The Bajocian stage followed the Aalenian and was followed in turn by the Bathonian. Its name comes from the Latin name (Bajocae) of the town of Bayeux, in the region of Normandy, France. Its base is the first appearance of the ammonite genus
. The Bajocian witnessed the emergence of new plesiosaurs and ichthyosaurs, including the first ‘proper-looking’ pliosaur with a short neck, large head, and paddle-like limbs. Several new oceangoing crocodylomorphs emerged, as well. In the realm of the terrestrial, it is during the Bajocian that we see the first ‘proper-looking’ stegosaur,
.
was a pliosaur that would survive into the Tithonian of the Late Jurassic. It reached fifteen feet in length, though some may have grown up to twenty feet long.
had salt-secreting glands, which would’ve enabled it to maintain its salt balance and drink seawater.
likely preyed upon squids and ammonites in the shallow northern Laurasian seas. Later on in the Middle Jurassic, other pliosaurs who fed upon the same diet appeared, such as
; scientists speculate that these pliosaurs practiced a sort of ‘niche partitioning’ by feeding at different times. Perhaps
hunted in deeper waters or at night, as modern squid exhibit diurnal feeding cycles.
may have spent the daylight hours in deeper, safer water, only rising at night to feed. In the realm of ichthyosaurs, the Scottish
continued swimming in northern Laurasian. Off the shores of western Gondwana (modern South America), two new ichthyosaurs came to light:
continued hunting in the shallow seas of prehistoric Europe, it was joined by two other crocodylomorphs:
. The latter was one of the first metriorhynchids – oceangoing crocodilians with paddle-like flippers, tail flukes, and lacking in the body armor inherited from their ancestors. Moving west to the newly-christened Sundance Sea, we find the crocodylomorph
. This crocodylomorph was a transitional form between the fully-marine metriorhynchids and earlier non-marine crocodylomorphs.
had a streamlined skull with eyes that faced to the side – like those of the metriorhynchids – rather than the upward-facing eyes of the non-marine aquatic crocodylomorphs. The shift in eye position is attributed to changes in feeding habits: whereas upward-facing eyes were designed for semi-aquatic crocodilians ambushing terrestrial prey from beneath the surface of the water (like modern crocodiles), side-facing eyes were designed for fully marine crocodilians hunting in the open waters. However,
forelimbs weren’t flattened into paddles, but the lower arm bone was reduced in length, indicating that the forelimb reduction of the metriorhynchids began at the lower limb (the ulna) and progressed upward. Thus it’s theorized that the metriorhynchids’ adaptation of a marine lifestyle began with a shift in feeding habits and only later resulted in evolutionary changes in swimming locomotion. The image above and to the right is a painting of
, except it includes a Native American canoe and Native American victims. “What’s the deal with that?!”
is named after a mythological creature who came into Native American folklore because of the bones of this prehistoric crocodylomorph. When Native Americans came across these bones, they recognized that it was a titanic oceangoing lizard; ancient accounts of the Kiowa Tribe tell of a large fearsome creature that dwelled in the deep mountain lakes and waterways of what is now the Canadian Rockies of British Columbia, Canada. They called this creature ‘
’, which describes a terrible being with large teeth. It was said to attack and eat unwary travelers of the mountain waterways. Unbeknownst to the Kiowa, this creature lived in the Middle Jurassic of the Bajocian.
As was the case in the Aelenian, dinosaur discoveries in the Bajocian are far and few between. Of particular interest, however, are two stegosaurs:
. The first was discovered in Argentina, and it's remarkable due to the fact that its stomach contents - a collection of seeds, largely from cycads - were preserved. This was an early stegosaur that had yet to become quadrupedal; like earlier thyreophorans of the Early Jurassic, such as
, it didn't have the 'look and feel' of the stegosaurs we know and love.
, however, is a different story: this is the earliest stegosaur that resembles the later Jurassic stegosaurs such as
. Though it was smaller than later stegosaurs - it was only about sixteen and a half feet long - it had tall, narrow plates running from its neck down its back. Around its hip region, these plates were replaced by spikes.
had meter-long spikes that jutted out of its shoulders; these were likely used for defense against predators. A discovery of multiple
of varying ages in France implies that they weren't solitary creatures; rather, they moved around in family groups.
The Bathonian stage followed the Bajocian stage and was followed in turn by the Callovian stage. The base of the Bathonian is the first appearance of the ammonite species
Parkinsonia convergens; the top of the Bathonian is the first appearance of the ammonite genus
Kepplerites. The Bathonian gets its name from the town of Bath, a spa town in England. It was during the Bathonian that we begin to see many of the 'trademarks' of the later Jurassic: large, long-necked sauropods; medium-sized, pack-hunting theropods; the genesis of the ornithopods; more radiation of the stegosaurs; and the the first ankylosaur,
Tianchisaurus of China.
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| the marine crocodylomorph Neptunidraco |
Marine reptiles are scant for the Bathonian stage: the pliosaur
Simolestes continued plowing the sea-lanes, and a new plesiosaur named
Yuzhoupliosaurus hunted in the freshwater basins and lagoons of prehistoric China. The thalattosuchians – ocean-going crocodylomorphs – overshot the marine reptiles in diversification. While
Teleosaurus continued from the Bajocian, several new marine crocodylomorphs appeared:
Eoneustes,
Gavialinum,
Gracilineustes,
Neptunidraco, and
Teleidosaurus all lived on the open ocean, hunting fish and squid and coming onto land only to lay eggs.
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| a Klobiodon takes a breather in prehistoric Europe |
Pterosaurs began to diversify in the Bathonian. In Europe, the pterosaur
Klobiodon darted hither and thither among the wooded islands scattered about the shallow sea that would become the North Sea. It had a six and a half foot wingspan, and the front of its jaws had fang-like teeth while the teeth towards the back of its jaws were short and robust. Further south in Laurasia, the pterosaur
Angustinaripterus of China had long, robust, curved front teeth that pointed forward to create an intermeshing ‘prey grab’ that was likely used to snatch fish from the water. Its back teeth were smaller, designed to hold prey that had been caught. Its 6.5-inch-long skull was flat and elongated with a low crest. It’s been estimated to have a wingspan of about 5.25 feet. Another Chinese pterosaur of Bathonian is
Jeholopterus, which first appears in the Middle Jurassic around 164 million years ago and lasted until the Oxfordian Stage of the Late Jurassic (and perhaps even continued into the Early Cretaceous). This pterosaur had a three-foot wingspan and is known from a complete articulated skeleton found in what had been fine lake deposits; the fossilization process revealed hairy coverings and wing membranes. While pterosaurs had a variety of feeding styles – some were fish-catchers, others insectivores, others were filter-feeders or lizard-lovers or crustacean-hunters –
Jeholopterus may have had the most unique diet of all. Its broad skull was flattened at the front, giving it a cat-like appearances; its jaws were designed to open wider than those of any other pterosaur; all its teeth were reduced except for a pair in the upper jaws at the front, and these were strong and protruding and deeply rooted in the palate; the claws were large and sharper than those of other pterosaurs whilst its tail was short for a rhamphorhynchid. These specialized designs have led scientists to theorize that
Jeholopterus was the ‘vampire bat’ of Jurassic China. Perhaps it used its big claws to anchor to the sides of big dinosaurs while wide-opening its mouth and driving its fang-like front teeth into thick skin to reach blood vessels!
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| Jeholopterus is cute until it sinks its fangs into your neck |
As we turn our attention to the dinosaurs of the Bathonian, we will do so in an east-to-west 'Silk Road' fashion. Our first stop will be in southern Laurasia, modern China, where we meet a host of new dinosaurs that lived in the same environment as
Angustinaripterus and
Jeholopterus (and we will do our best not to picture the latter pterosaur sucking dinosaur blood at any given moment). Let us begin our journey!
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| a pair of Monolophosaurus stalk a southern Laurasian beach |
Our First Stop: China. Our first stop in our east-to-west tour of Bathonian ‘hot-spots’ begins in what was then southern Laurasia. Sauropods from the river-cut and heavily-wooded environment include the fifty-foot-long
Klamelisaurus and the sixty-six-foot-long
Omeisaurus.
Omeisaurus was one of the first long-necked mamenchisaurids; it had an extremely long neck, stocky limbs, and a short body. The long neck may have been used to reach food high in the trees, or it may have been held horizontally over the ground to feed on large swathes of low-growing foliage. In this second manner of feeding,
Omeisaurus would take a few steps forward and then swoop its neck over the vegetation, slowly creating a crescent-shaped swathe of devastated vegetation. The small, bipedal herbivores
Agilisaurus and
Yandusaurus skittered underfoot these sauropod giants. These dinosaurs belonged to the neornithischians, a sister clade of the thyreophorans; radiation and evolution within neornithischia would lead to the ‘head-armored’ marginocephalians (which would later include ceratopsians and pachycephalosaurs) and the ornithopods. Theropods of Bathonian China included the thirteen-foot-long
Gasosaurus and the eighteen-foot-long
Monolophosaurus. This latter theropod is named after the single crest that ran along its skull. It resembled the later North American
Allosaurus and, like
Allosaurus, may have been a pack hunter that worked in hunting groups to take down plodding sauropods.
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| a pair of Huayangosaurus mingle with a herd of Omeisaurus |
Two other dinosaurs of Bathonian China are of note. The first is
Tianchisaurus, which is based on fragmentary remains and is a subject of debate. Some believe it's the earliest true ankylosaur, but still others - even though such a find so early in the Jurassic would be remarkable - are holding their breath for more fossils to come to light. The second is
Huayangosaurus, one of the earliest primitive stegosaurs (though
Lexivosaurus of the Bajocian beats it to the punch for 'Earliest Known Stegosaur').
Huayangosaurus had the distinctive double row of plates that characterize all stegosaurs; these plates began at its neck and ran along its back until it reached the hips, at which point the plates were replaced with four spikes. After this series of spikes, the plates resumed until they ended with two pairs of long spikes extending horizontally near the end of the tail. These spikes were undoubtedly defensive weapons against such predators as
Gasosaurus and
Monolophosaurus.
Huayangosaurus, like the earlier
Lexovisaurus, had two spikes that protruded either from the hips or the shoulders. The exact placement is unknown, with artistic depictions representing either location depending on artistic fancy. The current general consensus is that, as in
Lexivosaurus, they were placed on the shoulders; in this case, they would serve as defensive weapons: if an assailant attacked from the front or from the forward side quadrants,
Huayangosaurus could ‘thrust’ its spikes deep into the adversary’s hide. In a world without medicine, such penetrating attacks into an enemy’s organs could often be lethal. Only the most foolish of predators would attempt to make a meal out of the armed stegosaur. When drinking from lakes or rivers, even this armored stegosaur would need to keep a wary eye out for the ten-foot-long crocodylomorph
Hsisosuchus, which prowled the environment's waterways.
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| Hsisosuchus makes a nice perch for a Chinese pterosaur |
 |
a Cetiosaurus being chased island-to-island by a pack of
Megalosaurus |
Our Second Stop: Europe. As we move northwards into northern Laurasia, we come to prehistoric Europe. Much of England was underwater; spots of higher elevation created low-lying islands that peppered the shallow prehistoric sea that would one day become the north Atlantic. Movement between the islands was possible, either by swimming or via land-bridges or by crossing in supremely shallow areas. Several dinosaurs called this collection of islands home: the stegosaur
Lexovisaurus (which made its debut earlier in the Jurassic), the sauropod
Cetiosaurus, and the fierce theropod
Megalosaurus. This theropod was one of the first dinosaurs to be named in 1841. It was a large, muscular, brute of a theropod, quite distinct from the slender, more agile theropods that had come before.
Megalosaurus reached about twenty feet in length and likely hunted larger prey, perhaps in packs like North America's Late Jurassic
Allosaurus.
If we shift northeast, we come to what is now France. These French beaches, mangrove swamps, and wooded floodplains were rich in vegetation and water and no doubt frequented by sauropods and stegosaurs. Two theropods have been discovered from this region:
Poekilopleuron and
Dubreuillosaurus.
Poekilopleuron was a 'brute and brawn' theropod, chiseled in muscle and extremely powerful, and it likely hunted large prey;
Dubreuillosaurus, on the other hand, was like a fish-eater. It may have caught fish in tidal pools or combed French beaches looking for tidally-stranded fish or dead marine reptiles washed ashore. It may have used its oddly long head to stand still in bays, lagoons, or inlets, waiting for fish to come near before darting its jaws under the water.
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| a Dubreuillosaurus combs a French beachhead |
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| a pair of Atlasaurus on the Bathonian shores of North Africa |
Our Third Stop: Saharan Africa. During the Early Jurassic, our knowledge of African dinosaurs was mostly confined to the southern portion of the continent – at least until the rich, lush environments of Early Jurassic South Africa were inundated with lava flows during the Toarcian Turnover. As we shift into the Middle Jurassic, our knowledge of African dinosaurs shifts to northern Africa in what is now Saharan Niger. In the Middle Jurassic, this area was separated from North America by a sliver of shallow sea. This shallow sea was the ‘rift basin’ created as the African and North American plates were pulling apart, and it would eventually widen into the Middle Atlantic Ocean. During the Middle Jurassic, Saharan Africa wasn’t windswept desert but a lush mosaic of woodlands, rivers, and lakes. Bone-beds give us a snapshot of what was life during this time. Several sauropods plodded across the river-cut valleys.
Atlasaurus (fifty feet long) and
Spinophorosaurus (just under forty feet long) moved in herds across the lush Sahara; these sauropods had tall shoulders and elongated necks, giving them a ‘vertical’ posture.
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| two Afrovenator threaten a young Jobaria |
The largest sauropod of the area was
Jobaria, which reached up to seventy feet in length and who was hunted by the apex predator of the day,
Afrovenator: the rib bones of a juvenile have been discovered with bite-marks from this thirty-foot-long predator.
Afrovenator resembled the later North American
Allosaurus, but it was more lightweight and fleet-footed than its North American cousin. Its slender arm bones were longer and capped with vicious, curved claws designed for catching and holding prey. Its strong hind limbs indicate it was built for active hunting, and its jaws were filled with long, blade-shaped teeth perfect for slicing into tough sauropod hides. A smaller theropod,
Spinostropheus, measured about half
Afrovenator’s length and likely preyed upon early ornithischians that flocked hither-and-thither in the river valleys. These dinosaurs would form the ‘staple’ of the North African ecosystem during the Middle Jurassic. It won’t be until the Kimmeridgian stage of the Late Jurassic that the creatures showcased here are overwhelmed by a new panoply of North African dinosaurs.
~ The Callovian Stage ~
166.1 to 163.5 mya
Middle Jurassic
The Callovian stage is the last stage of the Middle Jurassic. It follows the Bathonian stage and is preceded by the Oxfordian stage, the first stage of the Late Jurassic. Its name comes from the Latinized name for Kellaways Bridge, a small hamlet northeast of Chippenham, Wiltshire, England. The base of the Callovian is the first appearance of the ammonite genus Kepplerites; the top of the Callovian is the first appearance of the ammonite species Brightia thuouxensis. During the Callovian, marine reptiles – the plesiosaurs and ichthyosaurs – diversified along with the oceangoing crocodylomorphs known as thalattosuchians. On land, new dinosaurs evolved in Asia, Europe, and South America. Theropods and sauropods both grew larger in an epic ‘arms race’ of gigantic proportions; stegosaurs grew larger and more advanced; one of the first ‘avian theropods’ appeared in China; and one of the first ankylosaurs, Sarcolestes, evolved in Europe. The landscape crept closer to what most people envision when they think of the Jurassic Period.
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| the 'Cruel Sea' of the Oxford Clay Formation, England |
Plesiosaurs continued diversifying in the Callovian, both the long-necked ‘plesiosaurid’ and short-necked ‘pliosaurid’ types.
Borealonectes was one of the few pliosaurs known from North America; the Chinese
Yuzhoupliosaurus continued hunting in the oceans of modern China;
Colymbosaurus prowled the northern Laurasian waterways; and the plesiosaur
Cryptoclidus enjoyed worldwide distribution in the seas bordering both Laurasia and Gondwana. Much of our knowledge of Callovian marine reptiles comes from the Oxford Clay Formation in England. In Jurassic times, this was an ancient sea that was less than 160 feet deep and relatively warm, around seventy degrees. It was peppered with numerous islands that were host to terrestrial sauropods, stegosaurs, and theropods. Because of its warmth and shallowness, the Oxford Sea was rich with nutrients as light filtered easily through the shallow water. The sea floor was home to bivalves, arthropods, gastropods, and foraminifera. The pelagic zone – the area above the sea floor – was filled with fish, marine crocodylomorphs, and marine reptiles. The Oxford Clay was so abundant with life forms that over a hundred genera have been recovered from the sediment. It’s from this shallow sea that we’ve discovered the pliosaur
Marmornectes, the plesiosaur
Tricleidus, the pliosaur
Simolestes (whom we met earlier), and the ten-foot-long pliosaur
Peloneustes. Another short pliosaur,
Pachycostasaurus, was ten feet long with a barrel-shaped torso, a relatively short neck, and small flippers; it likely wasn’t an agile swimmer.
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| the long-necked plesiosaur Muraenosaurus of the Oxford Sea |
Muraenosaurus is one of the most well-known plesiosaurs of the Oxford Sea. Its extremely long neck and small head gave it an eel-like appearance.
Muraenosaurus grew between sixteen and twenty feet in length. This plesiosaur, like its long-necked kin, likely ate fish and cephalopods. When fishing,
Muraenosaurus may have swam with the neck straight out; hunting in this manner would prevent an arched neck from causing drag. By swimming with its head directly in front of its body,
Muraenosaurus may have been able to reach fish before they felt the change in water pressure caused by the plesiosaur’s large body (the head would precede the change in water pressure).
Muraenosaurus may have fed upon benthic fish (those who lived along the sea floor) by floating above them and reaching down with their long necks. Another theory is that long-necked plesiosaurs employed ‘benthic grazing’ in which they harvested relatively immobile species such as cephalopods from the sea floor. Because some plesiosaurs have been found with gastroliths in their stomach, this may imply they swallowed shelled cephalopods and ground them up in their stomachs.
Muraenosaurus may have been the terror of fish and cephalopods, but it wasn’t at the top of the food chain. It had predators of its own, such as the short-necked pliosaurs like
Simolestes and
Liopleurodon. Long-necked plesiosaurs may have also been hunted by prehistoric sharks; after all, shark teeth aren’t uncommon with plesiosaur fossils (but whether the sharks attacked living plesiosaurs or scavenged dead ones on the sea floor is unknown). One of
Muraenosaurus’ enemies would’ve been the twenty-three-foot-long pliosaur
Liopleurodon. This was the apex predator of the shallow seas that coated Europe. Though BBC’s Walking with Dinosaurs TV series portrayed this pliosaur as reaching lengths up to 82 feet, this was exaggerated from fragmentary remains; scientists concur that the largest species of
Liopleurodon wouldn’t have reached more than twenty-three feet in length. Nevertheless,
Liopleurodon would’ve been the Terror of the Seas, attacking other marine reptiles and prehistoric sharks.
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| a Liopleurodon makes a meal out of an ichthyosaur in the prehistoric European sea |
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| a pair of Nannopterygius alongisde nautiloids |
Liopleurodon would’ve fed on ichthyosaurs (as the painting above captures), and there are two ichthyosaurs of note from the Callovian.
Nannopterygius patrolled the shallow seas of Europe, likely hanging around coral reefs than in the open ocean. It was a small ichthyosaur, only eight feet long. It had a small skull with a long, narrow rostrum. Its large eyes had bony sclerotic rings inside the eye socket. It was flexible, agile, and likely a fast swimmer. Its body was streamlined and torpedo-like, giving it fast speed, but it would’ve struggled to turn quickly. It would’ve been an inefficient long-distance swimmer but lightning-fast over short distance; thus it’s theorized that
Nannopterygius was an ambush predator that plunged into shoals of fish. The twenty-feet-long
Opthalmosaurus had large eyes – hence its name – and may have been a deep diver, pursuing squid up to a mile deep in the open Jurassic oceans. The only living animals with similarly large eyes are the giant and colossal squids. Despite having such robust eyes,
Opthalmosaurus probably had poor hearing, given the nature of their middle ear bones. They may have made up for this bad hearing with an acute sense of smell, or they may have possessed electro-sensory organs like those seen in modern sharks, rays, and dolphins; these adaptations could explain the grooves in ichthyosaur palates.
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| the deep-diving ichthyosaur Opthalmosaurus |
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| the 'blood-biting tyrant swimmer' Tyrannoneustes |
Many of the sea-going crocodylomorphs of the Bathonian continued into the Callovian;
Gracilineustes,
Neptunidraco, and
Teleosaurus continued hunting in the oceans. New thalattosuchians emerged, and many of them were the fully-marine, paddle-limbed metriorhynchids, such as
Ieldraan and
Metriorhynchus. This latter marine crocodylomorph was ten feet long, similar in size to modern crocodiles. It had a streamlined body and a finned tail. It had nasal salt glands for removing excess salt so that it could ‘drink’ saltwater and eat salty prey without dehydrating.
Metriorhynchus likely preyed upon the armored ammonites and fast-moving fish; it may even have been capable of capturing diving pterosaurs. It likely didn’t pass up the opportunity to scavenge dead creatures on the sea floor. Teleosaurids of the Callovian include
Lemmysuchus and
Mycterosuchus. The metriorhynchid
Tyrannoneustes ‘terrorized’ the Oxford Clay seas. Its name means ‘blood-biting tyrant swimmer’, and its lower jaw measured over two feet long and were filled with blade-like teeth designed for thrashing large prey.
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| the southern Laurasian pterosaur Pterorhynchus |
In the Callovian skies, the pterosaurs
Jeholopterus continued hunting in southern Laurasia and
Klobiodon skittered above the Oxford Sea in Europe. A new pterosaur,
Pterorhynchus, came onto the scene in China. This was a small pterosaur with a wingspan of only thirty-three inches. The nearly complete, articulated skeleton preserves the creature's long tail with the vane at the end, as well as the hair-like pycnofibers that covered the body. Tiny tufts of fibers also covered portions of the wing membrane; these tufts were similar to avian down feathers.
Pterorhynchus had a tall head-crest that consisted of a low bony base and a large keratin extension. This pterosaur lived in southern Laurasia, and if we were to step back in time to take a tour of the super-continents, we would no doubt see it - and the possibly vampirous
Jeholopterus - in the trees at our first stop in modern China.
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| two Huayangosaurus keep a wary eye on a Yangchuanosaurus |
Our First Stop: China. Our sightseeing tour of the Callovian landmasses begins in southern Laurasia in what is now China. This area was heavily wooded and cut by several rivers emptying into the ocean. Sauropods in this environment included holdovers from earlier stages: the fifty-foot-long
Klamelisaurus and the sixty-foot-long
Omeisaurus. A sauropod newcomer was the fifty-foot-long
Datousaurus, a mamenchisaurid that had the boxy head of a camarasaur and a tail designed like that of
Diplodocus. Its whip-like tail would’ve been able to make barrier-breaking snapping sounds that could’ve been used to intimidate rivals, ward off predators, and attract mates. Because the tail bones were fragile – and subject to fractures – it’s unlikely that the whip-like tail was used as a weapon. Herbivorous contemporaries of the sauropods included the stegosaur
Huayangosaurus and the early neornithischian
Agilisaurus. Predators in the environment included carnivorous theropods like the thirteen-foot-long
Gasosaurus, the eighteen-foot-long
Monolophosaurus, and the thirty-six-foot long
Yangchuanosaurus. The latter is a newcomer to the stage and would last well into the Late Jurassic. It resembled
Allosaurus and may have hunted in packs like its later North American counterpart.
Yangchuanosaurus was indeed the apex predator of its day.
Underfoot these dinosaurs was the crocodylomorphs
Hsisosuchus and
Junggarsuchus. The latter crocodylomorph has been touted as a ‘transitional species’ between the greyhound-like terrestrial sphenosuchians and the more ‘crocodile-like’ mesoeucrocodylomorphs.
Junggarsuchus was a terrestrial hunter who went to the water not to ambush prey or fish but to drink. It would’ve prowled the woodlands and river valleys looking for smaller ornithischians, early mammals, and it may have made a tasty treat out of the late temnospondyl
Gobiops. Though temnospondyls were in rapid decline, with their amphibian cousins taking center-stage (Middle Jurassic China was host to many primitive salamanders, such as
Chunerpeton and
Pangerpeton),
Gobiops was a holdout who may have made its home in the many waterways or pools throughout Middle Jurassic China.
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| the late great temnospondyl Gobiops |
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| the feathered Serikornis |
Before we move into northern Laurasia, we must acknowledge yet another critter of the Middle Jurassic: the strange, chicken-like
Serikornis. This tiny theropod was only two feet long beak-to-tail and stood only half a foot tall at the hips.
Serikornis had wispy bundles of feathers along its neck, short and symmetrical vaned feathers on its arms, and both fuzz and long pennaceous feathers (also called ‘contour feathers’) on its hind legs. Its tail was covered by filaments and fine tail feathers. Scientists have long puzzled its placement in the dinosaur ‘family tree,’ with its current placement hovering somewhere near the origin of birds as we know them. Does this mean
Serikornis was a flyer? Some believe it was capable of gliding branch-to-branch far above the forest floor; in their mind, it was an arboreal creature that spent most of its time climbing trees, snapping up Jurassic insects, and gliding perch-to-perch. Others believe it was incapable of any sort of flight, gliding or powered, and that the feathers served a different function: perhaps they were brightly-colored and used to attract mates, intimidate rivals, or warn off predators? Whatever the reason,
Serikornis is the first in a long line of ‘avian’ theropod dinosaurs that will emerge during the Jurassic Period as time plods on!
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| a pair of Proceratosaurus, the earliest 'tyrannosaurs' |
Our Second Stop: Europe. As we move northwards across Laurasia and reach modern Europe, it looks nothing like it does today. France and Germany are cut by inlets and bays of brackish water that support lush mangrove ecosystems; farther inland, dense woodlands are cut by rivers and lakes. The French and German shoreline is farther east than it is today, and much of modern western France and Germany lies under the warm, shallow North Sea; archipelagos dot this shallow sea, and farther west, modern England is a series of wooded islands cut by the burgeoning North Atlantic, parts of which are known as the Oxford Sea. In Germany we know a thirty-foot-long apex predator stalked the woodlands and river valleys;
Wiehenvenator was the largest of the megalosaurs, but the Middle Jurassic ‘reign’ of the megalosaurs was coming to an end as the coelurosaurs and allosaurs were beginning to emerge. One of these lineages got its kick-off in the wooded islands of England:
Proceratosaurus was only ten feet long with a snout crest used for display, but it was a coelurosaur and one of the earliest tyrannosauroids (the kind of theropod that would grow to titanic sizes and dominate the northern hemisphere during the Cretaceous). Compared to the later tyrannosauroids,
Proceratosaurus was a pipsqueak rustling in the underbrush. Its contemporaries among the wooded isles of England included the early ornithopod
Callovosaurus, the sauropod
Cetiosauriscus, the primitive stegosaur
Lexovisaurus, one of the earliest ankylosaurs
Sarcolestes, and the pterosaur
Klobiodon.
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| Wiehenvenator, the 'tyrant megalosaur' and one of the last of its kind |
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| the sauropod Patagosaurus keeps an eye on a Eoabelisaurus |
Our Third Stop: South America. Our last stop on our journey through the Callovian takes us to western Gondwana in what is now Argentina. The Canadon Asfalto Formation in Argentina gives us an exquisite snapshot of the environment during this last stage of the Middle Jurassic. One researcher noted, in regards to the Canadon Asfalto Formation, that 'the fossil record of this formation represents the most completely known biota from the continental Middle to Late Jurassic of the Southern Hemisphere and one of the most complete of the entire world.’ The assemblage of fossils allows us to get a pretty accurate picture of what the environment was like back then. During the late Middle Jurassic and early Late Jurassic, the plants of this area were largely conifers, though ferns are also abundant. Directly beneath the formation is a layer of ash, indicating a nearby volcano (not surprising, given the intense amount of volcanic activity in the Jurassic due to the splitting of the super-continents).
 |
a pair of Manidens examine a primitive mammal hanging out
on the tail spike of an unidentified South American stegosaur |
Terrestrial organisms in this lush, tropical environment include the primitive frog
Notobatrachus, the turtle
Condorchelys, the lizard-like rhynchocephalian
Sphenocondor, and a numerous small, early mammals such as
Argentoconodon,
Asfaltomylos, and
Henosferus. The largest creatures were, of course, the dinosaurs. These include the sauropods
Patagosaurus and
Volkheimeria; the herbivorous heterodont
Manidens is also represented, and scientists theorize that it was an arboreal (tree-dwelling) dinosaur due to its feet, which were structured like those of tree-perching birds. Theropods of the environment included
Condorraptor, the abelisaur
Eoabelisaurus, and the early allosaur
Asfaltovenator. The apex predator of the day was
Piatnitzkysaurus, which grew as large as the Late Jurassic
Allosaurus and was the prime menace to South American herbivores. The small pterosaur
Allkaruen flitted about the trees above the heads of these terrestrial dinosaurs.
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