Often quite different from their more familiar North American counterparts and adorned with bizarre frills, bumps, dorsal sails, and crests, these new southern “terrible lizards” are changing many of our perceptions about dinosaurs. As an example, consider the now-diminished status of the iconic Tyrannosaurus rex, the fiercest North American predator. The most widely recognized of all dinosaurs, T. rex had long been considered the biggest, baddest carnivore ever to walk the Earth. But now it seems that T. rex, whose name loosely means “king of the tyrant lizards,” is not really the king after all. It has recently been surpassed in both size and probable ferocity by Giganotosaurus from South America and Spinosaurus from Africa. This discussion about southern dinosaurs was inspired by my opportunity to view the spectacular traveling exhibition, Ultimate Dinosaurs. In the presentation, seventeen of these strange southern dinosaurs are displayed. The collection was created and produced by the Royal Ontario Museum, Toronto, Canada, and presented by the Science Museum of Minnesota. The exhibition explains the southern dinosaurs as products of continental drift and subsequent evolutionary isolation through spectacular skeletal mounts and outstanding interpretive displays.
DYNAMIC DINOSAUR DISCOVERIES
Southern dinosaurs are the latest chapter in dinosaur paleontology, a discipline that began in the late 1800s when dinosaur fossils were discovered in the American West. At that time, the United States, as a rapidly developing nation, was ready and eager to fully exploit its dinosaur-fossil resources. It had paleontologists available to excavate the bones, museums, and universities to display them, and newspapers and magazines to publicize them.
Attracting worldwide attention, these fossil recoveries established the United States as the center of dinosaur excavation and research. During the following decades, many Americans grew up believing that such familiar North American dinosaurs as Tyrannosaurus, the long-necked sauropod Brontosaurus (now Apatosaurus), and the duckbilled hadrosaurs were representative of dinosaurs worldwide. But now, the plethora of recent southerndinosaur discoveries are revealing that dinosaur diversity is far greater than previously realized.
When the first dinosaurs appeared during the early Triassic Period some 240 million years ago, the Earth’s continental geography was radically different. Each a large, solid tectonic plate, the continents were grouped together into a supercontinent called Pangaea. Dinosaurs roamed freely across this vast landmass, shared many of the same genes, and exhibited relatively little diversity.
But after dinosaurs had become well-established, Pangaea’s tectonic plates began to separate. By the dawn of the Cretaceous Period 145 million years ago, Pangaea had broken apart into two large landmasses: Laurasia to the north, consisting of the stillgrouped, future continents of North America, Europe, and Asia; and Gondwana to the south, which included the future continents of Africa, South America, Australia, and Antarctica.
The breakup of Pangaea into Laurasia and Gondwana, and the subsequent separation into the individual continents we know today, divided dinosaur communities into groups isolated by oceans. With gene-sharing no longer possible, these dinosaur groups began to evolve independently, developing features and traits suited to their specific environments.
Although the idea that continents could shift geographically had been suggested as early as 1600, it was not considered seriously until 1910 when German geophysicist Alfred Wegener observed that the coastal outlines of western Africa and eastern South America fit together as if they had once been joined. Citing similarities in particular African and South American plant and animal fossils, Wegener concluded that these two continents had once formed a single landmass, and, prior to this, all the continents had been consolidated into a single “supercontinent.” Wegener named this supercontinent “Pangaea” from the Greek words for “all earth.”
But becaute geologists could not yet explain the mechanics of continental movement, Wegener’s idea remained controversial. Finally, a half-century later, geologists realized that slowly circulating currents within the Earth’s semisolid mantle did indeed move the continents. This discovery of currents validated Wegener’s theory and led to the now-accepted principle of continental drift.
Perhaps the best-known South American dinosaur that developed through continental drift and subsequent isolated evolution is the carnivore Giganotosaurus (jig-a-NOT-a-SOR-us), a name meaning “giant southern lizard.” An amateur fossil hunter discovered Giganotosaurus’s bones in 1993 in the badlands of southern Argentina’s Neuquén Province.
Despite their similar appearance, Giganotosaurusand T. Rex are not closely related. These two predators arose independently after the breakup of Pangaea. Giganotosaurus lived about 98 million years ago in South America, while T. rex existed some 30 million years later in North America.
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