Plateosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order:

Family: Plateosauridae

Genus:Plateosaurus

Species:Plateosaurus engelhardti

Introduction

One of the first of what would be many giant, plant-eating dinosaurs, Plateosaurus existed throughout Europe, ranging mostly through areas in what is now France, Switzerland, and Germany during the Late Triassic period. A wealth of fossil evidence—including a single discovery in Germany during the 1930s of some 40 Plateosaurus skeletons thought to have perished simultaneously in a natural disaster—has allowed paleontologists to develop a full, if changing, understanding of the creature and its habits over the decades.

Among the earliest true dinosaurs, the herbivorous, long-necked Plateosaurus was a prosauropod, a group of dinosaurs once considered to be the evolutionary ancestor of the massive plant-eating sauropod dinosaurs, which flourished some 50 million years later during the Late Jurassic period. Although Plateosaurus was considerably smaller than sauropods such as Apatosaurus and Diplodocus, it had a similar body structure and eating habits. However, more recent scholarship has dismissed this idea, even arguing that prosauropods had no evolutionary descendants and were instead a separate, independent chain.

Classification

Paleontologists use two major systems for classifying organisms. Linnaean taxonomy uses overall physical similarity to place organisms into different groups. By contrast, cladistics seeks to create groups of organisms based on evolutionary relationships; these groups are called “clades.” Cladistic analysis focuses on important key traits and attempts to trace the inheritance of a trait among descendants of a common ancestor.

Under a Linnaean analysis,Plateosaurus, like all other dinosaurs and modern-day birds, is categorized into the class Sauropsida. It is further classified as a member of the Saurischia, or “lizard-hipped,” order, and further under the suborder Sauropodomorpha and infraorder Prosauropoda, commonly known as prosauropods. Plateosaurus lends its name to its family, Plateosauridae, which also includes the relatively recently discovered Unaysaurus. The genus Plateosaurus is generally accepted to contain two species, Plateosaurus engelhardti and Plateosaurus longiceps.

Under a cladistic analysis, Plateosaurus falls under the Sauropodomorpha clade because of its elongated neck and small head, and further under the Prosauropoda group because of its skull, jaw, and teeth structure. Dinosaurs considered prosauropods include Melanosaurus, Massospondylus, and Coloradisaurus.

Anatomy

Widely considered the prototypical prosauropod, Plateosaurus had a large, pear-shaped body, a long neck and tail, and a small, narrow head. It had about 50 vertebrae in its tail, allowing it to bend the appendage greatly upward. The creature carried much of its weight around its pelvis, and its hind legs were considerably longer than its front legs.

These strong legs allowed it to perform both quadrupedal (four-legged) and bipedal (two-legged) movements.

Like other prosauropods, Plateosaurus's front limbs ended in hands with a clawed thumb and four fingers. These fingers helped the creature use its hands for food gathering, defense, and balance while walking. Its hind legs had five-toed clawed feet. Its third and fourth toes were the longest, and the fifth toe is believed to have been an unused vestigial digit and was considerably shorter than the others. These strong toes helped Plateosaurus ground its great weight during bipedal movement, while the fingers curled under to help bear the creature's weight during quadrupedal movement.

Intelligence

Based on the encephalization quotient (EQ) scale, which attempts to determine the relative intelligence of creatures using a brain-to-body-weight ratio, prosauropods such as Plateosaurus were the least intelligent of all the dinosaurs. Plateosaurus had an EQ rating as low as 0.1, while other dinosaurs achieved ratios as high as 5.8.

Despite this lack of brainpower, Plateosaurus had well-developed senses of sight and smell to help it find food and avoid danger. With eyes positioned on the sides of its skull, the creature had a wide field of peripheral vision, and an enlarged frontal brain lobe in the dinosaur's braincase suggests a keen sense of smell. Although scientists remain unsure exactly how well Plateosaurus could hear, the linkage of the hearing cavity with the creature's nasal cavity suggests an acceptably acute sense of hearing.

Reproduction and Population

Despite the wealth of skeletal evidence extant for Plateosaurus, little information remains about the creature's specific reproductive habits. Egg discoveries do support the likelihood that prosauropods were generally oviparous, or egg-bearing. Scientists discovered a nest laid by related dinosaur Mussaurus in 1979, and a nest possibly belonging to prosauropod Massospondylus was found in 1987. Based on these findings and the generally accepted fact that Plateosaurus travelled in groups, it is possible to speculate that Plateosaurus laid multiple eggs at one time. After these eggs hatched, they remained in the nest and were cared for by one or both of their parents. Upon reaching sufficient maturity, these young then joined the family's herd.

Diet

Plateosaurus was the first giant herbivore, or plant-eating dinosaur. As such, it consumed great quantities of available plant matter, such as ferns, conifers, and cycads. The creature's long neck allowed it to reach tall tree tops, and its sturdy, powerful back legs permitted it to rear up to seek higher vegetation. Plateosaurus stripped plant matter from tree branches and trunks using flat, diamond shaped, coarsely serrated teeth. These teeth suggest that it probably preferred soft plant matter over woody bark, and its jaw structure implies that it removed food in fairly short sections. Additionally, these specialized teeth excelled at tearing, but not at chewing; instead, the creature may have swallowed small rocks, or gastroliths, to help crush the roughly torn plant matter in a way similar to a modern bird's gizzard.

Behavior

Fossil evidence suggests that Plateosaurus travelled in herds with perhaps as many as 50 members. These herds offered them some protection against small carnivorous dinosaurs or other predators, as the larger, stronger creatures could close ranks and strike out with their clawed hands in defense. Scientists believe that juvenile members of the herd were likely in the center of the herd, while large adult Plateosaurus took the more vulnerable front, rear, and side positions.

Because Plateosaurus required a great deal of food, herds probably moved from place to place as they consumed all of the available plant matter. This is believed to have kept Plateosaurus on the move, albeit slowly—due to the creature's large size and great weight, scientists have speculated that it could not walk very quickly. This slow speed combined with a tendency to travel in packs meant that entire Plateosaurus herds could fall victim to natural disasters such as flash floods, a likelihood supported by fossil discoveries.

Habitat and Other Life Forms

During the Late Triassic, the majority of all of the earth's landmasses were joined in a supercontinent called Pangaea.Plateosaurus roamed part of this vast continent, and its fossils have been found throughout modern-day Europe and as far distant as Greenland, although the greatest number have been localized in Germany, France, and Switzerland.

Although the Triassic landscape was a relatively dry, barren one, it nevertheless supported a great deal of life. Plants such as ferns, cycads, and coniferous trees grew near sources of water, and numerous large reptiles, flying pterosaurs, and even small, shrew-like mammals inhabited the land. This period marked the rise of the first dinosaurs, and fellow prosauropods such as Thecodontosaurus lived in the same general region as Plateosaurus.

Research

German paleontologist Hermann von Meyer first described Plateosaurus in 1837, following significant fossil discoveries in Germany. Because of the earliness of this discovery, Plateosaurus was not fully identified as a dinosaur until some years later, after Sir Richard Owen coined the term “dinosaur” in 1842.

Although Plateosaurus engelhardti is considered the type species for the genus, at least one other Plateosaurus species has been discovered. In 1913, German paleontologist Otto Jaekel described the species Plateosaurus longiceps based on skeletal remains discovered at a clay pit in the Trössingen Formation in Germany. Other Plateosaurus species have been described over the years, but scientists today now consider these species synonymous with either Plateosaurus engelhardti or Plateosaurus longiceps.

Bibliography

"Dinobase." University of Bristol, dinobase.gly.bris.ac.uk/index.htm. Accessed July 2010.

Galton, Peter M., and Paul Upchurch. “Prosauropoda.” Dinosauria, edited by David B. Weishampel, Peter Dodson, and Halszka Osmólska, University of California Press, 2004.

Holmes, Thom, and Laurie Holmes. Gigantic Long-Necked Plant-Eating Dinosaurs: The Prosauropods and Sauropods. Enslow, 2001.

Norell, M. A., et al. Discovering Dinosaurs at the American Museum of Natural History. Knopf, 1995.

"Plateosaurus." Fossilworks, fossilworks.org/. Accessed 2 June 2020.

Schomp, Virginia. Plateosaurus and Other Early Long-Necked Plant-Eaters. Marshall Cavendish, 2006.

Van Heerden, Jacques. “Prosauropods.” Complete Dinosaur, edited by James O. Farlow and M. K. Brett-Surman, Indiana UP, 1997.