Massospondylus

Type Species: Massospondylus carinatus
Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda
Time Period: Early Jurassic
Location: Africa & North America
Diet: Herbivore

This Lower Jurassic dinosaur has been found in Africa and North America. Stretching to between 15-20 feet, Massospondylus was smaller than many of the larger prosauropods that preceded it by millions of years. This dinosaur had a body kept long and low, and it stood no higher than five feet tall at the hips. Its body may have been smaller than its predecessors, but its neck was longer, made so by its neck vertebrae being four times long as they were wide (the presence of these elongated vertebrae gives the meaning of Massospondylus’ name: “the Longer Vertebrae”). The extra-long neck and long tail served as bookends for its bulky, low-slung body. Rounded, peg-like teeth designed for stripping leaves off trees lined the jaws of its small head. Massospondylus’ forelegs were half the length of the hind limbs, but they were by no means scrawny: the broad upper end of the humerus implies that these fore-arms had strong muscle attachments and could deliver a fatal punch. Such a “killer punch” would’ve been made that much more lethal by the gruesome thumb claw on each large hand. Though it was long thought that Massospondylus was confined to a quadrupedal stance, recent studies have shown that it could walk on two legs if it so desired.

The presence of a few large holes for blood vessels on the surface of the jaw bones implies that it had, like many prosauropods, cheeks (reptiles without cheeks have numerous small blood vessel holes in the jaws rather than a few large ones); these cheeks helped keep food from falling out of the mouth. Some scientists have speculated that Massospondylus may have had a beak, like the ornithischians, but the evidence for this is dubious at best. On the subject of its dietary apparatuses, it seems Massospondylus employed a gastric mill: a specimen from Zimbabwe was found with gastroliths in its gut area, and these particular stones had their origin nearly twelve miles from the gravesite. This specimen had probably ritualistically swallowed gizzard stones only hours or days before its death. 

Like Plateosaurus, Massospondylus possessed small air cavities in some of its bones. Most saurischian dinosaurs had these hollowed-out cavities (called pneumatic foramina) that served as a rudimentary “flow-through ventilation system” similar to that of present-day birds. The neck vertebrae and ribs are hollowed out by the cervical air sack; the upper back vertebrae, by the presence of the lungs; and the lower back and hip vertebrae by the abdominal air sack. Prosauropods are the only major group of saurischian dinosaurs that lack an extensive system of pneumatic foramina, despite some species—such as Massospondylus—possessing the miniscule “building-blocks” that could, one day, blossom into full-blown pneumatic foramina. The presence of air sacs in Massospondylus doesn’t mean that it had a full-blown pneumatic system like that of birds (or even like that of wider saurischian); it does mean that, at the least, we have glimpses of the plodding evolution of such structures. 

The remains of nearly eighty individuals have been unearthed, indicating that Massospondylus may have engaged in gregarious behavior, traveling in herds throughout both Laurasia and Gondwana. Such gregariousness is attested to by marked differences between the skulls of these prosauropods: such minor variations are often symptomatic of sexual dimorphism. Sexual dimorphism—changes in anatomy between males and females—is most prominent in gregarious animals. Furthermore, gregarious animals have a tendency to care for their young, and this is precisely what we see with Massospondylus. In 1976, a clutch of seven 190 million year old Massospondylus eggs were found in South Africa. They were attributed to Massospondylus from the get-go, but detailed examination of the eggs didn’t start until the turn of the century. Scientists were able to examine the actual embryos, making these embryonic dinosaurs the oldest known. More digging uncovered another ten more egg clutches, and each clutch contained up to 34 eggs. Because these egg clutches were found in at least four different time zones in the rock formation, we can deduce that we’ve stumbled across a nesting colony that was revisited on a cyclical basis. Nesting colonies are common among gregarious animals, and detailed studies of the hatchlings (and the track-ways they left behind) tell us that infant Massospondylus were unable to function well on their own. Not only were they ungainly (not optimal for running from predators), but they lacked teeth! It seems parental care may have been a necessity for the Massospondylus line to continue; without such parental care, the babies would starve to death and the species would go extinct.

Camelotia

Type Species: Camelotia borealis

Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda

Time Period: Late Triassic to Early Jurassic

Location: England

Diet: Herbivore

During the Upper Triassic, England was part of Laurasia, the northern continent produced by a splitting Pangaea, and this northern realm was cut by swathes of conifer forests. Camelotia—named after the infamous court and castle of the fabled King Arthur—roamed this pre-Arthurian world. Camelotia stretched thirty feet and reached up to three tons. This dinosaur has a rough history: it was originally named Avalonianus in the 1890s, but Avalonianus consisted of the teeth of an ornithopod and the body of a primitive sauropodomorph. In 1985 all the bones but the teeth were given their own name: Camelotia. The scant remains are limited to a few vertebrae, parts of the pelvis, parts of the hind legs, some fingers, and teeth. Many scientists think Camelotia and Plateosaurus were closely related.

Classifying Camelotia is no easy task, and its placement within the “dinosaur family tree” is changing one year to the next. It has features that belong to both advanced prosauropods and primitive sauropods, making its position on the spectrum murky. The curve of its thigh bone and muscle attachments echo those of the early sauropods; its femur has characteristics of both sauropods and prosauropods; the trochanter minor is a throwback to the prosauropods, but the presence of a fourth trochanter is strictly sauropod-like in nature. These features make Camelotia a mixed bag—a “mutt” of sorts—and scientists take a variety of positions on its identity. Some believe it to be a primitive sauropod, others take it as an advanced prosauropod, and still others point (rather hopefully) at Camelotia and proclaim it an “intermediate species” between prosauropods and sauropods. This last claim would forge a connection between sauropods and at least one line of prosauropod evolution.

Blikanasaurus

Type Species: Blikanasaurus cromptoni

Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda

Time Period: Late Triassic

Location: South America

Diet: Herbivore

This 16½ foot “Lizard from Blikana” hails from the Upper Triassic rocks of South Africa. This entire species is known only from a stout limb bone and feet fragments. These scant remains tells us a lot while raising more questions. The bones tells us, on the one hand, that Blikanasaurus had proportionally small feet, indicating that it probably had a fully quadrupedal lifestyle. On the other hand, the scant remains make Blikanasaurus’ relationship to other dinosaurs murky. Some scientists classify it as a prosauropod; still others think it’s the earliest known ancestor of the sauropods. However, Blikanasaurus had a reduced fifth toe while the later sauropods had well-developed fifth toes to assist with weight bearing. Perhaps, then, Blikanasaurus represents a failed off-shoot from the prosauropods that simply wasn’t cut from the right cloth to make it through the Jurassic.

Melanorosaurus

Type Species: Melanorosaurus readi

Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda

Time Period: Late Triassic

Location: Africa

Diet: Herbivore

The “Black Mountain Lizard” roamed the conifer forests of Upper Triassic South Africa, where it may have rubbed shoulders with Riojasaurus and Euskelosaurus. Melanorosaurus’ body is, in a lot of respects, morphologically similar to those of the later sauropods: its large body, sturdy limbs, and ponderous, fully quadrupedal gait have inspired numbers of scientists over the years to wonder if Melanorosaurus, like Riojasaurus, has eerily close family ties to the sauropods. Melanorosaurus had a pointed, tapering nose not unlike a bird’s beak; the skull was about nine inches long—definitely small for a head-to-tail length up to fifty feet!—and looked triangular when seen from above or below. The long tail tapered towards its end and had a good degree of flexibility; the neck, while long, is stubbier than those of the sauropods. 

The presence of sclerotic rings—rings of bony plates that protected the eyes—in Melanorosaurus allowed it to function during both the day and night; when comparing the sclerotic rings and orbit sizes of prosauropods and modern birds and reptiles, scientists have suggested that prosauropods were cathemeral, meaning that they could see best at dusk and dawn. Perhaps Melanorosaurus—along with many of its prosauropod blood-fellows—was most active in the morning and evening, avoiding the sweltering heat of the Triassic afternoons by basking in the shadows of Pangaean cliffs or under the shade offered by towering conifers.

Mussaurus

Type Species: Mussaurus patagonicus

Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda

Time Period: Early Jurassic

Location: South America

Diet: Herbivore

Jose Bonaparte made a hell of a discovery in the 1960s with Riojasaurus, and he made another in the 1970s: “the Mouse Lizard”. Mussaurus gets its name from its incredibly small size: the largest skeleton was only eight inches long! These Lower Jurassic herbivores had large heads, big eyes, and short necks. These bug-eyed critters were so small they could fit in the palm of your hand. Their skeletons evoked images of mice, and the media (and science) introduced the world to “the mouse lizard.” Hailed as the “Smallest Dinosaur Ever Found!” at a mere ¾ of a foot long, Mussaurus showed up (rather ironically, if you ask me) on all the Big 10 lists. Even notable science fiction author Michael Crichton included the mouse-sized Mussaurus in his sequel to Jurassic Park. 

But in all the excitement, a critical component of the Mussaurus dig site didn’t receive the attention it deserved: these eight-inch long dinosaurs were found amidst what turned out to be fragmented eggshells. Before being trampled, the eggs would’ve been about one inch long. As for Mussaurus, the bones speak for themselves: tall skulls with short snouts and big eyes are common features of vertebrate infants. This wasn’t the Smallest Dinosaur Ever; it was just a baby. It became clear that Bonaparte had stumbled across a newly-hatched nest forever frozen in time. The adults, however, were conspicuously absent—at least for a while. 

Later digs revealed adult specimens in the same rock formations as the infant Mussaurus. That discovery opened a treasure trove of specimens that we didn’t know we had: it turns out that the remains of several adult Mussaurus had already been found; they had just been “mislabeled” as variants on Plateosaurus. The adults reached up to ten feet in length (still fairly small for the prosauropods we’ve seen, but a titan compared to the eight-inch infants), and it had the look and feel of your basic prosauropod: a long neck and long tail, a small head with an elongated snout, and large, five-fingered hands sporting large thumb claws. Mussaurus was bipedal, but it may have been able to run on all four legs if the need arose. 

Mussaurus may not have been as small as a mouse, but more discoveries have shed further light not just on this dinosaur, but on its society as well. The paternal care (or lack thereof) among dinosaurs is a subject that remains, in some ways at least, hotly debated; and within this cacophony, Mussaurus has a booming voice. First, the fact that the babies remained at their nests after hatching—rather than scurrying fast and hard for the undergrowth, as vulnerable infants instinctively do—implies that someone was looking after them. Second, the anatomical proportions of an infant Mussaurus are reminiscent not only of infant vertebrates but, more poignantly, to species that exhibit parental care over their young while they’re vulnerable. Third, a further discovery of an intact nest with seven juvenile specimens—neither babies nor adults—crowded around it implies that, for a significant amount of time, the animals stayed around the nest. Without parental care, hovering around the nest would be tantamount to infanticide. Someone would find out about it at some point, and it’d be a bloodbath. Fourth, and finally, the first adult specimens of Mussaurus have been recognized as recently as 2013, and these specimens were found near the nests. These South American bone-beds give us a snapshot of a (rather unfortunate) day-in-the-life of a prosauropod nesting site—and at 215 million years old, it’s the oldest known nesting site in the geological record.

Euskelosaurus

Type Species: Euskelosaurus browni

Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda

Time Period: Late Triassic

Location: Africa

Diet: Herbivore

This Upper Triassic to Lower Jurassic prosauropod was the first dinosaur to be discovered in Africa, and the number of specimens found in South African sandstones imply it had been a staple of the area’s ecosystem. Euskelosaurus foreshadowed the giant sauropods of the Jurassic, with adults reaching up to forty feet long head-to-tail (that estimate may change depending on the head; though scientists have a good idea of what it looked like, a skull has yet to be found). Its name means “good-limbed lizard,” and it strikes a chord of irony: the shaft of its thigh bone was twisted, which may have rendered it bow-legged! Because dinosaurs positioned their legs underneath their bodies, this anatomical feature is a bit of a mystery. Some have proposed that Euskelosaurus’s earliest versions had an erect posture, but as its body grew larger, vastly exceeding the size of its proto-dinosaurian ancestors, its femur twisted in an evolutionary attempt to handle the added weight. This evolutionary sideshow would’ve been inefficient compared to keeping an erect stance, and perhaps this is seen in the fact that Euskelosaurus doesn’t seem to have made it past the Lower Jurassic.

Riojasaurus

Type Species: Riojasaurus incertus

Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda

Time Period: Late Triassic

Location: South America

Diet: Herbivore

While a dearth of prosauropods are found in what was Laurasia (the northern half of the rifting Pangaea), peculiar ones are found in Gondwana (the southern half), and the “Rioja Lizard” makes an excellent Gondwana specimen. Named by Jose Bonaparte in 1967, this herbivorous Upper Triassic prosauropod could reach a massive 36 feet long. Though greater sizes would develop in the Jurassic, Riojasaurus is a wonder for any paleontologist: how mysterious for a dinosaur of such massive size to evolve so early!

Around twenty skeletons representing different stages of growth have been found in Argentina. The earliest skeletons lacked skulls, and scientists originally deduced that Riojasaurus had been a predator, since pointed teeth were found among the bones. More specimens—with skulls this time!—showed up, and the leaf-shaped teeth showed it to be herbivorous. The pointed teeth among the earliest skeletons probably belonged to either meat-eating dinosaurs or those of early crocodilians feeding on the carcasses; the Triassic’s trophic (or top-of-the-food-chain) predators weren’t theropod dinosaurs but dinosaur-like archosaurs that would send most early dinosaurs fleeing in terror. 

Riojasaurus’ limb bones were large, dense, and heavy; combined with over-sized shoulder- and hip girdles, not to mention forelegs that were only slightly smaller than the hind legs, it seems a safe bet to assume that Riojasaurus was fully quadrupedal, completely restricted to life on all fours. (In all fairness, a 2016 study by Scott Hartman shows that Riojasaurus may have been able to not only rear up on its hind legs but also walk in a bipedal fashion; more research has yet to be done.) If Riojasaurus were fully quadrupedal, it puts a curious twist in prosauropod evolution: it’s been assumed that prosauropods started off bipedal, branching away from bipedal archosaurian ancestors, but Riojasaurus shows up “large and in charge” early on in prosauropod history. The curtain has barely drawn back when Riojasaurus ungainly limbers on stage, blinking stupidly at the lights (and because prosauropods were among the dumbest of dinosaurs, stupid blinking isn’t a figure of speech). 

Riojasaurus’ backbone was punctured by the presence of hollow, air-filled cavities that kept the backbone from being too heavy (no one likes to be crushed by their own spine). These hollow spaces are rare in prosauropods but predominant in sauropods. These hollow cavities continued up through the neck, helping to keep minimize the weight so that Riojasaurus could lift its long neck to reach higher vegetation. The presence of these air cavities have prompted a number of scientists to wonder if Riojasaurus’ relationship with sauropods is closer than that of “second cousins.”

Plateosaurus

A Plateosaurus threatens a duo of curious Liliensternus

Type Species: Plateosaurus engelhardti

Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda

Time Period: Late Triassic

Location: Europe

Diet: herbivore

Plateosaurus lived in Late Triassic Europe and could reach up to 30 feet in length. This dinosaur seems to have had a penchant for fossilization, as paleontologists have studied over a hundred skeletons found in the Triassic sandstones of Germany, France, and Switzerland. Though this dinosaur is one of the most well-known prosauropods, to the point that essays and articles on prosauropods tend to use Plateosaurus as a template, Plateosaurus’ first steps in paleontology were both awkward and ill-received. Its remains were first discovered in 1834, and Plateosaurus became the fifth named dinosaur genus still considered legitimate. When Richard Owen formally named Dinosauria in 1842, he didn’t include Plateosaurus in his trilogy of dinosaur genera used to define the group (he used Megalosaurus, Iguanodon, and the oft-ignored Hylaeosaurus). Nevertheless, the wealth of specimens enjoyed by modern scientists has turned Plateosaurus into the king of its castle. As of 2001, two species of Plateosaurus have been named: the earliest, Plateosaurus gracilis (formerly known as Sellosaurus), maxed out at around 15 feet; Plateosaurus engelhardti, the type species, showed up later in the Triassic and reached anywhere between 15 to 30 feet. 

A Plateosaurus prowling the river's edge

Plateosaurus had a long, small, and narrow skull, though its skull remained stronger and deeper than the skulls of its prosauropod kin. It had a pear-shaped body made longer by its long neck and tail, with the tail making up half its total length. Its jaws were filled with small, coarsely-serrated, and leaf-shaped teeth; the low-slung hinge of its lower jaw gave its jaw muscles greater leverage to produce a powerful bite. Small ridges of bone around its mouth supported fleshy cheek pouches in life: the front teeth stripped the leaves, and the pouch kept vegetation from falling out of the mouth before it could chew and/or swallow, thus preventing needless waste (an animal of Plateosaurus’ size needed all the food it could get!). Its front legs were shorter than its hind-legs, and it may have been able to rear up on its hind legs not only to reach higher foliage but to run from predators: because of the length of the lower leg bones, some scientists speculate that it could have reached top speeds running on two legs. The hind limbs had slightly flexed knees and ankles, and its feet were digitigrade, meaning they walked on their toes like modern birds. Its eyes were directed to the sides, rather than to the front (like predators), providing all-round vision to keep a wary eye out for threats. Some Plateosaurus skulls have preserved sclerotic rings (rings of bony plates that protected the eyes); by comparing the scleral rings and orbit sizes of Plateosaurus and modern birds and reptiles, scientists have suggested that Plateosaurus was cathemeral, meaning that it was active at any time during the day or night, depending on circumstances. Recent studies estimate that Plateosaurs tended to live between 12-20 years, but their maximum age is unknown (though one specimen seems to have been around 27 years of age).

Recent studies on the Plateosaurus ribcage indicate that these dinosaurs may have had more in common with modern birds than previously thought. Mathematical calculations seem to imply that Plateosaurus had a respiratory system more in common with modern birds than its contemporaneous reptiles. Furthermore, indicators of air sacs in the lungs to reduce weight can be found on the fossilized remains of some specimens, and the rapid growth rates of Plateosaurus have more in common with birds than reptiles. These little clues have led some scientists to speculate that Plateosaurus was endothermic, or “warm-blooded.” The debate on dinosaur metabolism—“Were they cold-blooded, like reptiles, and thus dependent on the heat from their natural surroundings to regulate body temperature? Or were they warm-blooded, like mammals and birds, generating body heat internally?”—has raged for decades, and there remains no consensus on the issue. 

A family group of Plateosaurus meanders down a Late Triassic creek bed

The vast number of disarticulated and articulated skeletons found in bone-beds in both Germany and Switzerland imply, at first glance, gregarious behavior. The image of innumerable herds traveling through the Triassic desert landscapes of Europe, kicking up vast clouds of dust and dirt in their wakes, is a tantalizing image. But things aren’t quite so simple. It’s equally possible that Plateosaurus lived a solitary lifestyle, but these parts of the world were prone to flooding, and dead Plateosaurs from across the landscape were jumbled together in fast floods, creating mesozoic "burial grounds". At the same time, the fact that most of the fossils from these bone-beds belong to Plateosaurus with few exceptions (a few theropod teeth here, an ancient turtle shell there) indicates that these bone-beds might be snapshots of some cataclysmic event that entombed a whole herd of the dinosaurs. But again: things aren’t quite so simple. Further study has shown that at least some of these bone-beds were, back in the Triassic, covered by acres of mud, which could act like quicksand. Coming to feed on the hardy plants that lived in these bog-like conditions, the heavy prosauropods could quickly become trapped in the mire; and the more they struggled to get free, the deeper they would sink. Theropod dinosaurs of Plateosaurus’ day-and-age were, for the most part, lightly-built and with big feet, allowing them to roam these Triassic-era “tar pits” with ease and grab easy meals from mired prey. This scenario makes sense of at least one discovery: in Switzerland, the fossilized remains of a Plateosaurus’ leg bones were found standing vertically in river sandstone while the rest of the skeleton was found scattered around the area and mixed with the teeth of theropod dinosaurs and crocodile-like carnivores. Having become ensnared, the helpless Plateosaurus was set upon by carnivores, and these predators hewed the dinosaur bone-to-bone and enjoyed their takings in the quiet seclusion of the trees. This scenario also explains why the skeletons in these bone-beds consist mostly of adult specimens; because they would’ve been smaller, juvenile Plateosaurs could walk through the bogs without fear of getting stuck. Though debate on the nature of the bone-beds continues, gregariousness remains a safe bet with the accumulated evidence from the wider prosauropoda.