Muttaburrasaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Iguanodontidae

Genus:Muttaburrasaurus

Species:Muttaburrasaurus langdoni

Introduction

Muttaburrasaurus was a large herbivorous dinosaur living in Early Cretaceous Australia. The species is an early representative of a group of dinosaurs that dominated the northern hemisphere in the Late Cretaceous period.

In the Triassic period (roughly 251–201 million years ago), the continents of the earth were united in a single land mass known as Pangaea. Dinosaurs evolved during this period and spread across the world. In the Jurassic and Cretaceous, tectonic forces and changing ocean levels caused Pangaea to split into two supercontinents, Laurasia in the north and Gondwana in the south.

Muttaburrasaurus represented a group of dinosaurs that evolved from a common ancestor present in both the southern and northern hemispheres before the breakup of Pangaea. In the Cretaceous period, the descendants of this ancestor species thrived in the northern hemisphere, while only a few species, including Muttaburrasaurus, survived in Australia, South America, and Africa in the southern hemisphere.

Classification

Paleontologists use two primary methods to classify organisms into different groups. Linnaean taxonomy, or “systematics,” groups organisms according to overall physical similarity, while an alternative system, called “cladistics,” creates groups of organisms called “clades” in an effort to reconstruct the evolutionary relationships between species.

Systematic analysis places Muttaburrasaurus in the order Ornithischia, based on the “bird-like” orientation of the animal's pelvis (though this longstanding division in dinosaur classification has been challenged by some scientists). From there, the species is placed in the Ornithopoda, or “bird-footed,” infraorder, which shared the development of beaks and teeth. The bird-hipped, herbivorous ornithopods have been found on all seven continents.

Cladistic analysis places Muttaburrasaurus in the clade Ornithopoda, which is defined by developments of the teeth, the articulation of the jaw, and other features of the skull. Next, Muttaburrasaurus is placed into the clade Iguanodontia, made up primarily of large, bipedal animals with characteristic features of the skull. Some classifications further place Muttaburrasaurus in the clade Rhabdodontomorpha, due to the species' similarities and differences with the Rhabdodontidae family. As with most dinosaur classification, there is considerable instability as systems are refined and new information emerges.

Anatomy

Muttaburrasaurus was a large dinosaur, reaching lengths of between 7 and 7.5 meters (22.9–24.6 ft) and weighing 1.7 to 2 metric tons (3,747.8–4,409 lbs). The species was possibly capable of both bipedal and quadrupedal movement, perhaps alternating as needed. However, views of its movement have varied.

Muttaburrasaurus’ legs were longer and thicker than its arms and terminated in hoof-like claws on its feet. Its arms were thinner and shorter, and the hands were adapted for terrestrial movement, with the three middle digits terminating in blunt claws.

The animal had a flexible neck, supporting a large head. The eyes were set on the sides of the skull, increasing the animal's vision, and it had an enlarged snout with wide nasal passages. The end of the snout evolved into a shearing beak, and the animal had teeth in its cheeks. The tail was long and heavy and reinforced for stability, possibly serving as a counterbalance.

Intelligence

The hadrosaurs, or “duck-billed” dinosaurs, were close relatives to the iguanodontids and had encephalization quotient (EQ) ratings in the range of 1.5, placing them mid-range in terms of dinosaur intelligence. Many of the hadrosaurs and iguanodontids were large-bodied animals and probably used their size to discourage predators, reducing the need for advanced intelligence.

Reproduction and Population

Paleontologists have not yet discovered Muttaburrasaurus eggs or juvenile specimens and currently know little about the animal's reproductive behavior. Eggs and nests have been found for the closely related hadrosaurs, indicating that many of these species laid eggs in shallow nests covered with vegetation and debris to insulate the eggs against the environment. Paleontologists suspect that many hadrosaurs were social breeders, gathering into groups to lay eggs in communal breeding grounds. However, this social breeding behavior may have evolved only among the hadrosaurs, while iguanodontids like Muttaburrasaurus may have been solitary breeders.

Muttaburrasaurus is known only from a few isolated specimens, raising the possibility that the species may have been rare within its range. Some paleontologists have suggested that the enlarged dome on the muzzle of Muttaburrasaurus may have been a characteristic specific to only males or females of the species, a phenomenon known as sexual dimorphism. If this was the case, the enlarged nose may have served a reproductive purpose, helping animals to attract or identify potential mates.

Diet

Most paleontologists believe that the ornithopod dinosaurs were primarily herbivorous. There were a wide variety of plants available in Early Cretaceous Australia (East Gondwana), including many representatives of the gymnosperm groups such as conifers. Another common plant group, the cycads, were abundant in the area, growing into a variety of tree and bush-like species that may have formed part of Muttaburrasaurus's diet.

Unlike some other iguanodontids, Muttaburrasaurus had unusual teeth that came together in such a way as to create a cutting surface. Some paleontologists have suggested that this adaptation may have allowed Muttaburrasaurus to lead an omnivorous lifestyle, though most paleontologists believe that the animal was primarily an herbivore.

Behavior

Little is known about the behavior of Muttaburrasaurus. Though later hadrosaurs are thought to have been social animals, travelling in herds and perhaps migrating in search of food, no evidence of social behavior exists for Muttaburrasaurus and closely related species.

The enlarged nose on Muttaburrasaurus may have allowed the animal to generate unique vocalizations, perhaps producing deep tones that could travel over greater distances. The species may have used their vocalizations to keep in contact with other members of its species, to find and attract mates, or to organize territory and warn intruders from straying into its feeding grounds.

Habitat and Other Life Forms

Paleontologists believe that Early Cretaceous Australia was a seasonal environment, with a cool, darker dry season alternating with a wet, warm season. There were a variety of species living in the environment, including a number of reptiles and amphibians, as well as pterosaurs, the flying reptiles that dominated the skies and lived among dinosaurs during the Mesozoic. Muttaburrasaurus fossils were discovered near the shores of what was once a large inland sea, and the animal may have foraged on coastal vegetation.

In addition to Muttaburrasaurus, other herbivorous dinosaurs living in early Cretaceous Australia included a sauropod dinosaur known as Austrosaurus, which is believed to have been a large herbivore. A variety of small herbivorous dinosaurs have been found in the region, including Leaellynasaura and Fulgurotherium, both also representatives of the ornithopod group. Australia was also home to the small ankylosaurid dinosaur Minmi, one of the best-known species from Australia.

Predatory dinosaurs in Australia included the large theropod Rapator, which may have been feathered and lived as a scavenger/predator on the scrub plains of Australia, and Australovenator, a large predatory dinosaur related to the North American Jurassic dinosaur Allosaurus.

Research

Muttaburrasaurus langdoni was discovered by Doug Langdon, who discovered the fossil by chance while riding his horse in the Muttaburra area in Queensland. Paleontologists Alan Bartholomai and Ralph Molnar named the species in a 1981 journal article. Additional partial skeletons and teeth belonging to Muttaburrasaurus have been found in other parts of Australia, suggesting that the species may have been widespread. Muttaburrasaurus remains well known as one of the most complete fossils uncovered within Australia, and research on the species is often covered in Australian mass media. In 2011 studies suggested that dinosaur footprints in Queensland once thought to belong to a large carnivore in fact belonged to a Muttaburrasaurus relative.

Because Australia was a temperate, seasonal environment, the presence of large dinosaurs like Muttaburrasaurus has provided evidence that dinosaurs may have been endothermic, or warm-blooded animals. Some paleontologists suggest that if dinosaurs were “cold-blooded,” or ectothermic, like modern reptiles, they would not have been able to survive in environments that reached such cold temperatures.

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