Eustreptospondylus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Megalosauridae

Genus: Eustreptospondylus

Species: Eustreptospondylus oxoniensis

Introduction

Eustreptospondylus was a large predatory dinosaur that lived in Middle Jurassic Europe and represented a large group of predators that appeared around the world in the Jurassic and Cretaceous.

In the Triassic period, the continents of the world were united in a single land mass known as Pangaea. In the Jurassic and Cretaceous (a time interval of almost 150 million years), the shifting of tectonic plates and changing ocean levels caused Pangaea to split into northern and southern continents. Dinosaurs emerged during the Triassic and, after the continents split apart, evolved into unique collections of species in both the southern and northern hemispheres.

Eustreptospondylus represents a subgroup of the theropod dinosaurs called the megalosaurids, which were present in both the southern and northern continents, indicating that the megalosaurid species evolved from a common ancestor that spread across the world before the breakup of Pangaea.

Classification

Scientists use two primary methods to classify organisms into different groups. Linnaean taxonomy, or “systematics,” groups organisms according to general similarities in appearance, while “cladistics” creates groups called “clades” in an effort to explore the evolutionary relationships between species.

Linnaean analysis places Eustreptospondylus in the order Saurischia, because of the lizard-like orientation of the animal's hips (however, by the beginning of the third decade of the twenty-first century, scientists were debating the long-standing classification division of dinosaurs into Saurischia and Ornithischia). From there, it is placed in the suborder Theropoda, a group of bipedal dinosaurs that were primarily predatory, and into the family Megalosauridae, a group of Jurassic predators with long skulls and arms.

Cladistic analysis places Eustreptospondylus into the clade Theropoda, which is defined by features of the skull and limb bones, and then into the clade Tetanurae, the members of which had larger hands, teeth only in the front of their jaws, and stiffened tails. The clade Megalosauridae divided from the Tetanurae due to the presence of longer skulls and thick arm bones.

An ongoing conversation that had been occurring within the scientific community regarded the Megalosauridae family. Some contended that the Megalosauridae family has been a sort of theropod “waste basket” classification of dinosaurs that did not quite fit elsewhere. Scientist Paul Sereno has advocated for dispensing with the family classification Megalosauridae in favor of the family name Torvosauridae. Others have argued that Megalosauridae should be refined or redefined.

Anatomy

Eustreptospondylus was a large predator, though it was somewhat small in comparison to some of the other theropod predators of the Jurassic and Cretaceous. Eustreptospondylus could reach lengths of 4 to 4.5 meters (13.1–14.7 ft) and stood 3 meters (9.2 ft) at the hip. Paleontologists estimate that the animal may have weighed 250 to 350 kilograms (551.1–771.6 lbs).

The species had a relatively slender build, with a long, stiff tail presumably used for balance. Its muzzle was long, with sharp teeth in the front of the jaws. The animal had powerful rear legs, terminating in feet with three large, clawed toes. The forelimbs were somewhat reduced, though not as small as in some species of theropod.

Eustreptospondylus lived in a patchwork collection of small islands and scattered forests. Paleontologists believe that the species probably evolved some form of cryptic coloration to help it stalk and ambush prey in forests and littoral environments. Eustreptospondylus was most likely covered in fine, mosaic scales, as seen on skin impressions for other dinosaur species.

Intelligence

James A. Hopson's research indicates that dinosaurs were generally less intelligent than modern mammals and birds living similar lifestyles. A few species of dinosaur, most notably Cretaceous theropods, had higher EQ ratings similar to small mammals and birds. Eustreptospondylus was likely similar in intelligence to a small bird, which would have made the species more intelligent than most of the herbivorous dinosaurs living in its environment.

Reproduction and Population

Paleontologists generally believe that most dinosaurs were oviparous, or egg-laying, animals. Nests and eggs have been found for several species of theropods, indicating that the young were born into clutches of between two and ten hatchlings. Some paleontologists believe that theropod dinosaurs provided protection to their young after hatching, though more evidence is needed to confirm this hypothesis.

While some small dinosaurs may have used their body heat to incubate their eggs, similar to the behavior of modern birds, other dinosaurs probably covered their nests in vegetation, which shielded the eggs from climatic changes and gave off heat as the vegetation decomposed, thereby incubating the eggs. Similar behavior is seen in modern crocodiles and alligators.

Diet

Eustreptospondylus was a carnivore, judging from its dentition, and probably lived an opportunistic existence, preying on a variety of animals and also eating carrion when available. As the species lived within an island chain, it may have supplemented its diet by scavenging along the sea, where it could find turtles and other aquatic reptiles.

There were a variety of herbivorous reptiles and dinosaurs living in Middle Jurassic England that might have fallen prey to predators like Eustreptospondylus. Fossils of the large sauropod herbivores have been found in the region, as well as representatives of the armored stegosaurs. While adults of these species may have been too large to fall prey to Eustreptospondylus, the species may have preyed upon juveniles and eggs of those species.

Behavior

Paleontologists have speculated that Eustreptospondylus may have been able to swim, as Middle Jurassic England was largely broken into a collection of semi-tropical islands. Some paleontologists have suggested that Eustreptospondylus may have needed to cross from island to island in order to obtain sufficient food. However, the skeleton of Eustreptospondylus does not contain any adaptations for swimming or living a semi-aquatic lifestyle.

Because Eustreptospondylus lived among an island chain, some paleontologists have suggested that the species may have lived off of carrion washed in by the tide. Modern ocean environments often support scavenger species that live similar lifestyles, feeding on dead sea turtles and other animals that wash to the shore.

Habitat and Other Life Forms

Middle Jurassic England was a collection of small islands with a semi-tropical climate and a variety of forest habitat. Gymnosperms, or naked seed-bearing plants, were the dominant form of vegetation in this environment, including early conifer species and cycads. The skies were dominated by pterosaurs, flying reptiles that evolved alongside the dinosaurs in the Mesozoic. Species of the genus Rhamphorhynchus, a pterosaur characterized by its long tail, lived in this habitat around what is now England.

There were a variety of dinosaurs on the European island chains of the Jurassic, including Emausaurus, an armored dinosaur, the stegosaur Lexovisaurus, and a number of sauropod species, such as Cardiodon and Cetiosaurus. Those in Europe were generally smaller than the giant sauropods of the Jurassic that inhabited North America and Africa.

In addition to Eustreptospondylus, other theropod predators in the environment included the much larger Proceratosaurus, though the species may not have lived on the same islands as other theropods.

Research

Eustreptospondylus is known only from a single fragmentary specimen described by paleontologist Richard Owen from an Oxford, England, fossil site in 1841. The fossil itself is believed to be a juvenile or not fully developed and was originally named Megalasaurus, but it was renamed Eustreptospondylus in 1964 by paleontologist Alick Walker.

The genus Eustreptospondylus has been placed into question by fossils from closely related species, belonging to another genus. Paleontologists hoped to find additional specimens of the species as part of the effort to create a more accurate account of the species' relationships to other theropods from the same era. In general, scientists continued to conduct research in areas that could help in distinguishing between theropods, especially when there is minimal material available. In 2015, a study was published that focused specifically on analyzing and describing megalosaurid teeth, as this information was less understood than for other theropods. A goal of the study was to determine how useful such dentition analysis could be in the identification of isolated theropod teeth. Other scientists believed that studying Eustreptospondylus was important for gaining a better understanding of related spinosaurids.

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