The Linxia Giant Rhino restored graph, illustrated by Chen Yuhui. But smaller species were more prone to extinction than their larger cousins, and a trend emerged in which increasingly larger species persisted longer than smaller species did. Their data showed that body size evolved in both directions in brontotheres - sometimes new species would be smaller, and sometimes they would be bigger. They found an important clue in extinction patterns across species. Through phylogenetic analysis - evaluating the evolutionary pathways of how new species take shape - the scientists could then determine how such changes might be linked to increases in body size. The researchers also generated computer models to track details of how genetic traits in brontothere species changed as the group evolved. Scientists unlock new secrets from a male woolly mammoth tuskįor their investigation into brontothere size evolution, the authors examined evidence from the group’s rich fossil record, which represents most of its evolutionary history. OLYMPUS DIGITAL CAMERA University of Michigan Other scientists later proposed that size increases were instead shaped as species adapted to environmental pressures such as food availability, competition for resources and presence of predators, but they struggled to define what might lead to rapid and extreme growth, said Raia, who was not involved in the research. In other words: Give animals enough time, and evolution toward large size is inevitable, regardless of environmental factors. Many early scientists argued that brontotheres got bigger as a result of “an inner motor pushing evolution towards attaining the largest and most specialized forms,” said Pasquale Raia, a paleontologist and a professor at the University of Naples Federico II in Italy. The fossil record shows that other extinct animal groups also steadily gained size over time, an evolutionary phenomenon called “Cope’s Rule” after the 19th century paleontologist Edward Drinker Cope. Megacerops coloradensis (background), one of the last giants, survived until the end of the Eocene Epoch. “What makes this group even more interesting is that it is the first in mammalian history to be consistently big,” said Sanisidro, who conducted the research while at the University of Alcalá in Spain and is now a postdoctoral researcher at the University of Valencia.Įotitanops borealis (foreground) was one of the earliest and smallest species of the group. Just 16 million years after the first brontotheres appeared, “the last members of this group were multi-ton behemoths with extravagant bony protrusions over the head,” lead study author Oscar Sanisidro said in an email. ![]() Once large dinosaurs were out of the picture, mammals began to fill those ecological niches, and brontotheres were especially successful at quickly evolving to be enormous. The dinosaurs’ reign ended when an asteroid impact triggered a mass extinction that wiped out 75% of life on Earth, and mammals that survived the carnage were rat-size on average.īut that would soon change. Previously, during the Mesozoic era (252 million to 66 million years ago), mammals living in the shadow of dinosaurs were typically no bigger than a badger. That modest size wasn’t unusual for mammals at the time. The earliest known brontotheres appeared about 53 million years ago they were hornless and about the size of a coyote, weighing around 40 pounds (18 kilograms), the scientists reported. The name Brontotherium - “thunder beast,” coined in the 19th century by paleontologist Othniel Charles Marsh - was inspired by Lakota oral histories about violent thunderstorms accompanied by giants, the park service says.Īsteroid that wiped out the dinosaurs also triggered a global tsunami Most brontothere species weighed over 2,200 pounds (1,000 kilograms), and the biggest lived in the South Dakota Badlands, measuring about 8 feet (2.4 meters) tall and 16 feet (4.9 meters) long, with giant Y-shaped horns on their noses, according to the National Park Service. They might have produced species that were even more massive, had they not all gone extinct due to environmental changes, scientists reported Thursday in the journal Science.īrontotheres are relatives of modern rhinos, horses and tapirs. In fact, brontotheres likely hadn’t reached the limits of how big they could get. Brontotheres started out as dog-size animals, but then most species evolved to become nearly as large as elephants, and they did so relatively quickly because smaller species were outcompeted into extinction, researchers recently discovered. ![]() That certainly was true for brontotheres, the enormous, rhino-like herbivorous mammals that lumbered across North America and Asia during the Eocene Epoch. ![]() Very large things often have small beginnings.
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