Dino of the Week: 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.