Euskelosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family:Plateosauridae

Genus: Euskelosaurus

Species: Euskelosaurus browni

Introduction

Euskelosaurus was a large herbivorous dinosaur that lived in Late Triassic South Africa and represented a group of dinosaurs that later evolved into the largest terrestrial animals in the history of the planet. Euskelosaurus represented an early adaptive radiation of dinosaurs, colonizing both the northern and southern hemispheres.

In the Triassic period, the continents of the world were united in a single land mass called Pangaea. The tectonic shifting of land masses eventually caused the supercontinent to split into northern and southern continents. Dinosaurs on either side of the oceanic divide then evolved into unique southern and northern assemblages of species.

Euskelosaurus was a member of the sauropodomorphs, a lineage of dinosaurs that became one of the most successful groups of species in the Triassic, and which gave rise to the giant sauropods of the Jurassic. Species like Euskelosaurus evolved before the continents diverged, leaving representatives of the sauropodomorphs in both the northern and southern hemisphere after the breakup of Pangaea.

Classification

Paleontologists use two primary methods to classify organisms. Linnaean taxonomy, or “systematics,” groups organisms into a nested hierarchy of categories based on overall physical similarity, while “cladistics” creates groups called “clades” in an effort to reflect the evolutionary relationships between species.

Systematic analysis places Euskelosaurus in the order Saurischia based on the “lizard-like” orientation of its pelvis, and then into the suborder Sauropodomorpha, because of its smaller head, herbivorous dentition, and adaptations of the feet. Historically, many paleontologists placed Euskelosaurus into the family Plateosauridae, based on similarity to the species Plateosaurus, another early member of the sauropodmorph group.

Cladistic analysis has traditionally placed Euskelosaurus into the clade Sauropodomorpha, largely based on reduced skull size, the presence of long, leaf-shaped teeth, and an elongated neck. Cladists are uncertain how to classify Euskelosaurus after the division into the sauropodomorpha, and do not generally support placing the species into the clade Plateosauridae or any of the other divisions. Because the fossilized remains available for study continued to prove limiting and minimal into the first decades of the twenty-first century, paleontologists further debated the genus and its classification. As early as 2003, some scientists had argued that the genus was questionable and may not be valid, particularly after further analysis had found that other fossils recovered from the same area that had initially been grouped with Euskelosaurus had been considered as needing to be rediagnosed.

Anatomy

Euskelosaurus is known only from incomplete fossils, largely of the limbs and vertebrae. Comparisons of Euskelosaurus fossils with other prosauropods indicates that the species was large, reaching lengths of between 9 and 10 meters (29.5–32.8 ft) and standing at least 3 meters (9.8 ft) at the hip. The species may have weighed as much as 2.5 metric tons (5,511 lbs).

Euskelosaurus seems to be close in body type to other early, large sauropodomorphs like Riojasaurus from Argentina and Melanorosaurus, which also had a long neck, small head, and leaf-shaped teeth. The sauropodomorphs in the Late Triassic were divided into two groups, bipedal/semi-bipedal species and quadrupedal (utilizing four limbs for terrestrial movement) species. Euskelosaurus may have been a quadrupedal animal, based on its heavy build, but might have been able to utilize bipedal movement as well, possibly when foraging in tall trees.

Euskelosaurus was most likely covered in fine mosaic scales, similar to skin impressions found for other species of herbivorous dinosaurs. One unusual feature of Euskelosaurus is the orientation of the femur, which was twisted, indicating that the species may have had a wide, bow-legged stance; the legs of most sauropodomorphs were oriented directly under the body.

Intelligence

Sauropodomorphs had low EQ ratings relative to other dinosaur groups. Euskelosaurus might have had similarly low intelligence, relying on strength and size to compensate for shortcomings in intelligence. Though Euskelosaurus was not as intelligent as many other dinosaurs, paleontologists estimate that dinosaurs were more intelligent than the prehistoric reptiles that preceded them as the dominant terrestrial species.

Reproduction and Population

Investigations in Argentina have revealed beds of sauropod eggs and embryos, indicating that at least some sauropods were egg layers. Sauropod embryos discovered so far indicate that sauropods began as small animals, hatching from eggs that were around 30 centimeters long (12 in) and growing throughout their lives to reach massive proportions. The nests were covered with vegetation, presumably for insulation and protection, similar to the behavior of modern crocodiles.

While paleontologists are uncertain about the reproductive behavior of Euskelosaurus, it may also have laid small eggs, similar to later sauropods. Although evidence suggests that some sauropods may have gathered into herds for breeding, evidence is lacking for many of the early sauropodomorphs, which may have been solitary breeders.

Diet

Euskelosaurus was an herbivore, using its tall, leaf-shaped teeth to strip vegetation from shrubs and trees. Paleontologists have discovered that some sauropodomorphs used gastroliths, stones swallowed in an effort to assist in grinding vegetation within the digestive tract. This strategy, combined with a large stomach, allowed sauropodomorphs to consume the massive quantities of vegetation needed to fuel their large bodies.

Late Triassic South Africa had a variety of vegetation, largely of the gymnosperm variety. The conifers, cycads, and other seed-bearing species formed large forests, providing feeding grounds for a variety of herbivores. Other common plants in the area were tree ferns, large spore-bearing members of the fern group that grew into tall, woody trees in the Mesozoic era.

Behavior

Fossil evidence suggests that some sauropods gathered in herds. This hypothesis is based both on the discovery of groups of sauropod fossils in close association and from trackways discovered at some fossil sites, suggesting that sauropods might have migrated in groups. Paleontologists are uncertain whether Euskelosaurus displayed similar social behavior, but generally believe that social groupings evolved among the Sauropodomorpha during the Triassic period.

Habitat and Other Life Forms

Late Triassic Africa was a mosaic of terrain, ranging from arid plains to lush, moist forest. There were a large variety of dinosaurs, reptiles, and amphibians living in the environment. One of the earliest known true mammals, a small insectivore called Megazostrodon, was present in South Africa. Africa was also home to some of the last labyrinthodonts, large predatory amphibians that include the genus Mastodontosaurus.

There were a variety of early sauropodomorphs in Africa, including the large species Melanorosaurus and Blikanasaurus. There were also a variety of ornithischians, the dinosaur group that gave rise to the hadrosaurs and ceratopsians, two of the most successful groups of the Jurassic and Cretaceous. The small herbivore Fabrosaurus was a representative of the early ornithischians in Late Triassic Africa.

Research

Euskelosaurus is known from a partial skeleton in 1866, in the Elliot Formation in South Africa. No confirmed additional specimens had been found as of early in the third decade of the twenty-first century, and while paleontologists found several closely related fossils that they expected might be included within the genus, it was typically argued that they deserved separate classification. In a 2017 paper published in Acta Palaeontologica Polonica, researchers argued that the original zonation of the Elliot Formation, in which the Euskelosaurus had been discovered, had been too simplistic and innacurate, meaning that many of the fossils described from that location had subsequently been incorrectly restricted to Euskelosaurus. At the same time, they continued to emphasize that more studies were needed as so many of the specimens were incomplete.

Bibliography

Briggs, Derek E. G., and Peter R. Crowther. Paleobiology II. Wiley-Blackwell, 2001.

Carpenter, Kenneth. Eggs, Nests and Baby Dinosaurs: A Look at Dinosaur Reproduction. Indiana UP, 1999.

Chinsamay-Turan, Anusuya. Microstructure of Dinosaur Bone: Deciphering Biology with Fine-Scale Techniques. Johns Hopkins UP, 2005.

Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. 3rd ed., Cambridge UP, 2016.

Fastovsky, David E., and David B. Weishampel. Evolution and Extinction of the Dinosaurs. 2nd ed., Cambridge UP, 2007.

Horner, Jack, and James Gorman. How to Build a Dinosaur: Extinction Doesn’t Have to Be Forever. Dutton, 2009.

Horner, John R., and Edwin Dobb. Dinosaur Lives: Unearthing an Evolutionary Saga. Mariner Books, 1998.

Lucas, Spencer G. Dinosaurs: The Textbook. 6th ed., Columbia UP, 2016.

Martin, Anthony J. Introduction to the Study of Dinosaurs. 2nd ed., Blackwell, 2006.

McPhee, Blair W., et al. "The Sauropodomorph Biostratigraphy of the Elliot Formation of Southern Africa: Tracking the Evolution of Sauropodomorpha across the Triassic-Jurassic Boundary." Acta Palaeontologica Polonica, vol. 62, no. 3, 2017, pp. 441–65, doi:10.4202/app.00377.2017.

Smith, Roger M. H., et al. “Sedimentology and Paleoecology of a Diverse Early Jurassic Tetrapod Tracksite in Lesotho, Southern Africa.” Palaios, vol. 24, 2009, pp. 672–84.

Weishampel, David B., et al., editors. The Dinosauria. 2nd ed., U of California P, 2004.

Wilson, Jeffrey A. “Integrating Ichnofossil and Body Fossil Records to Estimate Locomotor Posture and Spatiotemporal Distribution of Early Sauropod Dinosaurs: A Stratocladistic Approach.” Paleobiology, vol. 31, 2005, pp. 400–23.

Yates, Adam M., and James W. Kitching. “The Earliest Known Sauropod Dinosaur and the First Steps Towards Sauropod Locomotion.” Proceedings of the Royal Society of Biology, vol. 270, 2003, pp. 1753–58.