosaurus harrisonii

Classification: Dinosauria – Ornithischia – Thyreophora – Scelidosauridae

Time Period: Early Jurassic

Location: British Isles and North America

Diet: Herbivore

The thirteen-foot-long herbivore Scelidosaurus lived among the scattered wooded islands of the British Isles during the Sinemurian and Pliensbachian stages of the Early Jurassic some 196-183 million years ago. It also 'migrated' into northern Laurasia, or North America as we know it now, as its remains have recently been discovered in Arizona. Scelidosaurus is the most completely known dinosaur from the British Isles and the only classified dinosaur from Ireland. For 150 years Scelidosaurus has been the epicenter of a fierce debate regarding its placement in the ‘dinosaur family tree.’ Some scientists argue that it’s an early ankylosaurs; others that it’s an early stegosaur; still others that it’s an early thyrophoroidean; and still others insist that it’s its own type of dinosaur with its own family, the Scelidosauridae (perhaps along with Scutellosaurus and Emausaurus). The general consensus at the moment – though, you can imagine, it is quite subject to change! – is that it belongs to Scelidosauridae, a thyreophoran sister taxon of the ankylosaurs and stegosaurs.

Scelidosaurus had a small head with a horny, beak-like front to its mouth. It was quadrupedal, with its rear legs longer and stronger than its forelegs, so that its back sloped up towards the hips (these features would be developed and exaggerated later on by the stegosaurs). Though primarily a low browser feasting on ferns and cycads, Scelidosaurus may have been able to rear up on its hind limbs to reach higher foliage such as conifers, but this is debated; even if it could become bipedal for eating, it wouldn’t have been able to move on two legs, and the bipedal stance would be awkward and cumbersome. Thus, though Scelidosaurus was capable of a bipedal stance, it likely only did so when the environment forced its hand. Scelidosaurus fed with a puncture-crush system of tooth-on-tooth action with a precise up-and-down jaw movement without the teeth actually touching each other. The later stegosaurs, with their primitive teeth and simple jaws, fed likewise. Its tail was stiff due to tendons that lay alongside its backbone and which became ossified with bony minerals.

The most notable facet of Scelidosaurus was the ‘light armor’ it sported: its neck, body, and tail were studded with small, pebble-like scales and large bony plates called scutes. The scutes were generally longer at the front of the body and diminishing in size towards the rear, especially at the thighs. Scelidosaurus’ bony armor – called osteoderms – are seen in modern crocodiles, armadillos, and some lizards. Compared to the later ankylosaurs, Scelidosaurus’ armor was ‘amateur hour,’ for it lacked continuous plating, spikes, or pelvic shields. Scelidosaurus’ osteoderms were arranged in horizontal parallel rows down the length of its body. The osteoderms ranged in both size and shape. Most were smaller or larger oval plates with a high keel on the outside, the highest point of the keel positioned more to the rear. Some scutes were small, flat and hollowed-out at the inside. The larger keeled scutes were aligned in regular horizontal rows. There were three rows of these along each side of the torso. The scutes of the lowest lateral row were more conical, rather than the blade-like osteoderms of Scutellosaurus. Between these main series, one or two rows of smaller oval keeled scutes were present. There were in total four rows of large scutes on the tail: one at the top midline, one at the midline of the underside, and one at each tail side. Whether the midline tail scutes continued over the torso and neck to the front is unknown and unlikely for the neck, though Scelidosaurus is often pictured this way. The neck had at each side two rows of large scutes. The osteoderms of the lower neck row were very large, flat, and plate-like. The first osteoderms of the top neck rows formed a pair of unique three-pointed scutes directly behind the head. These points seem to have been connected by tendons to the rear joint processes. Some of the latest Scelidosaurus specimens show different osteoderms, including scutes on which the keel is more like a thorn or spike. These specimens also have little horns on the rear corners of the head. These differences could indicate a variant species of Scelidosaurus or could be instances of sexual dimorphism (i.e. perhaps males and females had different patterns and types of armor). 

Scelidosaurus is one of the dinosaurs for which we have skin impressions. Between the bony scutes, Scelidosaurus had rounded, non-overlapping scales like the modern Gila monster. Between the large scutes, very small, flat ‘granules’ of bone were distributed within the skin. In the later ankylosaurs, these small scutes may have developed into larger scutes, fusing into the multi-osteodermal plate armor seen in species such as Ankylosaurus. 

Sarcosaurus

a Sarcosaurus in futile pursuit of two Dimorphodon

Type Species: Sarcosaurus woodi

Classification: Dinosauria - Saurischia – Theropoda

Time Period: Early Jurassic

Location: England

Diet: Carnivore

Early Jurassic England was a scattering of low islands stitched across a shallow sea that ran along the northern edge of Laurasia. The wooded islands were home to plenty of wildlife and supported rich ecosystems. The eleven-foot-long Sarcosaurus was the mega-predator of these islands, likely swimming the narrow channels running between them. Sarcosaurus is known from scattered remains – a partial pelvis, a femur, and some vertebrae – but from these scientists extrapolate that it was a lightly-built theropod predator. Its pelvis is remarkably similar to the later – and much larger – Ceratosaurus (hence its reconstruction with a ceratosaur-like head crest), and some scientists believe it’s actually an early species of Ceratosaurus, the direct ‘ancestor’ of the twenty-two-foot-long Ceratosaurus that would dominate the Late Jurassic. 

Saltriovenator

Type Species: Saltriovenator zanellai

Classification: Dinosauria - Saurischia – Theropoda - Ceratosauria

Time Period: Early Jurassic

Location: Italy

Diet: Carnivore

The twenty-five-foot long and one-ton Saltriovenator was the megapredator of the Early Jurassic. Its remains were discovered in modern Italy (what would’ve been southern Laurasia) in what would’ve been a watery grave. The specimen had died and been washed out to sea (or in a bay) where it was scavenged by marine organisms. At least thirty bore marks on the bones come from a variety of marine invertebrates, and its remains were entombed with a single tooth and jaw fragment from a bony fish. Saltriovenator has the unlucky distinction of being the first dinosaur discovered to have been gnawed upon by marine animals. 

The find gets even more intriguing: Saltriovenator was a large, bipedal carnivore similar to the much later Jurassic predator Ceratosaurus, and it’s classified as the oldest known ceratosaur. It was much stockier and larger than other Early Jurassic theropods, and other theropods of its size wouldn’t crop up in the fossil record until another 25 million years later. Saltriovenator’s large size took place in tandem with the emergence and gradual enlargement of sauropod herbivores, suggesting a prehistoric ‘arms race’ between predator and prey. As Dr. Simone Maganuco writes, “The evolutionary ‘arms race’ between stockier predatory and giant herbivorous dinosaurs, involving progressively larger species, [began] 200 million years ago” – more than twenty million years earlier than scientists had previously believed. 

Kotasaurus

Type Species: Kotasaurus yamanpalliensis

Classification: Dinosauria - Saurischia – Sauropoda - Gravisauria - Eusauropoda

Time Period: Early Jurassic

Location: India

Diet: Herbivore

The thirty-foot-long and 2.5-ton Kotasaurus was one of the earliest known sauropods. It shared its habitat with another sauropod, Barapasaurus. The fossilized remains of twelve individuals – lacking, unfortunately, their skulls (though two teeth have been recovered!) – were discovered in India. The remains were jumbled together in what had been a Jurassic riverbed, and scientists speculate that the herd drowned in a flash flood and was washed to a bend in the river where they were deposited en masse. Only the heaviest bones remained to be fossilized, for after the floodwaters receded, their carcasses would’ve been set upon by scavengers. The absence of skulls isn’t surprising, since skulls are very loosely connected to the spine and thus easily wrenched free and taken to other locations for eating. Kotasaurus had a heavy body, a long neck and tail, columnar limbs, spoon-shaped teeth, and a horizontal posture.  

Aardonyx

Type Species: Aardonyx celestae

Classification: Dinosauria - Saurischia – Prosauropoda

Time Period: Early Jurassic

Location: Africa

Diet: Herbivore

The twenty-foot-long Aardonyx is known from the jumbled bones of two individuals, both estimated at less than ten years of age. Aardonyx is beloved among paleontologists because it shows numerous ‘transitional features’ between the prosauropods of the Late Triassic and the sauropods of the Early Jurassic in terms of anatomy and feeding habits. Dr. Matthew Bonnan, who has studied Aardonyx at length, notes, “We already knew that the earliest sauropods and near-sauropods would be bipeds. What Aardonyx shows us, however, is that walking quadrupedally and bearing weight on the inside of the foot is a trend that started very early in these dinosaurs, much earlier than previously hypothesized… On a scientific level, it’s really fulfilling to have a hypothesis on how you think dinosaurs got large, then to test that in the field and get back these kind of data – a new dinosaur – that really does start to fill in some of those anatomical gaps.” 

Aardonyx had an elongated neck leading to a small head, a massive torso, and long tail. It was primarily bipedal, though it could drop down on all fours, and the forearm bones were in the process of evolving into the pillar-like legs of the sauropods. The leg bones were beginning to interlock for more strength at the price of flexibility, but flexibility isn’t good when you’re bearing a lot of weight, as the weight could cause the joints to buckle and break. Aardonyx gives us a snapshot of the genesis of the skeletal structures that would enable later sauropods to reach behemoth weights up to eighty tons. Aardonyx lacked the fleshy cheeks of the prosauropods which enabled them to open their mouths wide to pick at choice leaves; Aardonyx would’ve had a ‘bulk-browsing’ method of eating, in which it stripped leaves off the branches wholesale, just as was the case with sauropods. 

Tachiraptor

a Tachiraptor flocks into a herd of Laquintasaurus

Type Species: Tachiraptor admirabilis

Classification: Dinosauria - Saurischia – Theropoda - Neotheropoda

Time Period: Early Jurassic

Location: Venezuela

Diet: Carnivore

The painting above depicts a scene from Early Jurassic Venezuela that was uncovered in fossilized remains during the construction of a highway. When paleontologists descended upon the unearthed bones of a small plant eating dinosaur about three feet long, they found small theropod teeth nearby. The herbivore was named Laquintasaura, and later that year, theropod bones – a tibia and ischium – were found nearby. These were attributed to a new theropod dubbed Tachiraptor. Though little is known about Laquintasaura or its predator Tachiraptor, it’s been deduced that Tachiraptor was a small theropod that reached just over five feet in length. Because of their size, it’s theorized they preyed on smaller dinosaurs – such as the unlucky Laquintasaura – and on early lizards and mammals. 

Leonerasaurus

Type Species: Leonerasaurus taquetrensis

Classification: Dinosauria - Saurischia – Prosauropoda

Time Period: Late Triassic or Early Jurassic

Location: Argentina

Diet: Herbivore

Leonerasaurus was an unusually small prosauropod from Argentina. It’s been dated to the Late Triassic or Early Jurassic (the exact dating of the rock formation is in question). It’s known from a single subadult specimen that would’ve grown to about seven and a half feet head-to-tail and reached about three feet in height. Though most of its anatomy is solidly like those of prosauropod, its teeth share a mixture of sauropod and prosauropod characteristics: while its teeth are spoon-shaped like those of more derived sauropods, the surface texture is more similar to that of most prosauropods. 

Dracoraptor

Type Species: Dracoraptor hanigani

Classification: Dinosauria - Saurischia – Theropoda - Coelophysoidea

Time Period: Early Jurassic

Location: Wales, United Kingdom

Diet: Carnivore

The ‘Dragon Thief’ lived during the Hettangian stage 201-199 million years ago in what is now Wales in the United Kingdom. It was discovered in 2014 and named in 2016. The fossils discovered indicate Dracoraptor was about seven feet long head-to-tail with a hip height at just over two feet; however, this individual is likely a juvenile, so adults may have grown as long as ten feet. During this point in the Jurassic Period, South Wales was a coastal area dotted with several small islands in a warm, shallow sea. The fossils were recovered from what would’ve been a point offshore, so Dracoraptor had been washed out to see from the northern landmass before being entombed in the seabed. Scientists speculate that this theropod prowled the shorelines, feasting on small vertebrate animals – its teeth were only about a centimeter long – and scavenging when it could. It may have made short hops between islands; on one trip, the discovered Dracoraptor may have been caught in a squall and been drowned before being washed farther out to sea. 

Xingxiulong

Type Species: Xingxiulong chengi

Classification: Dinosauria - Saurischia – Prosauropoda

Time Period: Early Jurassic

Location: China

Diet: Herbivore

The Hettangian stage Early Jurassic prosauropod Xingxiulong was discovered in 2017 when three specimens – two adults and a juvenile (known to be such because of the third’s incomplete vertebral fusion) – were uncovered in China. The adults measured thirteen to sixteen feet in length and reached between three feet and nearly five feet in height (making them relatively small when compared to their large sauropodomorph cousins). Despite their small size, they share similarities with the titanic sauropods: like sauropods, their hips, femurs, and feet were particularly robust. These suggest that it had a large gut and high body mass. However, it would’ve also been capable of assuming a bipedal stance, as sauropodan adaptations to quadrupedalism – such as relatively longer forelimbs – aren’t present. Because of the assemblage of fossils, it’s assumed these ‘small-sized’ prosauropods traveled in family groupings. 

Sinosaurus

Type Species: Sinosaurus sinensis

Classification: Dinosauria - Saurischia – Theropoda – Tetanurae

Time Period: Early Jurassic

Location: China

Diet: Carnivore

The medium-sized predatory theropod Sinosaurus lived 201-190 million years ago during the Hettangian and Sinemurian stages of Early Jurassic southern China. It bore a striking resemblance to the North American Dilophosaurus: it could grow up to eighteen feet in length, and both Sinosaurus and Dilophosaurus had dual crests atop their skulls. Sinosaurus is the only ‘dilophosaurid’ known from a complete braincase. Sinosaurus’ skull had a deep notch between the premaxilla and maxilla (bones of the upper jaw), which scientists speculate was used to house jaw muscles; if so, this meant that Sinosaurus had a terribly ferocious bite force. Some paleontologists have speculated that the premaxilla was covered in a narrow, hooked beak used to puncture and tear into the flesh of its prey. The function of the dual crest has been debated, as is the case with all dilophosaurids. Because it was relatively flimsy and would break in heated combat, it most likely played a role of sexual display or species recognition (though one scientist speculated, in the case of Sinosaurus, that it was used to ‘prop open’ the prey’s abdominal cavity while the carnivore rooted around). Sinosaurus’ feet were shaped like those of modern vultures and may have been used to help it feed on large-bodied sauropodomorphs. 

Lufengosaurus

Type Species: Lufengosaurus young

Classification: Dinosauria - Saurischia - Prosauropoda

Time Period: Early Jurassic

Location: China

Diet: Herbivore

Lufengosaurus lived in China during the Early Jurassic around 190 million years ago. It’s similar to its contemporary Yunnanosaurus: both were prosauropods that reached to about twenty-three feet in length and half a ton in weight (though some more recent estimates have put Lufengosaurus at up to thirty feet long); both had small heads with long necks and tails, tubby torsos, and both were quadrupedal; both had deep and broad snouts; both had shorter forelimbs than hind-limbs (though Lufengosaurus’ were slightly shorter relative to the hind-limbs); and both were named only one year apart by the same paleontologist. These coincidences prompted theories that Lufengosaurus and Yunnanosaurus were the same dinosaur with intraspecies variation. This would mean that Yunnanosaurus was actually a variant species of Lufengosaurus, since Lufengosaurus was named first, in 1941. Others have built upon this theory and added a twist: both Lufengosaurus and Yunnanosaurus may have been different species of the earlier Massospondylus. Thus all three would be species of Massospondylus, and paleontological textbooks would need to be rewritten. These theories have fallen out of vogue, however, due to the fact that Lufengosaurus and Yunnanosaurus differ wildly when it comes to their teeth. Whereas Yunnanosaurus teeth were narrow and spoon-shaped (like those of sauropods), Lufengosaurus retained the widely-spaced, leaf-shaped teeth common to early sauropodomorphs. 

Lufengosaurus was herbivorous, though – like all prosauropods – it had sharp claws, especially on its thumbs, and sharp, serrated teeth. This has led some to speculate that Lufengosaurus – along with its prosauropod kin – was omnivorous. However, modern herbivorous iguanas have sharp teeth and claws, and they don’t eat meat. The strongest theory is that Lufengosaurus was herbivorous, using its sharp claws for defense or for raking foliage from trees. This prosauropod has made headlines at least twice after its discovery. First, its fossilized embryos have been discovered, and they represent the earliest evidence of vertebrate soft tissue preservation. Second, in 2017 scientists discovered 195-million-year-old collagen protein (used in connective tissues) in the fossilized rib bone of a Lufengosaurus. 

Barapasaurus

Type Species: Barapasaurus tagorei

Classification: Dinosauria - Saurischia - Sauropoda - Gravisauria - Cetiosauridae

Time Period: Early Jurassic

Location: India

Diet: Herbivore

The Early Jurassic sauropod Barapasaurus is one of the few dinosaurs that have been discovered on the Indian subcontinent. It lived during the Sinemurian and Pliensbachian stages of the Early Jurassic (199-182 million years ago). Over 300 Barapasaurus fossils were discovered in the Godavari Valley of south central Indian in 1961. The remains included no skulls or feet, but it was determined that the remains belonged to at least six individuals. The fossils were found among large tree trunks scattered over an area of over 250 square meters. Paleontologists speculate this assemblage was due to a catastrophic flood, in which the herd of these early sauropods in a conifer forest were swept away – along with the trunks of their foodstuffs – and deposited a distance away. As they began to decompose, the bones began to disarticulate, and the disarticulated skull bones were removed by the residual water streams because they were light. 

Barapasaurus was an early sauropod, and it exemplified many of the derived sauropod traits. An adult reached about sixty-six feet from head-to-tail, and it had the elongated neck and tail of the sauropods. It had a short trunk and columnar limbs. Its vertebrae show signs of transitioning to the type seen in more derived sauropods: though Barapasaurus had rudimentary weight-saving scoops or hollows common in sauropods, they were less prevalent than those found in later sauropods. Only three whole teeth and three crowns have been discovered. The largest known tooth is 5.8 centimeters in height. Its teeth were spoon-shaped and show wrinkled enamel, as is the case with derived sauropods. Barapasaurus was likely slow and plodding, feeding for many hours a day. It stripped vegetation and swallowed its food without chewing, allowing gastroliths in the gut to break down the food for processing. 

Yunnanosaurus

Type Species: Yunnanosaurus youngi

Classification: Dinosauria - Saurischia - Prosauropoda

Time Period: Early to Middle Jurassic

Location: China

Diet: Herbivore

Yunnanosaurus lived in China during the Early to Middle Jurassic Period. Fossils from more than twenty different individuals have been found in the southern Chinese Yunnan Province (hence the creature’s name). Of these fossils, two include skulls, one complete with sixty teeth. Yunnanosaurus’ discovery – along with that of its contemporary Lufengosaurus – showed the worldwide distribution of sauropodomorphs by the Early Jurassic. 

Yunnanosaurus was a prosauropod that resembled earlier prosauropods such as Plateosaurus. It could grow up to twenty-three feet in length and – in the largest specimens – up to thirteen feet tall. It had a small head with a relatively short snout; a long neck and bulging body; sturdy legs with the rear pair slightly longer and stronger than the forelimbs; and a long, tapering tail. It was likely a gregarious herbivore that moved about in herds. These creatures would’ve spent most of their days plodding among the early Jurassic forests of conifers, cycads, and tree-ferns, feeding on soft leaves, shoots, and buds – and keeping a wary eye out for large theropod predators such as Sinosaurus and Shuangbaisaurus. Yunnanosaurus’ teeth were spoon-shaped and numbered more than sixty. The type of teeth makes it an oddball among prosauropods, most of which had leaf-shaped teeth. Though sauropods had spoon-shaped teeth, scientists doubt that Yunnanosaurus is a ‘missing link’ between prosauropods and sauropods, since Yunnanosaurus lacks any other ‘transitional features’: in anatomical build, except for the teeth, it’s a strict prosauropod. The spoon-shaped teeth, then, are viewed as a matter of convergent evolution, wherein Yunnanosaurus evolved spoon-shaped teeth to suit its environment and did so separately from sauropods. 

Shuangbaisaurus

Type Species: Shuangbaisaurus anlongbaoensis

Classification: Dinosauria - Saurischia - Theropoda

Time Period: Early Jurassic

Location: China

Diet: Carnivore

Shuangbaisaurus was a theropod dinosaur from Early Jurassic China who’s become famous for the pair of thin, midline crests on its skull that extended backwards over its eyes. Shuangbaisaurus is one of several Jurassic theropods known to certainly have head crests; such crests have been positively found upon such Early Jurassic theropods as Dilophosaurus (from North America), Cryolophosaurus (from Antarctica), Sinosaurus (from China), and at least one species of Early Jurassic Coelophysis (from North America).  Other theropods such as Liliensternus of the Late Triassic, Dracovenator from Early Jurassic, and Lophostropheus from the Late Triassic and Early Jurassic are assumed to have head crests because of skull similarities to the known crested theropods (such as mysterious bumps and pitting on parts of the skull). The purpose of the crests are unknown, but most believe they served as sexual displays to attract mates or intimidate rivals, or as instances of species recognition. Though some scientists believe Shaungbaisaurus is none other than its Chinese contemporary Sinosaurus, the skull crests on the two differ (Sinosaurus’ crest doesn’t extend over the eyes), so most paleontologists believe them to be different genera rather than two species of the same kind of dinosaur.

Shaungbaisaurus’ length is unknown, as its known only from skull fragments, but its head stretched just under two feet long and robustly designed. This has led researchers to argue that it was a medium-sized theropod who could take down large prey. Its environment would’ve been populated by early ornithischians, numerous crocodylomorphs, turtles and amphibians, and early mammals and their relatives. The largest creatures of its habitat were the sauropodomorphs, such as the early sauropod Chinshakiangosaurus and the prosauropods Lufengosaurus, Yimenosaurus, and Yunnanosaurus. It’s likely it hunted sauropodomorphs in its Early Jurassic environment. 

Panguraptor

Type Species: Panguraptor lufengensis

Classification: Dinosauria - Saurischia - Theropoda - Coelophysoidea - Coelophysidae

Time Period: Early Jurassic

Location: China

Diet: Carnivore

Panguraptor – whose name means ‘Chinese plunderer’ – was a coelophysoid theropod from Early Jurassic China. Its remains were found in the Lufeng Formation, which captures snapshots of an alluvial plain of sandstone and mudstone. This was the first coelophysoid dinosaur found on the Asian continent. Being small, it was nowhere near the top of the food chain: its environment was dominated by crocodylomorph predators and the much larger, eighteen-foot theropod Sinosaurus. While Sinosaurus likely preyed upon sauropodomorphs of the area, or even upon smaller ornithischians, Panguraptor likely hunted small animals like lizards and mammals. Undoubtedly it would’ve been an optimistic scavenger, ransacking the bloated corpses left behind by a satisfied Sinosaurus.

Pegomastax

Type Species: Pegomastax africana

Classification: Dinosauria - Ornithischia - Heterodontosauridae

Time Period: Early Jurassic

Location: South Africa

Diet: Opportunistic Omnivore

Pegomastax lived in Early Jurassic South Africa between 200 to 190 million years ago. This creature was much smaller than other heterodontosaurs of the environment, such as Heterodontosaurus and Lesothosaurus. While the latter dinosaurs reached between four and six feet, Pegomastax measured just under two feet head-to-tail. The parrot-like Pegomastax had a robust lower jaw with a short beak and an enlarged canine-like tooth at the beginning of the lower jaw’s tooth row. This canine-like tooth may have been a defensive weapon, or it may have been used to dig for roots and shrubs. 

Pegomastax had thin, porcupine-like spikes that sprouted over its body. These could’ve been used as a defensive function, like porcupines, or to make the creature unappealing to predators. Or, perhaps, they were used to make it look bigger – it was a little squirt, after all, who weighed less than an average housecat – in order to intimidate rivals or predators. Another theory is that they were used for sexual display to attract mates. World-renowned paleontologist Paul Sereno described Pegomastax as a ‘nimble two-legged porcupine,’ adding, ‘I think the bristles would’ve made it look at least a little bigger than it was – perhaps they could poke out more strongly when excited… [Its] main defense would be the speed of escape. These were very fast long-legged critters. They could inflict a nipping bite if cornered, using the fangs much like a peccary or fanged deer.’

Lesothosaurus

Type Species: Lesothosaurus diagnosticus

Classification: Dinosauria - Ornithischia - Heterodontosauridae

Time Period: Early Jurassic

Location: South Africa

Diet: Opportunistic Omnivore

Lesothosaurus was an herbivorous or omnivorous heterodontosaur from South Africa. It lived in a semi-arid environment about 200-190 million years ago during the Early Jurassic. It could grow up to six feet in length. It had long, slender legs, small arms with four-fingered hands that weren’t great at grasping, and a slender tail. It was probably a fast runner. Its neck was short but flexible; its skull was short and flat; and it had large eye sockets. It had a short, pointed snout that ended in a horny beak. Behind the beak were leaf-shaped teeth lining the jaws, and near the front of the upper jaws it had twelve fang-like teeth. Lesothosaurus sliced up its food with the beak, but it wouldn’t have been able to chew very well. Studies of tooth wear show less abrasion on the teeth than are expected with an herbivore, indicating that Lesothosaurus was an opportunistic omnivore that fed on plants during the wet seasons and small animals during the dry seasons. It had a distinctive femoral head not seen in other dinosaurs, and it was likely gregarious, living in social groups. 

Abrictosaurus

Type Species: Abrictosaurus consors

Classification: Dinosauria - Ornithischia - Heterodontosauridae

Time Period: Early Jurassic

Location: South Africa

Diet: Herbivore or Omnivore

Abrictosaurus was a heterodontosaur that lived in South Africa during the Hettangian and Sinemurian stages of the Early Jurassic 200-190 million years ago. It’s known from the fossil remains of two individuals. Its habitat consisted of sand dunes and seasonal floodplains in a semiarid environment with sporadic rainfall. It likely practiced niche partitioning in its herbivorous eating habits, sharing the ecosystem with other heterodontosaurs like Heterodontosaurus and Lycorhinus. Other organisms in the environment included land-dwelling crocodylomorphs, early mammals, the theropod Coelophysis, and the prosauropod Massospondylus. 

Abrictosaurus had large, canine-like tusks – called ‘caniniforms’ – in both its upper and lower jaws. It had no teeth in the front of its jaws; in its place was a hard beak likely used to crop vegetation. A handful of primitive heterodontosaur features indicate that it is the most basal member of Heterodontosauridae. For example, Abrictosaurus had widely separated cheek teeth with low crowns more similar to other ornithischians, whereas Heterodontosaurus and other heterodontosaurs had high-crowned cheek teeth that overlapped each other in the jaw to form a continuous chewing surface similar to the later Cretaceous hadrosaurs. Another example is in Abrictosaurus’ tusks, which were more primitive than those of more derived heterodontosaurs. It’s widely believed that Abrictosaurus was a gregarious creature; this is indicated by the fact that one of the two specimens recovered has much smaller tusks. This may be an example of sexual dimorphism; in many modern mammals, tusks of different sizes are used to differentiate gender with musk deer, walrus, Asian elephants, and many pigs. Thus it’s likely that the fossilized remains belong to both a male and a female Abrictosaurus.